decode_2to1.c

xmms-1.2.10.tar.gz学习使用的就下吧

/*
 * Mpeg Layer-1,2,3 audio decoder
 * ------------------------------
 * copyright (c) 1995 by Michael Hipp, All rights reserved. See also 'README'
 * version for slower machines .. decodes only every second sample
 * sounds like 24000,22050 or 16000 kHz .. (depending on original sample freq.)
 *
 */

#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_2to1_8bit(real * bandPtr, int channel, unsigned char *samples, int *pnt)
{
	short samples_tmp[32];
	short *tmp1 = samples_tmp + channel;
	int i, ret;
	int pnt1 = 0;

	ret = mpg123_synth_2to1(bandPtr, channel, (unsigned char *) samples_tmp, &pnt1);
	samples += channel + *pnt;

	for (i = 0; i < 16; i++)
	{
		*samples = (*tmp1 >> 8) ^ 128;
		samples += 2;
		tmp1 += 2;
	}
	*pnt += 32;

	return ret;
}

int mpg123_synth_2to1_8bit_mono(real * bandPtr, unsigned char *samples, int *pnt)
{
	short samples_tmp[32];
	short *tmp1 = samples_tmp;
	int i, ret;
	int pnt1 = 0;

	ret = mpg123_synth_2to1(bandPtr, 0, (unsigned char *) samples_tmp, &pnt1);
	samples += *pnt;

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

	return ret;
}

#if 0
int mpg123_synth_2to1_8bit_mono2stereo(real * bandPtr, unsigned char *samples, int *pnt)
{
	short samples_tmp[32];
	short *tmp1 = samples_tmp;
	int i, ret;
	int pnt1 = 0;

	ret = mpg123_synth_2to1(bandPtr, 0, (unsigned char *) samples_tmp, &pnt1);
	samples += *pnt;

	for (i = 0; i < 16; i++)
	{
		*samples++ = (*tmp1 >> 8) ^ 128;
		*samples++ = (*tmp1 >> 8) ^ 128;
		tmp1 += 2;
	}
	*pnt += 32;

	return ret;
}
#endif

int mpg123_synth_2to1_mono(real * bandPtr, unsigned char *samples, int *pnt)
{
	short samples_tmp[32];
	short *tmp1 = samples_tmp;
	int i, ret;
	int pnt1 = 0;

	ret = mpg123_synth_2to1(bandPtr, 0, (unsigned char *) samples_tmp, &pnt1);
	samples += *pnt;

	for (i = 0; i < 16; i++)
	{
		*((short *) samples) = *tmp1;
		samples += 2;
		tmp1 += 2;
	}
	*pnt += 32;

	return ret;
}

#if 0
int mpg123_synth_2to1_mono2stereo(real * bandPtr, unsigned char *samples, int *pnt)
{
	int i, ret;

	ret = mpg123_synth_2to1(bandPtr, 0, samples, pnt);
	samples = samples + *pnt - 64;

	for (i = 0; i < 16; i++)
	{
		((short *) samples)[1] = ((short *) samples)[0];
		samples += 4;
	}

	return ret;
}
#endif

int mpg123_synth_2to1(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 = 8; j; j--, b0 += 0x10, window += 0x30)
		{
			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;
#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;
#endif
			b0 -= 0x20, window -= 0x40;
		}
		window += bo1 << 1;

		for (j = 7; j; j--, b0 -= 0x30, window -= 0x30)
		{
			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;
#endif
		}
	}

	*pnt += 64;

	return clip;
}