/* This is the Porter stemming algorithm, coded up as thread-safe ANSI C by the author. It may be be regarded as cononical, in that it follows the algorithm presented in Porter, 1980, An algorithm for suffix stripping, Program, Vol. 14, no. 3, pp 130-137, only differing from it at the points marked --DEPARTURE-- below. See also http://www.tartarus.org/~martin/PorterStemmer The algorithm as described in the paper could be exactly replicated by adjusting the points of DEPARTURE, but this is barely necessary, because (a) the points of DEPARTURE are definitely improvements, and (b) no encoding of the Porter stemmer I have seen is anything like as exact as this version, even with the points of DEPARTURE! You can compile it on Unix with 'gcc -O3 -o stem stem.c' after which 'stem' takes a list of inputs and sends the stemmed equivalent to stdout. The algorithm as encoded here is particularly fast. Release 1: the basic non-thread safe version Release 2: this thread-safe version Release 3: 11 Apr 2013, fixes the bug noted by Matt Patenaude (see the basic version for details) Release 4: 25 Mar 2014, fixes the bug noted by Klemens Baum (see the basic version for details) */ #include /* for malloc, free */ #include /* for memcmp, memmove */ /* You will probably want to move the following declarations to a central header file. */ struct stemmer; extern struct stemmer * create_stemmer(void); extern void free_stemmer(struct stemmer * z); extern int stem(struct stemmer * z, char * b, int k); /* The main part of the stemming algorithm starts here. */ #define TRUE 1 #define FALSE 0 /* stemmer is a structure for a few local bits of data, */ struct stemmer { char * b; /* buffer for word to be stemmed */ int k; /* offset to the end of the string */ int j; /* a general offset into the string */ }; /* Member b is a buffer holding a word to be stemmed. The letters are in b[0], b[1] ... ending at b[z->k]. Member 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. Typical usage is: struct stemmer * z = create_stemmer(); char b[] = "pencils"; int res = stem(z, b, 6); /- stem the 7 characters of b[0] to b[6]. The result, res, will be 5 (the 's' is removed). -/ free_stemmer(z); */ extern struct stemmer * create_stemmer(void) { return (struct stemmer *) malloc(sizeof(struct stemmer)); /* assume malloc succeeds */ } extern void free_stemmer(struct stemmer * z) { free(z); } /* cons(z, i) is TRUE <=> b[i] is a consonant. ('b' means 'z->b', but here and below we drop 'z->' in comments. */ static int cons(struct stemmer * z, int i) { switch (z->b[i]) { case 'a': case 'e': case 'i': case 'o': case 'u': return FALSE; case 'y': return (i == 0) ? TRUE : !cons(z, i - 1); default: return TRUE; } } /* m(z) measures the number of consonant sequences between 0 and j. if c is a consonant sequence and v a vowel sequence, and <..> indicates arbitrary presence, gives 0 vc gives 1 vcvc gives 2 vcvcvc gives 3 .... */ static int m(struct stemmer * z) { int n = 0; int i = 0; int j = z->j; while(TRUE) { if (i > j) return n; if (! cons(z, i)) break; i++; } i++; while(TRUE) { while(TRUE) { if (i > j) return n; if (cons(z, i)) break; i++; } i++; n++; while(TRUE) { if (i > j) return n; if (! cons(z, i)) break; i++; } i++; } } /* vowelinstem(z) is TRUE <=> 0,...j contains a vowel */ static int vowelinstem(struct stemmer * z) { int j = z->j; int i; for (i = 0; i <= j; i++) if (! cons(z, i)) return TRUE; return FALSE; } /* doublec(z, j) is TRUE <=> j,(j-1) contain a double consonant. */ static int doublec(struct stemmer * z, int j) { char * b = z->b; if (j < 1) return FALSE; if (b[j] != b[j - 1]) return FALSE; return cons(z, j); } /* cvc(z, 