Optimize array_slice for packed arrays with large offsets

If the offset is 100000, and there are no gaps in the packed array,
then advance the pointer once by 100000,
instead of looping and skipping 100000 times.

Author: TysonAndre

ext/standard/array.c

@@ -3511,11 +3511,21 @@ PHP_FUNCTION(array_slice)
 	if (HT_IS_PACKED(Z_ARRVAL_P(input)) &&
 	    (!preserve_keys ||
 	     (offset == 0 && HT_IS_WITHOUT_HOLES(Z_ARRVAL_P(input))))) {
+
+		zend_bool can_skip = offset > 0 && HT_IS_WITHOUT_HOLES(Z_ARRVAL_P(input));
 		zend_hash_real_init_packed(Z_ARRVAL_P(return_value));
 		ZEND_HASH_FILL_PACKED(Z_ARRVAL_P(return_value)) {
 			ZEND_HASH_FOREACH_VAL(Z_ARRVAL_P(input), entry) {
 				pos++;
 				if (pos <= offset) {
+					if (can_skip) {
+						/* Optimization: Instead of advancing offset times over a packed array without holes, */
+						/* advance just once (useful when offset is a million). */
+						/* The above code checked that the offset was between 0 and the length of the array (inclusive). */
+						/* TODO: Better abstraction to advance hash pointer in ZEND_HASH_FOREACH? */
+						_p += (offset - pos);
+						pos = offset;
+					}
 					continue;
 				}
 				if (pos > offset + length) {