getbits.c

来自「从 IEEE 1394总线接收传输流」· C语言 代码 · 共 128 行

#include "mpg123.h"
#include "common.h"

#if 0
static void check_buffer_range(int size)
{
	int pos = (bsi.wordpointer-bsbuf) + (size>>3);

	if( pos >= fsizeold) {
		fprintf(stderr,"Pointer out of range (%d,%d)!\n",pos,fsizeold);
	}
}
#endif

void backbits(int number_of_bits)
{
  bsi.bitindex    -= number_of_bits;
  bsi.wordpointer += (bsi.bitindex>>3);
  bsi.bitindex    &= 0x7;
}

int getbitoffset(void) 
{
  return (-bsi.bitindex)&0x7;
}

int getbyte(void)
{
#ifdef DEBUG_GETBITS
  if(bsi.bitindex) 
    fprintf(stderr,"getbyte called unsynched!\n");
#endif
  return *bsi.wordpointer++;
}

unsigned int getbits(int number_of_bits)
{
  unsigned long rval;

#ifdef DEBUG_GETBITS
fprintf(stderr,"g%d",number_of_bits);
#endif

  if(!number_of_bits)
    return 0;

#if 0
   check_buffer_range(number_of_bits+bsi.bitindex);
#endif

  {
    rval = bsi.wordpointer[0];
    rval <<= 8;
    rval |= bsi.wordpointer[1];
    rval <<= 8;
    rval |= bsi.wordpointer[2];

    rval <<= bsi.bitindex;
    rval &= 0xffffff;

    bsi.bitindex += number_of_bits;

    rval >>= (24-number_of_bits);

    bsi.wordpointer += (bsi.bitindex>>3);
    bsi.bitindex &= 7;
  }

#ifdef DEBUG_GETBITS
fprintf(stderr,":%x ",rval);
#endif

  return rval;
}

unsigned int getbits_fast(int number_of_bits)
{
  unsigned int rval;
#ifdef DEBUG_GETBITS
fprintf(stderr,"g%d",number_of_bits);
#endif

#if 0
   check_buffer_range(number_of_bits+bsi.bitindex);
#endif

  rval =  (unsigned char) (bsi.wordpointer[0] << bsi.bitindex);
  rval |= ((unsigned int) bsi.wordpointer[1]<<bsi.bitindex)>>8;
  rval <<= number_of_bits;
  rval >>= 8;

  bsi.bitindex += number_of_bits;

  bsi.wordpointer += (bsi.bitindex>>3);
  bsi.bitindex &= 7;

#ifdef DEBUG_GETBITS
fprintf(stderr,":%x ",rval);
#endif
  return rval;
}

unsigned int get1bit(void)
{
  unsigned char rval;

#ifdef DEBUG_GETBITS
fprintf(stderr,"g%d",1);
#endif

#if 0
   check_buffer_range(1+bsi.bitindex);
#endif

  rval = *bsi.wordpointer << bsi.bitindex;

  bsi.bitindex++;
  bsi.wordpointer += (bsi.bitindex>>3);
  bsi.bitindex &= 7;

#ifdef DEBUG_GETBITS
fprintf(stderr,":%d ",rval>>7);
#endif

  return rval>>7;
}