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* string.c (rb_str_index): search using Karp-Rabin algolithm.

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git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@3429 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
matz 2003-01-31 06:48:54 +00:00
parent 466d685a76
commit d18922065b
2 changed files with 28 additions and 2 deletions
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4
ChangeLog
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@ -1,3 +1,7 @@
Fri Jan 31 14:16:59 2003 Yukihiro Matsumoto <matz@ruby-lang.org>
* string.c (rb_str_index): search using Karp-Rabin algolithm.
Fri Jan 31 12:45:11 2003 Yukihiro Matsumoto <matz@ruby-lang.org>
* variable.c (rb_obj_classname): new function.

26
string.c
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@ -840,6 +840,7 @@ rb_str_index(str, sub, offset)
{
char *s, *e, *p;
long len;
int d, hx, hy, i;
if (offset < 0) {
offset += RSTRING(str)->len;
@ -851,10 +852,31 @@ rb_str_index(str, sub, offset)
len = RSTRING(sub)->len;
if (len == 0) return offset;
e = RSTRING(str)->ptr + RSTRING(str)->len - len + 1;
/* seach using Karp-Rabin algolithm described in:
EXACT STRING MATCHING ALGORITHMS
http://www-igm.univ-mlv.fr/~lecroq/string/index.html
*/
#define KR_REHASH(a, b, h) ((((h) - (a)*d) << 1) + (b))
/* Preprocessing */
/* computes d = 2^(m-1) with
the left-shift operator */
for (d = i = 1; i < len; ++i)
d = (d<<1);
for (hy = hx = i = 0; i < len; ++i) {
hx = ((hx<<1) + p[i]);
hy = ((hy<<1) + s[i]);
}
/* Searching */
while (s < e) {
if (rb_memcmp(s, p, len) == 0) {
if (hx == hy && rb_memcmp(p, s, len) == 0)
return (s-(RSTRING(str)->ptr));
}
hy = KR_REHASH(*s, *(s+len), hy);
s++;
}
return -1;