getbits.c

实现在linux下的mpeg4编解码

/************************************************************************
 *
 *  getbits.c, bit level routines for tmndecode (H.263 decoder)
 *  Copyright (C) 1995, 1996  Telenor R&D, Norway
 *
 *  Contacts:
 *  Robert Danielsen                  <[e-mail]>
 *
 *  Telenor Research and Development  http://www.nta.no/brukere/DVC/
 *  P.O.Box 83                        tel.:   [phone]
 *  N-2007 Kjeller, Norway            fax.:   [phone]
 *
 *  Copyright (C) 1997  University of BC, Canada
 *  Modified by: Michael Gallant <[e-mail]>
 *               Guy Cote <[e-mail]>
 *               Berna Erol <[e-mail]>
 *
 *  Contacts:
 *  Michael Gallant                   <[e-mail]>
 *
 *  UBC Image Processing Laboratory   http://www.ee.ubc.ca/image
 *  2356 Main Mall                    tel.: [phone]
 *  Vancouver BC Canada V6T1Z4        fax.: [phone]
 *
 ************************************************************************/

/* Disclaimer of Warranty
 * 
 * These software programs are available to the user without any license fee
 * or royalty on an "as is" basis. The University of British Columbia
 * disclaims any and all warranties, whether express, implied, or
 * statuary, including any implied warranties or merchantability or of
 * fitness for a particular purpose.  In no event shall the
 * copyright-holder be liable for any incidental, punitive, or
 * consequential damages of any kind whatsoever arising from the use of
 * these programs.
 * 
 * This disclaimer of warranty extends to the user of these programs and
 * user's customers, employees, agents, transferees, successors, and
 * assigns.
 * 
 * The University of British Columbia does not represent or warrant that the
 * programs furnished hereunder are free of infringement of any
 * third-party patents.
 * 
 * Commercial implementations of H.263, including shareware, are subject to
 * royalty fees to patent holders.  Many of these patents are general
 * enough such that they are unavoidable regardless of implementation
 * design.
 * 
 */


/* based on mpeg2decode, (C) 1994, MPEG Software Simulation Group and
 * mpeg2play, (C) 1994 Stefan Eckart <[e-mail]>
 * 
 */

/**
*  Copyright (C) 2001 - Project Mayo
 *
 * adapted by Andrea Graziani (Ag)
 *
 * DivX Advanced Research Center <[e-mail]>
*
**/

#include <stdlib.h>

#include "mp4_vars.h"

#include "getbits.h"

#define SE_CODE 31


/* initialize buffer, call once before first getbits or showbits */

void initbits (unsigned char * stream, int length)
{
  ld->incnt = 0;
  ld->bitcnt = 0;
  ld->rdptr = ld->rdbfr + 2048;

#ifdef _DECORE
  ld->rdptr = stream;
	ld->length = length;
#endif
}

/* return next bit (could be made faster than getbits(1)) */

unsigned int getbits1 ()
{
  return getbits (1);
}

/* return next n bits (right adjusted) */