Optimize mb_check_encoding (cut execution time by 50%+)

Previously, mb_check_encoding did an awful lot of unneeded work. In order to determine
whether a string was valid or not, it would convert the whole string into wchar (code
points), which required dynamically allocating a (potentially large) buffer. Then it
would turn right around and convert that big 'ol buffer of code points back to the
original encoding again. Finally, it would check whether any invalid bytes were
detected during that long and onerous process.

The thing is, mbstring _already_ has machinery for detecting whether a string is
valid in a certain encoding or not, and it doesn't require copying any data around
or allocating buffers. Better yet, it can fail fast when an invalid byte is found.
Why not use it? It's sure a lot faster!

Author: alexdowad

ext/mbstring/mbstring.c

@@ -3980,84 +3980,50 @@ PHP_FUNCTION(mb_get_info)
 /* }}} */
 
 
-static inline mbfl_buffer_converter *php_mb_init_convd(const mbfl_encoding *encoding)
+MBSTRING_API int php_mb_check_encoding(const char *input, size_t length, const mbfl_encoding *encoding)
 {
-	mbfl_buffer_converter *convd;
-
-	convd = mbfl_buffer_converter_new(encoding, encoding, 0);
-	if (convd == NULL) {
-		return NULL;
-	}
-	mbfl_buffer_converter_illegal_mode(convd, MBFL_OUTPUTFILTER_ILLEGAL_MODE_NONE);
-	mbfl_buffer_converter_illegal_substchar(convd, 0);
-	return convd;
-}
-
-
-static inline int php_mb_check_encoding_impl(mbfl_buffer_converter *convd, const char *input, size_t length, const mbfl_encoding *encoding) {
-	mbfl_string string, result;
-
-	mbfl_string_init_set(&string, encoding);
-	mbfl_string_init(&result);
-
-	string.val = (unsigned char *) input;
-	string.len = length;
-
-	mbfl_string *ret = mbfl_buffer_converter_feed_result(convd, &string, &result);
-	size_t illegalchars = mbfl_buffer_illegalchars(convd);
-
-	if (ret != NULL) {
-		if (illegalchars == 0 && string.len == result.len && memcmp(string.val, result.val, string.len) == 0) {
-			mbfl_string_clear(&result);
-			return 1;
+	mbfl_identify_filter *ident = mbfl_identify_filter_new2(encoding);
+
+	while (length--) {
+		unsigned char c = *input++;
+		(ident->filter_function)(c, ident);
+		if (ident->flag) {
+			mbfl_identify_filter_delete(ident);
+			return 0;
 		}
-		mbfl_string_clear(&result);
 	}
-	return 0;
-}
-
-MBSTRING_API int php_mb_check_encoding(const char *input, size_t length, const mbfl_encoding *encoding)
-{
-	mbfl_buffer_converter *convd = php_mb_init_convd(encoding);
-	/* If this assertion fails this means some memory allocation failure which is a bug */
-	ZEND_ASSERT(convd != NULL);
 
-	int result = php_mb_check_encoding_impl(convd, input, length, encoding);
-	mbfl_buffer_converter_delete(convd);
+	/* String must not end in the middle of a multi-byte character */
+	int result = (ident->status == 0);
+	mbfl_identify_filter_delete(ident);
 	return result;
 }
 
 static int php_mb_check_encoding_recursive(HashTable *vars, const mbfl_encoding *encoding)
 {
-	mbfl_buffer_converter *convd;
 	zend_long idx;
 	zend_string *key;
 	zval *entry;
 	int valid = 1;
 
-	(void)(idx);
-
-	convd = php_mb_init_convd(encoding);
-	/* If this assertion fails this means some memory allocation failure which is a bug */
-	ZEND_ASSERT(convd != NULL);
+	(void)(idx); /* Suppress spurious compiler warning that `idx` is not used */
 
 	if (GC_IS_RECURSIVE(vars)) {
-		mbfl_buffer_converter_delete(convd);
 		php_error_docref(NULL, E_WARNING, "Cannot not handle circular references");
 		return 0;
 	}
 	GC_TRY_PROTECT_RECURSION(vars);
 	ZEND_HASH_FOREACH_KEY_VAL(vars, idx, key, entry) {
 		ZVAL_DEREF(entry);
 		if (key) {
-			if (!php_mb_check_encoding_impl(convd, ZSTR_VAL(key), ZSTR_LEN(key), encoding)) {
+			if (!php_mb_check_encoding(ZSTR_VAL(key), ZSTR_LEN(key), encoding)) {
 				valid = 0;
 				break;
 			}
 		}
 		switch (Z_TYPE_P(entry)) {
 			case IS_STRING:
-				if (!php_mb_check_encoding_impl(convd, Z_STRVAL_P(entry), Z_STRLEN_P(entry), encoding)) {
+				if (!php_mb_check_encoding(Z_STRVAL_P(entry), Z_STRLEN_P(entry), encoding)) {
 					valid = 0;
 					break;
 				}
@@ -4081,11 +4047,9 @@ static int php_mb_check_encoding_recursive(HashTable *vars, const mbfl_encoding
 		}
 	} ZEND_HASH_FOREACH_END();
 	GC_TRY_UNPROTECT_RECURSION(vars);
-	mbfl_buffer_converter_delete(convd);
 	return valid;
 }
 
-
 /* {{{ Check if the string is valid for the specified encoding */
 PHP_FUNCTION(mb_check_encoding)
 {