common.c

MP3的代码很实用 MP3的代码很实用

/*
 * $Id: common.c,v 1.9 2003/09/11 08:13:24 jwei Exp $
 */

#include "mpg123.h"


#define HDRCMPMASK 0xfffffd00

/*
 * the code a header and write the information
 * into the frame structure
 */
int decode_header(struct frame *fr,unsigned long newhead)
{
    if( newhead & (1<<20) ) {
      fr->lsf = (newhead & (1<<19)) ? 0x0 : 0x1;
      fr->mpeg25 = 0;
    }
    else {
      fr->lsf = 1;
      fr->mpeg25 = 1;
    }
    
    fr->lay = 4-((newhead>>17)&3);
    if( ((newhead>>10)&0x3) == 0x3) {
//      fprintf(stderr,"Stream error\n");
//      exit(1);
		return -1;
    }
    if(fr->mpeg25) {
      fr->sampling_frequency = 6 + ((newhead>>10)&0x3);
    }
    else
      fr->sampling_frequency = ((newhead>>10)&0x3) + (fr->lsf*3);
    fr->error_protection = ((newhead>>16)&0x1)^0x1;

    if(fr->mpeg25) /* allow Bitrate change for 2.5 ... */
      fr->bitrate_index = ((newhead>>12)&0xf);

    fr->bitrate_index = ((newhead>>12)&0xf);
    fr->padding   = ((newhead>>9)&0x1);
    fr->extension = ((newhead>>8)&0x1);
    fr->mode      = ((newhead>>6)&0x3);
    fr->mode_ext  = ((newhead>>4)&0x3);
    fr->copyright = ((newhead>>3)&0x1);
    fr->original  = ((newhead>>2)&0x1);
    fr->emphasis  = newhead & 0x3;

    fr->stereo    = (fr->mode == MPG_MD_MONO) ? 1 : 2;

    if(!fr->bitrate_index)
    {
//      fprintf(stderr,"Free format not supported.\n");
      return (0);
    }

    switch(fr->lay)
    {
      case 1:
//        fprintf(stderr,"Not supported!\n");
        return (0);
        break;
      case 2:
//        fprintf(stderr,"Not supported!\n");
        return (0);
        break;
      case 3:
          fr->framesize  = (long) tabsel_123[fr->lsf][2][fr->bitrate_index] * 144000;
          fr->framesize /= freqs[fr->sampling_frequency]<<(fr->lsf);
          fr->framesize = fr->framesize + fr->padding;
        break; 
      default:
//        fprintf(stderr,"Sorry, unknown layer type.\n"); 
        return (0);
    }
    return 1;
}

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

  if(!number_of_bits)
    return 0;

  {
    rval = bufpointer[0];
    rval <<= 8;
    rval |= bufpointer[1];
    rval <<= 8;
    rval |= bufpointer[2];
    rval <<= bitindex;
    rval &= 0xffffff;

    bitindex += number_of_bits;

    rval >>= (24-number_of_bits);

    bufpointer += (bitindex>>3);
    bitindex &= 7;
  }
  return rval;
}
*/
#if 0
unsigned int getbits_fast(int number_of_bits)
{
  unsigned long rval;

  {
    rval = bufpointer[0];
    rval <<= 8;	
    rval |= bufpointer[1];
    rval <<= bitindex;
    rval &= 0xffff;
    bitindex += number_of_bits;

    rval >>= (16-number_of_bits);

    bufpointer += (bitindex>>3);
    bitindex &= 7;
  }
  return rval;
}
#endif

/*unsigned int get1bit(void)
{
  unsigned char rval;
  rval = *bufpointer << bitindex;

  bitindex++;
  bufpointer += (bitindex>>3);
  bitindex &= 7;

  return rval>>7;
}*/