System.Data.SQLite

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      </div>
      <p>

        </tr>
      </table>
    </div>
    <div id="mainSection">
    <div id="mainBody">

      <h1 class="heading">Version History</h1>
    <p><b>1.0.42.0 - June 1, 2007</b></p>
    <ul>
    <li>Code merge with SQLite 3.3.17</li>
      <li>Changed the SQLiteFunction static constructor so it only enumerates loaded modules
        that have referenced the SQLite assembly, which hopefully should cut down dramatically
        the time it takes for that function to execute.&nbsp;</li>
      <li>Added the FTS2 full-text search extension to the project.&nbsp; Look for FTS1
        to disappear within the next couple of revisions.&nbsp;</li>
      <li>Fixed a bug introduced with the finalizers that triggered an error when statements
        ended with a semi-colon or had other non-parsable comments at the end of a statement&nbsp;</li>
      <li>Fixed an intermittent multi-threaded race condition between the garbage collector
        thread and the main application thread which lead to an occasional SQLITE_MISUSE
        error.</li>
      <li>Fixed another issue relating to SQLite's inherent typelessness when dealing with
        aggregate functions which could return Int64 or Double or even String for a given
        row depending on what was aggregated.</li>
      <li>Remembered to recompile the DDEX portion of the engine this time, so Compact Framework
        users can once again use the design-time functionality</li>
    </ul>
    <p><b>1.0.41.0 - April 23, 2007</b></p>
    <ul>
    <li>Code merge with SQLite 3.3.16</li>
      <li>Second go at implementing proper finalizers to cleanup after folks who've forgotten to Dispose() of the SQLite objects</li>
      <li>Enhanced GetSchema(IndexColumns) to provide numeric scale and precision values</li>
      <li>Fixed the column ordinals in GetSchema(IndexColumns) to report the ordinal of the column in the index, not the table</li>
      <li>Fixed a bug whereby parameters named with an empty string (such as String.Empty) were treated like a named parameter instead of an unnamed parameter</li>
    </ul>
    <p><b>1.0.40.0 - January 31, 2007</b></p>
    <ul>
    <li>Code merge with SQLite 3.3.12</li>
      <li>Lots of new code to handle misuse of the library.&nbsp; Implemented finalizers
        where it made sense, fixed numerous garbage collector issues when objects are not
        disposed properly, &nbsp;fixed some object lifetime issues, etc.</li>
      <li>A failed Commit() on a transaction no longer leaves the transaction in an unusable
        state.</li>
    </ul>
    <p><b>1.0.39.1 - January 11, 2007</b></p>
    <ul>
    <li>Fixed a really dumb mistake that for some reason didn't trigger any errors in
      the testcases, whereby commands when associated with a connection were not adding
      or removing themselves from an internal list of commands for that connection --
      causing a "database is locked" error when trying to close the connection.</li>
    </ul>

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/* The author disclaims copyright to this source code.
 *
 * This is an SQLite module implementing full-text search.
 */

/*
** The code in this file is only compiled if:
**
**     * The FTS2 module is being built as an extension
**       (in which case SQLITE_CORE is not defined), or
**
**     * The FTS2 module is being built into the core of
**       SQLite (in which case SQLITE_ENABLE_FTS2 is defined).
*/

/* TODO(shess) Consider exporting this comment to an HTML file or the
** wiki.
*/
/* The full-text index is stored in a series of b+tree (-like)
** structures called segments which map terms to doclists.  The
** structures are like b+trees in layout, but are constructed from the
** bottom up in optimal fashion and are not updatable.  Since trees
** are built from the bottom up, things will be described from the
** bottom up.
**
**
**** Varints ****
** The basic unit of encoding is a variable-length integer called a
** varint.  We encode variable-length integers in little-endian order
** using seven bits * per byte as follows:
**
** KEY:
**         A = 0xxxxxxx    7 bits of data and one flag bit
**         B = 1xxxxxxx    7 bits of data and one flag bit
**
**  7 bits - A
** 14 bits - BA
** 21 bits - BBA
** and so on.
**
** This is identical to how sqlite encodes varints (see util.c).
**
**
**** Document lists ****
** A doclist (document list) holds a docid-sorted list of hits for a
** given term.  Doclists hold docids, and can optionally associate
** token positions and offsets with docids.
**
** A DL_POSITIONS_OFFSETS doclist is stored like this:
**
** array {
**   varint docid;
**   array {                (position list for column 0)
**     varint position;     (delta from previous position plus POS_BASE)
**     varint startOffset;  (delta from previous startOffset)
**     varint endOffset;    (delta from startOffset)
**   }
**   array {
**     varint POS_COLUMN;   (marks start of position list for new column)
**     varint column;       (index of new column)
**     array {
**       varint position;   (delta from previous position plus POS_BASE)
**       varint startOffset;(delta from previous startOffset)
**       varint endOffset;  (delta from startOffset)
**     }
**   }
**   varint POS_END;        (marks end of positions for this document.
** }
**
** Here, array { X } means zero or more occurrences of X, adjacent in
** memory.  A "position" is an index of a token in the token stream
** generated by the tokenizer, while an "offset" is a byte offset,
** both based at 0.  Note that POS_END and POS_COLUMN occur in the
** same logical place as the position element, and act as sentinals
** ending a position list array.
**
** A DL_POSITIONS doclist omits the startOffset and endOffset
** information.  A DL_DOCIDS doclist omits both the position and
** offset information, becoming an array of varint-encoded docids.
**
** On-disk data is stored as type DL_DEFAULT, so we don't serialize
** the type.  Due to how deletion is implemented in the segmentation
** system, on-disk doclists MUST store at least positions.
**
**
**** Segment leaf nodes ****
** Segment leaf nodes store terms and doclists, ordered by term.  Leaf
** nodes are written using LeafWriter, and read using LeafReader (to
** iterate through a single leaf node's data) and LeavesReader (to
** iterate through a segment's entire leaf layer).  Leaf nodes have
** the format:
**
** varint iHeight;             (height from leaf level, always 0)
** varint nTerm;               (length of first term)
** char pTerm[nTerm];          (content of first term)
** varint nDoclist;            (length of term's associated doclist)
** char pDoclist[nDoclist];    (content of doclist)
** array {
**                             (further terms are delta-encoded)
**   varint nPrefix;           (length of prefix shared with previous term)
**   varint nSuffix;           (length of unshared suffix)
**   char pTermSuffix[nSuffix];(unshared suffix of next term)
**   varint nDoclist;          (length of term's associated doclist)
**   char pDoclist[nDoclist];  (content of doclist)
** }
**
** Here, array { X } means zero or more occurrences of X, adjacent in
** memory.
**
** Leaf nodes are broken into blocks which are stored contiguously in
** the %_segments table in sorted order.  This means that when the end
** of a node is reached, the next term is in the node with the next
** greater node id.
**
** New data is spilled to a new leaf node when the current node
** exceeds LEAF_MAX bytes (default 2048).  New data which itself is
** larger than STANDALONE_MIN (default 1024) is placed in a standalone
** node (a leaf node with a single term and doclist).  The goal of
** these settings is to pack together groups of small doclists while
** making it efficient to directly access large doclists.  The
** assumption is that large doclists represent terms which are more
** likely to be query targets.
**
** TODO(shess) It may be useful for blocking decisions to be more
** dynamic.  For instance, it may make more sense to have a 2.5k leaf
** node rather than splitting into 2k and .5k nodes.  My intuition is
** that this might extend through 2x or 4x the pagesize.
**
**
**** Segment interior nodes ****
** Segment interior nodes store blockids for subtree nodes and terms
** to describe what data is stored by the each subtree.  Interior
** nodes are written using InteriorWriter, and read using
** InteriorReader.  InteriorWriters are created as needed when
** SegmentWriter creates new leaf nodes, or when an interior node
** itself grows too big and must be split.  The format of interior
** nodes:
**
** varint iHeight;           (height from leaf level, always >0)
** varint iBlockid;          (block id of node's leftmost subtree)
** optional {
**   varint nTerm;           (length of first term)
**   char pTerm[nTerm];      (content of first term)
**   array {
**                                (further terms are delta-encoded)
**     varint nPrefix;            (length of shared prefix with previous term)
**     varint nSuffix;            (length of unshared suffix)
**     char pTermSuffix[nSuffix]; (unshared suffix of next term)
**   }
** }
**
** Here, optional { X } means an optional element, while array { X }
** means zero or more occurrences of X, adjacent in memory.
**
** An interior node encodes n terms separating n+1 subtrees.  The
** subtree blocks are contiguous, so only the first subtree's blockid
** is encoded.  The subtree at iBlockid will contain all terms less
** than the first term encoded (or all terms if no term is encoded).
** Otherwise, for terms greater than or equal to pTerm[i] but less
** than pTerm[i+1], the subtree for that term will be rooted at
** iBlockid+i.  Interior nodes only store enough term data to
** distinguish adjacent children (if the rightmost term of the left
** child is "something", and the leftmost term of the right child is
** "wicked", only "w" is stored).
**
** New data is spilled to a new interior node at the same height when
** the current node exceeds INTERIOR_MAX bytes (default 2048).
** INTERIOR_MIN_TERMS (default 7) keeps large terms from monopolizing
** interior nodes and making the tree too skinny.  The interior nodes
** at a given height are naturally tracked by interior nodes at
** height+1, and so on.
**
**
**** Segment directory ****
** The segment directory in table %_segdir stores meta-information for
** merging and deleting segments, and also the root node of the
** segment's tree.
**
** The root node is the top node of the segment's tree after encoding
** the entire segment, restricted to ROOT_MAX bytes (default 1024).
** This could be either a leaf node or an interior node.  If the top
** node requires more than ROOT_MAX bytes, it is flushed to %_segments
** and a new root interior node is generated (which should always fit
** within ROOT_MAX because it only needs space for 2 varints, the
** height and the blockid of the previous root).
**
** The meta-information in the segment directory is:
**   level               - segment level (see below)
**   idx                 - index within level
**                       - (level,idx uniquely identify a segment)
**   start_block         - first leaf node
**   leaves_end_block    - last leaf node
**   end_block           - last block (including interior nodes)
**   root                - contents of root node
**
** If the root node is a leaf node, then start_block,
** leaves_end_block, and end_block are all 0.
**
**
**** Segment merging ****
** To amortize update costs, segments are groups into levels and
** merged in matches.  Each increase in level represents exponentially
** more documents.
**
** New documents (actually, document updates) are tokenized and
** written individually (using LeafWriter) to a level 0 segment, with
** incrementing idx.  When idx reaches MERGE_COUNT (default 16), all
** level 0 segments are merged into a single level 1 segment.  Level 1
** is populated like level 0, and eventually MERGE_COUNT level 1
** segments are merged to a single level 2 segment (representing
** MERGE_COUNT^2 updates), and so on.
**
** A segment merge traverses all segments at a given level in
** parallel, performing a straightforward sorted merge.  Since segment
** leaf nodes are written in to the %_segments table in order, this
** merge traverses the underlying sqlite disk structures efficiently.
** After the merge, all segment blocks from the merged level are
** deleted.
**
** MERGE_COUNT controls how often we merge segments.  16 seems to be
** somewhat of a sweet spot for insertion performance.  32 and 64 show
** very similar performance numbers to 16 on insertion, though they're
** a tiny bit slower (perhaps due to more overhead in merge-time
** sorting).  8 is about 20% slower than 16, 4 about 50% slower than
** 16, 2 about 66% slower than 16.
**
** At query time, high MERGE_COUNT increases the number of segments
** which need to be scanned and merged.  For instance, with 100k docs
** inserted:
**
**    MERGE_COUNT   segments
**       16           25
**        8           12
**        4           10
**        2            6
**
** This appears to have only a moderate impact on queries for very
** frequent terms (which are somewhat dominated by segment merge
** costs), and infrequent and non-existent terms still seem to be fast
** even with many segments.
**
** TODO(shess) That said, it would be nice to have a better query-side
** argument for MERGE_COUNT of 16.  Also, it's possible/likely that
** optimizations to things like doclist merging will swing the sweet
** spot around.
**
**
**
**** Handling of deletions and updates ****
** Since we're using a segmented structure, with no docid-oriented
** index into the term index, we clearly cannot simply update the term
** index when a document is deleted or updated.  For deletions, we
** write an empty doclist (varint(docid) varint(POS_END)), for updates
** we simply write the new doclist.  Segment merges overwrite older
** data for a particular docid with newer data, so deletes or updates
** will eventually overtake the earlier data and knock it out.  The
** query logic likewise merges doclists so that newer data knocks out
** older data.
**
** TODO(shess) Provide a VACUUM type operation to clear out all
** deletions and duplications.  This would basically be a forced merge
** into a single segment.
*/

#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2)

#if defined(SQLITE_ENABLE_FTS2) && !defined(SQLITE_CORE)
# define SQLITE_CORE 1
#endif

#include <assert.h>
#if !defined(__APPLE__)
#include <malloc.h>
#endif
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

#include "fts2.h"
#include "fts2_hash.h"
#include "fts2_tokenizer.h"
#include "sqlite3.h"
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1


/* TODO(shess) MAN, this thing needs some refactoring.  At minimum, it
** would be nice to order the file better, perhaps something along the
** lines of:
**
**  - utility functions
**  - table setup functions
**  - table update functions
**  - table query functions
**
** Put the query functions last because they're likely to reference
** typedefs or functions from the table update section.
*/

#if 0
# define TRACE(A)  printf A; fflush(stdout)
#else
# define TRACE(A)
#endif

/* It is not safe to call isspace(), tolower(), or isalnum() on
** hi-bit-set characters.  This is the same solution used in the
** tokenizer.
*/
/* TODO(shess) The snippet-generation code should be using the
** tokenizer-generated tokens rather than doing its own local
** tokenization.
*/
/* TODO(shess) Is __isascii() a portable version of (c&0x80)==0? */
static int safe_isspace(char c){
  return (c&0x80)==0 ? isspace(c) : 0;
}
static int safe_tolower(char c){
  return (c&0x80)==0 ? tolower(c) : c;
}
static int safe_isalnum(char c){
  return (c&0x80)==0 ? isalnum(c) : 0;
}

typedef enum DocListType {
  DL_DOCIDS,              /* docids only */
  DL_POSITIONS,           /* docids + positions */
  DL_POSITIONS_OFFSETS    /* docids + positions + offsets */
} DocListType;

/*
** By default, only positions and not offsets are stored in the doclists.
** To change this so that offsets are stored too, compile with
**
**          -DDL_DEFAULT=DL_POSITIONS_OFFSETS
**
** If DL_DEFAULT is set to DL_DOCIDS, your table can only be inserted
** into (no deletes or updates).
*/
#ifndef DL_DEFAULT
# define DL_DEFAULT DL_POSITIONS
#endif

enum {
  POS_END = 0,        /* end of this position list */
  POS_COLUMN,         /* followed by new column number */
  POS_BASE
};

/* MERGE_COUNT controls how often we merge segments (see comment at
** top of file).
*/
#define MERGE_COUNT 16

/* utility functions */

/* CLEAR() and SCRAMBLE() abstract memset() on a pointer to a single
** record to prevent errors of the form:
**
** my_function(SomeType *b){
**   memset(b, '\0', sizeof(b));  // sizeof(b)!=sizeof(*b)
** }
*/
/* TODO(shess) Obvious candidates for a header file. */
#define CLEAR(b) memset(b, '\0', sizeof(*(b)))

#ifndef NDEBUG
#  define SCRAMBLE(b) memset(b, 0x55, sizeof(*(b)))
#else
#  define SCRAMBLE(b)
#endif

/* We may need up to VARINT_MAX bytes to store an encoded 64-bit integer. */
#define VARINT_MAX 10

/* Write a 64-bit variable-length integer to memory starting at p[0].
 * The length of data written will be between 1 and VARINT_MAX bytes.
 * The number of bytes written is returned. */
static int putVarint(char *p, sqlite_int64 v){
  unsigned char *q = (unsigned char *) p;
  sqlite_uint64 vu = v;
  do{
    *q++ = (unsigned char) ((vu & 0x7f) | 0x80);
    vu >>= 7;
  }while( vu!=0 );
  q[-1] &= 0x7f;  /* turn off high bit in final byte */
  assert( q - (unsigned char *)p <= VARINT_MAX );
  return (int) (q - (unsigned char *)p);
}

/* Read a 64-bit variable-length integer from memory starting at p[0].
 * Return the number of bytes read, or 0 on error.
 * The value is stored in *v. */
static int getVarint(const char *p, sqlite_int64 *v){
  const unsigned char *q = (const unsigned char *) p;
  sqlite_uint64 x = 0, y = 1;
  while( (*q & 0x80) == 0x80 ){
    x += y * (*q++ & 0x7f);
    y <<= 7;
    if( q - (unsigned char *)p >= VARINT_MAX ){  /* bad data */
      assert( 0 );
      return 0;
    }
  }
  x += y * (*q++);
  *v = (sqlite_int64) x;
  return (int) (q - (unsigned char *)p);
}

static int getVarint32(const char *p, int *pi){
 sqlite_int64 i;
 int ret = getVarint(p, &i);
 *pi = (int) i;
 assert( *pi==i );
 return ret;
}

/*******************************************************************/
/* DataBuffer is used to collect data into a buffer in piecemeal
** fashion.  It implements the usual distinction between amount of
** data currently stored (nData) and buffer capacity (nCapacity).
**
** dataBufferInit - create a buffer with given initial capacity.
** dataBufferReset - forget buffer's data, retaining capacity.
** dataBufferDestroy - free buffer's data.
** dataBufferExpand - expand capacity without adding data.
** dataBufferAppend - append data.
** dataBufferAppend2 - append two pieces of data at once.
** dataBufferReplace - replace buffer's data.
*/
typedef struct DataBuffer {
  char *pData;          /* Pointer to malloc'ed buffer. */
  int nCapacity;        /* Size of pData buffer. */
  int nData;            /* End of data loaded into pData. */
} DataBuffer;

static void dataBufferInit(DataBuffer *pBuffer, int nCapacity){
  assert( nCapacity>=0 );
  pBuffer->nData = 0;
  pBuffer->nCapacity = nCapacity;
  pBuffer->pData = nCapacity==0 ? NULL : malloc(nCapacity);
}
static void dataBufferReset(DataBuffer *pBuffer){
  pBuffer->nData = 0;
}
static void dataBufferDestroy(DataBuffer *pBuffer){
  if( pBuffer->pData!=NULL ) free(pBuffer->pData);
  SCRAMBLE(pBuffer);
}
static void dataBufferExpand(DataBuffer *pBuffer, int nAddCapacity){
  assert( nAddCapacity>0 );
  /* TODO(shess) Consider expanding more aggressively.  Note that the
  ** underlying malloc implementation may take care of such things for
  ** us already.
  */
  if( pBuffer->nData+nAddCapacity>pBuffer->nCapacity ){
    pBuffer->nCapacity = pBuffer->nData+nAddCapacity;
    pBuffer->pData = realloc(pBuffer->pData, pBuffer->nCapacity);
  }
}
static void dataBufferAppend(DataBuffer *pBuffer,
                             const char *pSource, int nSource){
  assert( nSource>0 && pSource!=NULL );
  dataBufferExpand(pBuffer, nSource);
  memcpy(pBuffer->pData+pBuffer->nData, pSource, nSource);
  pBuffer->nData += nSource;
}
static void dataBufferAppend2(DataBuffer *pBuffer,
                              const char *pSource1, int nSource1,
                              const char *pSource2, int nSource2){
  assert( nSource1>0 && pSource1!=NULL );
  assert( nSource2>0 && pSource2!=NULL );
  dataBufferExpand(pBuffer, nSource1+nSource2);
  memcpy(pBuffer->pData+pBuffer->nData, pSource1, nSource1);
  memcpy(pBuffer->pData+pBuffer->nData+nSource1, pSource2, nSource2);
  pBuffer->nData += nSource1+nSource2;
}
static void dataBufferReplace(DataBuffer *pBuffer,
                              const char *pSource, int nSource){
  dataBufferReset(pBuffer);
  dataBufferAppend(pBuffer, pSource, nSource);
}

/* StringBuffer is a null-terminated version of DataBuffer. */
typedef struct StringBuffer {
  DataBuffer b;            /* Includes null terminator. */
} StringBuffer;

static void initStringBuffer(StringBuffer *sb){
  dataBufferInit(&sb->b, 100);
  dataBufferReplace(&sb->b, "", 1);
}
static int stringBufferLength(StringBuffer *sb){
  return sb->b.nData-1;
}
static char *stringBufferData(StringBuffer *sb){
  return sb->b.pData;
}
static void stringBufferDestroy(StringBuffer *sb){
  dataBufferDestroy(&sb->b);
}

static void nappend(StringBuffer *sb, const char *zFrom, int nFrom){
  assert( sb->b.nData>0 );
  if( nFrom>0 ){
    sb->b.nData--;
    dataBufferAppend2(&sb->b, zFrom, nFrom, "", 1);
  }
}
static void append(StringBuffer *sb, const char *zFrom){
  nappend(sb, zFrom, strlen(zFrom));
}

/* Append a list of strings separated by commas. */
static void appendList(StringBuffer *sb, int nString, char **azString){
  int i;
  for(i=0; i<nString; ++i){
    if( i>0 ) append(sb, ", ");
    append(sb, azString[i]);
  }
}

static int endsInWhiteSpace(StringBuffer *p){
  return stringBufferLength(p)>0 &&
    safe_isspace(stringBufferData(p)[stringBufferLength(p)-1]);
}

/* If the StringBuffer ends in something other than white space, add a
** single space character to the end.
*/
static void appendWhiteSpace(StringBuffer *p){
  if( stringBufferLength(p)==0 ) return;
  if( !endsInWhiteSpace(p) ) append(p, " ");
}

/* Remove white space from the end of the StringBuffer */
static void trimWhiteSpace(StringBuffer *p){
  while( endsInWhiteSpace(p) ){
    p->b.pData[--p->b.nData-1] = '\0';
  }
}

/*******************************************************************/
/* DLReader is used to read document elements from a doclist.  The
** current docid is cached, so dlrDocid() is fast.  DLReader does not
** own the doclist buffer.
**
** dlrAtEnd - true if there's no more data to read.
** dlrDocid - docid of current document.
** dlrDocData - doclist data for current document (including docid).
** dlrDocDataBytes - length of same.
** dlrAllDataBytes - length of all remaining data.
** dlrPosData - position data for current document.
** dlrPosDataLen - length of pos data for current document (incl POS_END).
** dlrStep - step to current document.
** dlrInit - initial for doclist of given type against given data.
** dlrDestroy - clean up.
**
** Expected usage is something like:
**
**   DLReader reader;
**   dlrInit(&reader, pData, nData);
**   while( !dlrAtEnd(&reader) ){
**     // calls to dlrDocid() and kin.
**     dlrStep(&reader);
**   }
**   dlrDestroy(&reader);
*/
typedef struct DLReader {
  DocListType iType;
  const char *pData;
  int nData;

  sqlite_int64 iDocid;
  int nElement;
} DLReader;

static int dlrAtEnd(DLReader *pReader){
  assert( pReader->nData>=0 );
  return pReader->nData==0;
}
static sqlite_int64 dlrDocid(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->iDocid;
}
static const char *dlrDocData(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->pData;
}
static int dlrDocDataBytes(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->nElement;
}
static int dlrAllDataBytes(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );
  return pReader->nData;
}
/* TODO(shess) Consider adding a field to track iDocid varint length
** to make these two functions faster.  This might matter (a tiny bit)
** for queries.
*/
static const char *dlrPosData(DLReader *pReader){
  sqlite_int64 iDummy;
  int n = getVarint(pReader->pData, &iDummy);
  assert( !dlrAtEnd(pReader) );
  return pReader->pData+n;
}
static int dlrPosDataLen(DLReader *pReader){
  sqlite_int64 iDummy;
  int n = getVarint(pReader->pData, &iDummy);
  assert( !dlrAtEnd(pReader) );
  return pReader->nElement-n;
}
static void dlrStep(DLReader *pReader){
  assert( !dlrAtEnd(pReader) );

