layer1.c

来自「从FFMPEG转换而来的H264解码程序,VC下编译..」· C语言 代码 · 共 163 行

/*
 * Mpeg Layer-1 audio decoder
 * --------------------------
 * copyright (c) 1995 by Michael Hipp, All rights reserved. See also 'README'
 * near unoptimzed ...
 *
 * may have a few bugs after last optimization ...
 *
 */

//#include "mpg123.h"

static void I_step_one(mp3lib_ctx *ctx,unsigned int balloc[], unsigned int scale_index[2][SBLIMIT],struct frame *fr)
{
  unsigned int *ba=balloc;
  unsigned int *sca = (unsigned int *) scale_index;

  if(fr->stereo==2) {
    int i;
    int jsbound = fr->jsbound;
    for (i=0;i<jsbound;i++) {
      *ba++ = getbits(ctx,4);
      *ba++ = getbits(ctx,4);
    }
    for (i=jsbound;i<SBLIMIT;i++)
      *ba++ = getbits(ctx,4);

    ba = balloc;

    for (i=0;i<jsbound;i++) {
      if ((*ba++))
        *sca++ = getbits(ctx,6);
      if ((*ba++))
        *sca++ = getbits(ctx,6);
    }
    for (i=jsbound;i<SBLIMIT;i++)
      if ((*ba++)) {
        *sca++ =  getbits(ctx,6);
        *sca++ =  getbits(ctx,6);
      }
  }
  else {
    int i;
    for (i=0;i<SBLIMIT;i++)
      *ba++ = getbits(ctx,4);
    ba = balloc;
    for (i=0;i<SBLIMIT;i++)
      if ((*ba++))
        *sca++ = getbits(ctx,6);
  }
}

static void I_step_two(mp3lib_ctx *ctx,real fraction[2][SBLIMIT],unsigned int balloc[2*SBLIMIT],
        unsigned int scale_index[2][SBLIMIT],struct frame *fr)
{
  int i,n;
  int smpb[2*SBLIMIT]; /* values: 0-65535 */
  int *sample;
  register unsigned int *ba;
  register unsigned int *sca = (unsigned int *) scale_index;

  if(fr->stereo==2) {
    int jsbound = fr->jsbound;
    register real *f0 = fraction[0];
    register real *f1 = fraction[1];
    ba = balloc;
    for (sample=smpb,i=0;i<jsbound;i++)  {
      if ((n = *ba++))
        *sample++ = getbits(ctx,n+1);
      if ((n = *ba++))
        *sample++ = getbits(ctx,n+1);
    }
    for (i=jsbound;i<SBLIMIT;i++)
      if ((n = *ba++))
        *sample++ = getbits(ctx,n+1);

    ba = balloc;
    for (sample=smpb,i=0;i<jsbound;i++) {
      if((n=*ba++))
        *f0++ = (real) ( ((-1)<<n) + (*sample++) + 1) * muls[n+1][*sca++];
      else
        *f0++ = 0.0;
      if((n=*ba++))
        *f1++ = (real) ( ((-1)<<n) + (*sample++) + 1) * muls[n+1][*sca++];
      else
        *f1++ = 0.0;
    }
    for (i=jsbound;i<SBLIMIT;i++) {
      if ((n=*ba++)) {
        real samp = (real)( ((-1)<<n) + (*sample++) + 1);
        *f0++ = samp * muls[n+1][*sca++];
        *f1++ = samp * muls[n+1][*sca++];
      }
      else
        *f0++ = *f1++ = 0.0;
    }
    for(i=fr->down_sample_sblimit;i<32;i++)
      fraction[0][i] = fraction[1][i] = 0.0;
  }
  else {
    register real *f0 = fraction[0];
    ba = balloc;
    for (sample=smpb,i=0;i<SBLIMIT;i++)
      if ((n = *ba++))
        *sample++ = getbits(ctx,n+1);
    ba = balloc;
    for (sample=smpb,i=0;i<SBLIMIT;i++) {
      if((n=*ba++))
        *f0++ = (real) ( ((-1)<<n) + (*sample++) + 1) * muls[n+1][*sca++];
      else
        *f0++ = 0.0;
    }
    for(i=fr->down_sample_sblimit;i<32;i++)
      fraction[0][i] = 0.0;
  }
}

static int do_layer1(mp3lib_ctx *ctx,int single)
{
  struct frame *fr=&ctx->fr;
  int clip=0;
  int i,stereo = fr->stereo;
  unsigned int balloc[2*SBLIMIT];
  unsigned int scale_index[2][SBLIMIT];
  real fraction[2][SBLIMIT];
//  int single = fr->single;

//  printf("do_layer1(0x%02X 0x%02X 0x%02X 0x%02X 0x%02X 0x%02X 0x%02X 0x%02X )\n",
//    wordpointer[0],wordpointer[1],wordpointer[2],wordpointer[3],wordpointer[4],wordpointer[5],wordpointer[6],wordpointer[7]);

  fr->jsbound = (fr->mode == MPG_MD_JOINT_STEREO) ?
                         (fr->mode_ext<<2)+4 : 32;

  if(stereo == 1 || single == 3)
    single = 0;

  I_step_one(ctx,balloc,scale_index,fr);

  for (i=0;i<SCALE_BLOCK;i++)
  {
    I_step_two(ctx,fraction,balloc,scale_index,fr);

    if(single >= 0)
    {
      clip += (fr->synth_mono)( ctx,(real *) fraction[single],ctx->pcm_sample,&ctx->pcm_point);
    }
    else {
        int p1 = ctx->pcm_point;
        clip += (fr->synth)( ctx,(real *) fraction[0],0,ctx->pcm_sample,&p1);
        clip += (fr->synth)( ctx,(real *) fraction[1],1,ctx->pcm_sample,&ctx->pcm_point);
    }

  }

  return clip;
}