added function "int levdist(string str1, string str2)"

that will calculate the Levenshtein distance between two
strings (faster and possibly more accurate than similar_text())

ext/standard/Makefile.in

@@ -7,7 +7,7 @@ LTLIBRARY_SOURCES=\
 	link.c mail.c math.c md5.c metaphone.c microtime.c pack.c pageinfo.c \
 	parsedate.c quot_print.c rand.c reg.c soundex.c string.c \
 	syslog.c type.c uniqid.c url.c url_scanner.c var.c output.c assert.c \
-	strnatcmp.c
+	strnatcmp.c levenshtein.c
 
 include $(top_srcdir)/build/dynlib.mk
 

ext/standard/basic_functions.c

@@ -162,6 +162,7 @@ function_entry basic_functions[] = {
 	PHP_FE(implode,									NULL)
 	PHP_FE(setlocale,								NULL)
 	PHP_FE(soundex,									NULL)
+	PHP_FE(levdist,									NULL)
 	PHP_FE(chr,										NULL)
 	PHP_FE(ord,										NULL)
 	PHP_FE(parse_str,								NULL)

ext/standard/levenshtein.c

@@ -0,0 +1,117 @@
+/*
+   +----------------------------------------------------------------------+
+   | PHP version 4.0                                                      |
+   +----------------------------------------------------------------------+
+   | Copyright (c) 1997, 1998, 1999, 2000 The PHP Group                   |
+   +----------------------------------------------------------------------+
+   | This source file is subject to version 2.02 of the PHP license,      |
+   | that is bundled with this package in the file LICENSE, and is        |
+   | available at through the world-wide-web at                           |
+   | http://www.php.net/license/2_02.txt.                                 |
+   | If you did not receive a copy of the PHP license and are unable to   |
+   | obtain it through the world-wide-web, please send a note to          |
+   | license@php.net so we can mail you a copy immediately.               |
+   +----------------------------------------------------------------------+
+   | Author: Bjørn Borud - Guardian Networks AS <borud@guardian.no>       |
+   +----------------------------------------------------------------------+
+ */
+/* $Id$ */
+
+#include "php.h"
+#include <stdlib.h>
+#include <errno.h>
+#include <ctype.h>
+#include "php_string.h"
+
+int calc_levdist(const char *s1, const char *s2) /* faster, but obfuscated */
+{
+	register char *p1,*p2;
+	register int i,j,n;
+	int l1=0,l2=0;
+	char r[512];
+
+	/* skip equal start sequence, if any */
+	while(*s1==*s2) {
+		if(!*s1) break;
+		s1++; s2++;
+	}
+	
+	/* if we already used up one string, then
+      the result is the length of the other */
+	if(*s1=='\0') return strlen(s2);
+	if(*s2=='\0') return strlen(s1);
+
+	/* length count */
+	while(*s1++) l1++;
+	while(*s2++) l2++;
+	
+	/* cut of equal tail sequence, if any */
+	while(*--s1 == *--s2) {
+		l1--; l2--;		
+	}
+	
+
+	/* reset pointers, adjust length */
+	s1-=l1++;
+	s2-=l2++;
+
+	/* possible dist to great? */
+ 	if(abs(l1-l2)>=255) return -1;
+
+	/* swap if l2 longer than l1 */
+	if(l1<l2) {
+		(long)s1 ^= (long)s2; (long)s2 ^= (long)s1; (long)s1 ^= (long)s2;
+		l1 ^= l2; l2 ^= l1; l1 ^= l2;
+	}
+
+	
+	/* fill initial row */
+	n=(*s1!=*s2);
+	for(i=0,p1=r;i<l1;i++,*p1++=n++,p1++) {/*empty*/}
+	
+	/* calc. rowwise */
+	for(j=1;j<l2;j++) {
+		/* init pointers and col#0 */
+		p1 = r + !(j&1);
+		p2 = r + (j&1);
+		n=*p1+1;
+		*p2++=n;p2++;
+		s2++;
+		
+		/* foreach column */
+		for(i=1;i<l1;i++) {
+			if(*p1<n) n=*p1+(*(s1+i)!=*(s2)); /* replace cheaper than delete? */
+			p1++;
+			if(*++p1<n) n=*p1+1; /* insert cheaper then insert ? */
+			*p2++=n++; /* update field and cost for next col's delete */
+			p2++;
+		}	
+	}
+
+	/* return result */
+	return n-1;
+}
+
+
+/* {{{ proto int levdist(string str1, string str2)
+   Calculate Levenshtein distance between two strings */
+PHP_FUNCTION(levdist){
+	zval **str1, **str2;
+	int l;
+
+	if (ARG_COUNT(ht) != 2 || zend_get_parameters_ex(2, &str1, &str2) == FAILURE) {
+		WRONG_PARAM_COUNT;
+	}
+	convert_to_string_ex(str1);
+	convert_to_string_ex(str2);
+	
+	l = calc_levdist((*str1)->value.str.val, (*str2)->value.str.val);
+
+	if(l<0) {
+		php_error(E_WARNING,"levdist(): argument string(s) to long");
+	}
+
+	RETURN_LONG(l);
+}
+/* }}} */
+

ext/standard/php_string.h

@@ -43,6 +43,7 @@ PHP_FUNCTION(chop);
 PHP_FUNCTION(trim);
 PHP_FUNCTION(ltrim);
 PHP_FUNCTION(soundex);
+PHP_FUNCTION(levdist);
 
 PHP_FUNCTION(count_chars);
 PHP_FUNCTION(explode);