decode.c

mepg 1 layer3软解码源代码,实现了对MP3文件的软件解码

void II_dequantize_sample(sample, bit_alloc, fraction, fr_ps)
unsigned int FAR sample[2][3][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
double FAR fraction[2][3][SBLIMIT];
frame_params *fr_ps;
{
    int i, j, k, x;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
    al_table *alloc = fr_ps->alloc;

    for (i=0;i<sblimit;i++)  for (j=0;j<3;j++) for (k=0;k<stereo;k++)
        if (bit_alloc[k][i]) {

            /* locate MSB in the sample */
            x = 0;
#ifndef MS_DOS
            while ((1L<<x) < (*alloc)[i][bit_alloc[k][i]].steps) x++;
#else
            /* microsoft C thinks an int is a short */
            while (( (unsigned long) (1L<<(long)x) <
                    (unsigned long)( (*alloc)[i][bit_alloc[k][i]].steps)
                    ) && ( x < 16) ) x++;
#endif

            /* MSB inversion */
            if (((sample[k][j][i] >> x-1) & 1) == 1)
                fraction[k][j][i] = 0.0;
            else  fraction[k][j][i] = -1.0;

            /* Form a 2's complement sample */
            fraction[k][j][i] += (double) (sample[k][j][i] & ((1<<x-1)-1)) /
                (double) (1L<<x-1);

            /* Dequantize the sample */
            fraction[k][j][i] += d[(*alloc)[i][bit_alloc[k][i]].quant];
            fraction[k][j][i] *= c[(*alloc)[i][bit_alloc[k][i]].quant];
        }
        else fraction[k][j][i] = 0.0;   
   
    for (i=sblimit;i<SBLIMIT;i++) for (j=0;j<3;j++) for(k=0;k<stereo;k++)
        fraction[k][j][i] = 0.0;
}

/***************************** Layer I stuff ***********************/

void I_dequantize_sample(sample, fraction, bit_alloc, fr_ps)
unsigned int FAR sample[2][3][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
double FAR fraction[2][3][SBLIMIT];
frame_params *fr_ps;
{
    int i, nb, k;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;

    for (i=0;i<SBLIMIT;i++)
        for (k=0;k<stereo;k++)
            if (bit_alloc[k][i]) {
                nb = bit_alloc[k][i] + 1;
                if (((sample[k][0][i] >> nb-1) & 1) == 1) fraction[k][0][i] = 0.0;
                else fraction[k][0][i] = -1.0;
                fraction[k][0][i] += (double) (sample[k][0][i] & ((1<<nb-1)-1)) /
                    (double) (1L<<nb-1);

                fraction[k][0][i] =
                    (double) (fraction[k][0][i]+1.0/(double)(1L<<nb-1)) *
                        (double) (1L<<nb) / (double) ((1L<<nb)-1);
            }
            else fraction[k][0][i] = 0.0;
}

/************************************************************
/*
/*   Restore the original value of the sample ie multiply
/*    the fraction value by its scalefactor.
/*
/************************************************************/

/************************* Layer II Stuff **********************/

void II_denormalize_sample(fraction, scale_index,fr_ps,x)
double FAR fraction[2][3][SBLIMIT];
unsigned int scale_index[2][3][SBLIMIT];
frame_params *fr_ps;
int x;
{
    int i,j,k;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;

    for (i=0;i<sblimit;i++) for (j=0;j<stereo;j++) {
        fraction[j][0][i] *= multiple[scale_index[j][x][i]];
        fraction[j][1][i] *= multiple[scale_index[j][x][i]];
        fraction[j][2][i] *= multiple[scale_index[j][x][i]];
    }
}

/**************************** Layer I stuff ******************************/

void I_denormalize_sample(fraction,scale_index,fr_ps)
double FAR fraction[2][3][SBLIMIT];
unsigned int scale_index[2][3][SBLIMIT];
frame_params *fr_ps;
{
    int i,j,k;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;

    for (i=0;i<SBLIMIT;i++) for (j=0;j<stereo;j++)
        fraction[j][0][i] *= multiple[scale_index[j][0][i]];
}

/*****************************************************************
/*
/* The following are the subband synthesis routines. They apply
/* to both layer I and layer II stereo or mono. The user has to
/* decide what parameters are to be passed to the routines.
/*
/***************************************************************/

/*************************************************************
/*
/*   Pass the subband sample through the synthesis window
/*
/**************************************************************/

