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sqlite/ext/fts3/fts3_porter.c
drh 063970a15f Fix comment typos reported on the mailing list. No changes to code. 
FossilOrigin-Name: 93a71c9f058b58d11187293a1e8d5324d0911880
2014-12-04 14:01:39 +00:00

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/*
** 2006 September 30
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
** Implementation of the full-text-search tokenizer that implements
** a Porter stemmer.
*/
/*
** The code in this file is only compiled if:
**
** * The FTS3 module is being built as an extension
** (in which case SQLITE_CORE is not defined), or
**
** * The FTS3 module is being built into the core of
** SQLite (in which case SQLITE_ENABLE_FTS3 is defined).
*/
#include "fts3Int.h"
#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "fts3_tokenizer.h"
/*
** Class derived from sqlite3_tokenizer
*/
typedef struct porter_tokenizer {
sqlite3_tokenizer base; /* Base class */
} porter_tokenizer;
/*
** Class derived from sqlite3_tokenizer_cursor
*/
typedef struct porter_tokenizer_cursor {
sqlite3_tokenizer_cursor base;
const char *zInput; /* input we are tokenizing */
int nInput; /* size of the input */
int iOffset; /* current position in zInput */
int iToken; /* index of next token to be returned */
char *zToken; /* storage for current token */
int nAllocated; /* space allocated to zToken buffer */
} porter_tokenizer_cursor;
/*
** Create a new tokenizer instance.
*/
static int porterCreate(
int argc, const char * const *argv,
sqlite3_tokenizer **ppTokenizer
){
porter_tokenizer *t;
UNUSED_PARAMETER(argc);
UNUSED_PARAMETER(argv);
t = (porter_tokenizer *) sqlite3_malloc(sizeof(*t));
if( t==NULL ) return SQLITE_NOMEM;
memset(t, 0, sizeof(*t));
*ppTokenizer = &t->base;
return SQLITE_OK;
}
/*
** Destroy a tokenizer
*/
static int porterDestroy(sqlite3_tokenizer *pTokenizer){
sqlite3_free(pTokenizer);
return SQLITE_OK;
}
/*
** Prepare to begin tokenizing a particular string. The input
** string to be tokenized is zInput[0..nInput-1]. A cursor
** used to incrementally tokenize this string is returned in
** *ppCursor.
*/
static int porterOpen(
sqlite3_tokenizer *pTokenizer, /* The tokenizer */
const char *zInput, int nInput, /* String to be tokenized */
sqlite3_tokenizer_cursor **ppCursor /* OUT: Tokenization cursor */
){
porter_tokenizer_cursor *c;
UNUSED_PARAMETER(pTokenizer);
c = (porter_tokenizer_cursor *) sqlite3_malloc(sizeof(*c));
if( c==NULL ) return SQLITE_NOMEM;
c->zInput = zInput;
if( zInput==0 ){
c->nInput = 0;
}else if( nInput<0 ){
c->nInput = (int)strlen(zInput);
}else{
c->nInput = nInput;
}
c->iOffset = 0; /* start tokenizing at the beginning */
c->iToken = 0;
c->zToken = NULL; /* no space allocated, yet. */
c->nAllocated = 0;
*ppCursor = &c->base;
return SQLITE_OK;
}
/*
** Close a tokenization cursor previously opened by a call to
** porterOpen() above.
*/
static int porterClose(sqlite3_tokenizer_cursor *pCursor){
porter_tokenizer_cursor *c = (porter_tokenizer_cursor *) pCursor;
sqlite3_free(c->zToken);
sqlite3_free(c);
return SQLITE_OK;
}
/*
** Vowel or consonant
*/
static const char cType[] = {
0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0,
1, 1, 1, 2, 1
};
