cc: Fix BytesPerPixel issue and refactor.

cc/resources/resource_util.h

+// Copyright 2015 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.
+
+#ifndef CC_RESOURCES_RESOURCE_UTIL_H_
+#define CC_RESOURCES_RESOURCE_UTIL_H_
+
+#include <limits>
+
+#include "base/numerics/safe_math.h"
+#include "cc/base/cc_export.h"
+#include "cc/resources/resource_format.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace cc {
+
+class CC_EXPORT ResourceUtil {
+ public:
+  // Returns true if the size is valid and fits in bytes, false otherwise.
+  template <typename T>
+  static bool VerifySizeInBytes(const gfx::Size& size, ResourceFormat format) {
+    static_assert(std::numeric_limits<T>::is_integer,
+                  "T must be an integer type");
+    base::CheckedNumeric<T> checked_value = BitsPerPixel(format);
+    checked_value *= size.width();
+    checked_value *= size.height();
+    if (!checked_value.IsValid())
+      return false;
+    size_t value = checked_value.ValueOrDie();
+    if ((value % 8) != 0)
+      return false;
+    return true;
+  }
+
+  // Dies with a CRASH() if the size can not be represented as a positive
+  // number of bytes.
+  template <typename T>
+  static T CheckedSizeInBytes(const gfx::Size& size, ResourceFormat format) {
+    static_assert(std::numeric_limits<T>::is_integer,
+                  "T must be an integer type");
+    DCHECK(VerifySizeInBytes<T>(size, format));
+    base::CheckedNumeric<T> checked_value = BitsPerPixel(format);
+    checked_value *= size.width();
+    checked_value *= size.height();
+    checked_value /= 8;
+    return checked_value.ValueOrDie();
+  }
+
+  // Returns the width in bytes but may overflow or return 0. Only do this for
+  // computing widths for sizes that have already been checked.
+  static size_t UncheckedWidthInBytes(size_t width, ResourceFormat format);

[ericrk, 2015/07/24 20:03:52]

I like the templatization - can you templatize the rest of these as well for
consistency?

[prashant.n, 2015/07/25 07:15:43]

Hmm, I had thought of this earlier, but then we should prevent users using other
than size_t. I'll check how we can do it and update.

+  // Returns the size in bytes but may overflow or return 0. Only do this for
+  // sizes that have already been checked.
+  static size_t UncheckedSizeInBytes(const gfx::Size& size,
+                                     ResourceFormat format);
+  // Same as above, but bytes are aligned on 4-bytes boundaries for upload
+  // performance, assuming that GL_PACK_ALIGNMENT or GL_UNPACK_ALIGNMENT have
+  // not changed from default.
+  static size_t UncheckedWidthInBytesAligned(size_t width,
+                                             ResourceFormat format);
+  static size_t UncheckedSizeInBytesAligned(const gfx::Size& size,
+                                            ResourceFormat format);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ResourceUtil);
+};
+
+}  // namespace cc
+
+#endif  // CC_RESOURCES_RESOURCE_UTIL_H_