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sqlite3_result_text(pCtx, (const char*)ctx.zOut, -1, SQLITE_TRANSIENT);
}else{
sqlite3_result_error_code(pCtx, rc);
}
sqlite3_free(ctx.zOut);
}
/*
** End of highlight() implementation.
**************************************************************************/
/*
** Implementation of snippet() function.
*/
static void fts5SnippetFunction(
const Fts5ExtensionApi *pApi, /* API offered by current FTS version */
Fts5Context *pFts, /* First arg to pass to pApi functions */
sqlite3_context *pCtx, /* Context for returning result/error */
int nVal, /* Number of values in apVal[] array */
sqlite3_value **apVal /* Array of trailing arguments */
){
HighlightContext ctx;
int rc = SQLITE_OK; /* Return code */
int iCol; /* 1st argument to snippet() */
const char *zEllips; /* 4th argument to snippet() */
int nToken; /* 5th argument to snippet() */
int nInst; /* Number of instance matches this row */
int i; /* Used to iterate through instances */
int nPhrase; /* Number of phrases in query */
unsigned char *aSeen; /* Array of "seen instance" flags */
int iBestCol; /* Column containing best snippet */
int iBestStart = 0; /* First token of best snippet */
int iBestLast = nToken; /* Last token of best snippet */
int iBestLast; /* Last token of best snippet */
int nBestScore = 0; /* Score of best snippet */
int nColSize; /* Total size of iBestCol in tokens */
if( nVal!=5 ){
const char *zErr = "wrong number of arguments to function snippet()";
sqlite3_result_error(pCtx, zErr, -1);
return;
}
memset(&ctx, 0, sizeof(HighlightContext));
rc = pApi->xColumnText(pFts, iCol, &ctx.zIn, &ctx.nIn);
iCol = sqlite3_value_int(apVal[0]);
rc = pApi->xColumnText(pFts, iCol, &ctx.zIn, &ctx.nIn);
ctx.zOpen = (const char*)sqlite3_value_text(apVal[1]);
ctx.zClose = (const char*)sqlite3_value_text(apVal[2]);
zEllips = (const char*)sqlite3_value_text(apVal[3]);
nToken = sqlite3_value_int(apVal[4]);
iBestLast = nToken-1;
iBestCol = (iCol>=0 ? iCol : 0);
nPhrase = pApi->xPhraseCount(pFts);
aSeen = sqlite3_malloc(nPhrase);
if( aSeen==0 ){
rc = SQLITE_NOMEM;
}
|
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}
sqlite3_free(ctx.zOut);
sqlite3_free(aSeen);
}
/************************************************************************/
/*
** The first time the bm25() function is called for a query, an instance
** Context object passed by fts5GatherTotals() to xQueryPhrase callback
** of the following structure is allocated and populated.
** fts5GatherCallback().
*/
typedef struct Fts5Bm25Data Fts5Bm25Data;
struct Fts5GatherCtx {
int nCol; /* Number of columns in FTS table */
int iPhrase; /* Phrase currently under investigation */
int *anVal; /* Array to populate */
struct Fts5Bm25Data {
int nPhrase; /* Number of phrases in query */
double avgdl; /* Average number of tokens in each row */
double *aIDF; /* IDF for each phrase */
double *aFreq; /* Array used to calculate phrase freq. */
};
/*
** Callback used by fts5GatherTotals() with the xQueryPhrase() API.
** Callback used by fts5Bm25GetData() to count the number of rows in the
** table matched by each individual phrase within the query.
*/
static int fts5GatherCallback(
static int fts5CountCb(
const Fts5ExtensionApi *pApi,
Fts5Context *pFts,
void *pUserData /* Pointer to Fts5GatherCtx object */
void *pUserData /* Pointer to sqlite3_int64 variable */
){
struct Fts5GatherCtx *p = (struct Fts5GatherCtx*)pUserData;
int i = 0;
int iPrev = -1;
i64 iPos = 0;
sqlite3_int64 *pn = (sqlite3_int64*)pUserData;
while( 0==pApi->xPoslist(pFts, 0, &i, &iPos) ){
int iCol = FTS5_POS2COLUMN(iPos);
if( iCol!=iPrev ){
p->anVal[p->iPhrase * p->nCol + iCol]++;
iPrev = iCol;
}
}
(*pn)++;
return SQLITE_OK;