  /* Skip past current doclist element. */
  assert( pReader->nElement<=pReader->nData );
  pReader->pData += pReader->nElement;
  pReader->nData -= pReader->nElement;

  /* If there is more data, read the next doclist element. */
  if( pReader->nData!=0 ){
    sqlite_int64 iDocidDelta;
    int iDummy, n = getVarint(pReader->pData, &iDocidDelta);
    pReader->iDocid += iDocidDelta;
    if( pReader->iType>=DL_POSITIONS ){
      assert( n<pReader->nData );
      while( 1 ){
        n += getVarint32(pReader->pData+n, &iDummy);
        assert( n<=pReader->nData );
        if( iDummy==POS_END ) break;
        if( iDummy==POS_COLUMN ){
          n += getVarint32(pReader->pData+n, &iDummy);
          assert( n<pReader->nData );
        }else if( pReader->iType==DL_POSITIONS_OFFSETS ){
          n += getVarint32(pReader->pData+n, &iDummy);
          n += getVarint32(pReader->pData+n, &iDummy);
          assert( n<pReader->nData );
        }
      }
    }
    pReader->nElement = n;
    assert( pReader->nElement<=pReader->nData );
  }
}
static void dlrInit(DLReader *pReader, DocListType iType,
                    const char *pData, int nData){
  assert( pData!=NULL && nData!=0 );
  pReader->iType = iType;
  pReader->pData = pData;
  pReader->nData = nData;
  pReader->nElement = 0;
  pReader->iDocid = 0;

  /* Load the first element's data.  There must be a first element. */
  dlrStep(pReader);
}
static void dlrDestroy(DLReader *pReader){
  SCRAMBLE(pReader);
}

#ifndef NDEBUG
/* Verify that the doclist can be validly decoded.  Also returns the
** last docid found because it's convenient in other assertions for
** DLWriter.
*/
static void docListValidate(DocListType iType, const char *pData, int nData,
                            sqlite_int64 *pLastDocid){
  sqlite_int64 iPrevDocid = 0;
  assert( nData>0 );
  assert( pData!=0 );
  assert( pData+nData>pData );
  while( nData!=0 ){
    sqlite_int64 iDocidDelta;
    int n = getVarint(pData, &iDocidDelta);
    iPrevDocid += iDocidDelta;
    if( iType>DL_DOCIDS ){
      int iDummy;
      while( 1 ){
        n += getVarint32(pData+n, &iDummy);
        if( iDummy==POS_END ) break;
        if( iDummy==POS_COLUMN ){
          n += getVarint32(pData+n, &iDummy);
        }else if( iType>DL_POSITIONS ){
          n += getVarint32(pData+n, &iDummy);
          n += getVarint32(pData+n, &iDummy);
        }
        assert( n<=nData );
      }
    }
    assert( n<=nData );
    pData += n;
    nData -= n;
  }
  if( pLastDocid ) *pLastDocid = iPrevDocid;
}
#define ASSERT_VALID_DOCLIST(i, p, n, o) docListValidate(i, p, n, o)
#else
#define ASSERT_VALID_DOCLIST(i, p, n, o) assert( 1 )
#endif

/*******************************************************************/
/* DLWriter is used to write doclist data to a DataBuffer.  DLWriter
** always appends to the buffer and does not own it.
**
** dlwInit - initialize to write a given type doclistto a buffer.
** dlwDestroy - clear the writer's memory.  Does not free buffer.
** dlwAppend - append raw doclist data to buffer.
** dlwAdd - construct doclist element and append to buffer.
**    Only apply dlwAdd() to DL_DOCIDS doclists (else use PLWriter).
*/
typedef struct DLWriter {
  DocListType iType;
  DataBuffer *b;
  sqlite_int64 iPrevDocid;
} DLWriter;

static void dlwInit(DLWriter *pWriter, DocListType iType, DataBuffer *b){
  pWriter->b = b;
  pWriter->iType = iType;
  pWriter->iPrevDocid = 0;
}
static void dlwDestroy(DLWriter *pWriter){
  SCRAMBLE(pWriter);
}
/* iFirstDocid is the first docid in the doclist in pData.  It is
** needed because pData may point within a larger doclist, in which
** case the first item would be delta-encoded.
**
** iLastDocid is the final docid in the doclist in pData.  It is
** needed to create the new iPrevDocid for future delta-encoding.  The
** code could decode the passed doclist to recreate iLastDocid, but
** the only current user (docListMerge) already has decoded this
** information.
*/
/* TODO(shess) This has become just a helper for docListMerge.
** Consider a refactor to make this cleaner.
*/
static void dlwAppend(DLWriter *pWriter,
                      const char *pData, int nData,
                      sqlite_int64 iFirstDocid, sqlite_int64 iLastDocid){
  sqlite_int64 iDocid = 0;
  char c[VARINT_MAX];
  int nFirstOld, nFirstNew;     /* Old and new varint len of first docid. */
#ifndef NDEBUG
  sqlite_int64 iLastDocidDelta;
#endif

  /* Recode the initial docid as delta from iPrevDocid. */
  nFirstOld = getVarint(pData, &iDocid);
  assert( nFirstOld<nData || (nFirstOld==nData && pWriter->iType==DL_DOCIDS) );
  nFirstNew = putVarint(c, iFirstDocid-pWriter->iPrevDocid);

  /* Verify that the incoming doclist is valid AND that it ends with
  ** the expected docid.  This is essential because we'll trust this
  ** docid in future delta-encoding.
  */
  ASSERT_VALID_DOCLIST(pWriter->iType, pData, nData, &iLastDocidDelta);
  assert( iLastDocid==iFirstDocid-iDocid+iLastDocidDelta );

  /* Append recoded initial docid and everything else.  Rest of docids
  ** should have been delta-encoded from previous initial docid.
  */
  if( nFirstOld<nData ){
    dataBufferAppend2(pWriter->b, c, nFirstNew,
                      pData+nFirstOld, nData-nFirstOld);
  }else{
    dataBufferAppend(pWriter->b, c, nFirstNew);
  }
  pWriter->iPrevDocid = iLastDocid;
}
static void dlwAdd(DLWriter *pWriter, sqlite_int64 iDocid){
  char c[VARINT_MAX];
  int n = putVarint(c, iDocid-pWriter->iPrevDocid);

  assert( pWriter->iPrevDocid<iDocid );
  assert( pWriter->iType==DL_DOCIDS );

  dataBufferAppend(pWriter->b, c, n);
  pWriter->iPrevDocid = iDocid;
}

/*******************************************************************/
/* PLReader is used to read data from a document's position list.  As
** the caller steps through the list, data is cached so that varints
** only need to be decoded once.
**
** plrInit, plrDestroy - create/destroy a reader.
** plrColumn, plrPosition, plrStartOffset, plrEndOffset - accessors
** plrAtEnd - at end of stream, only call plrDestroy once true.
** plrStep - step to the next element.
*/
typedef struct PLReader {
  /* These refer to the next position's data.  nData will reach 0 when
  ** reading the last position, so plrStep() signals EOF by setting
  ** pData to NULL.
  */
  const char *pData;
  int nData;

  DocListType iType;
  int iColumn;         /* the last column read */
  int iPosition;       /* the last position read */
  int iStartOffset;    /* the last start offset read */
  int iEndOffset;      /* the last end offset read */
} PLReader;

static int plrAtEnd(PLReader *pReader){
  return pReader->pData==NULL;
}
static int plrColumn(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iColumn;
}
static int plrPosition(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iPosition;
}
static int plrStartOffset(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iStartOffset;
}
static int plrEndOffset(PLReader *pReader){
  assert( !plrAtEnd(pReader) );
  return pReader->iEndOffset;
}
static void plrStep(PLReader *pReader){
  int i, n;

  assert( !plrAtEnd(pReader) );

  if( pReader->nData==0 ){
    pReader->pData = NULL;
    return;
  }

  n = getVarint32(pReader->pData, &i);
  if( i==POS_COLUMN ){
    n += getVarint32(pReader->pData+n, &pReader->iColumn);
    pReader->iPosition = 0;
    pReader->iStartOffset = 0;
    n += getVarint32(pReader->pData+n, &i);
  }
  /* Should never see adjacent column changes. */
  assert( i!=POS_COLUMN );

  if( i==POS_END ){
    pReader->nData = 0;
    pReader->pData = NULL;
    return;
  }

  pReader->iPosition += i-POS_BASE;
  if( pReader->iType==DL_POSITIONS_OFFSETS ){
    n += getVarint32(pReader->pData+n, &i);
    pReader->iStartOffset += i;
    n += getVarint32(pReader->pData+n, &i);
    pReader->iEndOffset = pReader->iStartOffset+i;
  }
  assert( n<=pReader->nData );
  pReader->pData += n;
  pReader->nData -= n;
}

static void plrInit(PLReader *pReader, DLReader *pDLReader){
  pReader->pData = dlrPosData(pDLReader);
  pReader->nData = dlrPosDataLen(pDLReader);
  pReader->iType = pDLReader->iType;
  pReader->iColumn = 0;
  pReader->iPosition = 0;
  pReader->iStartOffset = 0;
  pReader->iEndOffset = 0;
  plrStep(pReader);
}
static void plrDestroy(PLReader *pReader){
  SCRAMBLE(pReader);
}

/*******************************************************************/
/* PLWriter is used in constructing a document's position list.  As a
** convenience, if iType is DL_DOCIDS, PLWriter becomes a no-op.
** PLWriter writes to the associated DLWriter's buffer.
**
** plwInit - init for writing a document's poslist.
** plwDestroy - clear a writer.
** plwAdd - append position and offset information.
** plwTerminate - add any necessary doclist terminator.
**
** Calling plwAdd() after plwTerminate() may result in a corrupt
** doclist.
*/
/* TODO(shess) Until we've written the second item, we can cache the
** first item's information.  Then we'd have three states:
**
** - initialized with docid, no positions.
** - docid and one position.
** - docid and multiple positions.
**
** Only the last state needs to actually write to dlw->b, which would
** be an improvement in the DLCollector case.
*/
typedef struct PLWriter {
  DLWriter *dlw;

  int iColumn;    /* the last column written */
  int iPos;       /* the last position written */
  int iOffset;    /* the last start offset written */
} PLWriter;

/* TODO(shess) In the case where the parent is reading these values
** from a PLReader, we could optimize to a copy if that PLReader has
** the same type as pWriter.
*/
static void plwAdd(PLWriter *pWriter, int iColumn, int iPos,
                   int iStartOffset, int iEndOffset){
  /* Worst-case space for POS_COLUMN, iColumn, iPosDelta,
  ** iStartOffsetDelta, and iEndOffsetDelta.
  */
  char c[5*VARINT_MAX];
  int n = 0;

  /* Ban plwAdd() after plwTerminate(). */
  assert( pWriter->iPos!=-1 );

  if( pWriter->dlw->iType==DL_DOCIDS ) return;

  if( iColumn!=pWriter->iColumn ){
    n += putVarint(c+n, POS_COLUMN);
    n += putVarint(c+n, iColumn);
    pWriter->iColumn = iColumn;
    pWriter->iPos = 0;
    pWriter->iOffset = 0;
  }
  assert( iPos>=pWriter->iPos );
  n += putVarint(c+n, POS_BASE+(iPos-pWriter->iPos));
  pWriter->iPos = iPos;
  if( pWriter->dlw->iType==DL_POSITIONS_OFFSETS ){
    assert( iStartOffset>=pWriter->iOffset );
    n += putVarint(c+n, iStartOffset-pWriter->iOffset);
    pWriter->iOffset = iStartOffset;
    assert( iEndOffset>=iStartOffset );
    n += putVarint(c+n, iEndOffset-iStartOffset);
  }
  dataBufferAppend(pWriter->dlw->b, c, n);
}
static void plwInit(PLWriter *pWriter, DLWriter *dlw, sqlite_int64 iDocid){
  char c[VARINT_MAX];
  int n;

  pWriter->dlw = dlw;

  assert( iDocid>pWriter->dlw->iPrevDocid );
  n = putVarint(c, iDocid-pWriter->dlw->iPrevDocid);
  dataBufferAppend(pWriter->dlw->b, c, n);
  pWriter->dlw->iPrevDocid = iDocid;

  pWriter->iColumn = 0;
  pWriter->iPos = 0;
  pWriter->iOffset = 0;
}
/* TODO(shess) Should plwDestroy() also terminate the doclist?  But
** then plwDestroy() would no longer be just a destructor, it would
** also be doing work, which isn't consistent with the overall idiom.
** Another option would be for plwAdd() to always append any necessary
** terminator, so that the output is always correct.  But that would
** add incremental work to the common case with the only benefit being
** API elegance.  Punt for now.
*/
static void plwTerminate(PLWriter *pWriter){
  if( pWriter->dlw->iType>DL_DOCIDS ){
    char c[VARINT_MAX];
    int n = putVarint(c, POS_END);
    dataBufferAppend(pWriter->dlw->b, c, n);
  }
#ifndef NDEBUG
  /* Mark as terminated for assert in plwAdd(). */
  pWriter->iPos = -1;
#endif
}
static void plwDestroy(PLWriter *pWriter){
  SCRAMBLE(pWriter);
}

/*******************************************************************/
/* DLCollector wraps PLWriter and DLWriter to provide a
** dynamically-allocated doclist area to use during tokenization.
**
** dlcNew - malloc up and initialize a collector.
** dlcDelete - destroy a collector and all contained items.
** dlcAddPos - append position and offset information.
** dlcAddDoclist - add the collected doclist to the given buffer.
** dlcNext - terminate the current document and open another.
*/
typedef struct DLCollector {
  DataBuffer b;
  DLWriter dlw;
  PLWriter plw;
} DLCollector;

/* TODO(shess) This could also be done by calling plwTerminate() and
** dataBufferAppend().  I tried that, expecting nominal performance
** differences, but it seemed to pretty reliably be worth 1% to code
** it this way.  I suspect it's the incremental malloc overhead (some
** percentage of the plwTerminate() calls will cause a realloc), so
** this might be worth revisiting if the DataBuffer implementation
** changes.
*/
static void dlcAddDoclist(DLCollector *pCollector, DataBuffer *b){
  if( pCollector->dlw.iType>DL_DOCIDS ){
    char c[VARINT_MAX];
    int n = putVarint(c, POS_END);
    dataBufferAppend2(b, pCollector->b.pData, pCollector->b.nData, c, n);
  }else{
    dataBufferAppend(b, pCollector->b.pData, pCollector->b.nData);
  }
}
static void dlcNext(DLCollector *pCollector, sqlite_int64 iDocid){
  plwTerminate(&pCollector->plw);
  plwDestroy(&pCollector->plw);
  plwInit(&pCollector->plw, &pCollector->dlw, iDocid);
}
static void dlcAddPos(DLCollector *pCollector, int iColumn, int iPos,
                      int iStartOffset, int iEndOffset){
  plwAdd(&pCollector->plw, iColumn, iPos, iStartOffset, iEndOffset);
}

static DLCollector *dlcNew(sqlite_int64 iDocid, DocListType iType){
  DLCollector *pCollector = malloc(sizeof(DLCollector));
  dataBufferInit(&pCollector->b, 0);
  dlwInit(&pCollector->dlw, iType, &pCollector->b);
  plwInit(&pCollector->plw, &pCollector->dlw, iDocid);
  return pCollector;
}
static void dlcDelete(DLCollector *pCollector){
  plwDestroy(&pCollector->plw);
  dlwDestroy(&pCollector->dlw);
  dataBufferDestroy(&pCollector->b);
  SCRAMBLE(pCollector);
  free(pCollector);
}


/* Copy the doclist data of iType in pData/nData into *out, trimming
** unnecessary data as we go.  Only columns matching iColumn are
** copied, all columns copied if iColumn is -1.  Elements with no
** matching columns are dropped.  The output is an iOutType doclist.
*/
/* NOTE(shess) This code is only valid after all doclists are merged.
** If this is run before merges, then doclist items which represent
** deletion will be trimmed, and will thus not effect a deletion
** during the merge.
*/
static void docListTrim(DocListType iType, const char *pData, int nData,
                        int iColumn, DocListType iOutType, DataBuffer *out){
  DLReader dlReader;
  DLWriter dlWriter;

  assert( iOutType<=iType );

  dlrInit(&dlReader, iType, pData, nData);
  dlwInit(&dlWriter, iOutType, out);

  while( !dlrAtEnd(&dlReader) ){
    PLReader plReader;
    PLWriter plWriter;
    int match = 0;

    plrInit(&plReader, &dlReader);

    while( !plrAtEnd(&plReader) ){
      if( iColumn==-1 || plrColumn(&plReader)==iColumn ){
        if( !match ){
          plwInit(&plWriter, &dlWriter, dlrDocid(&dlReader));
          match = 1;
        }
        plwAdd(&plWriter, plrColumn(&plReader), plrPosition(&plReader),
               plrStartOffset(&plReader), plrEndOffset(&plReader));
      }
      plrStep(&plReader);
    }
    if( match ){
      plwTerminate(&plWriter);
      plwDestroy(&plWriter);
    }

    plrDestroy(&plReader);
    dlrStep(&dlReader);
  }
  dlwDestroy(&dlWriter);
  dlrDestroy(&dlReader);
}

/* Used by docListMerge() to keep doclists in the ascending order by
** docid, then ascending order by age (so the newest comes first).
*/
typedef struct OrderedDLReader {
  DLReader *pReader;

  /* TODO(shess) If we assume that docListMerge pReaders is ordered by
  ** age (which we do), then we could use pReader comparisons to break
  ** ties.
  */
  int idx;
} OrderedDLReader;

/* Order eof to end, then by docid asc, idx desc. */
static int orderedDLReaderCmp(OrderedDLReader *r1, OrderedDLReader *r2){
  if( dlrAtEnd(r1->pReader) ){
    if( dlrAtEnd(r2->pReader) ) return 0;  /* Both atEnd(). */
    return 1;                              /* Only r1 atEnd(). */
  }
  if( dlrAtEnd(r2->pReader) ) return -1;   /* Only r2 atEnd(). */

  if( dlrDocid(r1->pReader)<dlrDocid(r2->pReader) ) return -1;
  if( dlrDocid(r1->pReader)>dlrDocid(r2->pReader) ) return 1;

  /* Descending on idx. */
  return r2->idx-r1->idx;
}

/* Bubble p[0] to appropriate place in p[1..n-1].  Assumes that
** p[1..n-1] is already sorted.
*/
/* TODO(shess) Is this frequent enough to warrant a binary search?
** Before implementing that, instrument the code to check.  In most
** current usage, I expect that p[0] will be less than p[1] a very
** high proportion of the time.
*/
static void orderedDLReaderReorder(OrderedDLReader *p, int n){
  while( n>1 && orderedDLReaderCmp(p, p+1)>0 ){
    OrderedDLReader tmp = p[0];
    p[0] = p[1];
    p[1] = tmp;
    n--;
    p++;
  }
}

/* Given an array of doclist readers, merge their doclist elements
** into out in sorted order (by docid), dropping elements from older
** readers when there is a duplicate docid.  pReaders is assumed to be
** ordered by age, oldest first.
*/
/* TODO(shess) nReaders must be <= MERGE_COUNT.  This should probably
** be fixed.
*/
static void docListMerge(DataBuffer *out,
                         DLReader *pReaders, int nReaders){
  OrderedDLReader readers[MERGE_COUNT];
  DLWriter writer;
  int i, n;
  const char *pStart = 0;
  int nStart = 0;
  sqlite_int64 iFirstDocid = 0, iLastDocid = 0;

  assert( nReaders>0 );
  if( nReaders==1 ){
    dataBufferAppend(out, dlrDocData(pReaders), dlrAllDataBytes(pReaders));
    return;
  }

  assert( nReaders<=MERGE_COUNT );
  n = 0;
  for(i=0; i<nReaders; i++){
    assert( pReaders[i].iType==pReaders[0].iType );
    readers[i].pReader = pReaders+i;
    readers[i].idx = i;
    n += dlrAllDataBytes(&pReaders[i]);
  }
  /* Conservatively size output to sum of inputs.  Output should end
  ** up strictly smaller than input.
  */
  dataBufferExpand(out, n);

  /* Get the readers into sorted order. */
  while( i-->0 ){
    orderedDLReaderReorder(readers+i, nReaders-i);
  }

  dlwInit(&writer, pReaders[0].iType, out);
  while( !dlrAtEnd(readers[0].pReader) ){
    sqlite_int64 iDocid = dlrDocid(readers[0].pReader);

    /* If this is a continuation of the current buffer to copy, extend
    ** that buffer.  memcpy() seems to be more efficient if it has a
    ** lots of data to copy.
    */
    if( dlrDocData(readers[0].pReader)==pStart+nStart ){
      nStart += dlrDocDataBytes(readers[0].pReader);
    }else{
      if( pStart!=0 ){
        dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
      }
      pStart = dlrDocData(readers[0].pReader);
      nStart = dlrDocDataBytes(readers[0].pReader);
      iFirstDocid = iDocid;
    }
    iLastDocid = iDocid;
    dlrStep(readers[0].pReader);

    /* Drop all of the older elements with the same docid. */
    for(i=1; i<nReaders &&
             !dlrAtEnd(readers[i].pReader) &&
             dlrDocid(readers[i].pReader)==iDocid; i++){
      dlrStep(readers[i].pReader);
    }

    /* Get the readers back into order. */
    while( i-->0 ){
      orderedDLReaderReorder(readers+i, nReaders-i);
    }
  }

  /* Copy over any remaining elements. */
  if( nStart>0 ) dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
  dlwDestroy(&writer);
}

/* pLeft and pRight are DLReaders positioned to the same docid.
**
** If there are no instances in pLeft or pRight where the position
** of pLeft is one less than the position of pRight, then this
** routine adds nothing to pOut.
**
** If there are one or more instances where positions from pLeft
** are exactly one less than positions from pRight, then add a new
** document record to pOut.  If pOut wants to hold positions, then
** include the positions from pRight that are one more than a
** position in pLeft.  In other words:  pRight.iPos==pLeft.iPos+1.
*/
static void mergePosList(DLReader *pLeft, DLReader *pRight, DLWriter *pOut){
  PLReader left, right;
  PLWriter writer;
  int match = 0;

  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
  assert( pOut->iType!=DL_POSITIONS_OFFSETS );

  plrInit(&left, pLeft);
  plrInit(&right, pRight);

  while( !plrAtEnd(&left) && !plrAtEnd(&right) ){
    if( plrColumn(&left)<plrColumn(&right) ){
      plrStep(&left);
    }else if( plrColumn(&left)>plrColumn(&right) ){
      plrStep(&right);
    }else if( plrPosition(&left)+1<plrPosition(&right) ){
      plrStep(&left);
    }else if( plrPosition(&left)+1>plrPosition(&right) ){
      plrStep(&right);
    }else{
      if( !match ){
        plwInit(&writer, pOut, dlrDocid(pLeft));
        match = 1;
      }
      plwAdd(&writer, plrColumn(&right), plrPosition(&right), 0, 0);
      plrStep(&left);
      plrStep(&right);
    }
  }

  if( match ){
    plwTerminate(&writer);
    plwDestroy(&writer);
  }

  plrDestroy(&left);
  plrDestroy(&right);
}

/* We have two doclists with positions:  pLeft and pRight.
** Write the phrase intersection of these two doclists into pOut.
**
** A phrase intersection means that two documents only match
** if pLeft.iPos+1==pRight.iPos.
**
** iType controls the type of data written to pOut.  If iType is
** DL_POSITIONS, the positions are those from pRight.
*/
static void docListPhraseMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DocListType iType,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 || nRight==0 ) return;

  assert( iType!=DL_POSITIONS_OFFSETS );

  dlrInit(&left, DL_POSITIONS, pLeft, nLeft);
  dlrInit(&right, DL_POSITIONS, pRight, nRight);
  dlwInit(&writer, iType, pOut);

