x265-1.7版本-common/bitstream.h注释
2016-01-21 21:35
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注:问号以及未注释部分 会在x265-1.8版本内更新
/***************************************************************************** * Copyright (C) 2013 x265 project * * Author: Steve Borho <steve@borho.org> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111, USA. * * This program is also available under a commercial proprietary license. * For more information, contact us at license @ x265.com. *****************************************************************************/ #ifndef X265_BITSTREAM_H #define X265_BITSTREAM_H 1 namespace x265 { // private namespace class BitInterface { public: virtual void write(uint32_t val, uint32_t numBits) = 0; virtual void writeByte(uint32_t val) = 0; virtual void resetBits() = 0; virtual uint32_t getNumberOfWrittenBits() const = 0; virtual void writeAlignOne() = 0; virtual void writeAlignZero() = 0; virtual ~BitInterface() {} }; class BitCounter : public BitInterface { protected: uint32_t m_bitCounter; public: BitCounter() : m_bitCounter(0) {} void write(uint32_t, uint32_t num) { m_bitCounter += num; } void writeByte(uint32_t) { m_bitCounter += 8; } void resetBits() { m_bitCounter = 0; } uint32_t getNumberOfWrittenBits() const { return m_bitCounter; } void writeAlignOne() { } void writeAlignZero() { } }; class Bitstream : public BitInterface { public: Bitstream(); ~Bitstream() { X265_FREE(m_fifo); } void resetBits() { m_partialByteBits = m_byteOccupancy = 0; m_partialByte = 0; } uint32_t getNumberOfWrittenBytes() const { return m_byteOccupancy; } uint32_t getNumberOfWrittenBits() const { return m_byteOccupancy * 8 + m_partialByteBits; } const uint8_t* getFIFO() const { return m_fifo; } void write(uint32_t val, uint32_t numBits); void writeByte(uint32_t val); void writeAlignOne(); // insert one bits until the bitstream is byte-aligned void writeAlignZero(); // insert zero bits until the bitstream is byte-aligned void writeByteAlignment(); // insert 1 bit, then pad to byte-align with zero private: uint8_t *m_fifo; uint32_t m_byteAlloc; uint32_t m_byteOccupancy; uint32_t m_partialByteBits; uint8_t m_partialByte; void push_back(uint8_t val); }; /* 无符号指数哥伦布码占用的位数 (注意:实际编码中需要对原有数字加一 再获得指数哥伦布码,所以必须加一才是实际占用的位数) 指数哥伦布编码分为:无符号和有符号: 无符号哥伦布编码: 有前缀和后缀的概念: 1 先将要编码的数值写成二进制:0x6 ==> 0b110 2 以最高位为界(左边第一个1的位置),后面的就是后缀(就是二进制10了),总共两位,所以前缀也是两位,而且必须是0, 3 得出数值6编码后的二进制表示为:00110 解码就是反过程: 从高位开始统计0的个数直至非零位, 假设0的个数是k, 那后面k+1位就是要找的数值了 **/ static const uint8_t bitSize[256] = { 1, 1, 3, 3, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, }; /** 函数功能 : 获取无符号指数哥伦布码占用的位数 * \参数 val : 当前待编码的值 * \返回 : 无符号指数哥伦布码占用的位数 * */ static inline int bs_size_ue(unsigned int val) { return bitSize[val + 1];//因为实际编码中需要先加一,固加一获得时间占用的位数 } static inline int bs_size_ue_big(unsigned int val) { if (val < 255) return bitSize[val + 1]; else return bitSize[(val + 1) >> 8] + 16; } /* 无符号指数哥伦布码 先将编码系数映射为整数 -10 --> 20 -9 --> 18 -8 --> 16 -7 --> 14 -6 --> 12 -5 --> 10 -4 --> 8 -3 --> 6 -2 --> 4 -1 --> 2 0 --> 0 1 --> 1 2 --> 3 3 --> 5 4 --> 7 5 --> 9 6 --> 11 7 --> 13 8 --> 15 9 --> 17 10 --> 19 再调用无符号指数哥伦布码 **/ /** 函数功能 : 获取有符号指数哥伦布码占用的位数 * \参数 val : 当前待编码的值 * \返回 : 有符号指数哥伦布码占用的位数 * */ static inline int bs_size_se(int val) { int tmp = 1 - val * 2;//这里:正数变负 负数变正 如果是负数 刚好就是对应val值+1 if (tmp < 0) tmp = val * 2;//说明当前是正数 直接乘以2 刚好是对应val值+1 如10 对应为19 19+1=20 if (tmp < 256) return bitSize[tmp];//获取bits (也是加一后数字) else return bitSize[tmp >> 8] + 16;//大于256情况 } class SyntaxElementWriter { public: BitInterface* m_bitIf; SyntaxElementWriter() : m_bitIf(NULL) {} /* silently discard the name of the syntax element */ inline void WRITE_CODE(uint32_t code, uint32_t length, const char *) { writeCode(code, length); } inline void WRITE_UVLC(uint32_t code, const char *) { writeUvlc(code); } inline void WRITE_SVLC(int32_t code, const char *) { writeSvlc(code); } inline void WRITE_FLAG(bool flag, const char *) { writeFlag(flag); } void writeCode(uint32_t code, uint32_t length) { m_bitIf->write(code, length); } void writeUvlc(uint32_t code); void writeSvlc(int32_t code) { uint32_t ucode = (code <= 0) ? -code << 1 : (code << 1) - 1; writeUvlc(ucode); } void writeFlag(bool code) { m_bitIf->write(code, 1); } }; } #endif // ifndef X265_BITSTREAM_Hx265-1.7版本-common/bitstream.h注释
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