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decode_4to1.c

/*
 * Mpeg Layer-1,2,3 audio decoder
 * ------------------------------
 * copyright (c) 1995,1996,1997 by Michael Hipp, All rights reserved.
 * See also 'README'
 * version for slower machines .. decodes only every fourth sample
 * dunno why it sounds THIS annoying (maybe we should adapt the window?)
 * absolutely not optimized for this operation
 */

#include <stdlib.h>
#include <math.h>
#include <string.h>

#include "mpg123.h"

#define WRITE_SAMPLE(samples,sum,clip) \
  if( (sum) > 32767.0) { *(samples) = 0x7fff; (clip)++; } \
  else if( (sum) < -32768.0) { *(samples) = -0x8000; (clip)++; } \
  else { *(samples) = sum; }

int
mpg123_synth_4to1_8bit(real * bandPtr, int channel,
                       unsigned char *samples, int *pnt)
{
    short samples_tmp[16];
    short *tmp1 = samples_tmp + channel;
    int i, ret;
    int pnt1 = 0;

    ret =
        mpg123_synth_4to1(bandPtr, channel, (unsigned char *) samples_tmp,
                          &pnt1);
    samples += channel + *pnt;

    for (i = 0; i < 8; i++) {
        *samples = (*tmp1 >> 8) ^ 128;
        samples += 2;
        tmp1 += 2;
    }
    *pnt += 16;

    return ret;
}

int
mpg123_synth_4to1_8bit_mono(real * bandPtr, unsigned char *samples, int *pnt)
{
    short samples_tmp[16];
    short *tmp1 = samples_tmp;
    int i, ret;
    int pnt1 = 0;

    ret = mpg123_synth_4to1(bandPtr, 0, (unsigned char *) samples_tmp, &pnt1);
    samples += *pnt;

    for (i = 0; i < 8; i++) {
        *samples++ = (*tmp1 >> 8) ^ 128;
        tmp1 += 2;
    }
    *pnt += 8;

    return ret;
}

#if 0
int
mpg123_synth_4to1_8bit_mono2stereo(real * bandPtr,
                                   unsigned char *samples, int *pnt)
{
    short samples_tmp[16];
    short *tmp1 = samples_tmp;
    int i, ret;
    int pnt1 = 0;

    ret = mpg123_synth_4to1(bandPtr, 0, (unsigned char *) samples_tmp, &pnt1);
    samples += *pnt;

    for (i = 0; i < 8; i++) {
        *samples++ = (*tmp1 >> 8) ^ 128;
        *samples++ = (*tmp1 >> 8) ^ 128;
        tmp1 += 2;
    }
    *pnt += 16;

    return ret;
}
#endif

int
mpg123_synth_4to1_mono(real * bandPtr, unsigned char *samples, int *pnt)
{
    short samples_tmp[16];
    short *tmp1 = samples_tmp;
    int i, ret;
    int pnt1 = 0;

    ret = mpg123_synth_4to1(bandPtr, 0, (unsigned char *) samples_tmp, &pnt1);
    samples += *pnt;

    for (i = 0; i < 8; i++) {
        *((short *) samples) = *tmp1;
        samples += 2;
        tmp1 += 2;
    }
    *pnt += 16;

    return ret;
}

#if 0
int
mpg123_synth_4to1_mono2stereo(real * bandPtr, unsigned char *samples,
                              int *pnt)
{
    int i, ret;

    ret = mpg123_synth_4to1(bandPtr, 0, samples, pnt);
    samples = samples + *pnt - 32;

    for (i = 0; i < 8; i++) {
        ((short *) samples)[1] = ((short *) samples)[0];
        samples += 4;
    }

    return ret;
}
#endif

int
mpg123_synth_4to1(real * bandPtr, int channel, unsigned char *out, int *pnt)
{
    static real buffs[2][2][0x110];
    static const int step = 2;
    static int bo = 1;
    short *samples = (short *) (out + *pnt);

    real *b0, (*buf)[0x110];
    int clip = 0;
    int bo1;

/*  if(param.equalizer)
   do_equalizer(bandPtr,channel); */

    if (!channel) {
        bo--;
        bo &= 0xf;
        buf = buffs[0];
    }
    else {
        samples++;
        buf = buffs[1];
    }

    if (bo & 0x1) {
        b0 = buf[0];
        bo1 = bo;
        mpg123_dct64(buf[1] + ((bo + 1) & 0xf), buf[0] + bo, bandPtr);
    }
    else {
        b0 = buf[1];
        bo1 = bo + 1;
        mpg123_dct64(buf[0] + bo, buf[1] + bo + 1, bandPtr);
    }

    {
        register int j;
        real *window = mpg123_decwin + 16 - bo1;

        for (j = 4; j; j--, b0 += 0x30, window += 0x70) {
            real sum;

            sum = *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;
            sum += *window++ * *b0++;
            sum -= *window++ * *b0++;

            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
#if 0
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
#endif
        }

        {
            real sum;

            sum = window[0x0] * b0[0x0];
            sum += window[0x2] * b0[0x2];
            sum += window[0x4] * b0[0x4];
            sum += window[0x6] * b0[0x6];
            sum += window[0x8] * b0[0x8];
            sum += window[0xA] * b0[0xA];
            sum += window[0xC] * b0[0xC];
            sum += window[0xE] * b0[0xE];
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
#if 0
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
#endif
            b0 -= 0x40, window -= 0x80;
        }
        window += bo1 << 1;

        for (j = 3; j; j--, b0 -= 0x50, window -= 0x70) {
            real sum;

            sum = -*(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;
            sum -= *(--window) * *b0++;

            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
#if 0
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
            WRITE_SAMPLE(samples, sum, clip);
            samples += step;
#endif
        }
    }

    *pnt += 32;

    return clip;
}

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