  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
    if( dlrDocid(&left)<dlrDocid(&right) ){
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }else{
      mergePosList(&left, &right, &writer);
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* We have two DL_DOCIDS doclists:  pLeft and pRight.
** Write the intersection of these two doclists into pOut as a
** DL_DOCIDS doclist.
*/
static void docListAndMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 || nRight==0 ) return;

  dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
  dlrInit(&right, DL_DOCIDS, pRight, nRight);
  dlwInit(&writer, DL_DOCIDS, pOut);

  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
    if( dlrDocid(&left)<dlrDocid(&right) ){
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }else{
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* We have two DL_DOCIDS doclists:  pLeft and pRight.
** Write the union of these two doclists into pOut as a
** DL_DOCIDS doclist.
*/
static void docListOrMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 ){
    dataBufferAppend(pOut, pRight, nRight);
    return;
  }
  if( nRight==0 ){
    dataBufferAppend(pOut, pLeft, nLeft);
    return;
  }

  dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
  dlrInit(&right, DL_DOCIDS, pRight, nRight);
  dlwInit(&writer, DL_DOCIDS, pOut);

  while( !dlrAtEnd(&left) || !dlrAtEnd(&right) ){
    if( dlrAtEnd(&right) ){
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
    }else if( dlrAtEnd(&left) ){
      dlwAdd(&writer, dlrDocid(&right));
      dlrStep(&right);
    }else if( dlrDocid(&left)<dlrDocid(&right) ){
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlwAdd(&writer, dlrDocid(&right));
      dlrStep(&right);
    }else{
      dlwAdd(&writer, dlrDocid(&left));
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* We have two DL_DOCIDS doclists:  pLeft and pRight.
** Write into pOut as DL_DOCIDS doclist containing all documents that
** occur in pLeft but not in pRight.
*/
static void docListExceptMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 ) return;
  if( nRight==0 ){
    dataBufferAppend(pOut, pLeft, nLeft);
    return;
  }

  dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
  dlrInit(&right, DL_DOCIDS, pRight, nRight);
  dlwInit(&writer, DL_DOCIDS, pOut);

  while( !dlrAtEnd(&left) ){
    while( !dlrAtEnd(&right) && dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }
    if( dlrAtEnd(&right) || dlrDocid(&left)<dlrDocid(&right) ){
      dlwAdd(&writer, dlrDocid(&left));
    }
    dlrStep(&left);
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

static char *string_dup_n(const char *s, int n){
  char *str = malloc(n + 1);
  memcpy(str, s, n);
  str[n] = '\0';
  return str;
}

/* Duplicate a string; the caller must free() the returned string.
 * (We don't use strdup() since it's not part of the standard C library and
 * may not be available everywhere.) */
static char *string_dup(const char *s){
  return string_dup_n(s, strlen(s));
}

/* Format a string, replacing each occurrence of the % character with
 * zDb.zName.  This may be more convenient than sqlite_mprintf()
 * when one string is used repeatedly in a format string.
 * The caller must free() the returned string. */
static char *string_format(const char *zFormat,
                           const char *zDb, const char *zName){
  const char *p;
  size_t len = 0;
  size_t nDb = strlen(zDb);
  size_t nName = strlen(zName);
  size_t nFullTableName = nDb+1+nName;
  char *result;
  char *r;

  /* first compute length needed */
  for(p = zFormat ; *p ; ++p){
    len += (*p=='%' ? nFullTableName : 1);
  }
  len += 1;  /* for null terminator */

  r = result = malloc(len);
  for(p = zFormat; *p; ++p){
    if( *p=='%' ){
      memcpy(r, zDb, nDb);
      r += nDb;
      *r++ = '.';
      memcpy(r, zName, nName);
      r += nName;
    } else {
      *r++ = *p;
    }
  }
  *r++ = '\0';
  assert( r == result + len );
  return result;
}

static int sql_exec(sqlite3 *db, const char *zDb, const char *zName,
                    const char *zFormat){
  char *zCommand = string_format(zFormat, zDb, zName);
  int rc;
  TRACE(("FTS2 sql: %s\n", zCommand));
  rc = sqlite3_exec(db, zCommand, NULL, 0, NULL);
  free(zCommand);
  return rc;
}

static int sql_prepare(sqlite3 *db, const char *zDb, const char *zName,
                       sqlite3_stmt **ppStmt, const char *zFormat){
  char *zCommand = string_format(zFormat, zDb, zName);
  int rc;
  TRACE(("FTS2 prepare: %s\n", zCommand));
  rc = sqlite3_prepare(db, zCommand, -1, ppStmt, NULL);
  free(zCommand);
  return rc;
}

/* end utility functions */

/* Forward reference */
typedef struct fulltext_vtab fulltext_vtab;

/* A single term in a query is represented by an instances of
** the following structure.
*/
typedef struct QueryTerm {
  short int nPhrase; /* How many following terms are part of the same phrase */
  short int iPhrase; /* This is the i-th term of a phrase. */
  short int iColumn; /* Column of the index that must match this term */
  signed char isOr;  /* this term is preceded by "OR" */
  signed char isNot; /* this term is preceded by "-" */
  char *pTerm;       /* text of the term.  '\000' terminated.  malloced */
  int nTerm;         /* Number of bytes in pTerm[] */
} QueryTerm;


/* A query string is parsed into a Query structure.
 *
 * We could, in theory, allow query strings to be complicated
 * nested expressions with precedence determined by parentheses.
 * But none of the major search engines do this.  (Perhaps the
 * feeling is that an parenthesized expression is two complex of
 * an idea for the average user to grasp.)  Taking our lead from
 * the major search engines, we will allow queries to be a list
 * of terms (with an implied AND operator) or phrases in double-quotes,
 * with a single optional "-" before each non-phrase term to designate
 * negation and an optional OR connector.
 *
 * OR binds more tightly than the implied AND, which is what the
 * major search engines seem to do.  So, for example:
 * 
 *    [one two OR three]     ==>    one AND (two OR three)
 *    [one OR two three]     ==>    (one OR two) AND three
 *
 * A "-" before a term matches all entries that lack that term.
 * The "-" must occur immediately before the term with in intervening
 * space.  This is how the search engines do it.
 *
 * A NOT term cannot be the right-hand operand of an OR.  If this
 * occurs in the query string, the NOT is ignored:
 *
 *    [one OR -two]          ==>    one OR two
 *
 */
typedef struct Query {
  fulltext_vtab *pFts;  /* The full text index */
  int nTerms;           /* Number of terms in the query */
  QueryTerm *pTerms;    /* Array of terms.  Space obtained from malloc() */
  int nextIsOr;         /* Set the isOr flag on the next inserted term */
  int nextColumn;       /* Next word parsed must be in this column */
  int dfltColumn;       /* The default column */
} Query;


/*
** An instance of the following structure keeps track of generated
** matching-word offset information and snippets.
*/
typedef struct Snippet {
  int nMatch;     /* Total number of matches */
  int nAlloc;     /* Space allocated for aMatch[] */
  struct snippetMatch { /* One entry for each matching term */
    char snStatus;       /* Status flag for use while constructing snippets */
    short int iCol;      /* The column that contains the match */
    short int iTerm;     /* The index in Query.pTerms[] of the matching term */
    short int nByte;     /* Number of bytes in the term */
    int iStart;          /* The offset to the first character of the term */
  } *aMatch;      /* Points to space obtained from malloc */
  char *zOffset;  /* Text rendering of aMatch[] */
  int nOffset;    /* strlen(zOffset) */
  char *zSnippet; /* Snippet text */
  int nSnippet;   /* strlen(zSnippet) */
} Snippet;


typedef enum QueryType {
  QUERY_GENERIC,   /* table scan */
  QUERY_ROWID,     /* lookup by rowid */
  QUERY_FULLTEXT   /* QUERY_FULLTEXT + [i] is a full-text search for column i*/
} QueryType;

typedef enum fulltext_statement {
  CONTENT_INSERT_STMT,
  CONTENT_SELECT_STMT,
  CONTENT_UPDATE_STMT,
  CONTENT_DELETE_STMT,

  BLOCK_INSERT_STMT,
  BLOCK_SELECT_STMT,
  BLOCK_DELETE_STMT,

  SEGDIR_MAX_INDEX_STMT,
  SEGDIR_SET_STMT,
  SEGDIR_SELECT_STMT,
  SEGDIR_SPAN_STMT,
  SEGDIR_DELETE_STMT,
  SEGDIR_SELECT_ALL_STMT,

  MAX_STMT                     /* Always at end! */
} fulltext_statement;

/* These must exactly match the enum above. */
/* TODO(shess): Is there some risk that a statement will be used in two
** cursors at once, e.g.  if a query joins a virtual table to itself?
** If so perhaps we should move some of these to the cursor object.
*/
static const char *const fulltext_zStatement[MAX_STMT] = {
  /* CONTENT_INSERT */ NULL,  /* generated in contentInsertStatement() */
  /* CONTENT_SELECT */ "select * from %_content where rowid = ?",
  /* CONTENT_UPDATE */ NULL,  /* generated in contentUpdateStatement() */
  /* CONTENT_DELETE */ "delete from %_content where rowid = ?",

  /* BLOCK_INSERT */ "insert into %_segments values (?)",
  /* BLOCK_SELECT */ "select block from %_segments where rowid = ?",
  /* BLOCK_DELETE */ "delete from %_segments where rowid between ? and ?",

  /* SEGDIR_MAX_INDEX */ "select max(idx) from %_segdir where level = ?",
  /* SEGDIR_SET */ "insert into %_segdir values (?, ?, ?, ?, ?, ?)",
  /* SEGDIR_SELECT */
  "select start_block, leaves_end_block, root from %_segdir "
  " where level = ? order by idx",
  /* SEGDIR_SPAN */
  "select min(start_block), max(end_block) from %_segdir "
  " where level = ? and start_block <> 0",
  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",
  /* SEGDIR_SELECT_ALL */ "select root from %_segdir order by level desc, idx",
};

/*
** A connection to a fulltext index is an instance of the following
** structure.  The xCreate and xConnect methods create an instance
** of this structure and xDestroy and xDisconnect free that instance.
** All other methods receive a pointer to the structure as one of their
** arguments.
*/
struct fulltext_vtab {
  sqlite3_vtab base;               /* Base class used by SQLite core */
  sqlite3 *db;                     /* The database connection */
  const char *zDb;                 /* logical database name */
  const char *zName;               /* virtual table name */
  int nColumn;                     /* number of columns in virtual table */
  char **azColumn;                 /* column names.  malloced */
  char **azContentColumn;          /* column names in content table; malloced */
  sqlite3_tokenizer *pTokenizer;   /* tokenizer for inserts and queries */

  /* Precompiled statements which we keep as long as the table is
  ** open.
  */
  sqlite3_stmt *pFulltextStatements[MAX_STMT];

  /* Precompiled statements used for segment merges.  We run a
  ** separate select across the leaf level of each tree being merged.
  */
  sqlite3_stmt *pLeafSelectStmts[MERGE_COUNT];
  /* The statement used to prepare pLeafSelectStmts. */
#define LEAF_SELECT \
  "select block from %_segments where rowid between ? and ? order by rowid"

  /* These buffer pending index updates during transactions.
  ** nPendingData estimates the memory size of the pending data.  It
  ** doesn't include the hash-bucket overhead, nor any malloc
  ** overhead.  When nPendingData exceeds kPendingThreshold, the
  ** buffer is flushed even before the transaction closes.
  ** pendingTerms stores the data, and is only valid when nPendingData
  ** is >=0 (nPendingData<0 means pendingTerms has not been
  ** initialized).  iPrevDocid is the last docid written, used to make
  ** certain we're inserting in sorted order.
  */
  int nPendingData;
#define kPendingThreshold (1*1024*1024)
  sqlite_int64 iPrevDocid;
  fts2Hash pendingTerms;
};

/*
** When the core wants to do a query, it create a cursor using a
** call to xOpen.  This structure is an instance of a cursor.  It
** is destroyed by xClose.
*/
typedef struct fulltext_cursor {
  sqlite3_vtab_cursor base;        /* Base class used by SQLite core */
  QueryType iCursorType;           /* Copy of sqlite3_index_info.idxNum */
  sqlite3_stmt *pStmt;             /* Prepared statement in use by the cursor */
  int eof;                         /* True if at End Of Results */
  Query q;                         /* Parsed query string */
  Snippet snippet;                 /* Cached snippet for the current row */
  int iColumn;                     /* Column being searched */
  DataBuffer result;               /* Doclist results from fulltextQuery */
  DLReader reader;                 /* Result reader if result not empty */
} fulltext_cursor;

static struct fulltext_vtab *cursor_vtab(fulltext_cursor *c){
  return (fulltext_vtab *) c->base.pVtab;
}

static const sqlite3_module fulltextModule;   /* forward declaration */

/* Return a dynamically generated statement of the form
 *   insert into %_content (rowid, ...) values (?, ...)
 */
static const char *contentInsertStatement(fulltext_vtab *v){
  StringBuffer sb;
  int i;

  initStringBuffer(&sb);
  append(&sb, "insert into %_content (rowid, ");
  appendList(&sb, v->nColumn, v->azContentColumn);
  append(&sb, ") values (?");
  for(i=0; i<v->nColumn; ++i)
    append(&sb, ", ?");
  append(&sb, ")");
  return stringBufferData(&sb);
}

/* Return a dynamically generated statement of the form
 *   update %_content set [col_0] = ?, [col_1] = ?, ...
 *                    where rowid = ?
 */
static const char *contentUpdateStatement(fulltext_vtab *v){
  StringBuffer sb;
  int i;

  initStringBuffer(&sb);
  append(&sb, "update %_content set ");
  for(i=0; i<v->nColumn; ++i) {
    if( i>0 ){
      append(&sb, ", ");
    }
    append(&sb, v->azContentColumn[i]);
    append(&sb, " = ?");
  }
  append(&sb, " where rowid = ?");
  return stringBufferData(&sb);
}

/* Puts a freshly-prepared statement determined by iStmt in *ppStmt.
** If the indicated statement has never been prepared, it is prepared
** and cached, otherwise the cached version is reset.
*/
static int sql_get_statement(fulltext_vtab *v, fulltext_statement iStmt,
                             sqlite3_stmt **ppStmt){
  assert( iStmt<MAX_STMT );
  if( v->pFulltextStatements[iStmt]==NULL ){
    const char *zStmt;
    int rc;
    switch( iStmt ){
      case CONTENT_INSERT_STMT:
        zStmt = contentInsertStatement(v); break;
      case CONTENT_UPDATE_STMT:
        zStmt = contentUpdateStatement(v); break;
      default:
        zStmt = fulltext_zStatement[iStmt];
    }
    rc = sql_prepare(v->db, v->zDb, v->zName, &v->pFulltextStatements[iStmt],
                         zStmt);
    if( zStmt != fulltext_zStatement[iStmt]) free((void *) zStmt);
    if( rc!=SQLITE_OK ) return rc;
  } else {
    int rc = sqlite3_reset(v->pFulltextStatements[iStmt]);
    if( rc!=SQLITE_OK ) return rc;
  }

  *ppStmt = v->pFulltextStatements[iStmt];
  return SQLITE_OK;
}

/* Step the indicated statement, handling errors SQLITE_BUSY (by
** retrying) and SQLITE_SCHEMA (by re-preparing and transferring
** bindings to the new statement).
** TODO(adam): We should extend this function so that it can work with
** statements declared locally, not only globally cached statements.
*/
static int sql_step_statement(fulltext_vtab *v, fulltext_statement iStmt,
                              sqlite3_stmt **ppStmt){
  int rc;
  sqlite3_stmt *s = *ppStmt;
  assert( iStmt<MAX_STMT );
  assert( s==v->pFulltextStatements[iStmt] );

  while( (rc=sqlite3_step(s))!=SQLITE_DONE && rc!=SQLITE_ROW ){
    sqlite3_stmt *pNewStmt;

    if( rc==SQLITE_BUSY ) continue;
    if( rc!=SQLITE_ERROR ) return rc;

    rc = sqlite3_reset(s);
    if( rc!=SQLITE_SCHEMA ) return SQLITE_ERROR;

    v->pFulltextStatements[iStmt] = NULL;   /* Still in s */
    rc = sql_get_statement(v, iStmt, &pNewStmt);
    if( rc!=SQLITE_OK ) goto err;
    *ppStmt = pNewStmt;

    rc = sqlite3_transfer_bindings(s, pNewStmt);
    if( rc!=SQLITE_OK ) goto err;

    rc = sqlite3_finalize(s);
    if( rc!=SQLITE_OK ) return rc;
    s = pNewStmt;
  }
  return rc;

 err:
  sqlite3_finalize(s);
  return rc;
}

/* Like sql_step_statement(), but convert SQLITE_DONE to SQLITE_OK.
** Useful for statements like UPDATE, where we expect no results.
*/
static int sql_single_step_statement(fulltext_vtab *v,
                                     fulltext_statement iStmt,
                                     sqlite3_stmt **ppStmt){
  int rc = sql_step_statement(v, iStmt, ppStmt);
  return (rc==SQLITE_DONE) ? SQLITE_OK : rc;
}

/* Like sql_get_statement(), but for special replicated LEAF_SELECT
** statements.
*/
/* TODO(shess) Write version for generic statements and then share
** that between the cached-statement functions.
*/
static int sql_get_leaf_statement(fulltext_vtab *v, int idx,
                                  sqlite3_stmt **ppStmt){
  assert( idx>=0 && idx<MERGE_COUNT );
  if( v->pLeafSelectStmts[idx]==NULL ){
    int rc = sql_prepare(v->db, v->zDb, v->zName, &v->pLeafSelectStmts[idx],
                         LEAF_SELECT);
    if( rc!=SQLITE_OK ) return rc;
  }else{
    int rc = sqlite3_reset(v->pLeafSelectStmts[idx]);
    if( rc!=SQLITE_OK ) return rc;
  }

  *ppStmt = v->pLeafSelectStmts[idx];
  return SQLITE_OK;
}

/* Like sql_step_statement(), but for special replicated LEAF_SELECT
** statements.
*/
/* TODO(shess) Write version for generic statements and then share
** that between the cached-statement functions.
*/
static int sql_step_leaf_statement(fulltext_vtab *v, int idx,
                                   sqlite3_stmt **ppStmt){
  int rc;
  sqlite3_stmt *s = *ppStmt;

  while( (rc=sqlite3_step(s))!=SQLITE_DONE && rc!=SQLITE_ROW ){
    sqlite3_stmt *pNewStmt;

    if( rc==SQLITE_BUSY ) continue;
    if( rc!=SQLITE_ERROR ) return rc;

    rc = sqlite3_reset(s);
    if( rc!=SQLITE_SCHEMA ) return SQLITE_ERROR;

    v->pLeafSelectStmts[idx] = NULL;   /* Still in s */
    rc = sql_get_leaf_statement(v, idx, &pNewStmt);
    if( rc!=SQLITE_OK ) goto err;
    *ppStmt = pNewStmt;

    rc = sqlite3_transfer_bindings(s, pNewStmt);
    if( rc!=SQLITE_OK ) goto err;

    rc = sqlite3_finalize(s);
    if( rc!=SQLITE_OK ) return rc;
    s = pNewStmt;
  }
  return rc;

 err:
  sqlite3_finalize(s);
  return rc;
}

/* insert into %_content (rowid, ...) values ([rowid], [pValues]) */
static int content_insert(fulltext_vtab *v, sqlite3_value *rowid,
                          sqlite3_value **pValues){
  sqlite3_stmt *s;
  int i;
  int rc = sql_get_statement(v, CONTENT_INSERT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_value(s, 1, rowid);
  if( rc!=SQLITE_OK ) return rc;

  for(i=0; i<v->nColumn; ++i){
    rc = sqlite3_bind_value(s, 2+i, pValues[i]);
    if( rc!=SQLITE_OK ) return rc;
  }

  return sql_single_step_statement(v, CONTENT_INSERT_STMT, &s);
}

/* update %_content set col0 = pValues[0], col1 = pValues[1], ...
 *                  where rowid = [iRowid] */
static int content_update(fulltext_vtab *v, sqlite3_value **pValues,
                          sqlite_int64 iRowid){
  sqlite3_stmt *s;
  int i;
  int rc = sql_get_statement(v, CONTENT_UPDATE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  for(i=0; i<v->nColumn; ++i){
    rc = sqlite3_bind_value(s, 1+i, pValues[i]);
    if( rc!=SQLITE_OK ) return rc;
  }

  rc = sqlite3_bind_int64(s, 1+v->nColumn, iRowid);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step_statement(v, CONTENT_UPDATE_STMT, &s);
}

static void freeStringArray(int nString, const char **pString){
  int i;

  for (i=0 ; i < nString ; ++i) {
    if( pString[i]!=NULL ) free((void *) pString[i]);
  }
  free((void *) pString);
}

/* select * from %_content where rowid = [iRow]
 * The caller must delete the returned array and all strings in it.
 * null fields will be NULL in the returned array.
 *
 * TODO: Perhaps we should return pointer/length strings here for consistency
 * with other code which uses pointer/length. */
static int content_select(fulltext_vtab *v, sqlite_int64 iRow,
                          const char ***pValues){
  sqlite3_stmt *s;
  const char **values;
  int i;
  int rc;

  *pValues = NULL;

  rc = sql_get_statement(v, CONTENT_SELECT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iRow);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_step_statement(v, CONTENT_SELECT_STMT, &s);
  if( rc!=SQLITE_ROW ) return rc;

  values = (const char **) malloc(v->nColumn * sizeof(const char *));
  for(i=0; i<v->nColumn; ++i){
    if( sqlite3_column_type(s, i)==SQLITE_NULL ){
      values[i] = NULL;
    }else{
      values[i] = string_dup((char*)sqlite3_column_text(s, i));
    }
  }

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_DONE ){
    *pValues = values;
    return SQLITE_OK;
  }

  freeStringArray(v->nColumn, values);
  return rc;
}

/* delete from %_content where rowid = [iRow ] */
static int content_delete(fulltext_vtab *v, sqlite_int64 iRow){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, CONTENT_DELETE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iRow);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step_statement(v, CONTENT_DELETE_STMT, &s);
}

/* insert into %_segments values ([pData])
**   returns assigned rowid in *piBlockid
*/
static int block_insert(fulltext_vtab *v, const char *pData, int nData,
                        sqlite_int64 *piBlockid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, BLOCK_INSERT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_blob(s, 1, pData, nData, SQLITE_STATIC);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_step_statement(v, BLOCK_INSERT_STMT, &s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;

  *piBlockid = sqlite3_last_insert_rowid(v->db);
  return SQLITE_OK;
}

/* delete from %_segments
**   where rowid between [iStartBlockid] and [iEndBlockid]
**
** Deletes the range of blocks, inclusive, used to delete the blocks
** which form a segment.
*/
static int block_delete(fulltext_vtab *v,
                        sqlite_int64 iStartBlockid, sqlite_int64 iEndBlockid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, BLOCK_DELETE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iStartBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 2, iEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step_statement(v, BLOCK_DELETE_STMT, &s);
}

