hash code cleanup - copy seed to local and use array indexing. 1.483 ms for 720p vs 2.225 ms for o…

media/base/djb2.cc

Index: media/base/djb2.cc
===================================================================
--- media/base/djb2.cc	(revision 131200)
+++ media/base/djb2.cc	(working copy)
@@ -1,16 +1,14 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/djb2.h"
 
-uint32 DJB2Hash(const void* buf, size_t len, uint32 hash) {
-  const uint8* s = reinterpret_cast<const uint8*>(buf);
-  if (len > 0) {
-    do {
-      hash = hash * 33 + *s++;
-    } while (--len);
+uint32 DJB2Hash(const void* buf, size_t len, uint32 seed) {
+  const uint8* src = reinterpret_cast<const uint8*>(buf);
+  uint32 hash = seed;
+  for (size_t i = 0; i < len; ++i) {
+    hash = hash * 33 + src[i];
   }
   return hash;
 }
-