mpeglayer1.cc

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/* MPEG/WAVE Sound library

   (C) 1997 by Jung woo-jae */

// Mpeglayer1.cc
// It's for MPEG Layer 1

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "mpegsound.h"

#ifndef FIXED_POINT
#define X( x )  (x)
#else
#define X( x )  {FL2FIX( x, FIXED_POINT_FRACBITS )}
#endif


// Tables for layer 1

static const REAL factortable[15] = {
    X(0.0),
    X((1.0 / 2.0) * (4.0 / 3.0)), X((1.0 / 4.0) * (8.0 / 7.0)),
    X((1.0 / 8.0) * (16.0 / 15.0)), X((1.0 / 16.0) * (32.0 / 31.0)),
    X((1.0 / 32.0) * (64.0 / 63.0)), X((1.0 / 64.0) * (128.0 / 127.0)),
    X((1.0 / 128.0) * (256.0 / 255.0)), X((1.0 / 256.0) * (512.0 / 511.0)),
    X((1.0 / 512.0) * (1024.0 / 1023.0)),
	X((1.0 / 1024.0) * (2048.0 / 2047.0)),
    X((1.0 / 2048.0) * (4096.0 / 4095.0)),
	X((1.0 / 4096.0) * (8192.0 / 8191.0)),
    X((1.0 / 8192.0) * (16384.0 / 16383.0)),
	X((1.0 / 16384.0) * (32768.0 / 32767.0))
};

static const REAL offsettable[15] = {
    X(0.0),
    X(((1.0 / 2.0) - 1.0) * (4.0 / 3.0)),
	X(((1.0 / 4.0) - 1.0) * (8.0 / 7.0)),
    X(((1.0 / 8.0) - 1.0) * (16.0 / 15.0)),
	X(((1.0 / 16.0) - 1.0) * (32.0 / 31.0)),
    X(((1.0 / 32.0) - 1.0) * (64.0 / 63.0)),
	X(((1.0 / 64.0) - 1.0) * (128.0 / 127.0)),
    X(((1.0 / 128.0) - 1.0) * (256.0 / 255.0)),
	X(((1.0 / 256.0) - 1.0) * (512.0 / 511.0)),
    X(((1.0 / 512.0) - 1.0) * (1024.0 / 1023.0)),
	X(((1.0 / 1024.0) - 1.0) * (2048.0 / 2047.0)),
    X(((1.0 / 2048.0) - 1.0) * (4096.0 / 4095.0)),
	X(((1.0 / 4096.0) - 1.0) * (8192.0 / 8191.0)),
    X(((1.0 / 8192.0) - 1.0) * (16384.0 / 16383.0)),
	X(((1.0 / 16384.0) - 1.0) * (32768.0 / 32767.0))
};


// Mpeg layer 1

void
Mpegtoraw::extractlayer1(void)
{
    REAL fraction[MAXCHANNEL][MAXSUBBAND];
    REAL scalefactor[MAXCHANNEL][MAXSUBBAND];

    int bitalloc[MAXCHANNEL][MAXSUBBAND], sample[MAXCHANNEL][MAXSUBBAND];

    register int i, j;
    int s = stereobound, l;


// Bitalloc
    for (i = 0; i < s; i++) {
	bitalloc[LS][i] = getbits(4);
	bitalloc[RS][i] = getbits(4);
    }
    for (; i < MAXSUBBAND; i++)
	bitalloc[LS][i] = bitalloc[RS][i] = getbits(4);

// Scale index
    if (inputstereo)
	for (i = 0; i < MAXSUBBAND; i++) {
	    if (bitalloc[LS][i])
		scalefactor[LS][i] = scalefactorstable[getbits(6)];
	    if (bitalloc[RS][i])
		scalefactor[RS][i] = scalefactorstable[getbits(6)];
    } else
	for (i = 0; i < MAXSUBBAND; i++)
	    if (bitalloc[LS][i])
		scalefactor[LS][i] = scalefactorstable[getbits(6)];

    for (l = 0; l < SCALEBLOCK; l++) {
	// Sample
	for (i = 0; i < s; i++) {
	    if ((j = bitalloc[LS][i]))
		sample[LS][i] = getbits(j + 1);
	    if ((j = bitalloc[RS][i]))
		sample[RS][i] = getbits(j + 1);
	}
	for (; i < MAXSUBBAND; i++)
	    if ((j = bitalloc[LS][i]))
		sample[LS][i] = sample[RS][i] = getbits(j + 1);


	// Fraction
	if (outputstereo)
	    for (i = 0; i < MAXSUBBAND; i++) {
		if ((j = bitalloc[LS][i]))
		    fraction[LS][i] =
			(sample[LS][i] * factortable[j] + offsettable[j])
			* scalefactor[LS][i];
		else
		    fraction[LS][i] = 0.0;
		if ((j = bitalloc[RS][i]))
		    fraction[RS][i] =
			(sample[RS][i] * factortable[j] + offsettable[j])
			* scalefactor[RS][i];
		else
		    fraction[RS][i] = 0.0;
	} else
	    for (i = 0; i < MAXSUBBAND; i++)
		if ((j = bitalloc[LS][i]))
		    fraction[LS][i] =
			(sample[LS][i] * factortable[j] + offsettable[j])
			* scalefactor[LS][i];
		else
		    fraction[LS][i] = 0.0;

	subbandsynthesis(fraction[LS], fraction[RS]);
    }
}