levenshtein.c

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/*
   +----------------------------------------------------------------------+
   | Copyright (c) The PHP Group                                          |
   +----------------------------------------------------------------------+
   | This source file is subject to version 3.01 of the PHP license,      |
   | that is bundled with this package in the file LICENSE, and is        |
   | available through the world-wide-web at the following url:           |
   | https://www.php.net/license/3_01.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: Hartmut Holzgraefe <hholzgra@php.net>                        |
   +----------------------------------------------------------------------+
 */
 
#include "php.h"
 
/* {{{ reference_levdist
 * reference implementation, only optimized for memory usage, not speed */
static zend_long reference_levdist(const zend_string *string1, const zend_string *string2, zend_long cost_ins, zend_long cost_rep, zend_long cost_del )
{
    zend_long *p1, *p2, *tmp;
    zend_long c0, c1, c2;
    size_t i1, i2;
 
    if (ZSTR_LEN(string1) == 0) {
        return ZSTR_LEN(string2) * cost_ins;
    }
    if (ZSTR_LEN(string2) == 0) {
        return ZSTR_LEN(string1) * cost_del;
    }
 
    /* When all costs are equal, levenshtein fulfills the requirements of a metric, which means
     * that the distance is symmetric. If string1 is shorter than string 2 we can save memory (and CPU time)
     * by having shorter rows (p1 & p2). */
    if (ZSTR_LEN(string1) < ZSTR_LEN(string2) && cost_ins == cost_rep && cost_rep == cost_del) {
        const zend_string *tmp = string1;
        string1 = string2;
        string2 = tmp;
    }
 
    p1 = safe_emalloc((ZSTR_LEN(string2) + 1), sizeof(zend_long), 0);
    p2 = safe_emalloc((ZSTR_LEN(string2) + 1), sizeof(zend_long), 0);
 
    for (i2 = 0; i2 <= ZSTR_LEN(string2); i2++) {
        p1[i2] = i2 * cost_ins;
    }
    for (i1 = 0; i1 < ZSTR_LEN(string1) ; i1++) {
        p2[0] = p1[0] + cost_del;
 
        for (i2 = 0; i2 < ZSTR_LEN(string2); i2++) {
            c0 = p1[i2] + ((ZSTR_VAL(string1)[i1] == ZSTR_VAL(string2)[i2]) ? 0 : cost_rep);
            c1 = p1[i2 + 1] + cost_del;
            if (c1 < c0) {
                c0 = c1;
            }
            c2 = p2[i2] + cost_ins;
            if (c2 < c0) {
                c0 = c2;
            }
            p2[i2 + 1] = c0;
        }
        tmp = p1;
        p1 = p2;
        p2 = tmp;
    }
    c0 = p1[ZSTR_LEN(string2)];
 
    efree(p1);
    efree(p2);
 
    return c0;
}
/* }}} */
 
/* {{{ Calculate Levenshtein distance between two strings */
PHP_FUNCTION(levenshtein)
{
    zend_string *string1, *string2;
    zend_long cost_ins = 1;
    zend_long cost_rep = 1;
    zend_long cost_del = 1;
 
    if (zend_parse_parameters(ZEND_NUM_ARGS(), "SS|lll", &string1, &string2, &cost_ins, &cost_rep, &cost_del) == FAILURE) {
        RETURN_THROWS();
    }
 
 
    RETURN_LONG(reference_levdist(string1, string2, cost_ins, cost_rep, cost_del));
}
/* }}} */