[Draft][Require RFC] mb_levenshtein function

ext/mbstring/mbstring.c

@@ -3166,6 +3166,124 @@ PHP_FUNCTION(mb_rtrim)
 	php_do_mb_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, MB_RTRIM);
 }
 
+PHP_FUNCTION(mb_levenshtein)
+{
+	zend_string *string1, *string2, *enc_name = NULL;
+	zend_long cost_ins = 1;
+	zend_long cost_rep = 1;
+	zend_long cost_del = 1;
+
+	ZEND_PARSE_PARAMETERS_START(2, 6)
+		Z_PARAM_STR(string1)
+		Z_PARAM_STR(string2)
+		Z_PARAM_OPTIONAL
+		Z_PARAM_LONG(cost_ins)
+		Z_PARAM_LONG(cost_rep)
+		Z_PARAM_LONG(cost_del)
+		Z_PARAM_STR_OR_NULL(enc_name)
+	ZEND_PARSE_PARAMETERS_END();
+
+	if (ZSTR_LEN(string1) == 0) {
+		RETVAL_LONG(ZSTR_LEN(string2) * cost_ins);
+	}
+
+	if (ZSTR_LEN(string2) == 0) {
+		RETVAL_LONG(ZSTR_LEN(string1) * cost_del);
+	}
+
+	const mbfl_encoding *enc = php_mb_get_encoding(enc_name, 6);
+	if (!enc) {
+		RETURN_THROWS();
+	}
+
+	/* 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) {
+		zend_string *tmp = string1;
+		string1 = string2;
+		string2 = tmp;
+	}
+
+	uint32_t wchar_buf_1[128], wchar_buf_2[128];
+	size_t i1, i2;
+	zend_long *p1, *p2, *tmp;
+	size_t strlen_1 = mb_get_strlen(string1, enc);
+	size_t strlen_2 = mb_get_strlen(string2, enc);
+	size_t len_2 = 0;
+	size_t in_len_1 = ZSTR_LEN(string1);
+	size_t in_len_2 = ZSTR_LEN(string2);
+	unsigned char *in_1 = (unsigned char*)ZSTR_VAL(string1);
+	unsigned char *in_2 = (unsigned char*)ZSTR_VAL(string2);
+	unsigned int state = 0;
+
+	zend_long c0, c1, c2;
+
+	p1 = safe_emalloc(strlen_1, sizeof(zend_long), 0);
+	p2 = safe_emalloc(strlen_2, sizeof(zend_long), 0);
+
+	for (i2 = 0; i2 <= strlen_2; i2++) {
+		p1[i2] = i2 * cost_ins;
+	}
+
+	zend_long tmp_wchar_len_1 = 0;
+	zend_long tmp_wchar_len_2 = 0;
+	bool first = true;
+
+	while (in_len_1) {
+		tmp_wchar_len_1 = enc->to_wchar(&in_1, &in_len_1, wchar_buf_1, 128, &state);
+		ZEND_ASSERT(in_len_1 <= 128);
+		tmp_wchar_len_2 = enc->to_wchar(&in_2, &in_len_2, wchar_buf_2, 128, &state);
+		len_2 += tmp_wchar_len_2;
+		ZEND_ASSERT(in_len_2 <= 128);
+
+		for (i1 = 0; i1 < tmp_wchar_len_1; i1++) {
+			/* First loop that does not cross a 128 code points */
+			if (first) {
+				p2[0] = p1[0] + cost_del;
+			}
+			/* Insertion process when there is a surplus of 128 code points. */
+			if (tmp_wchar_len_2 == 0) {
+				for (i2 = 0; i2 < tmp_wchar_len_1; i2++) {
+					c0 = p1[i2 + (len_2 - tmp_wchar_len_1)] + cost_rep;
+					c1 = p1[i2 + (len_2 - tmp_wchar_len_1) + 1] + cost_del;
+					if (c1 < c0) {
+						c0 = c1;
+					}
+					c2 = p2[i2 + (len_2 - tmp_wchar_len_1)] + cost_ins;
+					if (c2 < c0) {
+						c0 = c2;
+					}
+					p2[i2 + (len_2 - tmp_wchar_len_1) + 1] = c0;
+				}
+			} else {
+				for (i2 = 0; i2 < tmp_wchar_len_2; i2++) {
+					c0 = p1[i2 + (len_2 - tmp_wchar_len_2)] + (wchar_buf_1[i1] == wchar_buf_2[i2] ? 0 : cost_rep);
+					c1 = p1[i2 + (len_2 - tmp_wchar_len_2) + 1] + cost_del;
+					if (c1 < c0) {
+						c0 = c1;
+					}
+					c2 = p2[i2 + (len_2 - tmp_wchar_len_2)] + cost_ins;
+					if (c2 < c0) {
+						c0 = c2;
+					}
+					p2[i2 + (len_2 - tmp_wchar_len_2) + 1] = c0;
+				}
+			}
+			tmp = p1;
+			p1 = p2;
+			p2 = tmp;
+		}
+		first = false;
+	}
+
+	c0 = p1[strlen_2];
+	efree(p1);
+	efree(p2);
+
+	RETVAL_LONG(c0);
+}
+
 static const mbfl_encoding **duplicate_elist(const mbfl_encoding **elist, size_t size)
 {
 	const mbfl_encoding **new_elist = safe_emalloc(size, sizeof(mbfl_encoding*), 0);

ext/mbstring/mbstring.stub.php

@@ -145,6 +145,8 @@ function mb_ltrim(string $string, ?string $characters = null, ?string $encoding
 
 function mb_rtrim(string $string, ?string $characters = null, ?string $encoding = null): string {}
 
