/************************************************************************ * *  getbits.c, bit level routines for tmndecode (H.263 decoder) *  Copyright (C) 1996  Telenor R&D, Norway *        Karl Olav Lillevold <Karl.Lillevold@nta.no> * *  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., 675 Mass Ave, Cambridge, MA 02139, USA. * *  Karl Olav Lillevold               <Karl.Lillevold@nta.no> *  Telenor Research and Development *  P.O.Box 83                        tel.:   +47 63 84 84 00 *  N-2007 Kjeller, Norway            fax.:   +47 63 81 00 76 * *  Robert Danielsen                  e-mail: Robert.Danielsen@nta.no *  Telenor Research and Development  www:    http://www.nta.no/brukere/DVC/ *  P.O.Box 83                        tel.:   +47 63 84 84 00 *  N-2007 Kjeller, Norway            fax.:   +47 63 81 00 76 *   ************************************************************************//* * based on mpeg2decode, (C) 1994, MPEG Software Simulation Group * and mpeg2play, (C) 1994 Stefan Eckart *                         <stefan@lis.e-technik.tu-muenchen.de> * *///最卡的地方#include <stdlib.h>#include "config.h"#include "tmndec.h"#include "global.h"#ifdef WIN32#include <io.h>#endif/* to mask the n least significant bits of an integer */static unsigned int 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};/* initialize buffer, call once before first getbits or showbits */void initbits(){  ld->incnt = 0;  ld->rdptr = ld->rdbfr + 2048;  ld->bitcnt = 0;}void fillbfr(){  int l;  ld->inbfr[0] = ld->inbfr[8];  ld->inbfr[1] = ld->inbfr[9];  ld->inbfr[2] = ld->inbfr[10];  ld->inbfr[3] = ld->inbfr[11];  if (ld->rdptr>=ld->rdbfr+2048)  {    l = read(ld->infile,ld->rdbfr,2048);    ld->rdptr = ld->rdbfr;    if (l<2048)    {      if (l<0)        l = 0;      while (l<2048)   /* Add recognizable sequence end code */      {        ld->rdbfr[l++] = 0;        ld->rdbfr[l++] = 0;        ld->rdbfr[l++] = (1<<7) | (SE_CODE<<2);      }    }  }  for (l=0; l<8; l++)    ld->inbfr[l+4] = ld->rdptr[l];  ld->rdptr+= 8;  ld->incnt+= 64;}/* return next n bits (right adjusted) without advancing */unsigned int showbits(n)int n;{  unsigned char *v;  unsigned int b;  int c;  if (ld->incnt<n)    fillbfr();  v = ld->inbfr + ((96 - ld->incnt)>>3);  b = (v[0]<<24) | (v[1]<<16) | (v[2]<<8) | v[3];  c = ((ld->incnt-1) & 7) + 25;  return (b>>(c-n)) & msk[n];}/* return next bit (could be made faster than getbits(1))  ？？？？ */unsigned int getbits1(){  return getbits(1);}/* advance by n bits */void flushbits(n)int n;{  ld->bitcnt+= n;  ld->incnt-= n;  if (ld->incnt < 0)    fillbfr();}/* return next n bits (right adjusted) */unsigned int getbits(n)//怎樣得到這個字節？向下讀一個？int n;{  unsigned int l;  l = showbits(n);  flushbits(n);  return l;}