/*
** isConsonant() and isVowel() determine if their first character in
** the string they point to is a consonant or a vowel, according
** to Porter ruls.
**
** A consonate is any letter other than 'a', 'e', 'i', 'o', or 'u'.
** 'Y' is a consonant unless it follows another consonant,
** in which case it is a vowel.
**
** In these routine, the letters are in reverse order. So the 'y' rule
** is that 'y' is a consonant unless it is followed by another
** consonent.
*/
static int isVowel(const char*);
static int isConsonant(const char *z){
int j;
char x = *z;
if( x==0 ) return 0;
assert( x>='a' && x<='z' );
j = cType[x-'a'];
if( j<2 ) return j;
return z[1]==0 || isVowel(z + 1);
}
static int isVowel(const char *z){
int j;
char x = *z;
if( x==0 ) return 0;
assert( x>='a' && x<='z' );
j = cType[x-'a'];
if( j<2 ) return 1-j;
return isConsonant(z + 1);
}
/*
** Let any sequence of one or more vowels be represented by V and let
** C be sequence of one or more consonants. Then every word can be
** represented as:
**
** [C] (VC){m} [V]
**
** In prose: A word is an optional consonant followed by zero or
** vowel-consonant pairs followed by an optional vowel. "m" is the
** number of vowel consonant pairs. This routine computes the value
** of m for the first i bytes of a word.
**
** Return true if the m-value for z is 1 or more. In other words,
** return true if z contains at least one vowel that is followed
** by a consonant.
**
** In this routine z[] is in reverse order. So we are really looking
** for an instance of a consonant followed by a vowel.
*/
static int m_gt_0(const char *z){
while( isVowel(z) ){ z++; }
if( *z==0 ) return 0;
while( isConsonant(z) ){ z++; }
return *z!=0;
}
/* Like mgt0 above except we are looking for a value of m which is
** exactly 1
*/
static int m_eq_1(const char *z){
while( isVowel(z) ){ z++; }
if( *z==0 ) return 0;
while( isConsonant(z) ){ z++; }
if( *z==0 ) return 0;
while( isVowel(z) ){ z++; }
if( *z==0 ) return 1;
while( isConsonant(z) ){ z++; }
return *z==0;
}
/* Like mgt0 above except we are looking for a value of m>1 instead
** or m>0
*/
static int m_gt_1(const char *z){
while( isVowel(z) ){ z++; }
if( *z==0 ) return 0;
while( isConsonant(z) ){ z++; }
if( *z==0 ) return 0;
while( isVowel(z) ){ z++; }
if( *z==0 ) return 0;
while( isConsonant(z) ){ z++; }
return *z!=0;
}
/*
** Return TRUE if there is a vowel anywhere within z[0..n-1]
*/
static int hasVowel(const char *z){
while( isConsonant(z) ){ z++; }
return *z!=0;
}
/*
** Return TRUE if the word ends in a double consonant.
**
** The text is reversed here. So we are really looking at
** the first two characters of z[].
*/
static int doubleConsonant(const char *z){
return isConsonant(z) && z[0]==z[1];
}
/*
** Return TRUE if the word ends with three letters which
** are consonant-vowel-consonent and where the final consonant
** is not 'w', 'x', or 'y'.
**
** The word is reversed here. So we are really checking the
** first three letters and the first one cannot be in [wxy].
*/
static int star_oh(const char *z){
return
isConsonant(z) &&
z[0]!='w' && z[0]!='x' && z[0]!='y' &&
isVowel(z+1) &&
isConsonant(z+2);