+function mb_levenshtein(string $string1, string $string2, int $insertion_cost = 1, int $replacement_cost = 1, int $deletion_cost = 1, ?string $encoding = null): int {}
+
 /** @refcount 1 */
 function mb_detect_encoding(string $string, array|string|null $encodings = null, bool $strict = false): string|false {}
 

ext/mbstring/tests/mb_levenshtein.phpt

@@ -0,0 +1,86 @@
+--TEST--
+mb_levenshtein() function test
+--FILE--
+<?php
+
+echo '--- Equal ---' . \PHP_EOL;
+var_dump(mb_levenshtein('12345', '12345'));
+
+echo '--- First string empty ---' . \PHP_EOL;
+var_dump(mb_levenshtein('', 'xyz'));
+echo '--- Second string empty ---' . \PHP_EOL;
+var_dump(mb_levenshtein('xyz', ''));
+echo '--- Both empty ---' . \PHP_EOL;
+var_dump(mb_levenshtein('', ''));
+var_dump(mb_levenshtein('', '', 10, 10, 10));
+
+echo '--- 1 character ---' . \PHP_EOL;
+var_dump(mb_levenshtein('1', '2'));
+echo '--- 2 character swapped ---' . \PHP_EOL;
+var_dump(mb_levenshtein('12', '21'));
+
+echo '--- Inexpensive deletion ---' . \PHP_EOL;
+var_dump(mb_levenshtein('2121', '11', 2));
+echo '--- Expensive deletion ---' . \PHP_EOL;
+var_dump(mb_levenshtein('2121', '11', 2, 1, 5));
+
+echo '--- Inexpensive insertion ---' . \PHP_EOL;
+var_dump(mb_levenshtein('11', '2121'));
+echo '--- Expensive insertion ---' . \PHP_EOL;
+var_dump(mb_levenshtein('11', '2121', 5));
+
+echo '--- Expensive replacement ---' . \PHP_EOL;
+var_dump(mb_levenshtein('111', '121', 2, 3, 2));
+echo '--- Very expensive replacement ---' . \PHP_EOL;
+var_dump(mb_levenshtein('111', '121', 2, 9, 2));
+
+echo '--- 128 codepoints over ---' . \PHP_EOL;
+var_dump(mb_levenshtein(str_repeat("a", 128) . "abc", str_repeat("a", 128) . "aaa"));
+echo '--- 128 codepoints over only $string1 ---' . \PHP_EOL;
+var_dump(mb_levenshtein(str_repeat("a", 128) . "abc", "aaa"));
+echo '--- 128 codepoints over only $string2 ---' . \PHP_EOL;
+var_dump(mb_levenshtein("abc", str_repeat("a", 128) . "aaa"));
+echo '--- 128 codepoints over Hiragana ---' . \PHP_EOL;
+var_dump(mb_levenshtein(str_repeat("あ", 128) . "あああ", str_repeat("あ", 128) . "あいう"));
+
+echo '--- 128 codepoints over Hiragana in Shift_JIS ---' . \PHP_EOL;
+$hiragana_a = mb_convert_encoding("あ", "SJIS", "UTF-8");
+$hiragana_aiu = mb_convert_encoding("あいう", "SJIS", "UTF-8");
+var_dump(mb_levenshtein(str_repeat($hiragana_a, 128 + 3), str_repeat($hiragana_a, 128) . $hiragana_aiu, encoding: "SJIS"));
+?>
+--EXPECT--
+--- Equal ---
+int(0)
+--- First string empty ---
+int(3)
+--- Second string empty ---
+int(3)
+--- Both empty ---
+int(0)
+int(0)
+--- 1 character ---
+int(1)
+--- 2 character swapped ---
+int(2)
+--- Inexpensive deletion ---
+int(2)
+--- Expensive deletion ---
+int(10)
+--- Inexpensive insertion ---
+int(2)
+--- Expensive insertion ---
+int(10)
+--- Expensive replacement ---
+int(3)
+--- Very expensive replacement ---
+int(4)
+--- 128 codepoints over ---
+int(2)
+--- 128 codepoints over only $string1 ---
+int(128)
+--- 128 codepoints over only $string2 ---
+int(130)
+--- 128 codepoints over Hiragana ---
+int(2)
+--- 128 codepoints over Hiragana in Shift_JIS ---
+int(2)