mpeg4ip_bitstream.h

完整的RTP RTSP代码库

/*
 * The contents of this file are subject to the Mozilla Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/MPL/
 * 
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 * 
 * The Original Code is MPEG4IP.
 * 
 * The Initial Developer of the Original Code is Cisco Systems Inc.
 * Portions created by Cisco Systems Inc. are
 * Copyright (C) Cisco Systems Inc. 2001-2005.  All Rights Reserved.
 * 
 * Contributor(s): 
 *              Bill May        [e-mail]
 */

#ifndef __BITSTREAM_H__
#define __BITSTREAM_H__ 1
#include "mpeg4ip.h"

#ifndef MIN
#define MIN(a, b)  (((a) < (b)) ? (a) : (b))
#endif

typedef enum BitstreamErr_t {
  BITSTREAM_TOO_MANY_BITS, 
  BITSTREAM_PAST_END,
} BitstreamErr_t;

class CBitstream {
 public:
  CBitstream(void) { m_verbose = 0;};
  CBitstream(const uint8_t *buffer, uint32_t bit_len) {
    m_verbose = 0;
    init(buffer, bit_len);
  };
  ~CBitstream (void) {};
  void init(const uint8_t *buffer, uint32_t bit_len) {
    m_chDecBuffer = buffer;
    m_chDecBufferSize = bit_len;
    m_bBookmarkOn = 0;
    m_uNumOfBitsInBuffer = 0;

  };
  void init(const char *buffer, uint32_t bit_len) {
    init((const uint8_t *)buffer, (uint32_t)bit_len);
  };
  void init(const char *buffer, int bit_len) {
    init((const uint8_t *)buffer, (uint32_t)bit_len);
  };
  void init(const uint8_t *buffer, int bit_len) {
    init(buffer, (uint32_t)bit_len);
  };
  void init(const char *buffer, unsigned short bit_len) {
    init((const uint8_t *)buffer, (uint32_t)bit_len);
  };
  void init(const uint8_t *buffer, unsigned short bit_len) {
    init(buffer, (uint32_t)bit_len);
  };
  uint32_t GetBits(uint32_t numBits) {
    uint32_t retData;
    static const uint32_t msk[33] = {
      0x00000000, 0x00000001, 0x00000003, 0x00000007,
      0x0000000f, 0x0000001f, 0x0000003f, 0x0000007f,
      0x000000ff, 0x000001ff, 0x000003ff, 0x000007ff,
      0x00000fff, 0x00001fff, 0x00003fff, 0x00007fff,
      0x0000ffff, 0x0001ffff, 0x0003ffff, 0x0007ffff,
      0x000fffff, 0x001fffff, 0x003fffff, 0x007fffff,
      0x00ffffff, 0x01ffffff, 0x03ffffff, 0x07ffffff,
      0x0fffffff, 0x1fffffff, 0x3fffffff, 0x7fffffff,
      0xffffffff
    };

    if (numBits > 32) {
      throw BITSTREAM_TOO_MANY_BITS;
    }
  
    if (numBits == 0) {
      return 0;
    }
	
    if (m_uNumOfBitsInBuffer >= numBits) {  // don't need to read from FILE
      m_uNumOfBitsInBuffer -= numBits;
      retData = m_chDecData >> m_uNumOfBitsInBuffer;
      // wmay - this gets done below...retData &= msk[numBits];
    } else {
      uint32_t nbits;
      nbits = numBits - m_uNumOfBitsInBuffer;
      if (nbits == 32)
	retData = 0;
      else
	retData = m_chDecData << nbits;
      switch ((nbits - 1) / 8) {
      case 3:
	nbits -= 8;
	if (m_chDecBufferSize < 8) throw BITSTREAM_PAST_END;
	retData |= *m_chDecBuffer++ << nbits;
	m_chDecBufferSize -= 8;
	// fall through
      case 2:
	nbits -= 8;
	if (m_chDecBufferSize < 8) throw BITSTREAM_PAST_END;
	retData |= *m_chDecBuffer++ << nbits;
	m_chDecBufferSize -= 8;
      case 1:
	nbits -= 8;
	if (m_chDecBufferSize < 8) throw BITSTREAM_PAST_END;
	retData |= *m_chDecBuffer++ << nbits;
	m_chDecBufferSize -= 8;
      case 0:
	break;
      }
      if (m_chDecBufferSize < nbits) {
	throw BITSTREAM_PAST_END;
      }
      m_chDecData = *m_chDecBuffer++;
      m_uNumOfBitsInBuffer = MIN(8, m_chDecBufferSize) - nbits;
      m_chDecBufferSize -= MIN(8, m_chDecBufferSize);
      retData |= (m_chDecData >> m_uNumOfBitsInBuffer) & msk[nbits];
    }
    if (m_verbose)
      printf("bits %d value %x\n", numBits, retData&msk[numBits]);
    return (retData & msk[numBits]);
  };
  int getbits(uint32_t bits, uint32_t *retvalue) {
    try {
      *retvalue = GetBits(bits);
    } catch (...) {
      return -1;
    }
    return 0;
  }
  int peekbits(uint32_t bits, uint32_t *retvalue) {
    int ret;
    bookmark(1);
    ret = getbits(bits, retvalue);
    bookmark(0);
    return (ret);
  }
  uint32_t PeekBits(uint32_t bits) {
    uint32_t ret;
    bookmark(1);
    ret = GetBits(bits);
    bookmark(0);
    return ret;
  }
  void bookmark(int bSet) {
    if (m_verbose) {
      printf("bookmark\n");
    }
    if (bSet) {
      m_uNumOfBitsInBuffer_bookmark = m_uNumOfBitsInBuffer;
      m_chDecBuffer_bookmark = m_chDecBuffer;
      m_chDecBufferSize_bookmark = m_chDecBufferSize;
      m_bBookmarkOn = 1;
      m_chDecData_bookmark = m_chDecData;
    } else {
      m_uNumOfBitsInBuffer = m_uNumOfBitsInBuffer_bookmark;
      m_chDecBuffer = m_chDecBuffer_bookmark;
      m_chDecBufferSize = m_chDecBufferSize_bookmark;
      m_chDecData = m_chDecData_bookmark;
      m_bBookmarkOn = 0;
    }
  };
  int bits_remain (void) {
    return m_chDecBufferSize + m_uNumOfBitsInBuffer;
  };
  int byte_align(void) {
    int temp = 0;
    if (m_uNumOfBitsInBuffer != 0) {
      temp = GetBits(m_uNumOfBitsInBuffer);
#if 0
      temp = m_uNumOfBitsInBuffer;
      m_uNumOfBitsInBuffer = 0;
      m_chDecBuffer++;
      m_chDecBufferSize -= MIN(m_chDecBufferSize,8);
#endif
    } else {
      // if we are byte aligned, check for 0x7f value - this will indicate
      // we need to skip those bits
      uint8_t readval;
      readval = PeekBits(8);
      if (readval == 0x7f) {
	readval = GetBits(8);
      }
    }
    return (temp);
  };
  void set_verbose(int verbose) { m_verbose = verbose; };
 private:
  uint32_t m_uNumOfBitsInBuffer;
  const uint8_t *m_chDecBuffer;
  uint8_t m_chDecData, m_chDecData_bookmark;
  uint32_t m_chDecBufferSize;
  int m_bBookmarkOn;
  uint32_t m_uNumOfBitsInBuffer_bookmark;
  const uint8_t *m_chDecBuffer_bookmark;
  uint32_t m_chDecBufferSize_bookmark;
  int m_verbose;
};

#endif