/* Returns SQLITE_ROW with *pidx set to the maximum segment idx found
** at iLevel.  Returns SQLITE_DONE if there are no segments at
** iLevel.  Otherwise returns an error.
*/
static int segdir_max_index(fulltext_vtab *v, int iLevel, int *pidx){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_MAX_INDEX_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_step_statement(v, SEGDIR_MAX_INDEX_STMT, &s);
  /* Should always get at least one row due to how max() works. */
  if( rc==SQLITE_DONE ) return SQLITE_DONE;
  if( rc!=SQLITE_ROW ) return rc;

  /* NULL means that there were no inputs to max(). */
  if( SQLITE_NULL==sqlite3_column_type(s, 0) ){
    rc = sqlite3_step(s);
    if( rc==SQLITE_ROW ) return SQLITE_ERROR;
    return rc;
  }

  *pidx = sqlite3_column_int(s, 0);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;
  return SQLITE_ROW;
}

/* insert into %_segdir values (
**   [iLevel], [idx],
**   [iStartBlockid], [iLeavesEndBlockid], [iEndBlockid],
**   [pRootData]
** )
*/
static int segdir_set(fulltext_vtab *v, int iLevel, int idx,
                      sqlite_int64 iStartBlockid,
                      sqlite_int64 iLeavesEndBlockid,
                      sqlite_int64 iEndBlockid,
                      const char *pRootData, int nRootData){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SET_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 2, idx);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 3, iStartBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 4, iLeavesEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 5, iEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_blob(s, 6, pRootData, nRootData, SQLITE_STATIC);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step_statement(v, SEGDIR_SET_STMT, &s);
}

/* Queries %_segdir for the block span of the segments in level
** iLevel.  Returns SQLITE_DONE if there are no blocks for iLevel,
** SQLITE_ROW if there are blocks, else an error.
*/
static int segdir_span(fulltext_vtab *v, int iLevel,
                       sqlite_int64 *piStartBlockid,
                       sqlite_int64 *piEndBlockid){
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SPAN_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_step_statement(v, SEGDIR_SPAN_STMT, &s);
  if( rc==SQLITE_DONE ) return SQLITE_DONE;  /* Should never happen */
  if( rc!=SQLITE_ROW ) return rc;

  /* This happens if all segments at this level are entirely inline. */
  if( SQLITE_NULL==sqlite3_column_type(s, 0) ){
    /* We expect only one row.  We must execute another sqlite3_step()
     * to complete the iteration; otherwise the table will remain locked. */
    int rc2 = sqlite3_step(s);
    if( rc2==SQLITE_ROW ) return SQLITE_ERROR;
    return rc2;
  }

  *piStartBlockid = sqlite3_column_int64(s, 0);
  *piEndBlockid = sqlite3_column_int64(s, 1);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;
  return SQLITE_ROW;
}

/* Delete the segment blocks and segment directory records for all
** segments at iLevel.
*/
static int segdir_delete(fulltext_vtab *v, int iLevel){
  sqlite3_stmt *s;
  sqlite_int64 iStartBlockid, iEndBlockid;
  int rc = segdir_span(v, iLevel, &iStartBlockid, &iEndBlockid);
  if( rc!=SQLITE_ROW && rc!=SQLITE_DONE ) return rc;

  if( rc==SQLITE_ROW ){
    rc = block_delete(v, iStartBlockid, iEndBlockid);
    if( rc!=SQLITE_OK ) return rc;
  }

  /* Delete the segment directory itself. */
  rc = sql_get_statement(v, SEGDIR_DELETE_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  return sql_single_step_statement(v, SEGDIR_DELETE_STMT, &s);
}

/* TODO(shess) clearPendingTerms() is far down the file because
** writeZeroSegment() is far down the file because LeafWriter is far
** down the file.  Consider refactoring the code to move the non-vtab
** code above the vtab code so that we don't need this forward
** reference.
*/
static int clearPendingTerms(fulltext_vtab *v);

/*
** Free the memory used to contain a fulltext_vtab structure.
*/
static void fulltext_vtab_destroy(fulltext_vtab *v){
  int iStmt, i;

  TRACE(("FTS2 Destroy %p\n", v));
  for( iStmt=0; iStmt<MAX_STMT; iStmt++ ){
    if( v->pFulltextStatements[iStmt]!=NULL ){
      sqlite3_finalize(v->pFulltextStatements[iStmt]);
      v->pFulltextStatements[iStmt] = NULL;
    }
  }

  for( i=0; i<MERGE_COUNT; i++ ){
    if( v->pLeafSelectStmts[i]!=NULL ){
      sqlite3_finalize(v->pLeafSelectStmts[i]);
      v->pLeafSelectStmts[i] = NULL;
    }
  }

  if( v->pTokenizer!=NULL ){
    v->pTokenizer->pModule->xDestroy(v->pTokenizer);
    v->pTokenizer = NULL;
  }

  clearPendingTerms(v);

  free(v->azColumn);
  for(i = 0; i < v->nColumn; ++i) {
    sqlite3_free(v->azContentColumn[i]);
  }
  free(v->azContentColumn);
  free(v);
}

/*
** Token types for parsing the arguments to xConnect or xCreate.
*/
#define TOKEN_EOF         0    /* End of file */
#define TOKEN_SPACE       1    /* Any kind of whitespace */
#define TOKEN_ID          2    /* An identifier */
#define TOKEN_STRING      3    /* A string literal */
#define TOKEN_PUNCT       4    /* A single punctuation character */

/*
** If X is a character that can be used in an identifier then
** IdChar(X) will be true.  Otherwise it is false.
**
** For ASCII, any character with the high-order bit set is
** allowed in an identifier.  For 7-bit characters, 
** sqlite3IsIdChar[X] must be 1.
**
** Ticket #1066.  the SQL standard does not allow '$' in the
** middle of identfiers.  But many SQL implementations do. 
** SQLite will allow '$' in identifiers for compatibility.
** But the feature is undocumented.
*/
static const char isIdChar[] = {
/* x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 xA xB xC xD xE xF */
    0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  /* 2x */
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,  /* 3x */
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  /* 4x */
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,  /* 5x */
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  /* 6x */
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,  /* 7x */
};
#define IdChar(C)  (((c=C)&0x80)!=0 || (c>0x1f && isIdChar[c-0x20]))


/*
** Return the length of the token that begins at z[0]. 
** Store the token type in *tokenType before returning.
*/
static int getToken(const char *z, int *tokenType){
  int i, c;
  switch( *z ){
    case 0: {
      *tokenType = TOKEN_EOF;
      return 0;
    }
    case ' ': case '\t': case '\n': case '\f': case '\r': {
      for(i=1; safe_isspace(z[i]); i++){}
      *tokenType = TOKEN_SPACE;
      return i;
    }
    case '\'':
    case '"': {
      int delim = z[0];
      for(i=1; (c=z[i])!=0; i++){
        if( c==delim ){
          if( z[i+1]==delim ){
            i++;
          }else{
            break;
          }
        }
      }
      *tokenType = TOKEN_STRING;
      return i + (c!=0);
    }
    case '[': {
      for(i=1, c=z[0]; c!=']' && (c=z[i])!=0; i++){}
      *tokenType = TOKEN_ID;
      return i;
    }
    default: {
      if( !IdChar(*z) ){
        break;
      }
      for(i=1; IdChar(z[i]); i++){}
      *tokenType = TOKEN_ID;
      return i;
    }
  }
  *tokenType = TOKEN_PUNCT;
  return 1;
}

/*
** A token extracted from a string is an instance of the following
** structure.
*/
typedef struct Token {
  const char *z;       /* Pointer to token text.  Not '\000' terminated */
  short int n;         /* Length of the token text in bytes. */
} Token;

/*
** Given a input string (which is really one of the argv[] parameters
** passed into xConnect or xCreate) split the string up into tokens.
** Return an array of pointers to '\000' terminated strings, one string
** for each non-whitespace token.
**
** The returned array is terminated by a single NULL pointer.
**
** Space to hold the returned array is obtained from a single
** malloc and should be freed by passing the return value to free().
** The individual strings within the token list are all a part of
** the single memory allocation and will all be freed at once.
*/
static char **tokenizeString(const char *z, int *pnToken){
  int nToken = 0;
  Token *aToken = malloc( strlen(z) * sizeof(aToken[0]) );
  int n = 1;
  int e, i;
  int totalSize = 0;
  char **azToken;
  char *zCopy;
  while( n>0 ){
    n = getToken(z, &e);
    if( e!=TOKEN_SPACE ){
      aToken[nToken].z = z;
      aToken[nToken].n = n;
      nToken++;
      totalSize += n+1;
    }
    z += n;
  }
  azToken = (char**)malloc( nToken*sizeof(char*) + totalSize );
  zCopy = (char*)&azToken[nToken];
  nToken--;
  for(i=0; i<nToken; i++){
    azToken[i] = zCopy;
    n = aToken[i].n;
    memcpy(zCopy, aToken[i].z, n);
    zCopy[n] = 0;
    zCopy += n+1;
  }
  azToken[nToken] = 0;
  free(aToken);
  *pnToken = nToken;
  return azToken;
}

/*
** Convert an SQL-style quoted string into a normal string by removing
** the quote characters.  The conversion is done in-place.  If the
** input does not begin with a quote character, then this routine
** is a no-op.
**
** Examples:
**
**     "abc"   becomes   abc
**     'xyz'   becomes   xyz
**     [pqr]   becomes   pqr
**     `mno`   becomes   mno
*/
static void dequoteString(char *z){
  int quote;
  int i, j;
  if( z==0 ) return;
  quote = z[0];
  switch( quote ){
    case '\'':  break;
    case '"':   break;
    case '`':   break;                /* For MySQL compatibility */
    case '[':   quote = ']';  break;  /* For MS SqlServer compatibility */
    default:    return;
  }
  for(i=1, j=0; z[i]; i++){
    if( z[i]==quote ){
      if( z[i+1]==quote ){
        z[j++] = quote;
        i++;
      }else{
        z[j++] = 0;
        break;
      }
    }else{
      z[j++] = z[i];
    }
  }
}

/*
** The input azIn is a NULL-terminated list of tokens.  Remove the first
** token and all punctuation tokens.  Remove the quotes from
** around string literal tokens.
**
** Example:
**
**     input:      tokenize chinese ( 'simplifed' , 'mixed' )
**     output:     chinese simplifed mixed
**
** Another example:
**
**     input:      delimiters ( '[' , ']' , '...' )
**     output:     [ ] ...
*/
static void tokenListToIdList(char **azIn){
  int i, j;
  if( azIn ){
    for(i=0, j=-1; azIn[i]; i++){
      if( safe_isalnum(azIn[i][0]) || azIn[i][1] ){
        dequoteString(azIn[i]);
        if( j>=0 ){
          azIn[j] = azIn[i];
        }
        j++;
      }
    }
    azIn[j] = 0;
  }
}


/*
** Find the first alphanumeric token in the string zIn.  Null-terminate
** this token.  Remove any quotation marks.  And return a pointer to
** the result.
*/
static char *firstToken(char *zIn, char **pzTail){
  int n, ttype;
  while(1){
    n = getToken(zIn, &ttype);
    if( ttype==TOKEN_SPACE ){
      zIn += n;
    }else if( ttype==TOKEN_EOF ){
      *pzTail = zIn;
      return 0;
    }else{
      zIn[n] = 0;
      *pzTail = &zIn[1];
      dequoteString(zIn);
      return zIn;
    }
  }
  /*NOTREACHED*/
}

/* Return true if...
**
**   *  s begins with the string t, ignoring case
**   *  s is longer than t
**   *  The first character of s beyond t is not a alphanumeric
** 
** Ignore leading space in *s.
**
** To put it another way, return true if the first token of
** s[] is t[].
*/
static int startsWith(const char *s, const char *t){
  while( safe_isspace(*s) ){ s++; }
  while( *t ){
    if( safe_tolower(*s++)!=safe_tolower(*t++) ) return 0;
  }
  return *s!='_' && !safe_isalnum(*s);
}

/*
** An instance of this structure defines the "spec" of a
** full text index.  This structure is populated by parseSpec
** and use by fulltextConnect and fulltextCreate.
*/
typedef struct TableSpec {
  const char *zDb;         /* Logical database name */
  const char *zName;       /* Name of the full-text index */
  int nColumn;             /* Number of columns to be indexed */
  char **azColumn;         /* Original names of columns to be indexed */
  char **azContentColumn;  /* Column names for %_content */
  char **azTokenizer;      /* Name of tokenizer and its arguments */
} TableSpec;

/*
** Reclaim all of the memory used by a TableSpec
*/
static void clearTableSpec(TableSpec *p) {
  free(p->azColumn);
  free(p->azContentColumn);
  free(p->azTokenizer);
}

/* Parse a CREATE VIRTUAL TABLE statement, which looks like this:
 *
 * CREATE VIRTUAL TABLE email
 *        USING fts2(subject, body, tokenize mytokenizer(myarg))
 *
 * We return parsed information in a TableSpec structure.
 * 
 */
static int parseSpec(TableSpec *pSpec, int argc, const char *const*argv,
                     char**pzErr){
  int i, n;
  char *z, *zDummy;
  char **azArg;
  const char *zTokenizer = 0;    /* argv[] entry describing the tokenizer */

  assert( argc>=3 );
  /* Current interface:
  ** argv[0] - module name
  ** argv[1] - database name
  ** argv[2] - table name
  ** argv[3..] - columns, optionally followed by tokenizer specification
  **             and snippet delimiters specification.
  */

  /* Make a copy of the complete argv[][] array in a single allocation.
  ** The argv[][] array is read-only and transient.  We can write to the
  ** copy in order to modify things and the copy is persistent.
  */
  CLEAR(pSpec);
  for(i=n=0; i<argc; i++){
    n += strlen(argv[i]) + 1;
  }
  azArg = malloc( sizeof(char*)*argc + n );
  if( azArg==0 ){
    return SQLITE_NOMEM;
  }
  z = (char*)&azArg[argc];
  for(i=0; i<argc; i++){
    azArg[i] = z;
    strcpy(z, argv[i]);
    z += strlen(z)+1;
  }

  /* Identify the column names and the tokenizer and delimiter arguments
  ** in the argv[][] array.
  */
  pSpec->zDb = azArg[1];
  pSpec->zName = azArg[2];
  pSpec->nColumn = 0;
  pSpec->azColumn = azArg;
  zTokenizer = "tokenize simple";
  for(i=3; i<argc; ++i){
    if( startsWith(azArg[i],"tokenize") ){
      zTokenizer = azArg[i];
    }else{
      z = azArg[pSpec->nColumn] = firstToken(azArg[i], &zDummy);
      pSpec->nColumn++;
    }
  }
  if( pSpec->nColumn==0 ){
    azArg[0] = "content";
    pSpec->nColumn = 1;
  }

  /*
  ** Construct the list of content column names.
  **
  ** Each content column name will be of the form cNNAAAA
  ** where NN is the column number and AAAA is the sanitized
  ** column name.  "sanitized" means that special characters are
  ** converted to "_".  The cNN prefix guarantees that all column
  ** names are unique.
  **
  ** The AAAA suffix is not strictly necessary.  It is included
  ** for the convenience of people who might examine the generated
  ** %_content table and wonder what the columns are used for.
  */
  pSpec->azContentColumn = malloc( pSpec->nColumn * sizeof(char *) );
  if( pSpec->azContentColumn==0 ){
    clearTableSpec(pSpec);
    return SQLITE_NOMEM;
  }
  for(i=0; i<pSpec->nColumn; i++){
    char *p;
    pSpec->azContentColumn[i] = sqlite3_mprintf("c%d%s", i, azArg[i]);
    for (p = pSpec->azContentColumn[i]; *p ; ++p) {
      if( !safe_isalnum(*p) ) *p = '_';
    }
  }

  /*
  ** Parse the tokenizer specification string.
  */
  pSpec->azTokenizer = tokenizeString(zTokenizer, &n);
  tokenListToIdList(pSpec->azTokenizer);

  return SQLITE_OK;
}

/*
** Generate a CREATE TABLE statement that describes the schema of
** the virtual table.  Return a pointer to this schema string.
**
** Space is obtained from sqlite3_mprintf() and should be freed
** using sqlite3_free().
*/
static char *fulltextSchema(
  int nColumn,                  /* Number of columns */
  const char *const* azColumn,  /* List of columns */
  const char *zTableName        /* Name of the table */
){
  int i;
  char *zSchema, *zNext;
  const char *zSep = "(";
  zSchema = sqlite3_mprintf("CREATE TABLE x");
  for(i=0; i<nColumn; i++){
    zNext = sqlite3_mprintf("%s%s%Q", zSchema, zSep, azColumn[i]);
    sqlite3_free(zSchema);
    zSchema = zNext;
    zSep = ",";
  }
  zNext = sqlite3_mprintf("%s,%Q)", zSchema, zTableName);
  sqlite3_free(zSchema);
  return zNext;
}

/*
** Build a new sqlite3_vtab structure that will describe the
** fulltext index defined by spec.
*/
static int constructVtab(
  sqlite3 *db,              /* The SQLite database connection */
  TableSpec *spec,          /* Parsed spec information from parseSpec() */
  sqlite3_vtab **ppVTab,    /* Write the resulting vtab structure here */
  char **pzErr              /* Write any error message here */
){
  int rc;
  int n;
  fulltext_vtab *v = 0;
  const sqlite3_tokenizer_module *m = NULL;
  char *schema;

  v = (fulltext_vtab *) malloc(sizeof(fulltext_vtab));
  if( v==0 ) return SQLITE_NOMEM;
  CLEAR(v);
  /* sqlite will initialize v->base */
  v->db = db;
  v->zDb = spec->zDb;       /* Freed when azColumn is freed */
  v->zName = spec->zName;   /* Freed when azColumn is freed */
  v->nColumn = spec->nColumn;
  v->azContentColumn = spec->azContentColumn;
  spec->azContentColumn = 0;
  v->azColumn = spec->azColumn;
  spec->azColumn = 0;

  if( spec->azTokenizer==0 ){
    return SQLITE_NOMEM;
  }
  /* TODO(shess) For now, add new tokenizers as else if clauses. */
  if( spec->azTokenizer[0]==0 || startsWith(spec->azTokenizer[0], "simple") ){
    sqlite3Fts2SimpleTokenizerModule(&m);
  }else if( startsWith(spec->azTokenizer[0], "porter") ){
    sqlite3Fts2PorterTokenizerModule(&m);
  }else{
    *pzErr = sqlite3_mprintf("unknown tokenizer: %s", spec->azTokenizer[0]);
    rc = SQLITE_ERROR;
    goto err;
  }
  for(n=0; spec->azTokenizer[n]; n++){}
  if( n ){
    rc = m->xCreate(n-1, (const char*const*)&spec->azTokenizer[1],
                    &v->pTokenizer);
  }else{
    rc = m->xCreate(0, 0, &v->pTokenizer);
  }
  if( rc!=SQLITE_OK ) goto err;
  v->pTokenizer->pModule = m;

  /* TODO: verify the existence of backing tables foo_content, foo_term */

  schema = fulltextSchema(v->nColumn, (const char*const*)v->azColumn,
                          spec->zName);
  rc = sqlite3_declare_vtab(db, schema);
  sqlite3_free(schema);
  if( rc!=SQLITE_OK ) goto err;

  memset(v->pFulltextStatements, 0, sizeof(v->pFulltextStatements));

  /* Indicate that the buffer is not live. */
  v->nPendingData = -1;

  *ppVTab = &v->base;
  TRACE(("FTS2 Connect %p\n", v));

  return rc;

err:
  fulltext_vtab_destroy(v);
  return rc;
}

static int fulltextConnect(
  sqlite3 *db,
  void *pAux,
  int argc, const char *const*argv,
  sqlite3_vtab **ppVTab,
  char **pzErr
){
  TableSpec spec;
  int rc = parseSpec(&spec, argc, argv, pzErr);
  if( rc!=SQLITE_OK ) return rc;

  rc = constructVtab(db, &spec, ppVTab, pzErr);
  clearTableSpec(&spec);
  return rc;
}

/* The %_content table holds the text of each document, with
** the rowid used as the docid.
*/
/* TODO(shess) This comment needs elaboration to match the updated
** code.  Work it into the top-of-file comment at that time.
*/
static int fulltextCreate(sqlite3 *db, void *pAux,
                          int argc, const char * const *argv,
                          sqlite3_vtab **ppVTab, char **pzErr){
  int rc;
  TableSpec spec;
  StringBuffer schema;
  TRACE(("FTS2 Create\n"));

  rc = parseSpec(&spec, argc, argv, pzErr);
  if( rc!=SQLITE_OK ) return rc;

  initStringBuffer(&schema);
  append(&schema, "CREATE TABLE %_content(");
  appendList(&schema, spec.nColumn, spec.azContentColumn);
  append(&schema, ")");
  rc = sql_exec(db, spec.zDb, spec.zName, stringBufferData(&schema));
  stringBufferDestroy(&schema);
  if( rc!=SQLITE_OK ) goto out;

  rc = sql_exec(db, spec.zDb, spec.zName,
                "create table %_segments(block blob);");
  if( rc!=SQLITE_OK ) goto out;

  rc = sql_exec(db, spec.zDb, spec.zName,
                "create table %_segdir("
                "  level integer,"
                "  idx integer,"
                "  start_block integer,"
                "  leaves_end_block integer,"
                "  end_block integer,"
                "  root blob,"
                "  primary key(level, idx)"
                ");");
  if( rc!=SQLITE_OK ) goto out;

  rc = constructVtab(db, &spec, ppVTab, pzErr);

out:
  clearTableSpec(&spec);
  return rc;
}

/* Decide how to handle an SQL query. */
static int fulltextBestIndex(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
  int i;
  TRACE(("FTS2 BestIndex\n"));

  for(i=0; i<pInfo->nConstraint; ++i){
    const struct sqlite3_index_constraint *pConstraint;
    pConstraint = &pInfo->aConstraint[i];
    if( pConstraint->usable ) {
      if( pConstraint->iColumn==-1 &&
          pConstraint->op==SQLITE_INDEX_CONSTRAINT_EQ ){
        pInfo->idxNum = QUERY_ROWID;      /* lookup by rowid */
        TRACE(("FTS2 QUERY_ROWID\n"));
      } else if( pConstraint->iColumn>=0 &&
                 pConstraint->op==SQLITE_INDEX_CONSTRAINT_MATCH ){
        /* full-text search */
        pInfo->idxNum = QUERY_FULLTEXT + pConstraint->iColumn;
        TRACE(("FTS2 QUERY_FULLTEXT %d\n", pConstraint->iColumn));
      } else continue;

      pInfo->aConstraintUsage[i].argvIndex = 1;
      pInfo->aConstraintUsage[i].omit = 1;

      /* An arbitrary value for now.
       * TODO: Perhaps rowid matches should be considered cheaper than
       * full-text searches. */
      pInfo->estimatedCost = 1.0;   

      return SQLITE_OK;
    }
  }
  pInfo->idxNum = QUERY_GENERIC;
  return SQLITE_OK;
}

static int fulltextDisconnect(sqlite3_vtab *pVTab){
  TRACE(("FTS2 Disconnect %p\n", pVTab));
  fulltext_vtab_destroy((fulltext_vtab *)pVTab);
  return SQLITE_OK;
}

static int fulltextDestroy(sqlite3_vtab *pVTab){
  fulltext_vtab *v = (fulltext_vtab *)pVTab;
  int rc;

