Add VP9 raw bits reader

media/filters/vp9_raw_bits_reader.cc

Index: media/filters/vp9_raw_bits_reader.cc
diff --git a/media/filters/vp9_raw_bits_reader.cc b/media/filters/vp9_raw_bits_reader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a3d7353b90c412bc097af580a53b7204e823599c
--- /dev/null
+++ b/media/filters/vp9_raw_bits_reader.cc
@@ -0,0 +1,48 @@
+// 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.
+
+#include "media/filters/vp9_raw_bits_reader.h"
+
+#include <limits.h>
+
+#include "base/logging.h"
+#include "media/base/bit_reader.h"
+
+namespace media {
+
+Vp9RawBitsReader::Vp9RawBitsReader() : out_of_buffer_(false) {}
+
+Vp9RawBitsReader::~Vp9RawBitsReader() {}
+
+void Vp9RawBitsReader::Initialize(const uint8_t* data, size_t size) {
+  DCHECK(data);
+  reader_.reset(new BitReader(data, size));
+  out_of_buffer_ = false;
+}
+
+int Vp9RawBitsReader::ReadBit() {
+  DCHECK(reader_);
+  int value = 0;
+  out_of_buffer_ = !reader_->ReadBits(1, &value);
+  return value;
+}
+
+int Vp9RawBitsReader::ReadLiteral(int bits) {
+  DCHECK(reader_);
+  int value = 0;
+  out_of_buffer_ = !reader_->ReadBits(bits, &value);

[Owen Lin, 2015/08/01 11:35:37]

Use out_of_buffer |= !reader_->ReadBits ...
It looks more robust. Same for other places.

[Pawel Osciak, 2015/08/02 10:46:11]

Good idea, and you could also instead of out_of_buffer have the opposite, e.g.
valid_ member. Then you wouldn't have to negate each read:

class Vp9BitReader {
  bool valid_;
};

and then every time:

valid_ = valid_ && reader_->ReadBits(...);

And I'd replace OutOfBuffer() with IsValid() { return valid_; }

[kcwu, 2015/08/03 07:10:13]

Done.

+  return value;
+}
+
+int Vp9RawBitsReader::ReadSignedLiteral(int bits) {
+  int value = ReadLiteral(bits);
+  return ReadBit() ? -value : value;
+}
+
+size_t Vp9RawBitsReader::GetBytesRead() const {
+  DCHECK(reader_);
+  return (reader_->bits_read() + 7) / 8;
+}
+
+}  // namespace media