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jellyfish/cjellyfish/porter.c

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/* Copyright Martin Porter, released under BSD compatible licensing terms.
See http://tartarus.org/~martin/PorterStemmer/ for details.
*/
/* 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 maked --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 2 (the more old-fashioned, non-thread-safe version may be
regarded as release 1.)
*/
#include <stdlib.h> /* for malloc, free */
#include <string.h> /* 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,
<c><v> gives 0
<c>vc<v> gives 1
<c>vcvc<v> gives 2
<c>vcvcvc<v> 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 <c>vcvc<v>. */
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->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); step1c(z); step2(z); step3(z); step4(z); step5(z);
return z->k;
}
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