Save haystack length, and move out of bound offset check outside a specialized path

Author: Girgias

ext/mbstring/libmbfl/mbfl/mbfilter.c

@@ -817,6 +817,7 @@ mbfl_strpos(
     int reverse)
 {
 	size_t result;
+	size_t haystack_length;
 	mbfl_string _haystack_u8, _needle_u8;
 	const mbfl_string *haystack_u8, *needle_u8 = NULL;
 	const unsigned char *u8_tbl;
@@ -855,29 +856,31 @@ mbfl_strpos(
 		needle_u8 = needle;
 	}
 
+	/* Check if offset is out of bound */
+	haystack_length = mbfl_strlen(haystack_u8);
+	if (
+		(offset > 0 && offset > haystack_length)
+		|| (offset < 0 && -offset > haystack_length)
+	) {
+		result = -16;
+		goto out;
+	}
+
 	result = (size_t) -1;
 	if (haystack_u8->len < needle_u8->len) {
 		goto out;
 	}
 
 	if (needle_u8->len == 0) {
-		/* Out of bound offset */
-		if (
-			(offset > 0 && offset > mbfl_strlen(haystack_u8))
-			|| (offset < 0 && -offset > mbfl_strlen(haystack_u8))
-		) {
-			return -16;
-		}
-
 		if (reverse) {
 			if (offset < 0) {
 				result = (size_t) -offset;
 			} else {
-				result = mbfl_strlen(haystack_u8) - offset;;
+				result = haystack_length - offset;;
 			}
 		} else {
 			if (offset < 0) {
-				result = mbfl_strlen(haystack_u8) + offset;
+				result = haystack_length + offset;
 			} else {
 				result = (size_t) offset;
 			}