From: Dmitry Stogov <dmitry@zend.com>
Date: Mon, 11 Dec 2017 15:16:54 +0000 (+0300)
Subject: Reduce number of hash collisions during dulicate address detection.
X-Git-Tag: php-7.3.0alpha1~827
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=9f1e9700580245088d43cd6eef50edce3bce7abc;p=php

Reduce number of hash collisions during dulicate address detection.
---

diff --git a/ext/opcache/zend_shared_alloc.c b/ext/opcache/zend_shared_alloc.c
index 91496b15df..1ba1ac463c 100644
--- a/ext/opcache/zend_shared_alloc.c
+++ b/ext/opcache/zend_shared_alloc.c
@@ -337,8 +337,10 @@ void *zend_shared_alloc(size_t size)
 int zend_shared_memdup_size(void *source, size_t size)
 {
 	void *old_p;
+	zend_ulong key = (zend_ulong)source;
 
-	if ((old_p = zend_hash_index_find_ptr(&ZCG(xlat_table), (zend_ulong)source)) != NULL) {
+	key = (key >> 3) | (key << ((sizeof(key) * 8) - 3)); /* key  = _rotr(key, 3);*/
+	if ((old_p = zend_hash_index_find_ptr(&ZCG(xlat_table), key)) != NULL) {
 		/* we already duplicated this pointer */
 		return 0;
 	}
@@ -349,8 +351,10 @@ int zend_shared_memdup_size(void *source, size_t size)
 void *_zend_shared_memdup(void *source, size_t size, zend_bool free_source)
 {
 	void *old_p, *retval;
+	zend_ulong key = (zend_ulong)source;
 
-	if ((old_p = zend_hash_index_find_ptr(&ZCG(xlat_table), (zend_ulong)source)) != NULL) {
+	key = (key >> 3) | (key << ((sizeof(key) * 8) - 3)); /* key  = _rotr(key, 3);*/
+	if ((old_p = zend_hash_index_find_ptr(&ZCG(xlat_table), key)) != NULL) {
 		/* we already duplicated this pointer */
 		return old_p;
 	}
@@ -443,14 +447,19 @@ void zend_shared_alloc_clear_xlat_table(void)
 
 void zend_shared_alloc_register_xlat_entry(const void *old, const void *new)
 {
-	zend_hash_index_add_new_ptr(&ZCG(xlat_table), (zend_ulong)old, (void*)new);
+	zend_ulong key = (zend_ulong)old;
+
+	key = (key >> 3) | (key << ((sizeof(key) * 8) - 3)); /* key  = _rotr(key, 3);*/
+	zend_hash_index_add_new_ptr(&ZCG(xlat_table), key, (void*)new);
 }
 
 void *zend_shared_alloc_get_xlat_entry(const void *old)
 {
 	void *retval;
+	zend_ulong key = (zend_ulong)old;
 
-	if ((retval = zend_hash_index_find_ptr(&ZCG(xlat_table), (zend_ulong)old)) == NULL) {
+	key = (key >> 3) | (key << ((sizeof(key) * 8) - 3)); /* key  = _rotr(key, 3);*/
+	if ((retval = zend_hash_index_find_ptr(&ZCG(xlat_table), key)) == NULL) {
 		return NULL;
 	}
 	return retval;