}
/*
** This function returns a pointer to an array of integers containing entries
** indicating the number of rows in the table for which each phrase features
** Set *ppData to point to the Fts5Bm25Data object for the current query.
** If the object has not already been allocated, allocate and populate it
** at least once in each column.
**
** now.
** If nCol is the number of matchable columns in the table, and nPhrase is
** the number of phrases in the query, the array contains a total of
** (nPhrase*nCol) entries.
**
** For phrase iPhrase and column iCol:
**
** anVal[iPhrase * nCol + iCol]
**
** is set to the number of rows in the table for which column iCol contains
** at least one instance of phrase iPhrase.
*/
static int fts5GatherTotals(
const Fts5ExtensionApi *pApi, /* API offered by current FTS version */
Fts5Context *pFts, /* First arg to pass to pApi functions */
static int fts5Bm25GetData(
const Fts5ExtensionApi *pApi,
Fts5Context *pFts,
int **panVal
){
int rc = SQLITE_OK;
int *anVal = 0;
int i; /* For iterating through expression phrases */
int nPhrase = pApi->xPhraseCount(pFts);
int nCol = pApi->xColumnCount(pFts);
int nByte = nCol * nPhrase * sizeof(int);
struct Fts5GatherCtx sCtx;
Fts5Bm25Data **ppData /* OUT: bm25-data object for this query */
sCtx.nCol = nCol;
anVal = sCtx.anVal = (int*)sqlite3_malloc(nByte);
if( anVal==0 ){
rc = SQLITE_NOMEM;
}else{
memset(anVal, 0, nByte);
}
for(i=0; i<nPhrase && rc==SQLITE_OK; i++){
sCtx.iPhrase = i;
rc = pApi->xQueryPhrase(pFts, i, (void*)&sCtx, fts5GatherCallback);
}
if( rc!=SQLITE_OK ){
sqlite3_free(anVal);
anVal = 0;
}
*panVal = anVal;
return rc;
}
typedef struct Fts5Bm25Context Fts5Bm25Context;
struct Fts5Bm25Context {
int nPhrase; /* Number of phrases in query */
int nCol; /* Number of columns in FTS table */
double *aIDF; /* Array of IDF values */
double *aAvg; /* Average size of each column in tokens */
};
static int fts5Bm25GetContext(
const Fts5ExtensionApi *pApi, /* API offered by current FTS version */
Fts5Context *pFts, /* First arg to pass to pApi functions */
Fts5Bm25Context **pp /* OUT: Context object */
){
Fts5Bm25Context *p;
int rc = SQLITE_OK;
int rc = SQLITE_OK; /* Return code */
Fts5Bm25Data *p; /* Object to return */
p = pApi->xGetAuxdata(pFts, 0);
if( p==0 ){
int *anVal = 0;
int ic; /* For iterating through columns */
int ip; /* For iterating through phrases */
i64 nRow; /* Total number of rows in table */
int nPhrase = pApi->xPhraseCount(pFts);
int nPhrase; /* Number of phrases in query */
sqlite3_int64 nRow; /* Number of rows in table */
sqlite3_int64 nToken; /* Number of tokens in table */
int nByte; /* Bytes of space to allocate */
int i;
/* Allocate the Fts5Bm25Data object */
nPhrase = pApi->xPhraseCount(pFts);
int nCol = pApi->xColumnCount(pFts);
int nByte = sizeof(Fts5Bm25Context)
nByte = sizeof(Fts5Bm25Data) + nPhrase*2*sizeof(double);
+ sizeof(double) * nPhrase * nCol /* aIDF[] */
+ sizeof(double) * nCol; /* aAvg[] */
p = (Fts5Bm25Context*)sqlite3_malloc(nByte);
p = (Fts5Bm25Data*)sqlite3_malloc(nByte);
if( p==0 ){
rc = SQLITE_NOMEM;
}else{
memset(p, 0, nByte);
p->aAvg = (double*)&p[1];
p->aIDF = (double*)&p->aAvg[nCol];
p->nPhrase = nPhrase;
p->aIDF = (double*)&p[1];
p->nCol = nCol;
p->nPhrase = nPhrase;
p->aFreq = &p->aIDF[nPhrase];
}
/* Calculate the average document length for this FTS5 table */
if( rc==SQLITE_OK ){
rc = pApi->xRowCount(pFts, &nRow);
assert( nRow>0 || rc!=SQLITE_OK );
if( rc==SQLITE_OK ) rc = pApi->xRowCount(pFts, &nRow);
if( rc==SQLITE_OK ) rc = pApi->xColumnTotalSize(pFts, -1, &nToken);
if( rc==SQLITE_OK ) p->avgdl = (double)nToken / (double)nRow;
if( nRow<2 ) nRow = 2;
}
for(ic=0; rc==SQLITE_OK && ic<nCol; ic++){
i64 nToken = 0;
/* Calculate an IDF for each phrase in the query */
for(i=0; rc==SQLITE_OK && i<nPhrase; i++){
sqlite3_int64 nHit = 0;
rc = pApi->xColumnTotalSize(pFts, ic, &nToken);
p->aAvg[ic] = (double)nToken / (double)nRow;
}
if( rc==SQLITE_OK ){
rc = pApi->xQueryPhrase(pFts, i, (void*)&nHit, fts5CountCb);
if( rc==SQLITE_OK ){
rc = fts5GatherTotals(pApi, pFts, &anVal);
}
for(ic=0; ic<nCol; ic++){
for(ip=0; rc==SQLITE_OK && ip<nPhrase; ip++){
/* Calculate the IDF (Inverse Document Frequency) for phrase ip
** in column ic. This is done using the standard BM25 formula as
/* Calculate the IDF (Inverse Document Frequency) for phrase i.