}
/*
** If the word ends with zFrom and xCond() is true for the stem
** of the word that preceeds the zFrom ending, then change the
** ending to zTo.
**
** The input word *pz and zFrom are both in reverse order. zTo
** is in normal order.
**
** Return TRUE if zFrom matches. Return FALSE if zFrom does not
** match. Not that TRUE is returned even if xCond() fails and
** no substitution occurs.
*/
static int stem(
char **pz, /* The word being stemmed (Reversed) */
const char *zFrom, /* If the ending matches this... (Reversed) */
const char *zTo, /* ... change the ending to this (not reversed) */
int (*xCond)(const char*) /* Condition that must be true */
){
char *z = *pz;
while( *zFrom && *zFrom==*z ){ z++; zFrom++; }
if( *zFrom!=0 ) return 0;
if( xCond && !xCond(z) ) return 1;
while( *zTo ){
*(--z) = *(zTo++);
}
*pz = z;
return 1;
}
/*
** This is the fallback stemmer used when the porter stemmer is
** inappropriate. The input word is copied into the output with
** US-ASCII case folding. If the input word is too long (more
** than 20 bytes if it contains no digits or more than 6 bytes if
** it contains digits) then word is truncated to 20 or 6 bytes
** by taking 10 or 3 bytes from the beginning and end.
*/
static void copy_stemmer(const char *zIn, int nIn, char *zOut, int *pnOut){
int i, mx, j;
int hasDigit = 0;
for(i=0; i<nIn; i++){
char c = zIn[i];
if( c>='A' && c<='Z' ){
zOut[i] = c - 'A' + 'a';
}else{
if( c>='0' && c<='9' ) hasDigit = 1;
zOut[i] = c;
}
}
mx = hasDigit ? 3 : 10;
if( nIn>mx*2 ){
for(j=mx, i=nIn-mx; i<nIn; i++, j++){
zOut[j] = zOut[i];
}
i = j;
}
zOut[i] = 0;
*pnOut = i;
}
/*
** Stem the input word zIn[0..nIn-1]. Store the output in zOut.
** zOut is at least big enough to hold nIn bytes. Write the actual
** size of the output word (exclusive of the '\0' terminator) into *pnOut.
**
** Any upper-case characters in the US-ASCII character set ([A-Z])
** are converted to lower case. Upper-case UTF characters are
** unchanged.
**
** Words that are longer than about 20 bytes are stemmed by retaining
** a few bytes from the beginning and the end of the word. If the
** word contains digits, 3 bytes are taken from the beginning and
** 3 bytes from the end. For long words without digits, 10 bytes
** are taken from each end. US-ASCII case folding still applies.
**
** If the input word contains not digits but does characters not
** in [a-zA-Z] then no stemming is attempted and this routine just
** copies the input into the input into the output with US-ASCII
** case folding.
**
** Stemming never increases the length of the word. So there is
** no chance of overflowing the zOut buffer.
*/
static void porter_stemmer(const char *zIn, int nIn, char *zOut, int *pnOut){
int i, j;
char zReverse[28];
char *z, *z2;
if( nIn<3 || nIn>=(int)sizeof(zReverse)-7 ){
/* The word is too big or too small for the porter stemmer.
** Fallback to the copy stemmer */
copy_stemmer(zIn, nIn, zOut, pnOut);
return;
}
for(i=0, j=sizeof(zReverse)-6; i<nIn; i++, j--){
char c = zIn[i];
if( c>='A' && c<='Z' ){
zReverse[j] = c + 'a' - 'A';
}else if( c>='a' && c<='z' ){
zReverse[j] = c;
}else{
/* The use of a character not in [a-zA-Z] means that we fallback
** to the copy stemmer */
copy_stemmer(zIn, nIn, zOut, pnOut);