  TRACE(("FTS2 Destroy %p\n", pVTab));
  rc = sql_exec(v->db, v->zDb, v->zName,
                "drop table if exists %_content;"
                "drop table if exists %_segments;"
                "drop table if exists %_segdir;"
                );
  if( rc!=SQLITE_OK ) return rc;

  fulltext_vtab_destroy((fulltext_vtab *)pVTab);
  return SQLITE_OK;
}

static int fulltextOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
  fulltext_cursor *c;

  c = (fulltext_cursor *) calloc(sizeof(fulltext_cursor), 1);
  /* sqlite will initialize c->base */
  *ppCursor = &c->base;
  TRACE(("FTS2 Open %p: %p\n", pVTab, c));

  return SQLITE_OK;
}


/* Free all of the dynamically allocated memory held by *q
*/
static void queryClear(Query *q){
  int i;
  for(i = 0; i < q->nTerms; ++i){
    free(q->pTerms[i].pTerm);
  }
  free(q->pTerms);
  CLEAR(q);
}

/* Free all of the dynamically allocated memory held by the
** Snippet
*/
static void snippetClear(Snippet *p){
  free(p->aMatch);
  free(p->zOffset);
  free(p->zSnippet);
  CLEAR(p);
}
/*
** Append a single entry to the p->aMatch[] log.
*/
static void snippetAppendMatch(
  Snippet *p,               /* Append the entry to this snippet */
  int iCol, int iTerm,      /* The column and query term */
  int iStart, int nByte     /* Offset and size of the match */
){
  int i;
  struct snippetMatch *pMatch;
  if( p->nMatch+1>=p->nAlloc ){
    p->nAlloc = p->nAlloc*2 + 10;
    p->aMatch = realloc(p->aMatch, p->nAlloc*sizeof(p->aMatch[0]) );
    if( p->aMatch==0 ){
      p->nMatch = 0;
      p->nAlloc = 0;
      return;
    }
  }
  i = p->nMatch++;
  pMatch = &p->aMatch[i];
  pMatch->iCol = iCol;
  pMatch->iTerm = iTerm;
  pMatch->iStart = iStart;
  pMatch->nByte = nByte;
}

/*
** Sizing information for the circular buffer used in snippetOffsetsOfColumn()
*/
#define FTS2_ROTOR_SZ   (32)
#define FTS2_ROTOR_MASK (FTS2_ROTOR_SZ-1)

/*
** Add entries to pSnippet->aMatch[] for every match that occurs against
** document zDoc[0..nDoc-1] which is stored in column iColumn.
*/
static void snippetOffsetsOfColumn(
  Query *pQuery,
  Snippet *pSnippet,
  int iColumn,
  const char *zDoc,
  int nDoc
){
  const sqlite3_tokenizer_module *pTModule;  /* The tokenizer module */
  sqlite3_tokenizer *pTokenizer;             /* The specific tokenizer */
  sqlite3_tokenizer_cursor *pTCursor;        /* Tokenizer cursor */
  fulltext_vtab *pVtab;                /* The full text index */
  int nColumn;                         /* Number of columns in the index */
  const QueryTerm *aTerm;              /* Query string terms */
  int nTerm;                           /* Number of query string terms */  
  int i, j;                            /* Loop counters */
  int rc;                              /* Return code */
  unsigned int match, prevMatch;       /* Phrase search bitmasks */
  const char *zToken;                  /* Next token from the tokenizer */
  int nToken;                          /* Size of zToken */
  int iBegin, iEnd, iPos;              /* Offsets of beginning and end */

  /* The following variables keep a circular buffer of the last
  ** few tokens */
  unsigned int iRotor = 0;             /* Index of current token */
  int iRotorBegin[FTS2_ROTOR_SZ];      /* Beginning offset of token */
  int iRotorLen[FTS2_ROTOR_SZ];        /* Length of token */

  pVtab = pQuery->pFts;
  nColumn = pVtab->nColumn;
  pTokenizer = pVtab->pTokenizer;
  pTModule = pTokenizer->pModule;
  rc = pTModule->xOpen(pTokenizer, zDoc, nDoc, &pTCursor);
  if( rc ) return;
  pTCursor->pTokenizer = pTokenizer;
  aTerm = pQuery->pTerms;
  nTerm = pQuery->nTerms;
  if( nTerm>=FTS2_ROTOR_SZ ){
    nTerm = FTS2_ROTOR_SZ - 1;
  }
  prevMatch = 0;
  while(1){
    rc = pTModule->xNext(pTCursor, &zToken, &nToken, &iBegin, &iEnd, &iPos);
    if( rc ) break;
    iRotorBegin[iRotor&FTS2_ROTOR_MASK] = iBegin;
    iRotorLen[iRotor&FTS2_ROTOR_MASK] = iEnd-iBegin;
    match = 0;
    for(i=0; i<nTerm; i++){
      int iCol;
      iCol = aTerm[i].iColumn;
      if( iCol>=0 && iCol<nColumn && iCol!=iColumn ) continue;
      if( aTerm[i].nTerm!=nToken ) continue;
      if( memcmp(aTerm[i].pTerm, zToken, nToken) ) continue;
      if( aTerm[i].iPhrase>1 && (prevMatch & (1<<i))==0 ) continue;
      match |= 1<<i;
      if( i==nTerm-1 || aTerm[i+1].iPhrase==1 ){
        for(j=aTerm[i].iPhrase-1; j>=0; j--){
          int k = (iRotor-j) & FTS2_ROTOR_MASK;
          snippetAppendMatch(pSnippet, iColumn, i-j,
                iRotorBegin[k], iRotorLen[k]);
        }
      }
    }
    prevMatch = match<<1;
    iRotor++;
  }
  pTModule->xClose(pTCursor);  
}


/*
** Compute all offsets for the current row of the query.  
** If the offsets have already been computed, this routine is a no-op.
*/
static void snippetAllOffsets(fulltext_cursor *p){
  int nColumn;
  int iColumn, i;
  int iFirst, iLast;
  fulltext_vtab *pFts;

  if( p->snippet.nMatch ) return;
  if( p->q.nTerms==0 ) return;
  pFts = p->q.pFts;
  nColumn = pFts->nColumn;
  iColumn = p->iCursorType;
  if( iColumn<0 || iColumn>=nColumn ){
    iFirst = 0;
    iLast = nColumn-1;
  }else{
    iFirst = iColumn;
    iLast = iColumn;
  }
  for(i=iFirst; i<=iLast; i++){
    const char *zDoc;
    int nDoc;
    zDoc = (const char*)sqlite3_column_text(p->pStmt, i+1);
    nDoc = sqlite3_column_bytes(p->pStmt, i+1);
    snippetOffsetsOfColumn(&p->q, &p->snippet, i, zDoc, nDoc);
  }
}

/*
** Convert the information in the aMatch[] array of the snippet
** into the string zOffset[0..nOffset-1].
*/
static void snippetOffsetText(Snippet *p){
  int i;
  int cnt = 0;
  StringBuffer sb;
  char zBuf[200];
  if( p->zOffset ) return;
  initStringBuffer(&sb);
  for(i=0; i<p->nMatch; i++){
    struct snippetMatch *pMatch = &p->aMatch[i];
    zBuf[0] = ' ';
    sprintf(&zBuf[cnt>0], "%d %d %d %d", pMatch->iCol,
        pMatch->iTerm, pMatch->iStart, pMatch->nByte);
    append(&sb, zBuf);
    cnt++;
  }
  p->zOffset = stringBufferData(&sb);
  p->nOffset = stringBufferLength(&sb);
}

/*
** zDoc[0..nDoc-1] is phrase of text.  aMatch[0..nMatch-1] are a set
** of matching words some of which might be in zDoc.  zDoc is column
** number iCol.
**
** iBreak is suggested spot in zDoc where we could begin or end an
** excerpt.  Return a value similar to iBreak but possibly adjusted
** to be a little left or right so that the break point is better.
*/
static int wordBoundary(
  int iBreak,                   /* The suggested break point */
  const char *zDoc,             /* Document text */
  int nDoc,                     /* Number of bytes in zDoc[] */
  struct snippetMatch *aMatch,  /* Matching words */
  int nMatch,                   /* Number of entries in aMatch[] */
  int iCol                      /* The column number for zDoc[] */
){
  int i;
  if( iBreak<=10 ){
    return 0;
  }
  if( iBreak>=nDoc-10 ){
    return nDoc;
  }
  for(i=0; i<nMatch && aMatch[i].iCol<iCol; i++){}
  while( i<nMatch && aMatch[i].iStart+aMatch[i].nByte<iBreak ){ i++; }
  if( i<nMatch ){
    if( aMatch[i].iStart<iBreak+10 ){
      return aMatch[i].iStart;
    }
    if( i>0 && aMatch[i-1].iStart+aMatch[i-1].nByte>=iBreak ){
      return aMatch[i-1].iStart;
    }
  }
  for(i=1; i<=10; i++){
    if( safe_isspace(zDoc[iBreak-i]) ){
      return iBreak - i + 1;
    }
    if( safe_isspace(zDoc[iBreak+i]) ){
      return iBreak + i + 1;
    }
  }
  return iBreak;
}



/*
** Allowed values for Snippet.aMatch[].snStatus
*/
#define SNIPPET_IGNORE  0   /* It is ok to omit this match from the snippet */
#define SNIPPET_DESIRED 1   /* We want to include this match in the snippet */

/*
** Generate the text of a snippet.
*/
static void snippetText(
  fulltext_cursor *pCursor,   /* The cursor we need the snippet for */
  const char *zStartMark,     /* Markup to appear before each match */
  const char *zEndMark,       /* Markup to appear after each match */
  const char *zEllipsis       /* Ellipsis mark */
){
  int i, j;
  struct snippetMatch *aMatch;
  int nMatch;
  int nDesired;
  StringBuffer sb;
  int tailCol;
  int tailOffset;
  int iCol;
  int nDoc;
  const char *zDoc;
  int iStart, iEnd;
  int tailEllipsis = 0;
  int iMatch;
  

  free(pCursor->snippet.zSnippet);
  pCursor->snippet.zSnippet = 0;
  aMatch = pCursor->snippet.aMatch;
  nMatch = pCursor->snippet.nMatch;
  initStringBuffer(&sb);

  for(i=0; i<nMatch; i++){
    aMatch[i].snStatus = SNIPPET_IGNORE;
  }
  nDesired = 0;
  for(i=0; i<pCursor->q.nTerms; i++){
    for(j=0; j<nMatch; j++){
      if( aMatch[j].iTerm==i ){
        aMatch[j].snStatus = SNIPPET_DESIRED;
        nDesired++;
        break;
      }
    }
  }

  iMatch = 0;
  tailCol = -1;
  tailOffset = 0;
  for(i=0; i<nMatch && nDesired>0; i++){
    if( aMatch[i].snStatus!=SNIPPET_DESIRED ) continue;
    nDesired--;
    iCol = aMatch[i].iCol;
    zDoc = (const char*)sqlite3_column_text(pCursor->pStmt, iCol+1);
    nDoc = sqlite3_column_bytes(pCursor->pStmt, iCol+1);
    iStart = aMatch[i].iStart - 40;
    iStart = wordBoundary(iStart, zDoc, nDoc, aMatch, nMatch, iCol);
    if( iStart<=10 ){
      iStart = 0;
    }
    if( iCol==tailCol && iStart<=tailOffset+20 ){
      iStart = tailOffset;
    }
    if( (iCol!=tailCol && tailCol>=0) || iStart!=tailOffset ){
      trimWhiteSpace(&sb);
      appendWhiteSpace(&sb);
      append(&sb, zEllipsis);
      appendWhiteSpace(&sb);
    }
    iEnd = aMatch[i].iStart + aMatch[i].nByte + 40;
    iEnd = wordBoundary(iEnd, zDoc, nDoc, aMatch, nMatch, iCol);
    if( iEnd>=nDoc-10 ){
      iEnd = nDoc;
      tailEllipsis = 0;
    }else{
      tailEllipsis = 1;
    }
    while( iMatch<nMatch && aMatch[iMatch].iCol<iCol ){ iMatch++; }
    while( iStart<iEnd ){
      while( iMatch<nMatch && aMatch[iMatch].iStart<iStart
             && aMatch[iMatch].iCol<=iCol ){
        iMatch++;
      }
      if( iMatch<nMatch && aMatch[iMatch].iStart<iEnd
             && aMatch[iMatch].iCol==iCol ){
        nappend(&sb, &zDoc[iStart], aMatch[iMatch].iStart - iStart);
        iStart = aMatch[iMatch].iStart;
        append(&sb, zStartMark);
        nappend(&sb, &zDoc[iStart], aMatch[iMatch].nByte);
        append(&sb, zEndMark);
        iStart += aMatch[iMatch].nByte;
        for(j=iMatch+1; j<nMatch; j++){
          if( aMatch[j].iTerm==aMatch[iMatch].iTerm
              && aMatch[j].snStatus==SNIPPET_DESIRED ){
            nDesired--;
            aMatch[j].snStatus = SNIPPET_IGNORE;
          }
        }
      }else{
        nappend(&sb, &zDoc[iStart], iEnd - iStart);
        iStart = iEnd;
      }
    }
    tailCol = iCol;
    tailOffset = iEnd;
  }
  trimWhiteSpace(&sb);
  if( tailEllipsis ){
    appendWhiteSpace(&sb);
    append(&sb, zEllipsis);
  }
  pCursor->snippet.zSnippet = stringBufferData(&sb);
  pCursor->snippet.nSnippet = stringBufferLength(&sb);
}


/*
** Close the cursor.  For additional information see the documentation
** on the xClose method of the virtual table interface.
*/
static int fulltextClose(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  TRACE(("FTS2 Close %p\n", c));
  sqlite3_finalize(c->pStmt);
  queryClear(&c->q);
  snippetClear(&c->snippet);
  if( c->result.nData!=0 ) dlrDestroy(&c->reader);
  dataBufferDestroy(&c->result);
  free(c);
  return SQLITE_OK;
}

static int fulltextNext(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  int rc;

  TRACE(("FTS2 Next %p\n", pCursor));
  snippetClear(&c->snippet);
  if( c->iCursorType < QUERY_FULLTEXT ){
    /* TODO(shess) Handle SQLITE_SCHEMA AND SQLITE_BUSY. */
    rc = sqlite3_step(c->pStmt);
    switch( rc ){
      case SQLITE_ROW:
        c->eof = 0;
        return SQLITE_OK;
      case SQLITE_DONE:
        c->eof = 1;
        return SQLITE_OK;
      default:
        c->eof = 1;
        return rc;
    }
  } else {  /* full-text query */
    rc = sqlite3_reset(c->pStmt);
    if( rc!=SQLITE_OK ) return rc;

    if( c->result.nData==0 || dlrAtEnd(&c->reader) ){
      c->eof = 1;
      return SQLITE_OK;
    }
    rc = sqlite3_bind_int64(c->pStmt, 1, dlrDocid(&c->reader));
    dlrStep(&c->reader);
    if( rc!=SQLITE_OK ) return rc;
    /* TODO(shess) Handle SQLITE_SCHEMA AND SQLITE_BUSY. */
    rc = sqlite3_step(c->pStmt);
    if( rc==SQLITE_ROW ){   /* the case we expect */
      c->eof = 0;
      return SQLITE_OK;
    }
    /* an error occurred; abort */
    return rc==SQLITE_DONE ? SQLITE_ERROR : rc;
  }
}


/* TODO(shess) If we pushed LeafReader to the top of the file, or to
** another file, term_select() could be pushed above
** docListOfTerm().
*/
static int termSelect(fulltext_vtab *v, int iColumn,
                      const char *pTerm, int nTerm,
                      DocListType iType, DataBuffer *out);

/* Return a DocList corresponding to the query term *pTerm.  If *pTerm
** is the first term of a phrase query, go ahead and evaluate the phrase
** query and return the doclist for the entire phrase query.
**
** The resulting DL_DOCIDS doclist is stored in pResult, which is
** overwritten.
*/
static int docListOfTerm(
  fulltext_vtab *v,   /* The full text index */
  int iColumn,        /* column to restrict to.  No restriction if >=nColumn */
  QueryTerm *pQTerm,  /* Term we are looking for, or 1st term of a phrase */
  DataBuffer *pResult /* Write the result here */
){
  DataBuffer left, right, new;
  int i, rc;

  /* No phrase search if no position info. */
  assert( pQTerm->nPhrase==0 || DL_DEFAULT!=DL_DOCIDS );

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  dataBufferInit(&left, 0);
  rc = termSelect(v, iColumn, pQTerm->pTerm, pQTerm->nTerm,
                  0<pQTerm->nPhrase ? DL_POSITIONS : DL_DOCIDS, &left);
  if( rc ) return rc;
  for(i=1; i<=pQTerm->nPhrase && left.nData>0; i++){
    dataBufferInit(&right, 0);
    rc = termSelect(v, iColumn, pQTerm[i].pTerm, pQTerm[i].nTerm,
                    DL_POSITIONS, &right);
    if( rc ){
      dataBufferDestroy(&left);
      return rc;
    }
    dataBufferInit(&new, 0);
    docListPhraseMerge(left.pData, left.nData, right.pData, right.nData,
                       i<pQTerm->nPhrase ? DL_POSITIONS : DL_DOCIDS, &new);
    dataBufferDestroy(&left);
    dataBufferDestroy(&right);
    left = new;
  }
  *pResult = left;
  return SQLITE_OK;
}

/* Add a new term pTerm[0..nTerm-1] to the query *q.
*/
static void queryAdd(Query *q, const char *pTerm, int nTerm){
  QueryTerm *t;
  ++q->nTerms;
  q->pTerms = realloc(q->pTerms, q->nTerms * sizeof(q->pTerms[0]));
  if( q->pTerms==0 ){
    q->nTerms = 0;
    return;
  }
  t = &q->pTerms[q->nTerms - 1];
  CLEAR(t);
  t->pTerm = malloc(nTerm+1);
  memcpy(t->pTerm, pTerm, nTerm);
  t->pTerm[nTerm] = 0;
  t->nTerm = nTerm;
  t->isOr = q->nextIsOr;
  q->nextIsOr = 0;
  t->iColumn = q->nextColumn;
  q->nextColumn = q->dfltColumn;
}

/*
** Check to see if the string zToken[0...nToken-1] matches any
** column name in the virtual table.   If it does,
** return the zero-indexed column number.  If not, return -1.
*/
static int checkColumnSpecifier(
  fulltext_vtab *pVtab,    /* The virtual table */
  const char *zToken,      /* Text of the token */
  int nToken               /* Number of characters in the token */
){
  int i;
  for(i=0; i<pVtab->nColumn; i++){
    if( memcmp(pVtab->azColumn[i], zToken, nToken)==0
        && pVtab->azColumn[i][nToken]==0 ){
      return i;
    }
  }
  return -1;
}

/*
** Parse the text at pSegment[0..nSegment-1].  Add additional terms
** to the query being assemblied in pQuery.
**
** inPhrase is true if pSegment[0..nSegement-1] is contained within
** double-quotes.  If inPhrase is true, then the first term
** is marked with the number of terms in the phrase less one and
** OR and "-" syntax is ignored.  If inPhrase is false, then every
** term found is marked with nPhrase=0 and OR and "-" syntax is significant.
*/
static int tokenizeSegment(
  sqlite3_tokenizer *pTokenizer,          /* The tokenizer to use */
  const char *pSegment, int nSegment,     /* Query expression being parsed */
  int inPhrase,                           /* True if within "..." */
  Query *pQuery                           /* Append results here */
){
  const sqlite3_tokenizer_module *pModule = pTokenizer->pModule;
  sqlite3_tokenizer_cursor *pCursor;
  int firstIndex = pQuery->nTerms;
  int iCol;
  int nTerm = 1;
  
  int rc = pModule->xOpen(pTokenizer, pSegment, nSegment, &pCursor);
  if( rc!=SQLITE_OK ) return rc;
  pCursor->pTokenizer = pTokenizer;

  while( 1 ){
    const char *pToken;
    int nToken, iBegin, iEnd, iPos;

    rc = pModule->xNext(pCursor,
                        &pToken, &nToken,
                        &iBegin, &iEnd, &iPos);
    if( rc!=SQLITE_OK ) break;
    if( !inPhrase &&
        pSegment[iEnd]==':' &&
         (iCol = checkColumnSpecifier(pQuery->pFts, pToken, nToken))>=0 ){
      pQuery->nextColumn = iCol;
      continue;
    }
    if( !inPhrase && pQuery->nTerms>0 && nToken==2
         && pSegment[iBegin]=='O' && pSegment[iBegin+1]=='R' ){
      pQuery->nextIsOr = 1;
      continue;
    }
    queryAdd(pQuery, pToken, nToken);
    if( !inPhrase && iBegin>0 && pSegment[iBegin-1]=='-' ){
      pQuery->pTerms[pQuery->nTerms-1].isNot = 1;
    }
    pQuery->pTerms[pQuery->nTerms-1].iPhrase = nTerm;
    if( inPhrase ){
      nTerm++;
    }
  }

  if( inPhrase && pQuery->nTerms>firstIndex ){
    pQuery->pTerms[firstIndex].nPhrase = pQuery->nTerms - firstIndex - 1;
  }

  return pModule->xClose(pCursor);
}

/* Parse a query string, yielding a Query object pQuery.
**
** The calling function will need to queryClear() to clean up
** the dynamically allocated memory held by pQuery.
*/
static int parseQuery(
  fulltext_vtab *v,        /* The fulltext index */
  const char *zInput,      /* Input text of the query string */
  int nInput,              /* Size of the input text */
  int dfltColumn,          /* Default column of the index to match against */
  Query *pQuery            /* Write the parse results here. */
){
  int iInput, inPhrase = 0;

  if( zInput==0 ) nInput = 0;
  if( nInput<0 ) nInput = strlen(zInput);
  pQuery->nTerms = 0;
  pQuery->pTerms = NULL;
  pQuery->nextIsOr = 0;
  pQuery->nextColumn = dfltColumn;
  pQuery->dfltColumn = dfltColumn;
  pQuery->pFts = v;

  for(iInput=0; iInput<nInput; ++iInput){
    int i;
    for(i=iInput; i<nInput && zInput[i]!='"'; ++i){}
    if( i>iInput ){
      tokenizeSegment(v->pTokenizer, zInput+iInput, i-iInput, inPhrase,
                       pQuery);
    }
    iInput = i;
    if( i<nInput ){
      assert( zInput[i]=='"' );
      inPhrase = !inPhrase;
    }
  }

  if( inPhrase ){
    /* unmatched quote */
    queryClear(pQuery);
    return SQLITE_ERROR;
  }
  return SQLITE_OK;
}

/* TODO(shess) Refactor the code to remove this forward decl. */
static int flushPendingTerms(fulltext_vtab *v);

/* Perform a full-text query using the search expression in
** zInput[0..nInput-1].  Return a list of matching documents
** in pResult.
**
** Queries must match column iColumn.  Or if iColumn>=nColumn
** they are allowed to match against any column.
*/
static int fulltextQuery(
  fulltext_vtab *v,      /* The full text index */
  int iColumn,           /* Match against this column by default */
  const char *zInput,    /* The query string */
  int nInput,            /* Number of bytes in zInput[] */
  DataBuffer *pResult,   /* Write the result doclist here */
  Query *pQuery          /* Put parsed query string here */
){
  int i, iNext, rc;
  DataBuffer left, right, or, new;
  int nNot = 0;
  QueryTerm *aTerm;

  /* TODO(shess) Instead of flushing pendingTerms, we could query for
  ** the relevant term and merge the doclist into what we receive from
  ** the database.  Wait and see if this is a common issue, first.
  **
  ** A good reason not to flush is to not generate update-related
  ** error codes from here.
  */

  /* Flush any buffered updates before executing the query. */
  rc = flushPendingTerms(v);
  if( rc!=SQLITE_OK ) return rc;

  /* TODO(shess) I think that the queryClear() calls below are not
  ** necessary, because fulltextClose() already clears the query.
  */
  rc = parseQuery(v, zInput, nInput, iColumn, pQuery);
  if( rc!=SQLITE_OK ) return rc;

