Optimized getBytesFromString

Author: SakiTakamachi

ext/random/randomizer.c

@@ -388,7 +388,6 @@ PHP_METHOD(Random_Randomizer, getBytesFromString)
 
 	zend_long user_length;
 	zend_string *source, *retval;
-	size_t total_size = 0;
 
 	ZEND_PARSE_PARAMETERS_START(2, 2);
 		Z_PARAM_STR(source)
@@ -410,17 +409,21 @@ PHP_METHOD(Random_Randomizer, getBytesFromString)
 
 	size_t length = (size_t)user_length;
 	retval = zend_string_alloc(length, 0);
+	char *rptr = ZSTR_VAL(retval);
+	char *sptr = ZSTR_VAL(source);
 
+	size_t to_read = length;
 	if (max_offset > 0xff) {
-		while (total_size < length) {
+		while (to_read > 0) {
 			uint64_t offset = engine.algo->range(engine.state, 0, max_offset);
 
 			if (EG(exception)) {
 				zend_string_free(retval);
 				RETURN_THROWS();
 			}
 
-			ZSTR_VAL(retval)[total_size++] = ZSTR_VAL(source)[offset];
+			*rptr++ = sptr[offset];
+			to_read--;
 		}
 	} else {
 		uint64_t mask = max_offset;
@@ -432,31 +435,38 @@ PHP_METHOD(Random_Randomizer, getBytesFromString)
 		mask |= mask >> 2;
 		mask |= mask >> 4;
 
+		/* Example: if mask is 0xAB, will be 0xABABABABABABABAB */
+		uint64_t mask_repeat = (~((uint64_t) 0) / 0xFF) * mask;
 		int failures = 0;
-		while (total_size < length) {
+		while (to_read > 0) {
 			php_random_result result = engine.algo->generate(engine.state);
 			if (EG(exception)) {
 				zend_string_free(retval);
 				RETURN_THROWS();
 			}
 
-			for (size_t i = 0; i < result.size; i++) {
-				uint64_t offset = (result.result >> (i * 8)) & mask;
-
+			uint64_t offsets = result.result & mask_repeat;
+			size_t ret_size = result.size;
+			while (ret_size > 0) {
+				ret_size--;
+				uint64_t offset = offsets & 0xff;
+				offsets >>= 8;
 				if (offset > max_offset) {
-					if (++failures > PHP_RANDOM_RANGE_ATTEMPTS) {
+					if (failures == PHP_RANDOM_RANGE_ATTEMPTS) {
 						zend_string_free(retval);
 						zend_throw_error(random_ce_Random_BrokenRandomEngineError, "Failed to generate an acceptable random number in %d attempts", PHP_RANDOM_RANGE_ATTEMPTS);
 						RETURN_THROWS();
+					} else {
+						failures++;
+						continue;
 					}
-
-					continue;
 				}
 
 				failures = 0;
 
-				ZSTR_VAL(retval)[total_size++] = ZSTR_VAL(source)[offset];
-				if (total_size >= length) {
+				*rptr++ = sptr[offset];
+				to_read--;
+				if (to_read == 0) {
 					break;
 				}
 			}