H264 bitstream parser.

webrtc/base/bitbuffer.cc

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 169 matching lines @@
   // read the value.
   size_t value_bit_count = zero_bit_count + 1;
   if (value_bit_count > 32 || !ReadBits(val, value_bit_count)) {
     CHECK(Seek(original_byte_offset, original_bit_offset));
     return false;
   }
   *val -= 1;
   return true;
 }
 
+bool BitBuffer::ReadSignedExponentialGolomb(int32_t* val) {
+  // TODO(pbos): Is there a corner case I'm missing here?
+  uint32_t unsigned_val;
+  if (!ReadExponentialGolomb(&unsigned_val))

[noahric, 2015/09/03 17:48:58]

Brackets to match the rest of the file :-p

[pbos-webrtc, 2015/09/04 10:01:20]

Done.

+    return false;
+  if ((unsigned_val & 1) == 0)

[noahric, 2015/09/03 17:48:58]

This if just falls through and overwrites val, so that can't work correctly.
if/else?

Also it'd be helpful to have a short comment explaining what the sequence is,
e.g.
// Signed exponential golomb values are just the unsigned values
// mapped to the sequence 0, 1, -1, 2, -2, etc. in order.

(plus a unit test, for at least a small set of expected values)

[pbos-webrtc, 2015/09/04 10:01:20]

Done, which also uncovered additional bugs. That are now fixed. Thanks. :')

+    *val = (unsigned_val + 1) / 2;
+  *val = -(unsigned_val / 2);
+  return true;
+}
+
 void BitBuffer::GetCurrentOffset(
     size_t* out_byte_offset, size_t* out_bit_offset) {
   CHECK(out_byte_offset != NULL);
   CHECK(out_bit_offset != NULL);
   *out_byte_offset = byte_offset_;
   *out_bit_offset = bit_offset_;
 }
 
 bool BitBuffer::Seek(size_t byte_offset, size_t bit_offset) {
   if (byte_offset > byte_count_ || bit_offset > 7 ||
@@ skipping 74 matching lines @@
   }
   uint64_t val_to_encode = static_cast<uint64_t>(val) + 1;
 
   // We need to write CountBits(val+1) 0s and then val+1. Since val (as a
   // uint64_t) has leading zeros, we can just write the total golomb encoded
   // size worth of bits, knowing the value will appear last.
   return WriteBits(val_to_encode, CountBits(val_to_encode) * 2 - 1);
 }
 
 }  // namespace rtc