Parse VP9 compressed header

media/filters/vp9_bool_decoder.h

+// Copyright 2016 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 MEDIA_FILTERS_VP9_BOOL_DECODER_H_
+#define MEDIA_FILTERS_VP9_BOOL_DECODER_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <memory>
+
+#include "base/macros.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+class BitReader;
+
+class MEDIA_EXPORT Vp9BoolDecoder {
+ public:
+  Vp9BoolDecoder();
+  ~Vp9BoolDecoder();
+
+  // |data| is the input buffer with |size| bytes.
+  // Returns true if read first marker bit successfully.
+  bool Initialize(const uint8_t* data, size_t size);
+
+  // Returns true if none of the reads since the last Initialize() call has
+  // gone beyond the end of available data.
+  bool IsValid() const { return valid_; }
+
+  // Reads one bit. B(p).
+  // If the read goes beyond the end of buffer, the return value is undefined.
+  bool ReadBool(int prob);
+
+  // Reads a literal. L(n).
+  // If the read goes beyond the end of buffer, the return value is undefined.
+  int ReadLiteral(int bits);
+
+  // Consumes padding bits up to end of data. Returns true if no
+  // padding bits or they are all zero.
+  bool ConsumePaddingBits();
+
+ private:
+  // The highest 8 bits of BigBool is actual "bool value". The remain bits
+  // are optimization of prefill buffer.
+  using BigBool = size_t;

[Pawel Osciak, 2016/08/04 10:20:18]

Is this assuming size_t is 64bit? This may not always be the case.

[kcwu, 2016/08/05 11:38:47]

Not necessary. Any integer type >= 8bits is enough. For extra bits than 8bits,
it will be used for pre-fill optimization.

+  const int kBoolSize = 8;

[Pawel Osciak, 2016/08/04 10:20:18]

Could you please document what these are?

We should perhaps use size_t for sizes.

[kcwu, 2016/08/05 11:38:47]

Done.

+  const int kBigBoolSize = sizeof(BigBool) * 8;

[Pawel Osciak, 2016/08/04 10:20:18]

Should this be called kBigBoolBitSize or something similar?

[kcwu, 2016/08/05 11:38:47]

Done.

+
+  void Fill();
+
+  std::unique_ptr<BitReader> reader_;
+
+  // Indicates if none of the reads since the last Initialize() call has gone
+  // beyond the end of available data.
+  bool valid_;
+
+  BigBool bool_value_;
+
+  // Need to fill at least |count_to_fill_| bits.
+  int count_to_fill_;

[Pawel Osciak, 2016/08/04 10:20:18]

Should this be a size_t?

[kcwu, 2016/08/05 11:38:47]

No, it may be negative. Comment updated.

+  unsigned int bool_range_;
+
+  DISALLOW_COPY_AND_ASSIGN(Vp9BoolDecoder);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_VP9_BOOL_DECODER_H_