/* create in synthesis filter */

void create_syn_filter(filter)
double FAR filter[64][SBLIMIT];
{
    register int i,k;

    for (i=0; i<64; i++)
        for (k=0; k<32; k++) {
            if ((filter[i][k] = 1e9*cos((double)((PI64*i+PI4)*(2*k+1)))) >= 0)
                modf(filter[i][k]+0.5, &filter[i][k]);
            else
                modf(filter[i][k]-0.5, &filter[i][k]);
            filter[i][k] *= 1e-9;
        }
}

/***************************************************************
/*
/*   Window the restored sample
/*
/***************************************************************/

/* read in synthesis window */

void read_syn_window(window)
double FAR window[HAN_SIZE];
{
    int i,j[4];
    FILE *fp;
    double f[4];
    char t[150];

    if (!(fp = OpenTableFile("dewindow") )) {
        printf("Please check synthesis window table 'dewindow'\n");
        exit(1);
    }
    for (i=0;i<512;i+=4) {
        fgets(t, 150, fp);
        sscanf(t,"D[%d] = %lf D[%d] = %lf D[%d] = %lf D[%d] = %lf\n",
               j, f,j+1,f+1,j+2,f+2,j+3,f+3);
        if (i==j[0]) {
            window[i] = f[0];
            window[i+1] = f[1];
            window[i+2] = f[2];
            window[i+3] = f[3];
        }
        else {
            printf("Check index in synthesis window table\n");
            exit(1);
        }
        fgets(t,150,fp);
    }
    fclose(fp);
}

int SubBandSynthesis (bandPtr, channel, samples)
double *bandPtr;
int channel;
short *samples;
{
    register int i,j,k;
    register double *bufOffsetPtr, sum;
    static int init = 1;
    typedef double NN[64][32];
    static NN FAR *filter;
    typedef double BB[2][2*HAN_SIZE];
    static BB FAR *buf;
    static int bufOffset[2] = {64,64};
    static double FAR *window;
    int clip = 0;               /* count & return how many samples clipped */

    if (init) {
        buf = (BB FAR *) mem_alloc(sizeof(BB),"BB");
        filter = (NN FAR *) mem_alloc(sizeof(NN), "NN");
        create_syn_filter(*filter);
        window = (double FAR *) mem_alloc(sizeof(double) * HAN_SIZE, "WIN");
        read_syn_window(window);
        init = 0;
    }
/*    if (channel == 0) */
    bufOffset[channel] = (bufOffset[channel] - 64) & 0x3ff;
    bufOffsetPtr = &((*buf)[channel][bufOffset[channel]]);

    for (i=0; i<64; i++) {
        sum = 0;
        for (k=0; k<32; k++)
            sum += bandPtr[k] * (*filter)[i][k];
        bufOffsetPtr[i] = sum;
    }
    /*  S(i,j) = D(j+32i) * U(j+32i+((i+1)>>1)*64)  */
    /*  samples(i,j) = MWindow(j+32i) * bufPtr(j+32i+((i+1)>>1)*64)  */
    for (j=0; j<32; j++) {
        sum = 0;
        for (i=0; i<16; i++) {
            k = j + (i<<5);
            sum += window[k] * (*buf) [channel] [( (k + ( ((i+1)>>1) <<6) ) +
                                                  bufOffset[channel]) & 0x3ff];
        }

/*   {long foo = (sum > 0) ? sum * SCALE + 0.5 : sum * SCALE - 0.5; */
     {long foo = sum * SCALE;
     if (foo >= (long) SCALE)      {samples[j] = SCALE-1; ++clip;}
     else if (foo < (long) -SCALE) {samples[j] = -SCALE;  ++clip;}
     else                           samples[j] = foo;
 }
    }
    return(clip);
}

void out_fifo(pcm_sample, num, fr_ps, done, outFile, psampFrames)
short FAR pcm_sample[2][SSLIMIT][SBLIMIT];
int num;
frame_params *fr_ps;
int done;
FILE *outFile;
unsigned long *psampFrames;
{
    int i,j,l;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
    static short int outsamp[1600];
    static long k = 0;

    if (!done)
        for (i=0;i<num;i++) for (j=0;j<SBLIMIT;j++) {
            (*psampFrames)++;
            for (l=0;l<stereo;l++) {
                if (!(k%1600) && k) {
                    fwrite(outsamp,2,1600,outFile);
                    k = 0;
                }
                outsamp[k++] = pcm_sample[l][i][j];
            }
        }
    else {
        fwrite(outsamp,2,(int)k,outFile);
        k = 0;
    }
}

void  buffer_CRC(bs, old_crc)
Bit_stream_struc  *bs;
unsigned int  *old_crc;
{
    *old_crc = getbits(bs, 16);
}