** This is done using the standard BM25 formula as found on wikipedia:
** found on wikipedia:
**
** IDF = log( (N - nHit + 0.5) / (nHit + 0.5) )
**
** where "N" is the total number of documents in the set and nHit
** is the number that contain at least one instance of the phrase
** under consideration.
**
** The problem with this is that if (N < 2*nHit), the IDF is
** negative. Which is undesirable. So the mimimum allowable IDF is
** (1e-6) - roughly the same as a term that appears in just over
** half of set of 5,000,000 documents. */
int idx = ip * nCol + ic; /* Index in aIDF[] and anVal[] arrays */
int nHit = anVal[idx]; /* Number of docs matching "ic: ip" */
double idf = log( (nRow - nHit + 0.5) / (nHit + 0.5) );
p->aIDF[idx] = log( (0.5 + nRow - nHit) / (0.5 + nHit) );
if( p->aIDF[idx]<=0.0 ) p->aIDF[idx] = 1e-6;
assert( p->aIDF[idx]>=0.0 );
if( idf<=0.0 ) idf = 1e-6;
p->aIDF[i] = idf;
}
}
if( rc!=SQLITE_OK ){
sqlite3_free(anVal);
sqlite3_free(p);
if( rc==SQLITE_OK ){
}else{
rc = pApi->xSetAuxdata(pFts, p, sqlite3_free);
}
if( rc!=SQLITE_OK ){
if( rc!=SQLITE_OK ) p = 0;
sqlite3_free(p);
p = 0;
}
}
}
*pp = p;
*ppData = p;
return rc;
}
static void fts5Bm25DebugContext(
int *pRc, /* IN/OUT: Return code */
Fts5Buffer *pBuf, /* Buffer to populate */
Fts5Bm25Context *p /* Context object to decode */
){
int ip;
int ic;
/*
sqlite3Fts5BufferAppendString(pRc, pBuf, "idf ");
if( p->nPhrase>1 || p->nCol>1 ){
sqlite3Fts5BufferAppendString(pRc, pBuf, "{");
}
for(ip=0; ip<p->nPhrase; ip++){
if( ip>0 ) sqlite3Fts5BufferAppendString(pRc, pBuf, " ");
if( p->nCol>1 ) sqlite3Fts5BufferAppendString(pRc, pBuf, "{");
for(ic=0; ic<p->nCol; ic++){
if( ic>0 ) sqlite3Fts5BufferAppendString(pRc, pBuf, " ");
sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "%f", p->aIDF[ip*p->nCol+ic]);
}
if( p->nCol>1 ) sqlite3Fts5BufferAppendString(pRc, pBuf, "}");
}
if( p->nPhrase>1 || p->nCol>1 ){
sqlite3Fts5BufferAppendString(pRc, pBuf, "}");
