GETBITS.C

/* getbits.c, bit level routines                                            */

/*
 * tmndecode 
 * Copyright (C) 1995 Telenor R&D
 *                    Karl Olav Lillevold <kol@nta.no>                    
 *
 * based on mpeg2decode, (C) 1994, MPEG Software Simulation Group
 * and mpeg2play, (C) 1994 Stefan Eckart
 *                         <stefan@lis.e-technik.tu-muenchen.de>
 *
 */
#define GLOBAL

#include <io.h>
#include <stdlib.h>
#include <stdio.h>
#include <memory.h>

#include "config.h"
#include "global.h"


/* 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 + recv_buf_size;
  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];

  // bits_recv_buf: bit count in the recv buffer
  if (ld->rdptr >= ld->rdbfr + bits_recv_buf)
  {
        bits_recv_buf = recv(ld->pDataSock, recv_buf, recv_buf_size, 0);
        if((bits_recv_buf==SOCKET_ERROR)||(bits_recv_buf==0))
        {
                closesocket(ld->pDataSock);
                bits_recv_buf = 0;
                while (bits_recv_buf < recv_buf_size)          /* Add recognizable sequence end code */
                {
                        ld->rdbfr[bits_recv_buf ++] = 0;
                        ld->rdbfr[bits_recv_buf ++] = 0;
                        ld->rdbfr[bits_recv_buf ++] = (1 << 7) | (SE_CODE << 2);
                }
                //      fclose(video);    
                bits_recv_buf = recv_buf_size;
        }
        else
        {
                //      fwrite(recv_buf, 1, bits_recv_buf, video);  
                memcpy(ld->rdbfr, recv_buf, bits_recv_buf);
        }
                        
        ld->rdptr = ld->rdbfr;
  }

  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)
int n;
{
  unsigned int l;

  l = showbits(n);
  flushbits(n);

  return l;
}

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