void  recover_CRC_error(pcm_sample, error_count, fr_ps, outFile, psampFrames)
short FAR pcm_sample[2][SSLIMIT][SBLIMIT];
int error_count;
frame_params *fr_ps;
FILE *outFile;
unsigned long *psampFrames;
{
    int  stereo = fr_ps->stereo;
    int  num, done, i;
    int  samplesPerFrame, samplesPerSlot;
    layer  *hdr = fr_ps->header;
    long  offset;
    short  *temp;

    num = 3;
    if (hdr->lay == 1) num = 1;

    samplesPerSlot = SBLIMIT * num * stereo;
    samplesPerFrame = samplesPerSlot * 32;

    if (error_count == 1) {     /* replicate previous error_free frame */
        done = 1;
        /* flush out fifo */
        out_fifo(pcm_sample, num, fr_ps, done, outFile, psampFrames);
        /* go back to the beginning of the previous frame */
        offset = sizeof(short int) * samplesPerFrame;
        fseek(outFile, -offset, SEEK_CUR);
        done = 0;
        for (i = 0; i < SCALE_BLOCK; i++) {
            fread(pcm_sample, 2, samplesPerSlot, outFile);
            out_fifo(pcm_sample, num, fr_ps, done, outFile, psampFrames);
        }
    }
    else{                       /* mute the frame */
        temp = (short*) pcm_sample;
        done = 0;
        for (i = 0; i < 2*3*SBLIMIT; i++)
            *temp++ = MUTE;     /* MUTE value is in decoder.h */
        for (i = 0; i < SCALE_BLOCK; i++)
            out_fifo(pcm_sample, num, fr_ps, done, outFile, psampFrames);
    }
}

/************************* Layer III routines **********************/

void III_get_side_info(bs, si, fr_ps)
Bit_stream_struc *bs;
III_side_info_t *si;
frame_params *fr_ps;
{
   int ch, gr, i;
   int stereo = fr_ps->stereo;
   
   si->main_data_begin = getbits(bs, 9);
   if (stereo == 1)
      si->private_bits = getbits(bs,5);
      else si->private_bits = getbits(bs,3);

   for (ch=0; ch<stereo; ch++)
      for (i=0; i<4; i++)
      si->ch[ch].scfsi[i] = get1bit(bs);

   for (gr=0; gr<2; gr++) {
      for (ch=0; ch<stereo; ch++) {
         si->ch[ch].gr[gr].part2_3_length = getbits(bs, 12);
         si->ch[ch].gr[gr].big_values = getbits(bs, 9);
         si->ch[ch].gr[gr].global_gain = getbits(bs, 8);
         si->ch[ch].gr[gr].scalefac_compress = getbits(bs, 4);
         si->ch[ch].gr[gr].window_switching_flag = get1bit(bs);
         if (si->ch[ch].gr[gr].window_switching_flag) {
            si->ch[ch].gr[gr].block_type = getbits(bs, 2);
            si->ch[ch].gr[gr].mixed_block_flag = get1bit(bs);
            for (i=0; i<2; i++)
               si->ch[ch].gr[gr].table_select[i] = getbits(bs, 5);
            for (i=0; i<3; i++)
               si->ch[ch].gr[gr].subblock_gain[i] = getbits(bs, 3);
               
            /* Set region_count parameters since they are implicit in this case. */
            
            if (si->ch[ch].gr[gr].block_type == 0) {
               printf("Side info bad: block_type == 0 in split block.\n");
               exit(0);
               }
            else if (si->ch[ch].gr[gr].block_type == 2
                     && si->ch[ch].gr[gr].mixed_block_flag == 0)
               si->ch[ch].gr[gr].region0_count = 8; /* MI 9; */
            else si->ch[ch].gr[gr].region0_count = 7; /* MI 8; */
            si->ch[ch].gr[gr].region1_count = 20 -
				      si->ch[ch].gr[gr].region0_count;
            }
         else {
            for (i=0; i<3; i++)
               si->ch[ch].gr[gr].table_select[i] = getbits(bs, 5);
            si->ch[ch].gr[gr].region0_count = getbits(bs, 4);
            si->ch[ch].gr[gr].region1_count = getbits(bs, 3);
            si->ch[ch].gr[gr].block_type = 0;
            }      
         si->ch[ch].gr[gr].preflag = get1bit(bs);
         si->ch[ch].gr[gr].scalefac_scale = get1bit(bs);
         si->ch[ch].gr[gr].count1table_select = get1bit(bs);
         }
      }
}

void III_put_side_info(bs, si, fr_ps)
frame_params *fr_ps;
Bit_stream_struc *bs;