stemmer.cpp

良好的代码实现

// Stemmer.cpp: implementation of the CStemmer class.
//
//////////////////////////////////////////////////////////////////////

#include "stdafx.h"
#include "Stemmer.h"

#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif

CStemmer theStemmer;
//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

CStemmer::CStemmer()
{

}

CStemmer::~CStemmer()
{

}

/* The main part of the stemming algorithm starts here. b is a buffer
   holding a word to be stemmed. The letters are in b[k0], b[k0+1] ...
   ending at b[k]. In fact k0 = 0 in this demo program. k is readjusted
   downwards as the stemming progresses. Zero termination is not in fact
   used in the algorithm.

   Note that only lower case sequences are stemmed. Forcing to lower case
   should be done before stem(...) is called.
*/

/* cons(i) is TRUE <=> b[i] is a consonant. */

int CStemmer::cons(int i)
{  switch (b[i])
   {  case 'a': case 'e': case 'i': case 'o': case 'u': return FALSE;
      case 'y': return (i==k0) ? TRUE : !cons(i-1);
      default: return TRUE;
   }
}

/* m() measures the number of consonant sequences between k0 and j. if c is
   a consonant sequence and v a vowel sequence, and <..> indicates arbitrary
   presence,

      <c><v>       gives 0
      <c>vc<v>     gives 1
      <c>vcvc<v>   gives 2
      <c>vcvcvc<v> gives 3
      ....
*/

int CStemmer::m()
{  int n = 0;
   int i = k0;
   while(TRUE)
   {  if (i > j) return n;
      if (! cons(i)) break; i++;
   }
   i++;
   while(TRUE)
   {  while(TRUE)
      {  if (i > j) return n;
            if (cons(i)) break;
            i++;
      }
      i++;
      n++;
      while(TRUE)
      {  if (i > j) return n;
         if (! cons(i)) break;
         i++;
      }
      i++;
   }
}

/* vowelinstem() is TRUE <=> k0,...j contains a vowel */

int CStemmer::vowelinstem()
{  int i; for (i = k0; i <= j; i++) if (! cons(i)) return TRUE;
   return FALSE;
}

/* doublec(j) is TRUE <=> j,(j-1) contain a double consonant. */

int CStemmer::doublec(int j)
{  if (j < k0+1) return FALSE;
   if (b[j] != b[j-1]) return FALSE;
   return cons(j);
}

/* cvc(i) is TRUE <=> i-2,i-1,i has the form consonant - vowel - consonant
   and also if the second c is not w,x or y. this is used when trying to
   restore an e at the end of a short word. e.g.

      cav(e), lov(e), hop(e), crim(e), but
      snow, box, tray.

*/

int CStemmer::cvc(int i)
{  if (i < k0+2 || !cons(i) || cons(i-1) || !cons(i-2)) return FALSE;
   {  int ch = b[i];
      if (ch == 'w' || ch == 'x' || ch == 'y') return FALSE;
   }
   return TRUE;
}

/* ends(s) is TRUE <=> k0,...k ends with the string s. */

int CStemmer::ends(char * s)
{  int length = s[0];
   if (s[length] != b[k]) return FALSE; /* tiny speed-up */
   if (length > k-k0+1) return FALSE;
   if (memcmp(b+k-length+1,s+1,length) != 0) return FALSE;
   j = k-length;
   return TRUE;
}

/* setto(s) sets (j+1),...k to the characters in the string s, readjusting
   k. */

void CStemmer::setto(char * s)
{  int length = s[0];
   memmove(b+j+1,s+1,length);
   k = j+length;
}

/* r(s) is used further down. */

void CStemmer::r(char * s) { if (m() > 0) setto(s); }

/* step1ab() gets rid of plurals and -ed or -ing. e.g.

       caresses  ->  caress
       ponies    ->  poni
       ties      ->  ti
       caress    ->  caress
       cats      ->  cat

       feed      ->  feed
       agreed    ->  agree
       disabled  ->  disable

       matting   ->  mat
       mating    ->  mate
       meeting   ->  meet
       milling   ->  mill
       messing   ->  mess

       meetings  ->  meet

*/

void CStemmer::step1ab()
{  if (b[k] == 's')
   {  if (ends("\04" "sses")) k -= 2; else
      if (ends("\03" "ies")) setto("\01" "i"); else
      if (b[k-1] != 's') k--;
   }
   if (ends("\03" "eed")) { if (m() > 0) k--; } else
   if ((ends("\02" "ed") || ends("\03" "ing")) && vowelinstem())
   {  k = j;
      if (ends("\02" "at")) setto("\03" "ate"); else
      if (ends("\02" "bl")) setto("\03" "ble"); else
      if (ends("\02" "iz")) setto("\03" "ize"); else
      if (doublec(k))
      {  k--;
         {  int ch = b[k];
            if (ch == 'l' || ch == 's' || ch == 'z') k++;
         }
      }
      else if (m() == 1 && cvc(k)) setto("\01" "e");
   }
}

