www.pudn.com > encore50src.zip > bitstream.c

 
/************************************************************************** 
 *                                                                        * 
 * This code is developed by Adam Li.  This software is an                * 
 * implementation of a part of one or more MPEG-4 Video tools as          * 
 * specified in ISO/IEC 14496-2 standard.  Those intending to use this    * 
 * software module in hardware or software products are advised that its  * 
 * use may infringe existing patents or copyrights, and any such use      * 
 * would be at such party's own risk.  The original developer of this     * 
 * software module and his/her company, and subsequent editors and their  * 
 * companies (including Project Mayo), will have no liability for use of  * 
 * this software or modifications or derivatives thereof.                 * 
 *                                                                        * 
 * Project Mayo gives users of the Codec a license to this software       * 
 * module or modifications thereof for use in hardware or software        * 
 * products claiming conformance to the MPEG-4 Video Standard as          * 
 * described in the Open DivX license.                                    * 
 *                                                                        * 
 * The complete Open DivX license can be found at                         * 
 * http://www.projectmayo.com/opendivx/license.php .                      * 
 *                                                                        * 
 **************************************************************************/ 
 
/************************************************************************** 
 * 
 *  mom_bitstream.c 
 * 
 *  Copyright (C) 2001  Project Mayo 
 * 
 *  Adam Li 
 * 
 *  DivX Advance Research Center  
 * 
 **************************************************************************/ 
 
#include "bitstream.h" 
 
/* to mask the n least significant bits of an integer */ 
 
static unsigned int mask[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 
}; 
 
 
/* static data for pointers and counters */ 
 
/* byte pointer to the output bitstream */ 
static unsigned char *byteptr; 
/* counter of how many bytes got written to the bitstream */ 
static int bytecnt;  
 
/* a one byte temporary buffer */ 
static unsigned char outbfr; 
/* counter of how many unused bits left in the byte buffer */ 
static int outcnt; 
 
void Bitstream_Init(void *buffer) 
{ 
	byteptr = (unsigned char *)buffer; 
	bytecnt = 0; 
	outbfr = 0; 
	outcnt = 8; 
} 
 
void Bitstream_PutBits(int n, unsigned int val) 
{ 
	int diff; 
 
	while ((diff = n - outcnt) >= 0) { /* input is longer than what is left in the buffer */ 
		outbfr |= (unsigned char)(val >> diff); 
		/* note that the first byte of the integer is the least significant byte */ 
		n = diff; 
		val &= mask[n]; 
 
		*(byteptr ++) = outbfr; 
		bytecnt++; 
		outbfr = 0; 
		outcnt = 8; 
	} 
 
	if (n > 0) { /* input is short enough to fit in what is left in the buffer */ 
		outbfr |= (unsigned char)(val << (-diff)); 
		outcnt -= n; 
	} 
} 
 
 
int Bitstream_Close() 
{ 
	while (outcnt != 8) Bitstream_PutBits(1, 1); 
	return bytecnt; 
} 
 
 
int Bitstream_NextStartCode() 
{ 
	int count = outcnt; 
 
	Bitstream_PutBits(1,0); 
	while (outcnt != 8) Bitstream_PutBits(1, 1); 
 
	return (count); 
} 
 
 
int Bitstream_GetLength() 
{ 
	return bytecnt; 
}