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- // 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.
- //
- /*
- * Copyright (c) 2010, The WebM Project authors. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are
- * met:
- *
- * * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *
- * * Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in
- * the documentation and/or other materials provided with the
- * distribution.
- *
- * * Neither the name of Google, nor the WebM Project, nor the names
- * of its contributors may be used to endorse or promote products
- * derived from this software without specific prior written
- * permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
- // This file is modified from the dboolhuff.{c,h} from the WebM's libvpx
- // project. (http://www.webmproject.org/code)
- // It is used to decode bits from a vp8 stream.
- #ifndef MEDIA_PARSERS_VP8_BOOL_DECODER_H_
- #define MEDIA_PARSERS_VP8_BOOL_DECODER_H_
- #include <stddef.h>
- #include <stdint.h>
- #include <sys/types.h>
- #include "media/parsers/media_parsers_export.h"
- namespace media {
- // A class to decode the VP8's boolean entropy coded stream. It's a variant of
- // arithmetic coding. See RFC 6386 - Chapter 7. Boolean Entropy Decoder.
- class MEDIA_PARSERS_EXPORT Vp8BoolDecoder {
- public:
- Vp8BoolDecoder();
- Vp8BoolDecoder(const Vp8BoolDecoder&) = delete;
- Vp8BoolDecoder& operator=(const Vp8BoolDecoder&) = delete;
- // Initializes the decoder to start decoding |data|, |size| being size
- // of |data| in bytes. Returns false if |data| is NULL or empty.
- bool Initialize(const uint8_t* data, size_t size);
- // Reads a boolean from the coded stream. Returns false if it has reached the
- // end of |data| and failed to read the boolean. The probability of |out| to
- // be true is |probability| / 256, e.g., when |probability| is 0x80, the
- // chance is 1/2 (i.e., 0x80 / 256).
- bool ReadBool(bool* out, uint8_t probability);
- // Reads a boolean from the coded stream with the default probability 1/2.
- // Returns false if it has reached the end of |data| and failed to read the
- // boolean.
- bool ReadBool(bool* out);
- // Reads a "literal", that is, a "num_bits"-wide unsigned value whose bits
- // come high- to low-order, with each bit encoded at probability 1/2.
- // Returns false if it has reached the end of |data| and failed to read the
- // literal.
- bool ReadLiteral(size_t num_bits, int* out);
- // Reads a literal with sign from the coded stream. This is similar to
- // the ReadListeral(), it first read a "num_bits"-wide unsigned value, and
- // then read an extra bit as the sign of the literal. Returns false if it has
- // reached the end of |data| and failed to read the literal or the sign.
- // This is different from the "read_signed_literal(d, n)" defined in RFC 6386.
- bool ReadLiteralWithSign(size_t num_bits, int* out);
- // The following methods are used to get the internal states of the decoder.
- // Returns the bit offset to the current top bit of the coded stream. It is
- // also the number of bits that have been written in the corresponding
- // encoding state. More specifically, we have the following constraint:
- // w + (bottom * S) <= v < w + (bottom + range) * S,
- // where "w" is for the bits already written,
- // "v" is for the possible values of the coded number.
- // "S" is the scale for the current bit position,
- // i.e., S = pow(2, -(n + 8)), where "n" is the bit number of "w".
- // BitOffset() returns the bit count of "w", i.e., "n".
- size_t BitOffset();
- // Gets the "bottom" of the current coded value. See BitOffset() for
- // more details.
- uint8_t GetBottom();
- // Gets the "range" of the current coded value. See BitOffset() for
- // more details.
- uint8_t GetRange();
- private:
- // Reads the next bit from the coded stream. The probability of the bit to
- // be one is |probability| / 256.
- int ReadBit(int probability);
- // Fills more bits from |user_buffer_| to |value_|. We shall keep at least 8
- // bits of the current |user_buffer_| in |value_|.
- void FillDecoder();
- // Returns true iff we have ran out of bits.
- bool OutOfBuffer();
- const uint8_t* user_buffer_;
- const uint8_t* user_buffer_start_;
- const uint8_t* user_buffer_end_;
- size_t value_;
- int count_;
- size_t range_;
- };
- } // namespace media
- #endif // MEDIA_PARSERS_VP8_BOOL_DECODER_H_
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