common.c

一个将mp3/mp2文件解压成wav文件的源码

#include <ctype.h>
#include <stdlib.h>
#include <signal.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include "mpg123.h"


int tabsel_123[2][3][16] = {
   { {0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,},
     {0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384,},
     {0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320,} },

   { {0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,},
     {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,},
     {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,} }
};

long freqs[9] = { 44100, 48000, 32000,
                  22050, 24000, 16000 ,
                  11025 , 12000 , 8000 };

int bitindex;
unsigned char *wordpointer;


#define HDRCMPMASK 0xfffffd00


/*
 * the code a header and write the information
 * into the frame structure
 */
int decode_header(struct frame *fr,unsigned long newhead)
{
	long ltmp;  //wfz_added
    if( newhead & (1<<20) ) {
      fr->lsf = (newhead & (1<<19)) ? 0x0 : 0x1;   // lsf= 0(mpeg1), 1(mpeg2)
      fr->mpeg25 = 0;
    }
    else {
      fr->lsf = 1;
      fr->mpeg25 = 1;
    }


    fr->lay = 4-((newhead>>17)&3);
    if( ((newhead>>10)&0x3) == 0x3) {
#ifndef BE_QUIET
      fprintf(stderr,"Stream error\n");
      exit(1);
#else
      return (0);
#endif
    }
    if(fr->mpeg25) {
      fr->sampling_frequency = 6 + ((newhead>>10)&0x3);  // index of sampling_frequency in freqs[]
    }
    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)
    {
#ifndef BE_QUIET
      fprintf(stderr,"Free format not supported.\n");
#endif
      return (0);
    }

    switch(fr->lay)
    {
/*      case 1:
#if 0
		fr->do_layer = do_layer1;
        fr->jsbound = (fr->mode == MPG_MD_JOINT_STEREO) ?
                         (fr->mode_ext<<2)+4 : 32;
        fr->framesize  = (long) tabsel_123[fr->lsf][0][fr->bitrate_index] * 12000;
        fr->framesize /= freqs[fr->sampling_frequency];
        fr->framesize  = ((fr->framesize+fr->padding)<<2)-4;
#else
#ifndef BE_QUIET
        fprintf(stderr,"layer=1 Not supported!\n");
#endif
		
#endif
        break;*/
      case 2:
//#if 1
		fr->do_layer = do_layer2;
// in layer2.c
//        II_select_table(fr);
//        fr->jsbound = (fr->mode == MPG_MD_JOINT_STEREO) ?
//                         (fr->mode_ext<<2)+4 : fr->II_sblimit;
        fr->framesize = (long) tabsel_123[fr->lsf][1][fr->bitrate_index] * 144000;
        fr->framesize /= freqs[fr->sampling_frequency];
        fr->framesize += fr->padding - 4;
//#endif
        break;
      case 3:
        fr->do_layer = do_layer3;
/*
#if 0
        if(fr->lsf)
          ssize = (fr->stereo == 1) ? 9 : 17;
        else
          ssize = (fr->stereo == 1) ? 17 : 32;
#endif

#if 0
        if(fr->error_protection)
          ssize += 2;
#endif*/

/*        ------- BEGIN OF MODIFICATIONS FOR mpglib.dll
          Because LCC-Win32 made the Program crash at this
          point, the following modification was necessary.
          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 - 4;
*/  
		//long ltmp; this declaration moved to the beginning of the founction
		
		ltmp  = (long) tabsel_123[fr->lsf][2][fr->bitrate_index] * 144000;
		ltmp /= freqs[fr->sampling_frequency]<<(fr->lsf);
		ltmp  = ltmp + fr->padding - 4;
		fr->framesize=ltmp;
/*        ------- END OF MODIFICATIONS FOR mpglib.dll
*/

        break;
      default:
#ifndef BE_QUIET
        fprintf(stderr,"Sorry, unknown layer type.\n");
#endif
        return (0);
    }

    /*    print_header(fr); */

    return 1;
}


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

  if(!number_of_bits)
    return 0;

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

    bitindex += number_of_bits;

    rval >>= (24-number_of_bits);

    wordpointer += (bitindex>>3);
    bitindex &= 7;
  }
  return rval;
}

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

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

    rval >>= (16-number_of_bits);

    wordpointer += (bitindex>>3);
    bitindex &= 7;
  }
  return rval;
}