Fix SafeAdd and SafeMultiply

gpu/command_buffer/common/gles2_cmd_utils.h

 // 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.
 
 // This file is here so other GLES2 related files can have a common set of
 // includes where appropriate.
 
 #ifndef GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_UTILS_H_
 #define GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_UTILS_H_
 
+#include <limits>
 #include <string>
 #include <vector>
 
 #include "../common/types.h"
 #include "gpu/command_buffer/common/gles2_utils_export.h"
 
 namespace gpu {
 namespace gles2 {
 
 // Does a multiply and checks for overflow.  If the multiply did not overflow
 // returns true.
-template <typename T>
-inline bool SafeMultiply(T a, T b, T* dst) {
+
+// Multiplies 2 32 bit unsigned numbers checking for overflow.
+// If there was no overflow returns true.
+inline bool SafeMultiplyUint32(uint32 a, uint32 b, uint32* dst) {
   if (b == 0) {
     *dst = 0;
     return true;
   }
-  T v = a * b;
+  uint32 v = a * b;
   if (v / b != a) {
     *dst = 0;
     return false;
   }
   *dst = v;
   return true;
 }
 
-// A wrapper for SafeMultiply to remove the need to cast.
-inline bool SafeMultiplyUint32(uint32 a, uint32 b, uint32* dst) {
-  return SafeMultiply(a, b, dst);
-}
-
 // Does an add checking for overflow.  If there was no overflow returns true.
-template <typename T>
-inline bool SafeAdd(T a, T b, T* dst) {
+inline bool SafeAddUint32(uint32 a, uint32 b, uint32* dst) {
   if (a + b < a) {
     *dst = 0;
     return false;
   }
   *dst = a + b;
   return true;
 }
 
-// A wrapper for SafeAdd to remove the need to cast.
-inline bool SafeAddUint32(uint32 a, uint32 b, uint32* dst) {
-  return SafeAdd(a, b, dst);
+// Does an add checking for overflow.  If there was no overflow returns true.
+inline bool SafeAddInt32(int32 a, int32 b, int32* dst) {
+  int64 sum64 = static_cast<int64>(a) + b;
+  int32 sum32 = static_cast<int32>(sum64);
+  bool safe = sum64 == static_cast<int64>(sum32);
+  *dst = safe ? sum32 : 0;
+  return safe;
 }
 
 // Utilties for GLES2 support.
 class GLES2_UTILS_EXPORT GLES2Util {
  public:
   static const int kNumFaces = 6;
 
   // Bits returned by GetChannelsForFormat
   enum ChannelBits {
     kRed = 0x1,
@@ skipping 123 matching lines @@
   bool buffer_preserved_;
   bool share_resources_;
   bool bind_generates_resource_;
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_UTILS_H_