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. */ static int cvc(struct stemmer * z, int i) { if (i < 2 || !cons(z, i) || cons(z, i - 1) || !cons(z, i - 2)) return FALSE; { int ch = z->b[i]; if (ch == 'w' || ch == 'x' || ch == 'y') return FALSE; } return TRUE; } /* ends(z, s) is TRUE <=> 0,...k ends with the string s. */ static int ends(struct stemmer * z, char * s) { int length = s[0]; char * b = z->b; int k = z->k; if (s[length] != b[k]) return FALSE; /* tiny speed-up */ if (length > k + 1) return FALSE; if (memcmp(b + k - length + 1, s + 1, length) != 0) return FALSE; z->j = k-length; return TRUE; } /* setto(z, s) sets (j+1),...k to the characters in the string s, readjusting k. */ static void setto(struct stemmer * z, char * s) { int length = s[0]; int j = z->j; memmove(z->b + j + 1, s + 1, length); z->k = j+length; } /* r(z, s) is used further down. */ static void r(struct stemmer * z, char * s) { if (m(z) > 0) setto(z, s); } /* step1ab(z) 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 */ static void step1ab(struct stemmer * z) { char * b = z->b; if (b[z->k] == 's') { if (ends(z, "\04" "sses")) z->k -= 2; else if (ends(z, "\03" "ies")) setto(z, "\01" "i"); else if (b[z->k - 1] != 's') z->k--; } if (ends(z, "\03" "eed")) { if (m(z) > 0) z->k--; } else if ((ends(z, "\02" "ed") || ends(z, "\03" "ing")) && vowelinstem(z)) { z->k = z->j; if (ends(z, "\02" "at")) setto(z, "\03" "ate"); else if (ends(z, "\02" "bl")) setto(z, "\03" "ble"); else if (ends(z, "\02" "iz")) setto(z, "\03" "ize"); else if (doublec(z, z->k)) { z->k--; { int ch = b[z->k]; if (ch == 'l' || ch == 's' || ch == 'z') z->k++; } } else if (m(z) == 1 && cvc(z, z->k)) setto(z, "\01" "e"); } } /* step1c(z) turns terminal y to i when there is another vowel in the stem. */ static void step1c(struct stemmer * z) { if (ends(z, "\01" "y") && vowelinstem(z)) z->b[z->k] = 'i'; } /* step2(z) 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(z) > 0. */ static void step2(struct stemmer * z) { switch (z->b[z->k-1]) { case 'a': if (ends(z, "\07" "ational")) { r(z, "\03" "ate"); break; } if (ends(z, "\06" "tional")) { r(z, "\04" "tion"); break; } break; case 'c': if (ends(z, "\04" "enci")) { r(z, "\04" "ence"); break; } if (ends(z, "\04" "anci")) { r(z, "\04" "ance"); break; } break; case 'e': if (ends(z, "\04" "izer")) { r(z, "\03" "ize"); break; } break; case 'l': if (ends(z, "\03" "bli")) { r(z, "\03" "ble"); break; } /*-DEPARTURE-*/ /* To match the published algorithm, replace this line with case 'l': if (ends(z, "\04" "abli")) { r(z, "\04" "able"); break; } */ if (ends(z, "\04" "alli")) { r(z, "\02" "al"); break; } if (ends(z, "\05" "entli")) { r(z, "\03" "ent"); break; } if (ends(z, "\03" "eli")) { r(z, "\01" "e"); break; } if (ends(z, "\05" "ousli")) { r(z, "\03" "ous"); break; } break; case 'o': if (ends(z, "\07" "ization")) { r(z, "\03" "ize"); break; } if (ends(z, "\05" "ation")) { r(z, "\03" "ate"); break; } if (ends(z, "\04" "ator")) { r(z, "\03" "ate"); break; } break; case 's': if (ends(z, "\05" "alism")) { r(z, "\02" "al"); break; } if (ends(z, "\07" "iveness")) { r(z, "\03" "ive"); break; } if (ends(z, "\07" "fulness")) { r(z, "\03" "ful"); break; } if (ends(z, "\07" "ousness")) { r(z, "\03" "ous"); break; } break; case 't': if (ends(z, "\05" "aliti")) { r(z, "\02" "al"); break; } if (ends(z, "\05" "iviti")) { r(z, "\03" "ive"); break; } if (ends(z, "\06" "biliti")) { r(z, "\03" "ble"); break; } break; case 'g': if (ends(z, "\04" "logi")) { r(z, "\03" "log"); break; } /*-DEPARTURE-*/ /* To match the published algorithm, delete this line */ } } /* step3(z) deals with -ic-, -full, -ness etc. similar strategy to step2. */ static void