  /* Empty or NULL queries return no results. */
  if( pQuery->nTerms==0 ){
    dataBufferInit(pResult, 0);
    return SQLITE_OK;
  }

  /* Merge AND terms. */
  /* TODO(shess) I think we can early-exit if( i>nNot && left.nData==0 ). */
  aTerm = pQuery->pTerms;
  for(i = 0; i<pQuery->nTerms; i=iNext){
    if( aTerm[i].isNot ){
      /* Handle all NOT terms in a separate pass */
      nNot++;
      iNext = i + aTerm[i].nPhrase+1;
      continue;
    }
    iNext = i + aTerm[i].nPhrase + 1;
    rc = docListOfTerm(v, aTerm[i].iColumn, &aTerm[i], &right);
    if( rc ){
      if( i!=nNot ) dataBufferDestroy(&left);
      queryClear(pQuery);
      return rc;
    }
    while( iNext<pQuery->nTerms && aTerm[iNext].isOr ){
      rc = docListOfTerm(v, aTerm[iNext].iColumn, &aTerm[iNext], &or);
      iNext += aTerm[iNext].nPhrase + 1;
      if( rc ){
        if( i!=nNot ) dataBufferDestroy(&left);
        dataBufferDestroy(&right);
        queryClear(pQuery);
        return rc;
      }
      dataBufferInit(&new, 0);
      docListOrMerge(right.pData, right.nData, or.pData, or.nData, &new);
      dataBufferDestroy(&right);
      dataBufferDestroy(&or);
      right = new;
    }
    if( i==nNot ){           /* first term processed. */
      left = right;
    }else{
      dataBufferInit(&new, 0);
      docListAndMerge(left.pData, left.nData, right.pData, right.nData, &new);
      dataBufferDestroy(&right);
      dataBufferDestroy(&left);
      left = new;
    }
  }

  if( nNot==pQuery->nTerms ){
    /* We do not yet know how to handle a query of only NOT terms */
    return SQLITE_ERROR;
  }

  /* Do the EXCEPT terms */
  for(i=0; i<pQuery->nTerms;  i += aTerm[i].nPhrase + 1){
    if( !aTerm[i].isNot ) continue;
    rc = docListOfTerm(v, aTerm[i].iColumn, &aTerm[i], &right);
    if( rc ){
      queryClear(pQuery);
      dataBufferDestroy(&left);
      return rc;
    }
    dataBufferInit(&new, 0);
    docListExceptMerge(left.pData, left.nData, right.pData, right.nData, &new);
    dataBufferDestroy(&right);
    dataBufferDestroy(&left);
    left = new;
  }

  *pResult = left;
  return rc;
}

/*
** This is the xFilter interface for the virtual table.  See
** the virtual table xFilter method documentation for additional
** information.
**
** If idxNum==QUERY_GENERIC then do a full table scan against
** the %_content table.
**
** If idxNum==QUERY_ROWID then do a rowid lookup for a single entry
** in the %_content table.
**
** If idxNum>=QUERY_FULLTEXT then use the full text index.  The
** column on the left-hand side of the MATCH operator is column
** number idxNum-QUERY_FULLTEXT, 0 indexed.  argv[0] is the right-hand
** side of the MATCH operator.
*/
/* TODO(shess) Upgrade the cursor initialization and destruction to
** account for fulltextFilter() being called multiple times on the
** same cursor.  The current solution is very fragile.  Apply fix to
** fts2 as appropriate.
*/
static int fulltextFilter(
  sqlite3_vtab_cursor *pCursor,     /* The cursor used for this query */
  int idxNum, const char *idxStr,   /* Which indexing scheme to use */
  int argc, sqlite3_value **argv    /* Arguments for the indexing scheme */
){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  fulltext_vtab *v = cursor_vtab(c);
  int rc;
  char *zSql;

  TRACE(("FTS2 Filter %p\n",pCursor));

  zSql = sqlite3_mprintf("select rowid, * from %%_content %s",
                          idxNum==QUERY_GENERIC ? "" : "where rowid=?");
  sqlite3_finalize(c->pStmt);
  rc = sql_prepare(v->db, v->zDb, v->zName, &c->pStmt, zSql);
  sqlite3_free(zSql);
  if( rc!=SQLITE_OK ) return rc;

  c->iCursorType = idxNum;
  switch( idxNum ){
    case QUERY_GENERIC:
      break;

    case QUERY_ROWID:
      rc = sqlite3_bind_int64(c->pStmt, 1, sqlite3_value_int64(argv[0]));
      if( rc!=SQLITE_OK ) return rc;
      break;

    default:   /* full-text search */
    {
      const char *zQuery = (const char *)sqlite3_value_text(argv[0]);
      assert( idxNum<=QUERY_FULLTEXT+v->nColumn);
      assert( argc==1 );
      queryClear(&c->q);
      if( c->result.nData!=0 ){
        /* This case happens if the same cursor is used repeatedly. */
        dlrDestroy(&c->reader);
        dataBufferReset(&c->result);
      }else{
        dataBufferInit(&c->result, 0);
      }
      rc = fulltextQuery(v, idxNum-QUERY_FULLTEXT, zQuery, -1, &c->result, &c->q);
      if( rc!=SQLITE_OK ) return rc;
      if( c->result.nData!=0 ){
        dlrInit(&c->reader, DL_DOCIDS, c->result.pData, c->result.nData);
      }
      break;
    }
  }

  return fulltextNext(pCursor);
}

/* This is the xEof method of the virtual table.  The SQLite core
** calls this routine to find out if it has reached the end of
** a query's results set.
*/
static int fulltextEof(sqlite3_vtab_cursor *pCursor){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  return c->eof;
}

/* This is the xColumn method of the virtual table.  The SQLite
** core calls this method during a query when it needs the value
** of a column from the virtual table.  This method needs to use
** one of the sqlite3_result_*() routines to store the requested
** value back in the pContext.
*/
static int fulltextColumn(sqlite3_vtab_cursor *pCursor,
                          sqlite3_context *pContext, int idxCol){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;
  fulltext_vtab *v = cursor_vtab(c);

  if( idxCol<v->nColumn ){
    sqlite3_value *pVal = sqlite3_column_value(c->pStmt, idxCol+1);
    sqlite3_result_value(pContext, pVal);
  }else if( idxCol==v->nColumn ){
    /* The extra column whose name is the same as the table.
    ** Return a blob which is a pointer to the cursor
    */
    sqlite3_result_blob(pContext, &c, sizeof(c), SQLITE_TRANSIENT);
  }
  return SQLITE_OK;
}

/* This is the xRowid method.  The SQLite core calls this routine to
** retrive the rowid for the current row of the result set.  The
** rowid should be written to *pRowid.
*/
static int fulltextRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
  fulltext_cursor *c = (fulltext_cursor *) pCursor;

  *pRowid = sqlite3_column_int64(c->pStmt, 0);
  return SQLITE_OK;
}

/* Add all terms in [zText] to pendingTerms table.  If [iColumn] > 0,
** we also store positions and offsets in the hash table using that
** column number.
*/
static int buildTerms(fulltext_vtab *v, sqlite_int64 iDocid,
                      const char *zText, int iColumn){
  sqlite3_tokenizer *pTokenizer = v->pTokenizer;
  sqlite3_tokenizer_cursor *pCursor;
  const char *pToken;
  int nTokenBytes;
  int iStartOffset, iEndOffset, iPosition;
  int rc;

  rc = pTokenizer->pModule->xOpen(pTokenizer, zText, -1, &pCursor);
  if( rc!=SQLITE_OK ) return rc;

  pCursor->pTokenizer = pTokenizer;
  while( SQLITE_OK==pTokenizer->pModule->xNext(pCursor,
                                               &pToken, &nTokenBytes,
                                               &iStartOffset, &iEndOffset,
                                               &iPosition) ){
    DLCollector *p;
    int nData;                   /* Size of doclist before our update. */

    /* Positions can't be negative; we use -1 as a terminator internally. */
    if( iPosition<0 ){
      pTokenizer->pModule->xClose(pCursor);
      return SQLITE_ERROR;
    }

    p = fts2HashFind(&v->pendingTerms, pToken, nTokenBytes);
    if( p==NULL ){
      nData = 0;
      p = dlcNew(iDocid, DL_DEFAULT);
      fts2HashInsert(&v->pendingTerms, pToken, nTokenBytes, p);

      /* Overhead for our hash table entry, the key, and the value. */
      v->nPendingData += sizeof(struct fts2HashElem)+sizeof(*p)+nTokenBytes;
    }else{
      nData = p->b.nData;
      if( p->dlw.iPrevDocid!=iDocid ) dlcNext(p, iDocid);
    }
    if( iColumn>=0 ){
      dlcAddPos(p, iColumn, iPosition, iStartOffset, iEndOffset);
    }

    /* Accumulate data added by dlcNew or dlcNext, and dlcAddPos. */
    v->nPendingData += p->b.nData-nData;
  }

  /* TODO(shess) Check return?  Should this be able to cause errors at
  ** this point?  Actually, same question about sqlite3_finalize(),
  ** though one could argue that failure there means that the data is
  ** not durable.  *ponder*
  */
  pTokenizer->pModule->xClose(pCursor);
  return rc;
}

/* Add doclists for all terms in [pValues] to pendingTerms table. */
static int insertTerms(fulltext_vtab *v, sqlite_int64 iRowid,
                       sqlite3_value **pValues){
  int i;
  for(i = 0; i < v->nColumn ; ++i){
    char *zText = (char*)sqlite3_value_text(pValues[i]);
    int rc = buildTerms(v, iRowid, zText, i);
    if( rc!=SQLITE_OK ) return rc;
  }
  return SQLITE_OK;
}

/* Add empty doclists for all terms in the given row's content to
** pendingTerms.
*/
static int deleteTerms(fulltext_vtab *v, sqlite_int64 iRowid){
  const char **pValues;
  int i, rc;

  /* TODO(shess) Should we allow such tables at all? */
  if( DL_DEFAULT==DL_DOCIDS ) return SQLITE_ERROR;

  rc = content_select(v, iRowid, &pValues);
  if( rc!=SQLITE_OK ) return rc;

  for(i = 0 ; i < v->nColumn; ++i) {
    rc = buildTerms(v, iRowid, pValues[i], -1);
    if( rc!=SQLITE_OK ) break;
  }

  freeStringArray(v->nColumn, pValues);
  return SQLITE_OK;
}

/* TODO(shess) Refactor the code to remove this forward decl. */
static int initPendingTerms(fulltext_vtab *v, sqlite_int64 iDocid);

/* Insert a row into the %_content table; set *piRowid to be the ID of the
** new row.  Add doclists for terms to pendingTerms.
*/
static int index_insert(fulltext_vtab *v, sqlite3_value *pRequestRowid,
                        sqlite3_value **pValues, sqlite_int64 *piRowid){
  int rc;

  rc = content_insert(v, pRequestRowid, pValues);  /* execute an SQL INSERT */
  if( rc!=SQLITE_OK ) return rc;

  *piRowid = sqlite3_last_insert_rowid(v->db);
  rc = initPendingTerms(v, *piRowid);
  if( rc!=SQLITE_OK ) return rc;

  return insertTerms(v, *piRowid, pValues);
}

/* Delete a row from the %_content table; add empty doclists for terms
** to pendingTerms.
*/
static int index_delete(fulltext_vtab *v, sqlite_int64 iRow){
  int rc = initPendingTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  rc = deleteTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  return content_delete(v, iRow);  /* execute an SQL DELETE */
}

/* Update a row in the %_content table; add delete doclists to
** pendingTerms for old terms not in the new data, add insert doclists
** to pendingTerms for terms in the new data.
*/
static int index_update(fulltext_vtab *v, sqlite_int64 iRow,
                        sqlite3_value **pValues){
  int rc = initPendingTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  /* Generate an empty doclist for each term that previously appeared in this
   * row. */
  rc = deleteTerms(v, iRow);
  if( rc!=SQLITE_OK ) return rc;

  rc = content_update(v, pValues, iRow);  /* execute an SQL UPDATE */
  if( rc!=SQLITE_OK ) return rc;

  /* Now add positions for terms which appear in the updated row. */
  return insertTerms(v, iRow, pValues);
}

/*******************************************************************/
/* InteriorWriter is used to collect terms and block references into
** interior nodes in %_segments.  See commentary at top of file for
** format.
*/

/* How large interior nodes can grow. */
#define INTERIOR_MAX 2048

/* Minimum number of terms per interior node (except the root). This
** prevents large terms from making the tree too skinny - must be >0
** so that the tree always makes progress.  Note that the min tree
** fanout will be INTERIOR_MIN_TERMS+1.
*/
#define INTERIOR_MIN_TERMS 7
#if INTERIOR_MIN_TERMS<1
# error INTERIOR_MIN_TERMS must be greater than 0.
#endif

/* ROOT_MAX controls how much data is stored inline in the segment
** directory.
*/
/* TODO(shess) Push ROOT_MAX down to whoever is writing things.  It's
** only here so that interiorWriterRootInfo() and leafWriterRootInfo()
** can both see it, but if the caller passed it in, we wouldn't even
** need a define.
*/
#define ROOT_MAX 1024
#if ROOT_MAX<VARINT_MAX*2
# error ROOT_MAX must have enough space for a header.
#endif

/* InteriorBlock stores a linked-list of interior blocks while a lower
** layer is being constructed.
*/
typedef struct InteriorBlock {
  DataBuffer term;           /* Leftmost term in block's subtree. */
  DataBuffer data;           /* Accumulated data for the block. */
  struct InteriorBlock *next;
} InteriorBlock;

static InteriorBlock *interiorBlockNew(int iHeight, sqlite_int64 iChildBlock,
                                       const char *pTerm, int nTerm){
  InteriorBlock *block = calloc(1, sizeof(InteriorBlock));
  char c[VARINT_MAX+VARINT_MAX];
  int n;

  dataBufferInit(&block->term, 0);
  dataBufferReplace(&block->term, pTerm, nTerm);

  n = putVarint(c, iHeight);
  n += putVarint(c+n, iChildBlock);
  dataBufferInit(&block->data, INTERIOR_MAX);
  dataBufferReplace(&block->data, c, n);

  return block;
}

#ifndef NDEBUG
/* Verify that the data is readable as an interior node. */
static void interiorBlockValidate(InteriorBlock *pBlock){
  const char *pData = pBlock->data.pData;
  int nData = pBlock->data.nData;
  int n, iDummy;
  sqlite_int64 iBlockid;

  assert( nData>0 );
  assert( pData!=0 );
  assert( pData+nData>pData );

  /* Must lead with height of node as a varint(n), n>0 */
  n = getVarint32(pData, &iDummy);
  assert( n>0 );
  assert( iDummy>0 );
  assert( n<nData );
  pData += n;
  nData -= n;

  /* Must contain iBlockid. */
  n = getVarint(pData, &iBlockid);
  assert( n>0 );
  assert( n<=nData );
  pData += n;
  nData -= n;

  /* Zero or more terms of positive length */
  if( nData!=0 ){
    /* First term is not delta-encoded. */
    n = getVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>0 );
    assert( n+iDummy>0);
    assert( n+iDummy<=nData );
    pData += n+iDummy;
    nData -= n+iDummy;

    /* Following terms delta-encoded. */
    while( nData!=0 ){
      /* Length of shared prefix. */
      n = getVarint32(pData, &iDummy);
      assert( n>0 );
      assert( iDummy>=0 );
      assert( n<nData );
      pData += n;
      nData -= n;

      /* Length and data of distinct suffix. */
      n = getVarint32(pData, &iDummy);
      assert( n>0 );
      assert( iDummy>0 );
      assert( n+iDummy>0);
      assert( n+iDummy<=nData );
      pData += n+iDummy;
      nData -= n+iDummy;
    }
  }
}
#define ASSERT_VALID_INTERIOR_BLOCK(x) interiorBlockValidate(x)
#else
#define ASSERT_VALID_INTERIOR_BLOCK(x) assert( 1 )
#endif

typedef struct InteriorWriter {
  int iHeight;                   /* from 0 at leaves. */
  InteriorBlock *first, *last;
  struct InteriorWriter *parentWriter;

  DataBuffer term;               /* Last term written to block "last". */
  sqlite_int64 iOpeningChildBlock; /* First child block in block "last". */
#ifndef NDEBUG
  sqlite_int64 iLastChildBlock;  /* for consistency checks. */
#endif
} InteriorWriter;

/* Initialize an interior node where pTerm[nTerm] marks the leftmost
** term in the tree.  iChildBlock is the leftmost child block at the
** next level down the tree.
*/
static void interiorWriterInit(int iHeight, const char *pTerm, int nTerm,
                               sqlite_int64 iChildBlock,
                               InteriorWriter *pWriter){
  InteriorBlock *block;
  assert( iHeight>0 );
  CLEAR(pWriter);

  pWriter->iHeight = iHeight;
  pWriter->iOpeningChildBlock = iChildBlock;
#ifndef NDEBUG
  pWriter->iLastChildBlock = iChildBlock;
#endif
  block = interiorBlockNew(iHeight, iChildBlock, pTerm, nTerm);
  pWriter->last = pWriter->first = block;
  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
  dataBufferInit(&pWriter->term, 0);
}

/* Append the child node rooted at iChildBlock to the interior node,
** with pTerm[nTerm] as the leftmost term in iChildBlock's subtree.
*/
static void interiorWriterAppend(InteriorWriter *pWriter,
                                 const char *pTerm, int nTerm,
                                 sqlite_int64 iChildBlock){
  char c[VARINT_MAX+VARINT_MAX];
  int n, nPrefix = 0;

  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);

  /* The first term written into an interior node is actually
  ** associated with the second child added (the first child was added
  ** in interiorWriterInit, or in the if clause at the bottom of this
  ** function).  That term gets encoded straight up, with nPrefix left
  ** at 0.
  */
  if( pWriter->term.nData==0 ){
    n = putVarint(c, nTerm);
  }else{
    while( nPrefix<pWriter->term.nData &&
           pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
      nPrefix++;
    }

    n = putVarint(c, nPrefix);
    n += putVarint(c+n, nTerm-nPrefix);
  }

#ifndef NDEBUG
  pWriter->iLastChildBlock++;
#endif
  assert( pWriter->iLastChildBlock==iChildBlock );

  /* Overflow to a new block if the new term makes the current block
  ** too big, and the current block already has enough terms.
  */
  if( pWriter->last->data.nData+n+nTerm-nPrefix>INTERIOR_MAX &&
      iChildBlock-pWriter->iOpeningChildBlock>INTERIOR_MIN_TERMS ){
    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                           pTerm, nTerm);
    pWriter->last = pWriter->last->next;
    pWriter->iOpeningChildBlock = iChildBlock;
    dataBufferReset(&pWriter->term);
  }else{
    dataBufferAppend2(&pWriter->last->data, c, n,
                      pTerm+nPrefix, nTerm-nPrefix);
    dataBufferReplace(&pWriter->term, pTerm, nTerm);
  }
  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
}

/* Free the space used by pWriter, including the linked-list of
** InteriorBlocks, and parentWriter, if present.
*/
static int interiorWriterDestroy(InteriorWriter *pWriter){
  InteriorBlock *block = pWriter->first;

  while( block!=NULL ){
    InteriorBlock *b = block;
    block = block->next;
    dataBufferDestroy(&b->term);
    dataBufferDestroy(&b->data);
    free(b);
  }
  if( pWriter->parentWriter!=NULL ){
    interiorWriterDestroy(pWriter->parentWriter);
    free(pWriter->parentWriter);
  }
  dataBufferDestroy(&pWriter->term);
  SCRAMBLE(pWriter);
  return SQLITE_OK;
}

/* If pWriter can fit entirely in ROOT_MAX, return it as the root info
** directly, leaving *piEndBlockid unchanged.  Otherwise, flush
** pWriter to %_segments, building a new layer of interior nodes, and
** recursively ask for their root into.
*/
static int interiorWriterRootInfo(fulltext_vtab *v, InteriorWriter *pWriter,
                                  char **ppRootInfo, int *pnRootInfo,
                                  sqlite_int64 *piEndBlockid){
  InteriorBlock *block = pWriter->first;
  sqlite_int64 iBlockid = 0;
  int rc;

  /* If we can fit the segment inline */
  if( block==pWriter->last && block->data.nData<ROOT_MAX ){
    *ppRootInfo = block->data.pData;
    *pnRootInfo = block->data.nData;
    return SQLITE_OK;
  }

  /* Flush the first block to %_segments, and create a new level of
  ** interior node.
  */
  ASSERT_VALID_INTERIOR_BLOCK(block);
  rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
  if( rc!=SQLITE_OK ) return rc;
  *piEndBlockid = iBlockid;

  pWriter->parentWriter = malloc(sizeof(*pWriter->parentWriter));
  interiorWriterInit(pWriter->iHeight+1,
                     block->term.pData, block->term.nData,
                     iBlockid, pWriter->parentWriter);

  /* Flush additional blocks and append to the higher interior
  ** node.
  */
  for(block=block->next; block!=NULL; block=block->next){
    ASSERT_VALID_INTERIOR_BLOCK(block);
    rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
    if( rc!=SQLITE_OK ) return rc;
    *piEndBlockid = iBlockid;

    interiorWriterAppend(pWriter->parentWriter,
                         block->term.pData, block->term.nData, iBlockid);
  }

  /* Parent node gets the chance to be the root. */
  return interiorWriterRootInfo(v, pWriter->parentWriter,
                                ppRootInfo, pnRootInfo, piEndBlockid);
}

/****************************************************************/
/* InteriorReader is used to read off the data from an interior node
** (see comment at top of file for the format).
*/
typedef struct InteriorReader {
  const char *pData;
  int nData;

  DataBuffer term;          /* previous term, for decoding term delta. */

  sqlite_int64 iBlockid;
} InteriorReader;

static void interiorReaderDestroy(InteriorReader *pReader){
  SCRAMBLE(pReader);
}

static void interiorReaderInit(const char *pData, int nData,
                               InteriorReader *pReader){
  int n, nTerm;

  /* Require at least the leading flag byte */
  assert( nData>0 );
  assert( pData[0]!='\0' );

  CLEAR(pReader);

  /* Decode the base blockid, and set the cursor to the first term. */
  n = getVarint(pData+1, &pReader->iBlockid);
  assert( 1+n<=nData );
  pReader->pData = pData+1+n;
  pReader->nData = nData-(1+n);

  /* A single-child interior node (such as when a leaf node was too
  ** large for the segment directory) won't have any terms.
  ** Otherwise, decode the first term.
  */
  if( pReader->nData==0 ){
    dataBufferInit(&pReader->term, 0);
  }else{
    n = getVarint32(pReader->pData, &nTerm);
    dataBufferInit(&pReader->term, nTerm);
    dataBufferReplace(&pReader->term, pReader->pData+n, nTerm);
    assert( n+nTerm<=pReader->nData );
    pReader->pData += n+nTerm;
    pReader->nData -= n+nTerm;
  }
}

static int interiorReaderAtEnd(InteriorReader *pReader){
  return pReader->term.nData==0;
}

static sqlite_int64 interiorReaderCurrentBlockid(InteriorReader *pReader){
  return pReader->iBlockid;
}

static int interiorReaderTermBytes(InteriorReader *pReader){
  assert( !interiorReaderAtEnd(pReader) );
  return pReader->term.nData;
}
static const char *interiorReaderTerm(InteriorReader *pReader){
  assert( !interiorReaderAtEnd(pReader) );
  return pReader->term.pData;
}

/* Step forward to the next term in the node. */
static void interiorReaderStep(InteriorReader *pReader){
  assert( !interiorReaderAtEnd(pReader) );