}
** Implementation of bm25() function.
sqlite3Fts5BufferAppendString(pRc, pBuf, " avgdl ");
if( p->nCol>1 ) sqlite3Fts5BufferAppendString(pRc, pBuf, "{");
for(ic=0; ic<p->nCol; ic++){
if( ic>0 ) sqlite3Fts5BufferAppendString(pRc, pBuf, " ");
sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "%f", p->aAvg[ic]);
}
if( p->nCol>1 ) sqlite3Fts5BufferAppendString(pRc, pBuf, "}");
}
*/
static void fts5Bm25DebugRow(
int *pRc,
Fts5Buffer *pBuf,
Fts5Bm25Context *p,
const Fts5ExtensionApi *pApi,
Fts5Context *pFts
){
}
static void fts5Bm25Function(
const Fts5ExtensionApi *pApi, /* API offered by current FTS version */
Fts5Context *pFts, /* First arg to pass to pApi functions */
sqlite3_context *pCtx, /* Context for returning result/error */
int nVal, /* Number of values in apVal[] array */
sqlite3_value **apVal /* Array of trailing arguments */
){
const double k1 = 1.2;
const double B = 0.75;
int rc = SQLITE_OK;
Fts5Bm25Context *p;
const double k1 = 1.2; /* Constant "k1" from BM25 formula */
const double b = 0.75; /* Constant "b" from BM25 formula */
int rc = SQLITE_OK; /* Error code */
double score = 0.0; /* SQL function return value */
Fts5Bm25Data *pData; /* Values allocated/calculated once only */
int i; /* Iterator variable */
int nInst; /* Value returned by xInstCount() */
double D; /* Total number of tokens in row */
double *aFreq; /* Array of phrase freq. for current row */
/* Calculate the phrase frequency (symbol "f(qi,D)" in the documentation)
** for each phrase in the query for the current row. */
rc = fts5Bm25GetContext(pApi, pFts, &p);
rc = fts5Bm25GetData(pApi, pFts, &pData);
if( rc==SQLITE_OK ){
/* If the bDebug flag is set, instead of returning a numeric rank, this
** function returns a text value showing how the rank is calculated. */
Fts5Buffer debug;
int bDebug = (pApi->xUserData(pFts)!=0);
memset(&debug, 0, sizeof(Fts5Buffer));
int ip;
aFreq = pData->aFreq;
memset(aFreq, 0, sizeof(double) * pData->nPhrase);
rc = pApi->xInstCount(pFts, &nInst);
}
for(i=0; rc==SQLITE_OK && i<nInst; i++){
int ip; int ic; int io;
double score = 0.0;
if( bDebug ){
rc = pApi->xInst(pFts, i, &ip, &ic, &io);
if( rc==SQLITE_OK ){
fts5Bm25DebugContext(&rc, &debug, p);
fts5Bm25DebugRow(&rc, &debug, p, pApi, pFts);
double w = (nVal > ic) ? sqlite3_value_double(apVal[ic]) : 1.0;
aFreq[ip] += w;
}
}
for(ip=0; rc==SQLITE_OK && ip<p->nPhrase; ip++){
int iPrev = 0;
int nHit = 0;
int i = 0;
i64 iPos = 0;
while( rc==SQLITE_OK ){
int bDone = pApi->xPoslist(pFts, ip, &i, &iPos);
int iCol = FTS5_POS2COLUMN(iPos);
if( (iCol!=iPrev || bDone) && nHit>0 ){
int sz = 0;
/* Figure out the total size of the current row in tokens. */
if( rc==SQLITE_OK ){
int nTok;
int idx = ip * p->nCol + iPrev;
double bm25;
rc = pApi->xColumnSize(pFts, iPrev, &sz);
rc = pApi->xColumnSize(pFts, -1, &nTok);
D = (double)nTok;
bm25 = (p->aIDF[idx] * nHit * (k1+1.0)) /
(nHit + k1 * (1.0 - B + B * sz / p->aAvg[iPrev]));
}
/* Determine the BM25 score for the current row. */
for(i=0; rc==SQLITE_OK && i<pData->nPhrase; i++){
score = score + bm25;
nHit = 0;
score += pData->aIDF[i] * (
( aFreq[i] * (k1 + 1.0) ) /
( aFreq[i] + k1 * (1 - b + b * D / pData->avgdl) )
}
if( bDone ) break;
);
nHit++;
iPrev = iCol;
}
}
if( rc==SQLITE_OK ){
}
/* If no error has occurred, return the calculated score. Otherwise,
** throw an SQL exception. */
if( rc==SQLITE_OK ){
if( bDebug ){
sqlite3_result_text(pCtx, (const char*)debug.p, -1, SQLITE_TRANSIENT);
}else{
sqlite3_result_double(pCtx, score);
}
sqlite3_result_double(pCtx, score);
}else{
}
sqlite3_free(debug.p);
}
if( rc!=SQLITE_OK ){
sqlite3_result_error_code(pCtx, rc);
}
}
int sqlite3Fts5AuxInit(fts5_api *pApi){
struct Builtin {
const char *zFunc; /* Function name (nul-terminated) */
void *pUserData; /* User-data pointer */
fts5_extension_function xFunc;/* Callback function */
void (*xDestroy)(void*); /* Destructor function */
} aBuiltin [] = {
{ "bm25debug", (void*)1, fts5Bm25Function, 0 },
{ "snippet", 0, fts5SnippetFunction, 0 },
{ "highlight", 0, fts5HighlightFunction, 0 },
{ "bm25", 0, fts5Bm25Function, 0 },
};
int rc = SQLITE_OK; /* Return code */
int i; /* To iterate through builtin functions */
for(i=0; rc==SQLITE_OK && i<sizeof(aBuiltin)/sizeof(aBuiltin[0]); i++){
rc = pApi->xCreateFunction(pApi,
aBuiltin[i].zFunc,
aBuiltin[i].pUserData,
|