cup.c

vc++ mp3 源码下载 使用vc写的mp3 播放器

/*____________________________________________________________________________
	
	FreeAmp - The Free MP3 Player

        MP3 Decoder originally Copyright (C) 1995-1997 Xing Technology
        Corp.  http://www.xingtech.com

	Portions Copyright (C) 1998-1999 EMusic.com

	This program is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; if not, write to the Free Software
	Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
	
	$Id: cup.c,v 1.3 1999/10/19 07:13:08 elrod Exp $
____________________________________________________________________________*/

/****  cup.c  ***************************************************

MPEG audio decoder Layer I/II  mpeg1 and mpeg2
should be portable ANSI C, should be endian independent


mod  2/21/95 2/21/95  add bit skip, sb limiting

mods 11/15/95 for Layer I

******************************************************************/
/******************************************************************

       MPEG audio software decoder portable ANSI c.
       Decodes all Layer I/II to 16 bit linear pcm.
       Optional stereo to mono conversion.  Optional
       output sample rate conversion to half or quarter of
       native mpeg rate. dec8.c adds oupuut conversion features.

-------------------------------------
int audio_decode_init(MPEG_HEAD *h, int framebytes_arg,
         int reduction_code, int transform_code, int convert_code,
         int freq_limit)

initilize decoder:
       return 0 = fail, not 0 = success

MPEG_HEAD *h    input, mpeg header info (returned by call to head_info)
framebytes      input, mpeg frame size (returned by call to head_info)
reduction_code  input, sample rate reduction code
                    0 = full rate
                    1 = half rate
                    2 = quarter rate

transform_code  input, ignored
convert_code    input, channel conversion
                  convert_code:  0 = two chan output
                                 1 = convert two chan to mono
                                 2 = convert two chan to left chan
                                 3 = convert two chan to right chan
freq_limit      input, limits bandwidth of pcm output to specified
                frequency.  Special use. Set to 24000 for normal use.


---------------------------------
void audio_decode_info( DEC_INFO *info)

information return:
          Call after audio_decode_init.  See mhead.h for
          information returned in DEC_INFO structure.


---------------------------------
IN_OUT audio_decode(unsigned char *bs, void *pcmbuf)

decode one mpeg audio frame:
bs        input, mpeg bitstream, must start with
          sync word.  Caution: may read up to 3 bytes
          beyond end of frame.
pcmbuf    output, pcm samples.

IN_OUT structure returns:
          Number bytes conceptually removed from mpeg bitstream.
          Returns 0 if sync loss.
          Number bytes of pcm output.

*******************************************************************/


#include <stdlib.h>
#include <stdio.h>
#include <float.h>
#include <math.h>
#include "mhead.h"		/* mpeg header structure */


#ifdef _MSC_VER
#pragma warning(disable: 4709)
#endif


/*-------------------------------------------------------
NOTE:  Decoder may read up to three bytes beyond end of
frame.  Calling application must ensure that this does
not cause a memory access violation (protection fault)
---------------------------------------------------------*/

/*====================================================================*/
/*----------------*/
DEC_INFO decinfo;		/* global for Layer III */

/*----------------*/
static float look_c_value[18];	/* built by init */

/*----------------*/
static int outbytes;
static int framebytes;
static int outvalues;
static int pad;
static int look_joint[16] =
{				/* lookup stereo sb's by mode+ext */
   64, 64, 64, 64,		/* stereo */
   2 * 4, 2 * 8, 2 * 12, 2 * 16,	/* joint */
   64, 64, 64, 64,		/* dual */
   32, 32, 32, 32,		/* mono */
};

/*----------------*/
static int max_sb;
static int stereo_sb;

/*----------------*/
static int nsb_limit = 6;
static int bit_skip;
static int bat_bit_master[] =
{
   0, 5, 7, 9, 10, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48};

