Strict Overflow Prevention video_capture_oracle.cc

media/capture/content/video_capture_oracle.cc

 // Copyright (c) 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.
 
 #include "media/capture/content/video_capture_oracle.h"
 
 #include <algorithm>
 
 #include "base/format_macros.h"
 #include "base/numerics/safe_conversions.h"
@@ skipping 317 matching lines @@
   return frame_timestamps_[frame_number % kMaxFrameTimestamps];
 }
 
 void VideoCaptureOracle::SetFrameTimestamp(int frame_number,
                                            base::TimeTicks timestamp) {
   DCHECK(IsFrameInRecentHistory(frame_number));
   frame_timestamps_[frame_number % kMaxFrameTimestamps] = timestamp;
 }
 
 bool VideoCaptureOracle::IsFrameInRecentHistory(int frame_number) const {
-  return ((next_frame_number_ - frame_number) < kMaxFrameTimestamps &&
-          frame_number <= next_frame_number_ && frame_number >= 0);
+  // Adding (next_frame_number_ >= 0) helps the compiler deduce that there
+  // is no possibility of overflow here.
+  return (frame_number >= 0 && next_frame_number_ >= 0 &&
+          frame_number <= next_frame_number_ &&
+          (next_frame_number_ - frame_number) < kMaxFrameTimestamps);
 }
 
 void VideoCaptureOracle::CommitCaptureSizeAndReset(
     base::TimeTicks last_frame_time) {
   capture_size_ = resolution_chooser_.capture_size();
   VLOG(2) << "Now proposing a capture size of " << capture_size_.ToString();
 
   // Reset each short-term feedback accumulator with a stable-state starting
   // value.
   const base::TimeTicks ignore_before_time = JustAfter(last_frame_time);
@@ skipping 163 matching lines @@
   // Content is not animating, so permit an immediate increase in the capture
   // area.  This allows the system to quickly improve the quality of
   // non-animating content (frame drops are not much of a concern).
   VLOG(2) << "Proposing a "
           << (100.0 * (increased_area - current_area) / current_area)
           << "% increase in capture area for non-animating content.  :-)";
   return increased_area;
 }
 
 }  // namespace media