Improve PHP hash function.

See Daniel Lemire's blog post https://lemire.me/blog/2016/07/21/accelerating-php-hashing-by-unoptimizing-it/

1 files changed, 44 insertions, 0 deletions

diff --git a/Zend/zend_string.h b/Zend/zend_string.h
index 4ede3f0381..793a519ce2 100644
--- a/Zend/zend_string.h
+++ b/Zend/zend_string.h
@@ -361,6 +361,49 @@ static zend_always_inline zend_ulong zend_inline_hash_func(const char *str, size
 {
 	zend_ulong hash = Z_UL(5381);
 
+#if defined(_WIN32) || defined(__i386__) || defined(__x86_64__) || defined(__aarch64__)
+	/* Version with multiplication works better on modern CPU */
+	for (; len >= 8; len -= 8, str += 8) {
+		hash =
+			hash   * 33 * 33 * 33 * 33 +
+			str[0] * 33 * 33 * 33 +
+			str[1] * 33 * 33 +
+			str[2] * 33 +
+			str[3];
+		hash =
+			hash   * 33 * 33 * 33 * 33 +
+			str[4] * 33 * 33 * 33 +
+			str[5] * 33 * 33 +
+			str[6] * 33 +
+			str[7];
+	}
+	if (len >= 4) {
+		hash =
+			hash   * 33 * 33 * 33 * 33 +
+			str[0] * 33 * 33 * 33 +
+			str[1] * 33 * 33 +
+			str[2] * 33 +
+			str[3];
+		len -= 4;
+		str += 4;
+	}
+	if (len >= 2) {
+		if (len > 2) {
+			hash =
+				hash   * 33 * 33 * 33 +
+				str[0] * 33 * 33 +
+				str[1] * 33 +
+				str[2];
+		} else {
+			hash =
+				hash   * 33 * 33 +
+				str[0] * 33 +
+				str[1];
+		}
+	} else if (len != 0) {
+		hash = hash * 33 + *str;
+	}
+#else
 	/* variant with the hash unrolled eight times */
 	for (; len >= 8; len -= 8) {
 		hash = ((hash << 5) + hash) + *str++;
@@ -383,6 +426,7 @@ static zend_always_inline zend_ulong zend_inline_hash_func(const char *str, size
 		case 0: break;
 EMPTY_SWITCH_DEFAULT_CASE()
 	}
+#endif
 
 	/* Hash value can't be zero, so we always set the high bit */
 #if SIZEOF_ZEND_LONG == 8