  /* If the last term has been read, signal eof, else construct the
  ** next term.
  */
  if( pReader->nData==0 ){
    dataBufferReset(&pReader->term);
  }else{
    int n, nPrefix, nSuffix;

    n = getVarint32(pReader->pData, &nPrefix);
    n += getVarint32(pReader->pData+n, &nSuffix);

    /* Truncate the current term and append suffix data. */
    pReader->term.nData = nPrefix;
    dataBufferAppend(&pReader->term, pReader->pData+n, nSuffix);

    assert( n+nSuffix<=pReader->nData );
    pReader->pData += n+nSuffix;
    pReader->nData -= n+nSuffix;
  }
  pReader->iBlockid++;
}

/* Compare the current term to pTerm[nTerm], returning strcmp-style
** results.
*/
static int interiorReaderTermCmp(InteriorReader *pReader,
                                 const char *pTerm, int nTerm){
  const char *pReaderTerm = interiorReaderTerm(pReader);
  int nReaderTerm = interiorReaderTermBytes(pReader);
  int c, n = nReaderTerm<nTerm ? nReaderTerm : nTerm;

  if( n==0 ){
    if( nReaderTerm>0 ) return -1;
    if( nTerm>0 ) return 1;
    return 0;
  }

  c = memcmp(pReaderTerm, pTerm, n);
  if( c!=0 ) return c;
  return nReaderTerm - nTerm;
}

/****************************************************************/
/* LeafWriter is used to collect terms and associated doclist data
** into leaf blocks in %_segments (see top of file for format info).
** Expected usage is:
**
** LeafWriter writer;
** leafWriterInit(0, 0, &writer);
** while( sorted_terms_left_to_process ){
**   // data is doclist data for that term.
**   rc = leafWriterStep(v, &writer, pTerm, nTerm, pData, nData);
**   if( rc!=SQLITE_OK ) goto err;
** }
** rc = leafWriterFinalize(v, &writer);
**err:
** leafWriterDestroy(&writer);
** return rc;
**
** leafWriterStep() may write a collected leaf out to %_segments.
** leafWriterFinalize() finishes writing any buffered data and stores
** a root node in %_segdir.  leafWriterDestroy() frees all buffers and
** InteriorWriters allocated as part of writing this segment.
**
** TODO(shess) Document leafWriterStepMerge().
*/

/* Put terms with data this big in their own block. */
#define STANDALONE_MIN 1024

/* Keep leaf blocks below this size. */
#define LEAF_MAX 2048

typedef struct LeafWriter {
  int iLevel;
  int idx;
  sqlite_int64 iStartBlockid;     /* needed to create the root info */
  sqlite_int64 iEndBlockid;       /* when we're done writing. */

  DataBuffer term;                /* previous encoded term */
  DataBuffer data;                /* encoding buffer */

  /* bytes of first term in the current node which distinguishes that
  ** term from the last term of the previous node.
  */
  int nTermDistinct;

  InteriorWriter parentWriter;    /* if we overflow */
  int has_parent;
} LeafWriter;

static void leafWriterInit(int iLevel, int idx, LeafWriter *pWriter){
  CLEAR(pWriter);
  pWriter->iLevel = iLevel;
  pWriter->idx = idx;

  dataBufferInit(&pWriter->term, 32);

  /* Start out with a reasonably sized block, though it can grow. */
  dataBufferInit(&pWriter->data, LEAF_MAX);
}

#ifndef NDEBUG
/* Verify that the data is readable as a leaf node. */
static void leafNodeValidate(const char *pData, int nData){
  int n, iDummy;

  if( nData==0 ) return;
  assert( nData>0 );
  assert( pData!=0 );
  assert( pData+nData>pData );

  /* Must lead with a varint(0) */
  n = getVarint32(pData, &iDummy);
  assert( iDummy==0 );
  assert( n>0 );
  assert( n<nData );
  pData += n;
  nData -= n;

  /* Leading term length and data must fit in buffer. */
  n = getVarint32(pData, &iDummy);
  assert( n>0 );
  assert( iDummy>0 );
  assert( n+iDummy>0 );
  assert( n+iDummy<nData );
  pData += n+iDummy;
  nData -= n+iDummy;

  /* Leading term's doclist length and data must fit. */
  n = getVarint32(pData, &iDummy);
  assert( n>0 );
  assert( iDummy>0 );
  assert( n+iDummy>0 );
  assert( n+iDummy<=nData );
  ASSERT_VALID_DOCLIST(DL_DEFAULT, pData+n, iDummy, NULL);
  pData += n+iDummy;
  nData -= n+iDummy;

  /* Verify that trailing terms and doclists also are readable. */
  while( nData!=0 ){
    n = getVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>=0 );
    assert( n<nData );
    pData += n;
    nData -= n;
    n = getVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>0 );
    assert( n+iDummy>0 );
    assert( n+iDummy<nData );
    pData += n+iDummy;
    nData -= n+iDummy;

    n = getVarint32(pData, &iDummy);
    assert( n>0 );
    assert( iDummy>0 );
    assert( n+iDummy>0 );
    assert( n+iDummy<=nData );
    ASSERT_VALID_DOCLIST(DL_DEFAULT, pData+n, iDummy, NULL);
    pData += n+iDummy;
    nData -= n+iDummy;
  }
}
#define ASSERT_VALID_LEAF_NODE(p, n) leafNodeValidate(p, n)
#else
#define ASSERT_VALID_LEAF_NODE(p, n) assert( 1 )
#endif

/* Flush the current leaf node to %_segments, and adding the resulting
** blockid and the starting term to the interior node which will
** contain it.
*/
static int leafWriterInternalFlush(fulltext_vtab *v, LeafWriter *pWriter,
                                   int iData, int nData){
  sqlite_int64 iBlockid = 0;
  const char *pStartingTerm;
  int nStartingTerm, rc, n;

  /* Must have the leading varint(0) flag, plus at least some
  ** valid-looking data.
  */
  assert( nData>2 );
  assert( iData>=0 );
  assert( iData+nData<=pWriter->data.nData );
  ASSERT_VALID_LEAF_NODE(pWriter->data.pData+iData, nData);

  rc = block_insert(v, pWriter->data.pData+iData, nData, &iBlockid);
  if( rc!=SQLITE_OK ) return rc;
  assert( iBlockid!=0 );

  /* Reconstruct the first term in the leaf for purposes of building
  ** the interior node.
  */
  n = getVarint32(pWriter->data.pData+iData+1, &nStartingTerm);
  pStartingTerm = pWriter->data.pData+iData+1+n;
  assert( pWriter->data.nData>iData+1+n+nStartingTerm );
  assert( pWriter->nTermDistinct>0 );
  assert( pWriter->nTermDistinct<=nStartingTerm );
  nStartingTerm = pWriter->nTermDistinct;

  if( pWriter->has_parent ){
    interiorWriterAppend(&pWriter->parentWriter,
                         pStartingTerm, nStartingTerm, iBlockid);
  }else{
    interiorWriterInit(1, pStartingTerm, nStartingTerm, iBlockid,
                       &pWriter->parentWriter);
    pWriter->has_parent = 1;
  }

  /* Track the span of this segment's leaf nodes. */
  if( pWriter->iEndBlockid==0 ){
    pWriter->iEndBlockid = pWriter->iStartBlockid = iBlockid;
  }else{
    pWriter->iEndBlockid++;
    assert( iBlockid==pWriter->iEndBlockid );
  }

  return SQLITE_OK;
}
static int leafWriterFlush(fulltext_vtab *v, LeafWriter *pWriter){
  int rc = leafWriterInternalFlush(v, pWriter, 0, pWriter->data.nData);
  if( rc!=SQLITE_OK ) return rc;

  /* Re-initialize the output buffer. */
  dataBufferReset(&pWriter->data);

  return SQLITE_OK;
}

/* Fetch the root info for the segment.  If the entire leaf fits
** within ROOT_MAX, then it will be returned directly, otherwise it
** will be flushed and the root info will be returned from the
** interior node.  *piEndBlockid is set to the blockid of the last
** interior or leaf node written to disk (0 if none are written at
** all).
*/
static int leafWriterRootInfo(fulltext_vtab *v, LeafWriter *pWriter,
                              char **ppRootInfo, int *pnRootInfo,
                              sqlite_int64 *piEndBlockid){
  /* we can fit the segment entirely inline */
  if( !pWriter->has_parent && pWriter->data.nData<ROOT_MAX ){
    *ppRootInfo = pWriter->data.pData;
    *pnRootInfo = pWriter->data.nData;
    *piEndBlockid = 0;
    return SQLITE_OK;
  }

  /* Flush remaining leaf data. */
  if( pWriter->data.nData>0 ){
    int rc = leafWriterFlush(v, pWriter);
    if( rc!=SQLITE_OK ) return rc;
  }

  /* We must have flushed a leaf at some point. */
  assert( pWriter->has_parent );

  /* Tenatively set the end leaf blockid as the end blockid.  If the
  ** interior node can be returned inline, this will be the final
  ** blockid, otherwise it will be overwritten by
  ** interiorWriterRootInfo().
  */
  *piEndBlockid = pWriter->iEndBlockid;

  return interiorWriterRootInfo(v, &pWriter->parentWriter,
                                ppRootInfo, pnRootInfo, piEndBlockid);
}

/* Collect the rootInfo data and store it into the segment directory.
** This has the effect of flushing the segment's leaf data to
** %_segments, and also flushing any interior nodes to %_segments.
*/
static int leafWriterFinalize(fulltext_vtab *v, LeafWriter *pWriter){
  sqlite_int64 iEndBlockid;
  char *pRootInfo;
  int rc, nRootInfo;

  rc = leafWriterRootInfo(v, pWriter, &pRootInfo, &nRootInfo, &iEndBlockid);
  if( rc!=SQLITE_OK ) return rc;

  /* Don't bother storing an entirely empty segment. */
  if( iEndBlockid==0 && nRootInfo==0 ) return SQLITE_OK;

  return segdir_set(v, pWriter->iLevel, pWriter->idx,
                    pWriter->iStartBlockid, pWriter->iEndBlockid,
                    iEndBlockid, pRootInfo, nRootInfo);
}

static void leafWriterDestroy(LeafWriter *pWriter){
  if( pWriter->has_parent ) interiorWriterDestroy(&pWriter->parentWriter);
  dataBufferDestroy(&pWriter->term);
  dataBufferDestroy(&pWriter->data);
}

/* Encode a term into the leafWriter, delta-encoding as appropriate.
** Returns the length of the new term which distinguishes it from the
** previous term, which can be used to set nTermDistinct when a node
** boundary is crossed.
*/
static int leafWriterEncodeTerm(LeafWriter *pWriter,
                                const char *pTerm, int nTerm){
  char c[VARINT_MAX+VARINT_MAX];
  int n, nPrefix = 0;

  assert( nTerm>0 );
  while( nPrefix<pWriter->term.nData &&
         pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
    nPrefix++;
    /* Failing this implies that the terms weren't in order. */
    assert( nPrefix<nTerm );
  }

  if( pWriter->data.nData==0 ){
    /* Encode the node header and leading term as:
    **  varint(0)
    **  varint(nTerm)
    **  char pTerm[nTerm]
    */
    n = putVarint(c, '\0');
    n += putVarint(c+n, nTerm);
    dataBufferAppend2(&pWriter->data, c, n, pTerm, nTerm);
  }else{
    /* Delta-encode the term as:
    **  varint(nPrefix)
    **  varint(nSuffix)
    **  char pTermSuffix[nSuffix]
    */
    n = putVarint(c, nPrefix);
    n += putVarint(c+n, nTerm-nPrefix);
    dataBufferAppend2(&pWriter->data, c, n, pTerm+nPrefix, nTerm-nPrefix);
  }
  dataBufferReplace(&pWriter->term, pTerm, nTerm);

  return nPrefix+1;
}

/* Used to avoid a memmove when a large amount of doclist data is in
** the buffer.  This constructs a node and term header before
** iDoclistData and flushes the resulting complete node using
** leafWriterInternalFlush().
*/
static int leafWriterInlineFlush(fulltext_vtab *v, LeafWriter *pWriter,
                                 const char *pTerm, int nTerm,
                                 int iDoclistData){
  char c[VARINT_MAX+VARINT_MAX];
  int iData, n = putVarint(c, 0);
  n += putVarint(c+n, nTerm);

  /* There should always be room for the header.  Even if pTerm shared
  ** a substantial prefix with the previous term, the entire prefix
  ** could be constructed from earlier data in the doclist, so there
  ** should be room.
  */
  assert( iDoclistData>=n+nTerm );

  iData = iDoclistData-(n+nTerm);
  memcpy(pWriter->data.pData+iData, c, n);
  memcpy(pWriter->data.pData+iData+n, pTerm, nTerm);

  return leafWriterInternalFlush(v, pWriter, iData, pWriter->data.nData-iData);
}

/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
** %_segments.
*/
static int leafWriterStepMerge(fulltext_vtab *v, LeafWriter *pWriter,
                               const char *pTerm, int nTerm,
                               DLReader *pReaders, int nReaders){
  char c[VARINT_MAX+VARINT_MAX];
  int iTermData = pWriter->data.nData, iDoclistData;
  int i, nData, n, nActualData, nActual, rc, nTermDistinct;

  ASSERT_VALID_LEAF_NODE(pWriter->data.pData, pWriter->data.nData);
  nTermDistinct = leafWriterEncodeTerm(pWriter, pTerm, nTerm);

  /* Remember nTermDistinct if opening a new node. */
  if( iTermData==0 ) pWriter->nTermDistinct = nTermDistinct;

  iDoclistData = pWriter->data.nData;

  /* Estimate the length of the merged doclist so we can leave space
  ** to encode it.
  */
  for(i=0, nData=0; i<nReaders; i++){
    nData += dlrAllDataBytes(&pReaders[i]);
  }
  n = putVarint(c, nData);
  dataBufferAppend(&pWriter->data, c, n);

  docListMerge(&pWriter->data, pReaders, nReaders);
  ASSERT_VALID_DOCLIST(DL_DEFAULT,
                       pWriter->data.pData+iDoclistData+n,
                       pWriter->data.nData-iDoclistData-n, NULL);

  /* The actual amount of doclist data at this point could be smaller
  ** than the length we encoded.  Additionally, the space required to
  ** encode this length could be smaller.  For small doclists, this is
  ** not a big deal, we can just use memmove() to adjust things.
  */
  nActualData = pWriter->data.nData-(iDoclistData+n);
  nActual = putVarint(c, nActualData);
  assert( nActualData<=nData );
  assert( nActual<=n );

  /* If the new doclist is big enough for force a standalone leaf
  ** node, we can immediately flush it inline without doing the
  ** memmove().
  */
  /* TODO(shess) This test matches leafWriterStep(), which does this
  ** test before it knows the cost to varint-encode the term and
  ** doclist lengths.  At some point, change to
  ** pWriter->data.nData-iTermData>STANDALONE_MIN.
  */
  if( nTerm+nActualData>STANDALONE_MIN ){
    /* Push leaf node from before this term. */
    if( iTermData>0 ){
      rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
      if( rc!=SQLITE_OK ) return rc;

      pWriter->nTermDistinct = nTermDistinct;
    }

    /* Fix the encoded doclist length. */
    iDoclistData += n - nActual;
    memcpy(pWriter->data.pData+iDoclistData, c, nActual);

    /* Push the standalone leaf node. */
    rc = leafWriterInlineFlush(v, pWriter, pTerm, nTerm, iDoclistData);
    if( rc!=SQLITE_OK ) return rc;

    /* Leave the node empty. */
    dataBufferReset(&pWriter->data);

    return rc;
  }

  /* At this point, we know that the doclist was small, so do the
  ** memmove if indicated.
  */
  if( nActual<n ){
    memmove(pWriter->data.pData+iDoclistData+nActual,
            pWriter->data.pData+iDoclistData+n,
            pWriter->data.nData-(iDoclistData+n));
    pWriter->data.nData -= n-nActual;
  }

  /* Replace written length with actual length. */
  memcpy(pWriter->data.pData+iDoclistData, c, nActual);

  /* If the node is too large, break things up. */
  /* TODO(shess) This test matches leafWriterStep(), which does this
  ** test before it knows the cost to varint-encode the term and
  ** doclist lengths.  At some point, change to
  ** pWriter->data.nData>LEAF_MAX.
  */
  if( iTermData+nTerm+nActualData>LEAF_MAX ){
    /* Flush out the leading data as a node */
    rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
    if( rc!=SQLITE_OK ) return rc;

    pWriter->nTermDistinct = nTermDistinct;

    /* Rebuild header using the current term */
    n = putVarint(pWriter->data.pData, 0);
    n += putVarint(pWriter->data.pData+n, nTerm);
    memcpy(pWriter->data.pData+n, pTerm, nTerm);
    n += nTerm;

    /* There should always be room, because the previous encoding
    ** included all data necessary to construct the term.
    */
    assert( n<iDoclistData );
    /* So long as STANDALONE_MIN is half or less of LEAF_MAX, the
    ** following memcpy() is safe (as opposed to needing a memmove).
    */
    assert( 2*STANDALONE_MIN<=LEAF_MAX );
    assert( n+pWriter->data.nData-iDoclistData<iDoclistData );
    memcpy(pWriter->data.pData+n,
           pWriter->data.pData+iDoclistData,
           pWriter->data.nData-iDoclistData);
    pWriter->data.nData -= iDoclistData-n;
  }
  ASSERT_VALID_LEAF_NODE(pWriter->data.pData, pWriter->data.nData);

  return SQLITE_OK;
}

/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
** %_segments.
*/
/* TODO(shess) Revise writeZeroSegment() so that doclists are
** constructed directly in pWriter->data.
*/
static int leafWriterStep(fulltext_vtab *v, LeafWriter *pWriter,
                          const char *pTerm, int nTerm,
                          const char *pData, int nData){
  int rc;
  DLReader reader;

  dlrInit(&reader, DL_DEFAULT, pData, nData);
  rc = leafWriterStepMerge(v, pWriter, pTerm, nTerm, &reader, 1);
  dlrDestroy(&reader);

  return rc;
}


/****************************************************************/
/* LeafReader is used to iterate over an individual leaf node. */
typedef struct LeafReader {
  DataBuffer term;          /* copy of current term. */

  const char *pData;        /* data for current term. */
  int nData;
} LeafReader;

static void leafReaderDestroy(LeafReader *pReader){
  dataBufferDestroy(&pReader->term);
  SCRAMBLE(pReader);
}

static int leafReaderAtEnd(LeafReader *pReader){
  return pReader->nData<=0;
}

/* Access the current term. */
static int leafReaderTermBytes(LeafReader *pReader){
  return pReader->term.nData;
}
static const char *leafReaderTerm(LeafReader *pReader){
  assert( pReader->term.nData>0 );
  return pReader->term.pData;
}

/* Access the doclist data for the current term. */
static int leafReaderDataBytes(LeafReader *pReader){
  int nData;
  assert( pReader->term.nData>0 );
  getVarint32(pReader->pData, &nData);
  return nData;
}
static const char *leafReaderData(LeafReader *pReader){
  int n, nData;
  assert( pReader->term.nData>0 );
  n = getVarint32(pReader->pData, &nData);
  return pReader->pData+n;
}

static void leafReaderInit(const char *pData, int nData,
                           LeafReader *pReader){
  int nTerm, n;

  assert( nData>0 );
  assert( pData[0]=='\0' );

  CLEAR(pReader);

  /* Read the first term, skipping the header byte. */
  n = getVarint32(pData+1, &nTerm);
  dataBufferInit(&pReader->term, nTerm);
  dataBufferReplace(&pReader->term, pData+1+n, nTerm);

  /* Position after the first term. */
  assert( 1+n+nTerm<nData );
  pReader->pData = pData+1+n+nTerm;
  pReader->nData = nData-1-n-nTerm;
}

/* Step the reader forward to the next term. */
static void leafReaderStep(LeafReader *pReader){
  int n, nData, nPrefix, nSuffix;
  assert( !leafReaderAtEnd(pReader) );

  /* Skip previous entry's data block. */
  n = getVarint32(pReader->pData, &nData);
  assert( n+nData<=pReader->nData );
  pReader->pData += n+nData;
  pReader->nData -= n+nData;

  if( !leafReaderAtEnd(pReader) ){
    /* Construct the new term using a prefix from the old term plus a
    ** suffix from the leaf data.
    */
    n = getVarint32(pReader->pData, &nPrefix);
    n += getVarint32(pReader->pData+n, &nSuffix);
    assert( n+nSuffix<pReader->nData );
    pReader->term.nData = nPrefix;
    dataBufferAppend(&pReader->term, pReader->pData+n, nSuffix);

    pReader->pData += n+nSuffix;
    pReader->nData -= n+nSuffix;
  }
}

/* strcmp-style comparison of pReader's current term against pTerm. */
static int leafReaderTermCmp(LeafReader *pReader,
                             const char *pTerm, int nTerm){
  int c, n = pReader->term.nData<nTerm ? pReader->term.nData : nTerm;
  if( n==0 ){
    if( pReader->term.nData>0 ) return -1;
    if(nTerm>0 ) return 1;
    return 0;
  }

  c = memcmp(pReader->term.pData, pTerm, n);
  if( c!=0 ) return c;
  return pReader->term.nData - nTerm;
}


/****************************************************************/
/* LeavesReader wraps LeafReader to allow iterating over the entire
** leaf layer of the tree.
*/
typedef struct LeavesReader {
  int idx;                  /* Index within the segment. */

  sqlite3_stmt *pStmt;      /* Statement we're streaming leaves from. */
  int eof;                  /* we've seen SQLITE_DONE from pStmt. */

  LeafReader leafReader;    /* reader for the current leaf. */
  DataBuffer rootData;      /* root data for inline. */
} LeavesReader;

/* Access the current term. */
static int leavesReaderTermBytes(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderTermBytes(&pReader->leafReader);
}
static const char *leavesReaderTerm(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderTerm(&pReader->leafReader);
}

/* Access the doclist data for the current term. */
static int leavesReaderDataBytes(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderDataBytes(&pReader->leafReader);
}
static const char *leavesReaderData(LeavesReader *pReader){
  assert( !pReader->eof );
  return leafReaderData(&pReader->leafReader);
}

static int leavesReaderAtEnd(LeavesReader *pReader){
  return pReader->eof;
}

static void leavesReaderDestroy(LeavesReader *pReader){
  leafReaderDestroy(&pReader->leafReader);
  dataBufferDestroy(&pReader->rootData);
  SCRAMBLE(pReader);
}

/* Initialize pReader with the given root data (if iStartBlockid==0
** the leaf data was entirely contained in the root), or from the
** stream of blocks between iStartBlockid and iEndBlockid, inclusive.
*/
static int leavesReaderInit(fulltext_vtab *v,
                            int idx,
                            sqlite_int64 iStartBlockid,
                            sqlite_int64 iEndBlockid,
                            const char *pRootData, int nRootData,
                            LeavesReader *pReader){
  CLEAR(pReader);
  pReader->idx = idx;

  dataBufferInit(&pReader->rootData, 0);
  if( iStartBlockid==0 ){
    /* Entire leaf level fit in root data. */
    dataBufferReplace(&pReader->rootData, pRootData, nRootData);
    leafReaderInit(pReader->rootData.pData, pReader->rootData.nData,
                   &pReader->leafReader);
  }else{
    sqlite3_stmt *s;
    int rc = sql_get_leaf_statement(v, idx, &s);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3_bind_int64(s, 1, iStartBlockid);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3_bind_int64(s, 2, iEndBlockid);
    if( rc!=SQLITE_OK ) return rc;

    rc = sql_step_leaf_statement(v, idx, &s);
    if( rc==SQLITE_DONE ){
      pReader->eof = 1;
      return SQLITE_OK;
    }
    if( rc!=SQLITE_ROW ) return rc;

    pReader->pStmt = s;
    leafReaderInit(sqlite3_column_blob(pReader->pStmt, 0),
                   sqlite3_column_bytes(pReader->pStmt, 0),
                   &pReader->leafReader);
  }
  return SQLITE_OK;
}

