ext/standard: Optimize single-character searches in strcspn() and strpbrk()

UPGRADING

@@ -86,6 +86,8 @@ PHP 8.7 UPGRADE NOTES
 ========================================
 
 - Standard:
+  . Improved performance of strcspn() and strpbrk() when searching longer strings
+    with a single-byte character mask.
   . Improved performance of array_splice() when inserting without removing
     elements.
   . Improved performance of str_rot13().

ext/standard/string.c

@@ -1740,6 +1740,11 @@ static size_t php_strspn_strcspn_common(const char *haystack, const char *charac
 	 * We only compare in this case.
 	 * Empirically tested that the table lookup approach is only beneficial if characters is longer than 1 character. */
 	if (characters_end - characters == 1) {
+		/* Avoid memchr() overhead for short spans and an immediate match. */
+		if (!must_match && haystack_end - haystack >= 16 && *haystack != *characters) {
+			const char *ptr = memchr(haystack, (unsigned char) *characters, haystack_end - haystack);
+			return ptr ? (size_t) (ptr - haystack) : (size_t) (haystack_end - haystack);
+		}
 		const char *ptr = haystack;
 		while (ptr < haystack_end && (*ptr == *characters) == must_match) {
 			ptr++;