step3(struct stemmer * z) { switch (z->b[z->k]) { case 'e': if (ends(z, "\05" "icate")) { r(z, "\02" "ic"); break; } if (ends(z, "\05" "ative")) { r(z, "\00" ""); break; } if (ends(z, "\05" "alize")) { r(z, "\02" "al"); break; } break; case 'i': if (ends(z, "\05" "iciti")) { r(z, "\02" "ic"); break; } break; case 'l': if (ends(z, "\04" "ical")) { r(z, "\02" "ic"); break; } if (ends(z, "\03" "ful")) { r(z, "\00" ""); break; } break; case 's': if (ends(z, "\04" "ness")) { r(z, "\00" ""); break; } break; } } /* step4(z) takes off -ant, -ence etc., in context vcvc. */ static void step4(struct stemmer * z) { switch (z->b[z->k-1]) { case 'a': if (ends(z, "\02" "al")) break; return; case 'c': if (ends(z, "\04" "ance")) break; if (ends(z, "\04" "ence")) break; return; case 'e': if (ends(z, "\02" "er")) break; return; case 'i': if (ends(z, "\02" "ic")) break; return; case 'l': if (ends(z, "\04" "able")) break; if (ends(z, "\04" "ible")) break; return; case 'n': if (ends(z, "\03" "ant")) break; if (ends(z, "\05" "ement")) break; if (ends(z, "\04" "ment")) break; if (ends(z, "\03" "ent")) break; return; case 'o': if (ends(z, "\03" "ion") && z->j >= 0 && (z->b[z->j] == 's' || z->b[z->j] == 't')) break; if (ends(z, "\02" "ou")) break; return; /* takes care of -ous */ case 's': if (ends(z, "\03" "ism")) break; return; case 't': if (ends(z, "\03" "ate")) break; if (ends(z, "\03" "iti")) break; return; case 'u': if (ends(z, "\03" "ous")) break; return; case 'v': if (ends(z, "\03" "ive")) break; return; case 'z': if (ends(z, "\03" "ize")) break; return; default: return; } if (m(z) > 1) z->k = z->j; } /* step5(z) removes a final -e if m(z) > 1, and changes -ll to -l if m(z) > 1. */ static void step5(struct stemmer * z) { char * b = z->b; z->j = z->k; if (b[z->k] == 'e') { int a = m(z); if (a > 1 || a == 1 && !cvc(z, z->k - 1)) z->k--; } if (b[z->k] == 'l' && doublec(z, z->k) && m(z) > 1) z->k--; } /* In stem(z, b, k), b is a char pointer, and the string to be stemmed is from b[0] to b[k] inclusive. Possibly b[k+1] == '\0', but it is not important. The stemmer adjusts the characters b[0] ... b[k] and returns the new end-point of the string, k'. Stemming never increases word length, so 0 <= k' <= k. */ extern int stem(struct stemmer * z, char * b, int k) { if (k <= 1) return k; /*-DEPARTURE-*/ z->b = b; z->k = k; /* copy the parameters into z */ /* 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(z); if (z->k > 0) { step1c(z); step2(z); step3(z); step4(z); step5(z); } return z->k; } /*--------------------stemmer definition ends here------------------------*/ #include #include /* for malloc, free */ #include /* for isupper, islower, tolower */ static char * s; /* buffer for words tobe stemmed */ #define INC 50 /* size units in which s is increased */ static int i_max = INC; /* maximum offset in s */ #define LETTER(ch) (isupper(ch) || islower(ch)) void stemfile(struct stemmer * z, FILE * f) { while(TRUE) { int ch = getc(f); if (ch == EOF) return; if (LETTER(ch)) { int i = 0; while(TRUE) { if (i == i_max) { i_max += INC; s = realloc(s, i_max + 1); } ch = tolower(ch); /* forces lower case */ s[i] = ch; i++; ch = getc(f); if (!LETTER(ch)) { ungetc(ch,f); break; } } s[stem(z, s, i - 1) + 1] = 0; /* the previous line calls the stemmer and uses its result to zero-terminate the string in s */ printf("%s",s); } else putchar(ch); } } int main(int argc, char * argv[]) { int i; struct stemmer * z = create_stemmer(); s = (char *) malloc(i_max + 1); for (i = 1; i < argc; i++) { FILE * f = fopen(argv[i],"r"); if (f == 0) { fprintf(stderr,"File %s not found\n",argv[i]); exit(1); } stemfile(z, f); } free(s); free_stemmer(z); return 0; }