/* Step the current leaf forward to the next term.  If we reach the
** end of the current leaf, step forward to the next leaf block.
*/
static int leavesReaderStep(fulltext_vtab *v, LeavesReader *pReader){
  assert( !leavesReaderAtEnd(pReader) );
  leafReaderStep(&pReader->leafReader);

  if( leafReaderAtEnd(&pReader->leafReader) ){
    int rc;
    if( pReader->rootData.pData ){
      pReader->eof = 1;
      return SQLITE_OK;
    }
    rc = sql_step_leaf_statement(v, pReader->idx, &pReader->pStmt);
    if( rc!=SQLITE_ROW ){
      pReader->eof = 1;
      return rc==SQLITE_DONE ? SQLITE_OK : rc;
    }
    leafReaderDestroy(&pReader->leafReader);
    leafReaderInit(sqlite3_column_blob(pReader->pStmt, 0),
                   sqlite3_column_bytes(pReader->pStmt, 0),
                   &pReader->leafReader);
  }
  return SQLITE_OK;
}

/* Order LeavesReaders by their term, ignoring idx.  Readers at eof
** always sort to the end.
*/
static int leavesReaderTermCmp(LeavesReader *lr1, LeavesReader *lr2){
  if( leavesReaderAtEnd(lr1) ){
    if( leavesReaderAtEnd(lr2) ) return 0;
    return 1;
  }
  if( leavesReaderAtEnd(lr2) ) return -1;

  return leafReaderTermCmp(&lr1->leafReader,
                           leavesReaderTerm(lr2), leavesReaderTermBytes(lr2));
}

/* Similar to leavesReaderTermCmp(), with additional ordering by idx
** so that older segments sort before newer segments.
*/
static int leavesReaderCmp(LeavesReader *lr1, LeavesReader *lr2){
  int c = leavesReaderTermCmp(lr1, lr2);
  if( c!=0 ) return c;
  return lr1->idx-lr2->idx;
}

/* Assume that pLr[1]..pLr[nLr] are sorted.  Bubble pLr[0] into its
** sorted position.
*/
static void leavesReaderReorder(LeavesReader *pLr, int nLr){
  while( nLr>1 && leavesReaderCmp(pLr, pLr+1)>0 ){
    LeavesReader tmp = pLr[0];
    pLr[0] = pLr[1];
    pLr[1] = tmp;
    nLr--;
    pLr++;
  }
}

/* Initializes pReaders with the segments from level iLevel, returning
** the number of segments in *piReaders.  Leaves pReaders in sorted
** order.
*/
static int leavesReadersInit(fulltext_vtab *v, int iLevel,
                             LeavesReader *pReaders, int *piReaders){
  sqlite3_stmt *s;
  int i, rc = sql_get_statement(v, SEGDIR_SELECT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int(s, 1, iLevel);
  if( rc!=SQLITE_OK ) return rc;

  i = 0;
  while( (rc = sql_step_statement(v, SEGDIR_SELECT_STMT, &s))==SQLITE_ROW ){
    sqlite_int64 iStart = sqlite3_column_int64(s, 0);
    sqlite_int64 iEnd = sqlite3_column_int64(s, 1);
    const char *pRootData = sqlite3_column_blob(s, 2);
    int nRootData = sqlite3_column_bytes(s, 2);

    assert( i<MERGE_COUNT );
    rc = leavesReaderInit(v, i, iStart, iEnd, pRootData, nRootData,
                          &pReaders[i]);
    if( rc!=SQLITE_OK ) break;

    i++;
  }
  if( rc!=SQLITE_DONE ){
    while( i-->0 ){
      leavesReaderDestroy(&pReaders[i]);
    }
    return rc;
  }

  *piReaders = i;

  /* Leave our results sorted by term, then age. */
  while( i-- ){
    leavesReaderReorder(pReaders+i, *piReaders-i);
  }
  return SQLITE_OK;
}

/* Merge doclists from pReaders[nReaders] into a single doclist, which
** is written to pWriter.  Assumes pReaders is ordered oldest to
** newest.
*/
/* TODO(shess) Consider putting this inline in segmentMerge(). */
static int leavesReadersMerge(fulltext_vtab *v,
                              LeavesReader *pReaders, int nReaders,
                              LeafWriter *pWriter){
  DLReader dlReaders[MERGE_COUNT];
  const char *pTerm = leavesReaderTerm(pReaders);
  int i, nTerm = leavesReaderTermBytes(pReaders);

  assert( nReaders<=MERGE_COUNT );

  for(i=0; i<nReaders; i++){
    dlrInit(&dlReaders[i], DL_DEFAULT,
            leavesReaderData(pReaders+i),
            leavesReaderDataBytes(pReaders+i));
  }

  return leafWriterStepMerge(v, pWriter, pTerm, nTerm, dlReaders, nReaders);
}

/* Forward ref due to mutual recursion with segdirNextIndex(). */
static int segmentMerge(fulltext_vtab *v, int iLevel);

/* Put the next available index at iLevel into *pidx.  If iLevel
** already has MERGE_COUNT segments, they are merged to a higher
** level to make room.
*/
static int segdirNextIndex(fulltext_vtab *v, int iLevel, int *pidx){
  int rc = segdir_max_index(v, iLevel, pidx);
  if( rc==SQLITE_DONE ){              /* No segments at iLevel. */
    *pidx = 0;
  }else if( rc==SQLITE_ROW ){
    if( *pidx==(MERGE_COUNT-1) ){
      rc = segmentMerge(v, iLevel);
      if( rc!=SQLITE_OK ) return rc;
      *pidx = 0;
    }else{
      (*pidx)++;
    }
  }else{
    return rc;
  }
  return SQLITE_OK;
}

/* Merge MERGE_COUNT segments at iLevel into a new segment at
** iLevel+1.  If iLevel+1 is already full of segments, those will be
** merged to make room.
*/
static int segmentMerge(fulltext_vtab *v, int iLevel){
  LeafWriter writer;
  LeavesReader lrs[MERGE_COUNT];
  int i, rc, idx = 0;

  /* Determine the next available segment index at the next level,
  ** merging as necessary.
  */
  rc = segdirNextIndex(v, iLevel+1, &idx);
  if( rc!=SQLITE_OK ) return rc;

  /* TODO(shess) This assumes that we'll always see exactly
  ** MERGE_COUNT segments to merge at a given level.  That will be
  ** broken if we allow the developer to request preemptive or
  ** deferred merging.
  */
  memset(&lrs, '\0', sizeof(lrs));
  rc = leavesReadersInit(v, iLevel, lrs, &i);
  if( rc!=SQLITE_OK ) return rc;
  assert( i==MERGE_COUNT );

  leafWriterInit(iLevel+1, idx, &writer);

  /* Since leavesReaderReorder() pushes readers at eof to the end,
  ** when the first reader is empty, all will be empty.
  */
  while( !leavesReaderAtEnd(lrs) ){
    /* Figure out how many readers share their next term. */
    for(i=1; i<MERGE_COUNT && !leavesReaderAtEnd(lrs+i); i++){
      if( 0!=leavesReaderTermCmp(lrs, lrs+i) ) break;
    }

    rc = leavesReadersMerge(v, lrs, i, &writer);
    if( rc!=SQLITE_OK ) goto err;

    /* Step forward those that were merged. */
    while( i-->0 ){
      rc = leavesReaderStep(v, lrs+i);
      if( rc!=SQLITE_OK ) goto err;

      /* Reorder by term, then by age. */
      leavesReaderReorder(lrs+i, MERGE_COUNT-i);
    }
  }

  for(i=0; i<MERGE_COUNT; i++){
    leavesReaderDestroy(&lrs[i]);
  }

  rc = leafWriterFinalize(v, &writer);
  leafWriterDestroy(&writer);
  if( rc!=SQLITE_OK ) return rc;

  /* Delete the merged segment data. */
  return segdir_delete(v, iLevel);

 err:
  for(i=0; i<MERGE_COUNT; i++){
    leavesReaderDestroy(&lrs[i]);
  }
  leafWriterDestroy(&writer);
  return rc;
}

/* Read pData[nData] as a leaf node, and if the doclist for
** pTerm[nTerm] is present, merge it over *out (any duplicate doclists
** read from pData will overwrite those in *out).
*/
static int loadSegmentLeaf(fulltext_vtab *v, const char *pData, int nData,
                           const char *pTerm, int nTerm, DataBuffer *out){
  LeafReader reader;
  assert( nData>1 );
  assert( *pData=='\0' );

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  leafReaderInit(pData, nData, &reader);
  while( !leafReaderAtEnd(&reader) ){
    int c = leafReaderTermCmp(&reader, pTerm, nTerm);
    if( c==0 ){
      if( out->nData==0 ){
        dataBufferReplace(out,
                          leafReaderData(&reader), leafReaderDataBytes(&reader));
      }else{
        DLReader readers[2];
        DataBuffer result;
        dlrInit(&readers[0], DL_DEFAULT, out->pData, out->nData);
        dlrInit(&readers[1], DL_DEFAULT,
                leafReaderData(&reader), leafReaderDataBytes(&reader));
        dataBufferInit(&result, out->nData+leafReaderDataBytes(&reader));
        docListMerge(&result, readers, 2);
        dataBufferDestroy(out);
        *out = result;
      }
    }
    if( c>=0 ) break;
    leafReaderStep(&reader);
  }
  leafReaderDestroy(&reader);
  return SQLITE_OK;
}

/* Traverse the tree represented by pData[nData] looking for
** pTerm[nTerm], merging its doclist over *out if found (any duplicate
** doclists read from the segment rooted at pData will overwrite those
** in *out).
*/
static int loadSegment(fulltext_vtab *v, const char *pData, int nData,
                       const char *pTerm, int nTerm, DataBuffer *out){
  int rc;
  sqlite3_stmt *s = NULL;

  assert( nData>1 );

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  /* Process data as an interior node until we reach a leaf. */
  while( *pData!='\0' ){
    sqlite_int64 iBlockid;
    InteriorReader reader;

    /* Scan the node data until we find a term greater than our term.
    ** Our target child will be in the blockid under that term, or in
    ** the last blockid in the node if we never find such a term.
    */
    interiorReaderInit(pData, nData, &reader);
    while( !interiorReaderAtEnd(&reader) ){
      if( interiorReaderTermCmp(&reader, pTerm, nTerm)>0 ) break;
      interiorReaderStep(&reader);
    }

    /* Grab the child blockid before calling sql_get_statement(),
    ** because sql_get_statement() may reset our data out from under
    ** us.
    */
    iBlockid = interiorReaderCurrentBlockid(&reader);
    interiorReaderDestroy(&reader);

    rc = sql_get_statement(v, BLOCK_SELECT_STMT, &s);
    if( rc!=SQLITE_OK ) return rc;

    rc = sqlite3_bind_int64(s, 1, iBlockid);
    if( rc!=SQLITE_OK ) return rc;

    rc = sql_step_statement(v, BLOCK_SELECT_STMT, &s);
    if( rc==SQLITE_DONE ) return SQLITE_ERROR;
    if( rc!=SQLITE_ROW ) return rc;

    pData = sqlite3_column_blob(s, 0);
    nData = sqlite3_column_bytes(s, 0);
  }

  rc = loadSegmentLeaf(v, pData, nData, pTerm, nTerm, out);
  if( rc!=SQLITE_OK ) return rc;

  /* If we selected a child node, we need to finish that select. */
  if( s!=NULL ){
    /* We expect only one row.  We must execute another sqlite3_step()
     * to complete the iteration; otherwise the table will remain
     * locked. */
    rc = sqlite3_step(s);
    if( rc==SQLITE_ROW ) return SQLITE_ERROR;
    if( rc!=SQLITE_DONE ) return rc;
  }
  return SQLITE_OK;
}

/* Scan the database and merge together the posting lists for the term
** into *out.
*/
static int termSelect(fulltext_vtab *v, int iColumn,
                      const char *pTerm, int nTerm,
                      DocListType iType, DataBuffer *out){
  DataBuffer doclist;
  sqlite3_stmt *s;
  int rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  dataBufferInit(&doclist, 0);

  /* Traverse the segments from oldest to newest so that newer doclist
  ** elements for given docids overwrite older elements.
  */
  while( (rc=sql_step_statement(v, SEGDIR_SELECT_ALL_STMT, &s))==SQLITE_ROW ){
    rc = loadSegment(v, sqlite3_column_blob(s, 0), sqlite3_column_bytes(s, 0),
                     pTerm, nTerm, &doclist);
    if( rc!=SQLITE_OK ) goto err;
  }
  if( rc==SQLITE_DONE ){
    if( doclist.nData!=0 ){
      /* TODO(shess) The old term_select_all() code applied the column
      ** restrict as we merged segments, leading to smaller buffers.
      ** This is probably worthwhile to bring back, once the new storage
      ** system is checked in.
      */
      if( iColumn==v->nColumn) iColumn = -1;
      docListTrim(DL_DEFAULT, doclist.pData, doclist.nData,
                  iColumn, iType, out);
    }
    rc = SQLITE_OK;
  }

 err:
  dataBufferDestroy(&doclist);
  return rc;
}

/****************************************************************/
/* Used to hold hashtable data for sorting. */
typedef struct TermData {
  const char *pTerm;
  int nTerm;
  DLCollector *pCollector;
} TermData;

/* Orders TermData elements in strcmp fashion ( <0 for less-than, 0
** for equal, >0 for greater-than).
*/
static int termDataCmp(const void *av, const void *bv){
  const TermData *a = (const TermData *)av;
  const TermData *b = (const TermData *)bv;
  int n = a->nTerm<b->nTerm ? a->nTerm : b->nTerm;
  int c = memcmp(a->pTerm, b->pTerm, n);
  if( c!=0 ) return c;
  return a->nTerm-b->nTerm;
}

/* Order pTerms data by term, then write a new level 0 segment using
** LeafWriter.
*/
static int writeZeroSegment(fulltext_vtab *v, fts2Hash *pTerms){
  fts2HashElem *e;
  int idx, rc, i, n;
  TermData *pData;
  LeafWriter writer;
  DataBuffer dl;

  /* Determine the next index at level 0, merging as necessary. */
  rc = segdirNextIndex(v, 0, &idx);
  if( rc!=SQLITE_OK ) return rc;

  n = fts2HashCount(pTerms);
  pData = malloc(n*sizeof(TermData));

  for(i = 0, e = fts2HashFirst(pTerms); e; i++, e = fts2HashNext(e)){
    assert( i<n );
    pData[i].pTerm = fts2HashKey(e);
    pData[i].nTerm = fts2HashKeysize(e);
    pData[i].pCollector = fts2HashData(e);
  }
  assert( i==n );

  /* TODO(shess) Should we allow user-defined collation sequences,
  ** here?  I think we only need that once we support prefix searches.
  */
  if( n>1 ) qsort(pData, n, sizeof(*pData), termDataCmp);

  /* TODO(shess) Refactor so that we can write directly to the segment
  ** DataBuffer, as happens for segment merges.
  */
  leafWriterInit(0, idx, &writer);
  dataBufferInit(&dl, 0);
  for(i=0; i<n; i++){
    dataBufferReset(&dl);
    dlcAddDoclist(pData[i].pCollector, &dl);
    rc = leafWriterStep(v, &writer,
                        pData[i].pTerm, pData[i].nTerm, dl.pData, dl.nData);
    if( rc!=SQLITE_OK ) goto err;
  }
  rc = leafWriterFinalize(v, &writer);

 err:
  dataBufferDestroy(&dl);
  free(pData);
  leafWriterDestroy(&writer);
  return rc;
}

/* If pendingTerms has data, free it. */
static int clearPendingTerms(fulltext_vtab *v){
  if( v->nPendingData>=0 ){
    fts2HashElem *e;
    for(e=fts2HashFirst(&v->pendingTerms); e; e=fts2HashNext(e)){
      dlcDelete(fts2HashData(e));
    }
    fts2HashClear(&v->pendingTerms);
    v->nPendingData = -1;
  }
  return SQLITE_OK;
}

/* If pendingTerms has data, flush it to a level-zero segment, and
** free it.
*/
static int flushPendingTerms(fulltext_vtab *v){
  if( v->nPendingData>=0 ){
    int rc = writeZeroSegment(v, &v->pendingTerms);
    clearPendingTerms(v);
    return rc;
  }
  return SQLITE_OK;
}

/* If pendingTerms is "too big", or docid is out of order, flush it.
** Regardless, be certain that pendingTerms is initialized for use.
*/
static int initPendingTerms(fulltext_vtab *v, sqlite_int64 iDocid){
  /* TODO(shess) Explore whether partially flushing the buffer on
  ** forced-flush would provide better performance.  I suspect that if
  ** we ordered the doclists by size and flushed the largest until the
  ** buffer was half empty, that would let the less frequent terms
  ** generate longer doclists.
  */
  if( iDocid<=v->iPrevDocid || v->nPendingData>kPendingThreshold ){
    int rc = flushPendingTerms(v);
    if( rc!=SQLITE_OK ) return rc;
  }
  if( v->nPendingData<0 ){
    fts2HashInit(&v->pendingTerms, FTS2_HASH_STRING, 1);
    v->nPendingData = 0;
  }
  v->iPrevDocid = iDocid;
  return SQLITE_OK;
}

/* This function implements the xUpdate callback; it's the top-level entry
 * point for inserting, deleting or updating a row in a full-text table. */
static int fulltextUpdate(sqlite3_vtab *pVtab, int nArg, sqlite3_value **ppArg,
                   sqlite_int64 *pRowid){
  fulltext_vtab *v = (fulltext_vtab *) pVtab;
  int rc;

  TRACE(("FTS2 Update %p\n", pVtab));

  if( nArg<2 ){
    rc = index_delete(v, sqlite3_value_int64(ppArg[0]));
  } else if( sqlite3_value_type(ppArg[0]) != SQLITE_NULL ){
    /* An update:
     * ppArg[0] = old rowid
     * ppArg[1] = new rowid
     * ppArg[2..2+v->nColumn-1] = values
     * ppArg[2+v->nColumn] = value for magic column (we ignore this)
     */
    sqlite_int64 rowid = sqlite3_value_int64(ppArg[0]);
    if( sqlite3_value_type(ppArg[1]) != SQLITE_INTEGER ||
      sqlite3_value_int64(ppArg[1]) != rowid ){
      rc = SQLITE_ERROR;  /* we don't allow changing the rowid */
    } else {
      assert( nArg==2+v->nColumn+1);
      rc = index_update(v, rowid, &ppArg[2]);
    }
  } else {
    /* An insert:
     * ppArg[1] = requested rowid
     * ppArg[2..2+v->nColumn-1] = values
     * ppArg[2+v->nColumn] = value for magic column (we ignore this)
     */
    assert( nArg==2+v->nColumn+1);
    rc = index_insert(v, ppArg[1], &ppArg[2], pRowid);
  }

  return rc;
}

static int fulltextSync(sqlite3_vtab *pVtab){
  TRACE(("FTS2 xSync()\n"));
  return flushPendingTerms((fulltext_vtab *)pVtab);
}

static int fulltextBegin(sqlite3_vtab *pVtab){
  fulltext_vtab *v = (fulltext_vtab *) pVtab;
  TRACE(("FTS2 xBegin()\n"));

  /* Any buffered updates should have been cleared by the previous
  ** transaction.
  */
  assert( v->nPendingData<0 );
  return clearPendingTerms(v);
}

static int fulltextCommit(sqlite3_vtab *pVtab){
  fulltext_vtab *v = (fulltext_vtab *) pVtab;
  TRACE(("FTS2 xCommit()\n"));

  /* Buffered updates should have been cleared by fulltextSync(). */
  assert( v->nPendingData<0 );
  return clearPendingTerms(v);
}

static int fulltextRollback(sqlite3_vtab *pVtab){
  TRACE(("FTS2 xRollback()\n"));
  return clearPendingTerms((fulltext_vtab *)pVtab);
}

/*
** Implementation of the snippet() function for FTS2
*/
static void snippetFunc(
  sqlite3_context *pContext,
  int argc,
  sqlite3_value **argv
){
  fulltext_cursor *pCursor;
  if( argc<1 ) return;
  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    sqlite3_result_error(pContext, "illegal first argument to html_snippet",-1);
  }else{
    const char *zStart = "<b>";
    const char *zEnd = "</b>";
    const char *zEllipsis = "<b>...</b>";
    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    if( argc>=2 ){
      zStart = (const char*)sqlite3_value_text(argv[1]);
      if( argc>=3 ){
        zEnd = (const char*)sqlite3_value_text(argv[2]);
        if( argc>=4 ){
          zEllipsis = (const char*)sqlite3_value_text(argv[3]);
        }
      }
    }
    snippetAllOffsets(pCursor);
    snippetText(pCursor, zStart, zEnd, zEllipsis);
    sqlite3_result_text(pContext, pCursor->snippet.zSnippet,
                        pCursor->snippet.nSnippet, SQLITE_STATIC);
  }
}

/*
** Implementation of the offsets() function for FTS2
*/
static void snippetOffsetsFunc(
  sqlite3_context *pContext,
  int argc,
  sqlite3_value **argv
){
  fulltext_cursor *pCursor;
  if( argc<1 ) return;
  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    sqlite3_result_error(pContext, "illegal first argument to offsets",-1);
  }else{
    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    snippetAllOffsets(pCursor);
    snippetOffsetText(&pCursor->snippet);
    sqlite3_result_text(pContext,
                        pCursor->snippet.zOffset, pCursor->snippet.nOffset,
                        SQLITE_STATIC);
  }
}

/*
** This routine implements the xFindFunction method for the FTS2
** virtual table.
*/
static int fulltextFindFunction(
  sqlite3_vtab *pVtab,
  int nArg,
  const char *zName,
  void (**pxFunc)(sqlite3_context*,int,sqlite3_value**),
  void **ppArg
){
  if( strcmp(zName,"snippet")==0 ){
    *pxFunc = snippetFunc;
    return 1;
  }else if( strcmp(zName,"offsets")==0 ){
    *pxFunc = snippetOffsetsFunc;
    return 1;
  }
  return 0;
}

static const sqlite3_module fulltextModule = {
  /* iVersion      */ 0,
  /* xCreate       */ fulltextCreate,
  /* xConnect      */ fulltextConnect,
  /* xBestIndex    */ fulltextBestIndex,
  /* xDisconnect   */ fulltextDisconnect,
  /* xDestroy      */ fulltextDestroy,
  /* xOpen         */ fulltextOpen,
  /* xClose        */ fulltextClose,
  /* xFilter       */ fulltextFilter,
  /* xNext         */ fulltextNext,
  /* xEof          */ fulltextEof,
  /* xColumn       */ fulltextColumn,
  /* xRowid        */ fulltextRowid,
  /* xUpdate       */ fulltextUpdate,
  /* xBegin        */ fulltextBegin,
  /* xSync         */ fulltextSync,
  /* xCommit       */ fulltextCommit,
  /* xRollback     */ fulltextRollback,
  /* xFindFunction */ fulltextFindFunction,
};

int sqlite3Fts2Init(sqlite3 *db){
  sqlite3_overload_function(db, "snippet", -1);
  sqlite3_overload_function(db, "offsets", -1);
  return sqlite3_create_module(db, "fts2", &fulltextModule, 0);
}

#if !SQLITE_CORE
int sqlite3_extension_init(sqlite3 *db, char **pzErrMsg,
                           const sqlite3_api_routines *pApi){
  SQLITE_EXTENSION_INIT2(pApi)
  return sqlite3Fts2Init(db);
}
#endif

#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2) */