layer1.c

xmms-1.2.10.tar.gz学习使用的就下吧

/* 
 * 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"
#include "getbits.h"

/* Used by the getbits macros */
static unsigned long rval;

void I_step_one(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)
	{
		int i;
		int jsbound = fr->jsbound;

		for (i = 0; i < jsbound; i++)
		{
			*ba++ = mpg123_getbits(4);
			*ba++ = mpg123_getbits(4);
		}
		for (i = jsbound; i < SBLIMIT; i++)
			*ba++ = mpg123_getbits(4);

		ba = balloc;

		for (i = 0; i < jsbound; i++)
		{
			if ((*ba++))
				*sca++ = mpg123_getbits(6);
			if ((*ba++))
				*sca++ = mpg123_getbits(6);
		}
		for (i = jsbound; i < SBLIMIT; i++)
			if ((*ba++))
			{
				*sca++ = mpg123_getbits(6);
				*sca++ = mpg123_getbits(6);
			}
	}
	else
	{
		int i;

		for (i = 0; i < SBLIMIT; i++)
			*ba++ = mpg123_getbits(4);
		ba = balloc;
		for (i = 0; i < SBLIMIT; i++)
			if ((*ba++))
				*sca++ = mpg123_getbits(6);
	}
}

void I_step_two(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)
	{
		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++ = mpg123_getbits(n + 1);
			if ((n = *ba++))
				*sample++ = mpg123_getbits(n + 1);
		}
		for (i = jsbound; i < SBLIMIT; i++)
			if ((n = *ba++))
				*sample++ = mpg123_getbits(n + 1);

		ba = balloc;
		for (sample = smpb, i = 0; i < jsbound; i++)
		{
			if ((n = *ba++))
				*f0++ = (real) (((-1) << n) + (*sample++) + 1) * mpg123_muls[n + 1][*sca++];
			else
				*f0++ = 0.0;
			if ((n = *ba++))
				*f1++ = (real) (((-1) << n) + (*sample++) + 1) * mpg123_muls[n + 1][*sca++];
			else
				*f1++ = 0.0;
		}
		for (i = jsbound; i < SBLIMIT; i++)
		{
			if ((n = *ba++))
			{
				real samp = (((-1) << n) + (*sample++) + 1);

				*f0++ = samp * mpg123_muls[n + 1][*sca++];
				*f1++ = samp * mpg123_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++ = mpg123_getbits(n + 1);
		ba = balloc;
		for (sample = smpb, i = 0; i < SBLIMIT; i++)
		{
			if ((n = *ba++))
				*f0++ = (real) (((-1) << n) + (*sample++) + 1) * mpg123_muls[n + 1][*sca++];
			else
				*f0++ = 0.0;
		}
		for (i = fr->down_sample_sblimit; i < 32; i++)
			fraction[0][i] = 0.0;
	}
}

int mpg123_do_layer1(struct frame *fr)
{
	int i, stereo = fr->stereo;
	unsigned int balloc[2 * SBLIMIT];
	unsigned int scale_index[2][SBLIMIT];
	real fraction[2][SBLIMIT];
	int single = fr->single;

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

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

	I_step_one(balloc, scale_index, fr);

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

		if (single >= 0)
		{
			(fr->synth_mono) ((real *) fraction[single], mpg123_pcm_sample, &mpg123_pcm_point);
		}
		else
		{
			int p1 = mpg123_pcm_point;

			(fr->synth) ((real *) fraction[0], 0, mpg123_pcm_sample, &p1);
			(fr->synth) ((real *) fraction[1], 1, mpg123_pcm_sample, &mpg123_pcm_point);
		}

		if (mpg123_info->output_audio)
		{

			mpg123_ip.add_vis_pcm(mpg123_ip.output->written_time(), mpg123_cfg.resolution == 16 ? FMT_S16_NE : FMT_U8,
					      mpg123_cfg.channels == 2 ? fr->stereo : 1, mpg123_pcm_point, mpg123_pcm_sample);
			while (mpg123_ip.output->buffer_free() < mpg123_pcm_point && mpg123_info->going && mpg123_info->jump_to_time == -1)
				xmms_usleep(10000);
			if (mpg123_info->going && mpg123_info->jump_to_time == -1)
				mpg123_ip.output->write_audio(mpg123_pcm_sample, mpg123_pcm_point);
		}
		mpg123_pcm_point = 0;
	}

	return 1;
}