return;
}
}
memset(&zReverse[sizeof(zReverse)-5], 0, 5);
z = &zReverse[j+1];
/* Step 1a */
if( z[0]=='s' ){
if(
!stem(&z, "sess", "ss", 0) &&
!stem(&z, "sei", "i", 0) &&
!stem(&z, "ss", "ss", 0)
){
z++;
}
}
/* Step 1b */
z2 = z;
if( stem(&z, "dee", "ee", m_gt_0) ){
/* Do nothing. The work was all in the test */
}else if(
(stem(&z, "gni", "", hasVowel) || stem(&z, "de", "", hasVowel))
&& z!=z2
){
if( stem(&z, "ta", "ate", 0) ||
stem(&z, "lb", "ble", 0) ||
stem(&z, "zi", "ize", 0) ){
/* Do nothing. The work was all in the test */
}else if( doubleConsonant(z) && (*z!='l' && *z!='s' && *z!='z') ){
z++;
}else if( m_eq_1(z) && star_oh(z) ){
*(--z) = 'e';
}
}
/* Step 1c */
if( z[0]=='y' && hasVowel(z+1) ){
z[0] = 'i';
}
/* Step 2 */
switch( z[1] ){
case 'a':
if( !stem(&z, "lanoita", "ate", m_gt_0) ){
stem(&z, "lanoit", "tion", m_gt_0);
}
break;
case 'c':
if( !stem(&z, "icne", "ence", m_gt_0) ){
stem(&z, "icna", "ance", m_gt_0);
}
break;
case 'e':
stem(&z, "rezi", "ize", m_gt_0);
break;
case 'g':
stem(&z, "igol", "log", m_gt_0);
break;
case 'l':
if( !stem(&z, "ilb", "ble", m_gt_0)
&& !stem(&z, "illa", "al", m_gt_0)
&& !stem(&z, "iltne", "ent", m_gt_0)
&& !stem(&z, "ile", "e", m_gt_0)
){
stem(&z, "ilsuo", "ous", m_gt_0);
}
break;
case 'o':
if( !stem(&z, "noitazi", "ize", m_gt_0)
&& !stem(&z, "noita", "ate", m_gt_0)
){
stem(&z, "rota", "ate", m_gt_0);
}
break;
case 's':
if( !stem(&z, "msila", "al", m_gt_0)
&& !stem(&z, "ssenevi", "ive", m_gt_0)
&& !stem(&z, "ssenluf", "ful", m_gt_0)
){
stem(&z, "ssensuo", "ous", m_gt_0);
}
break;
case 't':
if( !stem(&z, "itila", "al", m_gt_0)
&& !stem(&z, "itivi", "ive", m_gt_0)
){
stem(&z, "itilib", "ble", m_gt_0);
}
break;
}
/* Step 3 */
switch( z[0] ){
case 'e':
if( !stem(&z, "etaci", "ic", m_gt_0)
&& !stem(&z, "evita", "", m_gt_0)
){
stem(&z, "ezila", "al", m_gt_0);
}
break;
case 'i':
stem(&z, "itici", "ic", m_gt_0);
break;
case 'l':
if( !stem(&z, "laci", "ic", m_gt_0) ){
stem(&z, "luf", "", m_gt_0);
}
break;
case 's':
stem(&z, "ssen", "", m_gt_0);
break;
}
/* Step 4 */
switch( z[1] ){
case 'a':
if( z[0]=='l' && m_gt_1(z+2) ){
z += 2;
}
break;
case 'c':
if( z[0]=='e' && z[2]=='n' && (z[3]=='a' || z[3]=='e') && m_gt_1(z+4) ){
z += 4;
}
break;
case 'e':
if( z[0]=='r' && m_gt_1(z+2) ){
z += 2;
}
break;
case 'i':
if( z[0]=='c' && m_gt_1(z+2) ){
z += 2;
}
break;
case 'l':
if( z[0]=='e' && z[2]=='b' && (z[3]=='a' || z[3]=='i') && m_gt_1(z+4) ){
z += 4;
}
break;
case 'n':
if( z[0]=='t' ){
if( z[2]=='a' ){
if( m_gt_1(z+3) ){
z += 3;
}
}else if( z[2]=='e' ){
if( !stem(&z, "tneme", "", m_gt_1)
&& !stem(&z, "tnem", "", m_gt_1)
){
stem(&z, "tne", "", m_gt_1);
}
}
}
break;
case 'o':
if( z[0]=='u' ){
if( m_gt_1(z+2) ){
z += 2;
}
}else if( z[3]=='s' || z[3]=='t' ){
stem(&z, "noi", "", m_gt_1);
}
break;
case 's':
if( z[0]=='m' && z[2]=='i' && m_gt_1(z+3) ){
z += 3;
}
break;
case 't':
if( !stem(&z, "eta", "", m_gt_1) ){
stem(&z, "iti", "", m_gt_1);
}
break;
case 'u':
if( z[0]=='s' && z[2]=='o' && m_gt_1(z+3) ){
z += 3;
}
break;
case 'v':
case 'z':
if( z[0]=='e' && z[2]=='i' && m_gt_1(z+3) ){
z += 3;
}
break;
}
/* Step 5a */
if( z[0]=='e' ){
if( m_gt_1(z+1) ){
z++;
}else if( m_eq_1(z+1) && !star_oh(z+1) ){
z++;
}
}
/* Step 5b */
if( m_gt_1(z) && z[0]=='l' && z[1]=='l' ){
z++;
