layer1.c

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/*
    layer1.c: the layer 1 decoder

    copyright 1995-2009 by the mpg123 project - free software under the terms of the LGPL 2.1
    see COPYING and AUTHORS files in distribution or http://mpg123.org
    initially written by Michael Hipp

    may have a few bugs after last optimization ... 
*/

#include "mpg123lib_intern.h"
#include "getbits.h"
#include "debug.h"

/*
    Allocation value is not allowed to be 15. Initially, libmad showed me the
    error that mpg123 used to ignore. Then, I found a quote on that in
    Shlien, S. (1994): Guide to MPEG-1 Audio Standard. 
    IEEE Transactions on Broadcasting 40, 4

    "To avoid conflicts with the synchronization code, code '1111' is defined
    to be illegal."
*/
static int check_balloc(mpg123_handle *fr, unsigned int *balloc, unsigned int *end)
{
    unsigned int *ba;
    for(ba=balloc; ba != end; ++ba)
    if(*ba == 15)
    {
        if(NOQUIET) error("Illegal bit allocation value.");
        return -1;
    }

    return 0;
}

static int I_step_one(unsigned int balloc[], unsigned int scale_index[2][SBLIMIT],mpg123_handle *fr)
{
    unsigned int *ba=balloc;
    unsigned int *sca = (unsigned int *) scale_index;

    if(fr->stereo == 2)
    {
        int i;
        int jsbound = fr->jsbound;
        for(i=0;i<jsbound;i++)
        {
            *ba++ = getbits(fr, 4);
            *ba++ = getbits(fr, 4);
        }
        for(i=jsbound;i<SBLIMIT;i++) *ba++ = getbits(fr, 4);

        if(check_balloc(fr, balloc, ba)) return -1;

        ba = balloc;

        for(i=0;i<jsbound;i++)
        {
            if ((*ba++))
                *sca++ = getbits(fr, 6);
            if ((*ba++))
                *sca++ = getbits(fr, 6);
        }
        for (i=jsbound;i<SBLIMIT;i++)
        if((*ba++))
        {
            *sca++ =  getbits(fr, 6);
            *sca++ =  getbits(fr, 6);
        }
    }
    else
    {
        int i;
        for(i=0;i<SBLIMIT;i++) *ba++ = getbits(fr, 4);

        if(check_balloc(fr, balloc, ba)) return -1;

        ba = balloc;
        for (i=0;i<SBLIMIT;i++)
        if ((*ba++))
        *sca++ = getbits(fr, 6);
    }

    return 0;
}

/* Something sane in place of undefined (-1)<<n. Well, not really. */
#define MINUS_SHIFT(n) ( (int)(((unsigned int)-1)<<(n)) )

static void I_step_two(real fraction[2][SBLIMIT],unsigned int balloc[2*SBLIMIT], unsigned int scale_index[2][SBLIMIT],mpg123_handle *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 == 2)
    {
        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++ = getbits(fr, n+1);

            if((n = *ba++)) *sample++ = getbits(fr, n+1);
        }
        for(i=jsbound;i<SBLIMIT;i++) 
        if((n = *ba++))
        *sample++ = getbits(fr, n+1);

        ba = balloc;
        for(sample=smpb,i=0;i<jsbound;i++)
        {
            if((n=*ba++))
            *f0++ = REAL_MUL_SCALE_LAYER12(DOUBLE_TO_REAL_15(MINUS_SHIFT(n) + (*sample++) + 1), fr->muls[n+1][*sca++]);
            else *f0++ = DOUBLE_TO_REAL(0.0);

            if((n=*ba++))
            *f1++ = REAL_MUL_SCALE_LAYER12(DOUBLE_TO_REAL_15(MINUS_SHIFT(n) + (*sample++) + 1), fr->muls[n+1][*sca++]);
            else *f1++ = DOUBLE_TO_REAL(0.0);
        }
        for(i=jsbound;i<SBLIMIT;i++)
        {
            if((n=*ba++))
            {
                real samp = DOUBLE_TO_REAL_15(MINUS_SHIFT(n) + (*sample++) + 1);
                *f0++ = REAL_MUL_SCALE_LAYER12(samp, fr->muls[n+1][*sca++]);
                *f1++ = REAL_MUL_SCALE_LAYER12(samp, fr->muls[n+1][*sca++]);
            }
            else *f0++ = *f1++ = DOUBLE_TO_REAL(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++ = getbits(fr, n+1);

        ba = balloc;
        for(sample=smpb,i=0;i<SBLIMIT;i++)
        {
            if((n=*ba++))
            *f0++ = REAL_MUL_SCALE_LAYER12(DOUBLE_TO_REAL_15(MINUS_SHIFT(n) + (*sample++) + 1), fr->muls[n+1][*sca++]);
            else *f0++ = DOUBLE_TO_REAL(0.0);
        }
        for(i=fr->down_sample_sblimit;i<32;i++)
        fraction[0][i] = DOUBLE_TO_REAL(0.0);
    }
}

int do_layer1(mpg123_handle *fr)
{
    int clip=0;
    int i,stereo = fr->stereo;
    unsigned int balloc[2*SBLIMIT];
    unsigned int scale_index[2][SBLIMIT];
    real (*fraction)[SBLIMIT] = fr->layer1.fraction; /* 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 == SINGLE_MIX) /* I don't see mixing handled here */
    single = SINGLE_LEFT;

    if(I_step_one(balloc,scale_index,fr))
    {
        if(NOQUIET) error("Aborting layer I decoding after step one.\n");
        return clip;
    }

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

        if(single != SINGLE_STEREO)
        clip += (fr->synth_mono)(fraction[single], fr);
        else
        clip += (fr->synth_stereo)(fraction[0], fraction[1], fr);
    }

    return clip;
}