/*----------------*/
static int nbat[4] =
{3, 8, 12, 7};
static int bat[4][16];
static int ballo[64];		/* set by unpack_ba */
static unsigned int samp_dispatch[66];	/* set by unpack_ba */
static float c_value[64];	/* set by unpack_ba */

/*----------------*/
static unsigned int sf_dispatch[66];	/* set by unpack_ba */
static float sf_table[64];
static float cs_factor[3][64];

/*----------------*/
float sample[2304];		/* global for use by Later 3 */
static signed char group3_table[32][3];
static signed char group5_table[128][3];
static signed short group9_table[1024][3];

/*----------------*/

typedef void (*SBT_FUNCTION) (float *sample, short *pcm, int n);
void sbt_mono(float *sample, short *pcm, int n);
void sbt_dual(float *sample, short *pcm, int n);
static SBT_FUNCTION sbt = sbt_mono;


typedef IN_OUT(*AUDIO_DECODE_ROUTINE) (unsigned char *bs, signed short *pcm);
IN_OUT L2audio_decode(unsigned char *bs, signed short *pcm);
static AUDIO_DECODE_ROUTINE audio_decode_routine = L2audio_decode;

/*======================================================================*/
/*======================================================================*/
/* get bits from bitstream in endian independent way */
static unsigned char *bs_ptr;
static unsigned long bitbuf;
static int bits;
static long bitval;

/*------------- initialize bit getter -------------*/
static void load_init(unsigned char *buf)
{
   bs_ptr = buf;
   bits = 0;
   bitbuf = 0;
}
/*------------- get n bits from bitstream -------------*/
static long load(int n)
{
   unsigned long x;

   if (bits < n)
   {				/* refill bit buf if necessary */
      while (bits <= 24)
      {
	 bitbuf = (bitbuf << 8) | *bs_ptr++;
	 bits += 8;
      }
   }
   bits -= n;
   x = bitbuf >> bits;
   bitbuf -= x << bits;
   return x;
}
/*------------- skip over n bits in bitstream -------------*/
static void skip(int n)
{
   int k;

   if (bits < n)
   {
      n -= bits;
      k = n >> 3;
/*--- bytes = n/8 --*/
      bs_ptr += k;
      n -= k << 3;
      bitbuf = *bs_ptr++;
      bits = 8;
   }
   bits -= n;
   bitbuf -= (bitbuf >> bits) << bits;
}
/*--------------------------------------------------------------*/
#define mac_load_check(n) if( bits < (n) ) {                           \
          while( bits <= 24 ) {               \
             bitbuf = (bitbuf << 8) | *bs_ptr++;  \
             bits += 8;                       \
          }                                   \
   }
/*--------------------------------------------------------------*/
#define mac_load(n) ( bits -= n,                    \
         bitval = bitbuf >> bits,      \
         bitbuf -= bitval << bits,     \
         bitval )
/*======================================================================*/
static void unpack_ba()
{
   int i, j, k;
   static int nbit[4] =
   {4, 4, 3, 2};
   int nstereo;

   bit_skip = 0;
   nstereo = stereo_sb;
   k = 0;
   for (i = 0; i < 4; i++)
   {
      for (j = 0; j < nbat[i]; j++, k++)
      {
	 mac_load_check(4);
	 ballo[k] = samp_dispatch[k] = bat[i][mac_load(nbit[i])];
	 if (k >= nsb_limit)
	    bit_skip += bat_bit_master[samp_dispatch[k]];
	 c_value[k] = look_c_value[samp_dispatch[k]];
	 if (--nstereo < 0)
	 {
	    ballo[k + 1] = ballo[k];
	    samp_dispatch[k] += 18;	/* flag as joint */
	    samp_dispatch[k + 1] = samp_dispatch[k];	/* flag for sf */
	    c_value[k + 1] = c_value[k];
	    k++;
	    j++;
	 }
      }
   }
   samp_dispatch[nsb_limit] = 37;	/* terminate the dispatcher with skip */