}
/* z[] is now the stemmed word in reverse order. Flip it back
** around into forward order and return.
*/
*pnOut = i = (int)strlen(z);
zOut[i] = 0;
while( *z ){
zOut[--i] = *(z++);
}
}
/*
** Characters that can be part of a token. We assume any character
** whose value is greater than 0x80 (any UTF character) can be
** part of a token. In other words, delimiters all must have
** values of 0x7f or lower.
*/
static const char porterIdChar[] = {
/* x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 xA xB xC xD xE xF */
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 isDelim(C) (((ch=C)&0x80)==0 && (ch<0x30 || !porterIdChar[ch-0x30]))
/*
** Extract the next token from a tokenization cursor. The cursor must
** have been opened by a prior call to porterOpen().
*/
static int porterNext(
sqlite3_tokenizer_cursor *pCursor, /* Cursor returned by porterOpen */
const char **pzToken, /* OUT: *pzToken is the token text */
int *pnBytes, /* OUT: Number of bytes in token */
int *piStartOffset, /* OUT: Starting offset of token */
int *piEndOffset, /* OUT: Ending offset of token */
int *piPosition /* OUT: Position integer of token */
){
porter_tokenizer_cursor *c = (porter_tokenizer_cursor *) pCursor;
const char *z = c->zInput;
while( c->iOffset<c->nInput ){
int iStartOffset, ch;
/* Scan past delimiter characters */
while( c->iOffset<c->nInput && isDelim(z[c->iOffset]) ){
c->iOffset++;
}
/* Count non-delimiter characters. */
iStartOffset = c->iOffset;
while( c->iOffset<c->nInput && !isDelim(z[c->iOffset]) ){
c->iOffset++;
}
if( c->iOffset>iStartOffset ){
int n = c->iOffset-iStartOffset;
if( n>c->nAllocated ){
char *pNew;
c->nAllocated = n+20;
pNew = sqlite3_realloc(c->zToken, c->nAllocated);
if( !pNew ) return SQLITE_NOMEM;
c->zToken = pNew;
}
porter_stemmer(&z[iStartOffset], n, c->zToken, pnBytes);
*pzToken = c->zToken;
*piStartOffset = iStartOffset;
*piEndOffset = c->iOffset;
*piPosition = c->iToken++;
return SQLITE_OK;
}
}
return SQLITE_DONE;
}
/*
** The set of routines that implement the porter-stemmer tokenizer
*/
static const sqlite3_tokenizer_module porterTokenizerModule = {
0,
porterCreate,
porterDestroy,
porterOpen,
porterClose,
porterNext,
0
};
/*
** Allocate a new porter tokenizer. Return a pointer to the new
** tokenizer in *ppModule
*/
void sqlite3Fts3PorterTokenizerModule(
sqlite3_tokenizer_module const**ppModule
){
*ppModule = &porterTokenizerModule;
}
#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3) */
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