134 lines
5.2 KiB
C++
134 lines
5.2 KiB
C++
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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//
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/*
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* Copyright (c) 2010, The WebM Project authors. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* * Neither the name of Google, nor the WebM Project, nor the names
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* of its contributors may be used to endorse or promote products
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* derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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// This file is modified from the dboolhuff.{c,h} from the WebM's libvpx
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// project. (http://www.webmproject.org/code)
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// It is used to decode bits from a vp8 stream.
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#ifndef VP8_BOOL_DECODER_H_
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#define VP8_BOOL_DECODER_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include "base/logging.h"
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#include "base/macros.h"
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namespace media {
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// A class to decode the VP8's boolean entropy coded stream. It's a variant of
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// arithmetic coding. See RFC 6386 - Chapter 7. Boolean Entropy Decoder.
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class Vp8BoolDecoder {
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public:
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Vp8BoolDecoder();
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// Initializes the decoder to start decoding |data|, |size| being size
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// of |data| in bytes. Returns false if |data| is NULL or empty.
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bool Initialize(const uint8_t* data, size_t size);
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// Reads a boolean from the coded stream. Returns false if it has reached the
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// end of |data| and failed to read the boolean. The probability of |out| to
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// be true is |probability| / 256, e.g., when |probability| is 0x80, the
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// chance is 1/2 (i.e., 0x80 / 256).
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bool ReadBool(bool* out, uint8_t probability);
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// Reads a boolean from the coded stream with the default probability 1/2.
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// Returns false if it has reached the end of |data| and failed to read the
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// boolean.
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bool ReadBool(bool* out);
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// Reads a "literal", that is, a "num_bits"-wide unsigned value whose bits
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// come high- to low-order, with each bit encoded at probability 1/2.
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// Returns false if it has reached the end of |data| and failed to read the
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// literal.
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bool ReadLiteral(size_t num_bits, int* out);
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// Reads a literal with sign from the coded stream. This is similar to
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// the ReadListeral(), it first read a "num_bits"-wide unsigned value, and
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// then read an extra bit as the sign of the literal. Returns false if it has
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// reached the end of |data| and failed to read the literal or the sign.
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// This is different from the "read_signed_literal(d, n)" defined in RFC 6386.
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bool ReadLiteralWithSign(size_t num_bits, int* out);
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// The following methods are used to get the internal states of the decoder.
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// Returns the bit offset to the current top bit of the coded stream. It is
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// also the number of bits that have been written in the corresponding
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// encoding state. More specifically, we have the following constraint:
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// w + (bottom * S) <= v < w + (bottom + range) * S,
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// where "w" is for the bits already written,
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// "v" is for the possible values of the coded number.
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// "S" is the scale for the current bit position,
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// i.e., S = pow(2, -(n + 8)), where "n" is the bit number of "w".
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// BitOffset() returns the bit count of "w", i.e., "n".
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size_t BitOffset();
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// Gets the "bottom" of the current coded value. See BitOffset() for
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// more details.
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uint8_t GetBottom();
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// Gets the "range" of the current coded value. See BitOffset() for
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// more details.
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uint8_t GetRange();
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private:
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// Reads the next bit from the coded stream. The probability of the bit to
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// be one is |probability| / 256.
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int ReadBit(int probability);
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// Fills more bits from |user_buffer_| to |value_|. We shall keep at least 8
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// bits of the current |user_buffer_| in |value_|.
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void FillDecoder();
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// Returns true iff we have ran out of bits.
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bool OutOfBuffer();
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const uint8_t* user_buffer_;
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const uint8_t* user_buffer_start_;
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const uint8_t* user_buffer_end_;
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size_t value_;
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int count_;
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size_t range_;
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DISALLOW_COPY_AND_ASSIGN(Vp8BoolDecoder);
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};
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} // namespace media
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#endif // VP8_BOOL_DECODER_H_
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