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getbits.c

#include "mpg123.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 mpg123_backbits(int number_of_bits)
{
      bsi.bitindex    -= number_of_bits;
      bsi.wordpointer += (bsi.bitindex>>3);
      bsi.bitindex    &= 0x7;
}

int mpg123_getbitoffset(void) 
{
      return (-bsi.bitindex)&0x7;
}

int mpg123_getbyte(void)
{
#ifdef DEBUG_GETBITS
      if(bsi.bitindex) 
            fprintf(stderr,"getbyte called unsynched!\n");
#endif
      return *bsi.wordpointer++;
}

unsigned int mpg123_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 mpg123_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 mpg123_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;
}


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