/* step1c() turns terminal y to i when there is another vowel in the stem. */

void CStemmer::step1c() { if (ends("\01" "y") && vowelinstem()) b[k] = 'i'; }


/* step2() maps double suffices to single ones. so -ization ( = -ize plus
   -ation) maps to -ize etc. note that the string before the suffix must give
   m() > 0. */

void CStemmer::step2() { switch (b[k-1])
{
    case 'a': if (ends("\07" "ational")) { r("\03" "ate"); break; }
              if (ends("\06" "tional")) { r("\04" "tion"); break; }
              break;
    case 'c': if (ends("\04" "enci")) { r("\04" "ence"); break; }
              if (ends("\04" "anci")) { r("\04" "ance"); break; }
              break;
    case 'e': if (ends("\04" "izer")) { r("\03" "ize"); break; }
              break;
    case 'l': if (ends("\03" "bli")) { r("\03" "ble"); break; } /*-DEPARTURE-*/

 /* To match the published algorithm, replace this line with
    case 'l': if (ends("\04" "abli")) { r("\04" "able"); break; } */

              if (ends("\04" "alli")) { r("\02" "al"); break; }
              if (ends("\05" "entli")) { r("\03" "ent"); break; }
              if (ends("\03" "eli")) { r("\01" "e"); break; }
              if (ends("\05" "ousli")) { r("\03" "ous"); break; }
              break;
    case 'o': if (ends("\07" "ization")) { r("\03" "ize"); break; }
              if (ends("\05" "ation")) { r("\03" "ate"); break; }
              if (ends("\04" "ator")) { r("\03" "ate"); break; }
              break;
    case 's': if (ends("\05" "alism")) { r("\02" "al"); break; }
              if (ends("\07" "iveness")) { r("\03" "ive"); break; }
              if (ends("\07" "fulness")) { r("\03" "ful"); break; }
              if (ends("\07" "ousness")) { r("\03" "ous"); break; }
              break;
    case 't': if (ends("\05" "aliti")) { r("\02" "al"); break; }
              if (ends("\05" "iviti")) { r("\03" "ive"); break; }
              if (ends("\06" "biliti")) { r("\03" "ble"); break; }
              break;
    case 'g': if (ends("\04" "logi")) { r("\03" "log"); break; } /*-DEPARTURE-*/

 /* To match the published algorithm, delete this line */

} }

/* step3() deals with -ic-, -full, -ness etc. similar strategy to step2. */

void CStemmer::step3() { switch (b[k])
{
    case 'e': if (ends("\05" "icate")) { r("\02" "ic"); break; }
              if (ends("\05" "ative")) { r("\00" ""); break; }
              if (ends("\05" "alize")) { r("\02" "al"); break; }
              break;
    case 'i': if (ends("\05" "iciti")) { r("\02" "ic"); break; }
              break;
    case 'l': if (ends("\04" "ical")) { r("\02" "ic"); break; }
              if (ends("\03" "ful")) { r("\00" ""); break; }
              break;
    case 's': if (ends("\04" "ness")) { r("\00" ""); break; }
              break;
} }

/* step4() takes off -ant, -ence etc., in context <c>vcvc<v>. */

void CStemmer::step4()
{  switch (b[k-1])
    {  case 'a': if (ends("\02" "al")) break; return;
       case 'c': if (ends("\04" "ance")) break;
                 if (ends("\04" "ence")) break; return;
       case 'e': if (ends("\02" "er")) break; return;
       case 'i': if (ends("\02" "ic")) break; return;
       case 'l': if (ends("\04" "able")) break;
                 if (ends("\04" "ible")) break; return;
       case 'n': if (ends("\03" "ant")) break;
                 if (ends("\05" "ement")) break;
                 if (ends("\04" "ment")) break;
                 if (ends("\03" "ent")) break; return;
       case 'o': if (ends("\03" "ion") && (b[j] == 's' || b[j] == 't')) break;
                 if (ends("\02" "ou")) break; return;
                 /* takes care of -ous */
       case 's': if (ends("\03" "ism")) break; return;
       case 't': if (ends("\03" "ate")) break;
                 if (ends("\03" "iti")) break; return;
       case 'u': if (ends("\03" "ous")) break; return;
       case 'v': if (ends("\03" "ive")) break; return;
       case 'z': if (ends("\03" "ize")) break; return;
       default: return;
    }
    if (m() > 1) k = j;
}

/* step5() removes a final -e if m() > 1, and changes -ll to -l if
   m() > 1. */

void CStemmer::step5()
{  j = k;
   if (b[k] == 'e')
   {  int a = m();
      if (a > 1 || a == 1 && !cvc(k-1)) k--;
   }
   if (b[k] == 'l' && doublec(k) && m() > 1) k--;
}

/* In stem(p,i,j), p is a char pointer, and the string to be stemmed is from
   p[i] to p[j] inclusive. Typically i is zero and j is the offset to the last
   character of a string, (p[j+1] == '\0'). The stemmer adjusts the
   characters p[i] ... p[j] and returns the new end-point of the string, k.
   Stemming never increases word length, so i <= k <= j. To turn the stemmer
   into a module, declare 'stem' as extern, and delete the remainder of this
   file.
*/

int CStemmer::stem(char * p, int i, int j)
{  b = p; k = j; k0 = i; /* copy the parameters into statics */
   if (k <= k0+1) return k; /*-DEPARTURE-*/

   /* With this line, strings of length 1 or 2 don't go through the
      stemming process, although no mention is made of this in the
      published algorithm. Remove the line to match the published
      algorithm. */

   step1ab(); step1c(); step2(); step3(); step4(); step5();
   return k;
}

void CStemmer::stem(char *p)
{
	stem(p,0,strlen(p)-1);
}