fts2_porter.c

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**
** 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, c;
  char zReverse[28];
  char *z, *z2;
  if( nIn<3 || nIn>=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--){
    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':
     stem(&z, "lanoita", "ate", m_gt_0) ||
     stem(&z, "lanoit", "tion", m_gt_0);
     break;
   case 'c':
     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':
     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':
     stem(&z, "noitazi", "ize", m_gt_0) ||
     stem(&z, "noita", "ate", m_gt_0) ||
     stem(&z, "rota", "ate", m_gt_0);
     break;
   case 's':
     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':
     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':
     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':
     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' ){
         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':
     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 = 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 ){
        c->nAllocated = n+20;
        c->zToken = realloc(c->zToken, c->nAllocated);
        if( c->zToken==NULL ) return SQLITE_NOMEM;
      }
      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,
};

/*
** Allocate a new porter tokenizer.  Return a pointer to the new
** tokenizer in *ppModule
*/
void sqlite3Fts2PorterTokenizerModule(
  sqlite3_tokenizer_module const**ppModule
){
  *ppModule = &porterTokenizerModule;
}

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