decode.c

mepg 1 layer3软解码源代码,实现了对MP3文件的软件解码

/**********************************************************************
Copyright (c) 1991 MPEG/audio software simulation group, All Rights Reserved
decode.c
**********************************************************************/
/**********************************************************************
 * MPEG/audio coding/decoding software, work in progress              *
 *   NOT for public distribution until verified and approved by the   *
 *   MPEG/audio committee.  For further information, please contact   *
 *   Chad Fogg email: <[e-mail]>                               *
 *                                                                    *
 * VERSION 4.1                                                        *
 *   changes made since last update:                                  *
 *   date   programmers         comment                               *
 * 2/25/91  Douglas Wong,       start of version 1.0 records          *
 *          Davis Pan                                                 *
 * 3/06/91  Douglas Wong        rename: setup.h to dedef.h            *
 *                                      dfilter to defilter           *
 *                                      dwindow to dewindow           *
 *                              integrated "quantizer", "scalefactor" *
 *                              combined window_samples routine into  *
 *                              filter samples                        *
 * 3/31/91  Bill Aspromonte     replaced read_filter by               *
 *                              create_syn_filter and introduced a    *
 *                              new Sub-Band Synthesis routine called *
 *                              SubBandSynthesis()                    *
 * 5/10/91  Vish (PRISM)        Ported to Macintosh and Unix.         *
 *                              Changed "out_fifo()" so that last     *
 *                              unfilled block is also written out.   *
 *                              "create_syn_filter()" was modified so *
 *                              that calculation precision is same as *
 *                              in specification tables.              *
 *                              Changed "decode_scale()" to reflect   *
 *                              specifications.                       *
 *                              Removed all routines used by          *
 *                              "synchronize_buffer()".  This is now  *
 *                              replaced by "seek_sync()".            *
 *                              Incorporated Jean-Georges Fritsch's   *
 *                              "bitstream.c" package.                *
 *                              Deleted "reconstruct_sample()".       *
 * 27jun91  dpwe (Aware)        Passed outFile and &sampFrames as     *
 *                              args to out_fifo() - were global.     *
 *                              Moved "alloc_*" reader to common.c.   *
 *                              alloc, sblimit, stereo passed via new *
 *                              'frame_params struct (were globals).  *
 *                              Added JOINT STEREO decoding, lyrs I&II*
 *                              Affects: decode_bitalloc,buffer_samps *
 *                              Plus a few other cleanups.            *
 * 6/10/91   Earle Jennings     conditional expansion added in        *
 *                              II_dequantize_sample to handle range  *
 *                              problems in MSDOS version             *
 * 8/8/91    Jens Spille        Change for MS-C6.00                   *
 *10/1/91    S.I. Sudharsanan,  Ported to IBM AIX platform.           *
 *           Don H. Lee,                                              *
 *           Peter W. Farrett                                         *
 *10/3/91    Don H. Lee         implemented CRC-16 error protection   *
 *                              newly introduced functions are        *
 *                              buffer_CRC and recover_CRC_error.     *
 * 2/11/92  W. Joseph Carter    Ported new code to Macintosh.  Most   *
 *                              important fixes involved changing     *
 *                              16-bit ints to long or unsigned in    *
 *                              bit alloc routines for quant of 65535 *
 *                              and passing proper function args.     *
 *                              Removed "Other Joint Stereo" option   *
 *                              and made bitrate be total channel     *
 *                              bitrate, irrespective of the mode.    *
 *                              Fixed many small bugs & reorganized.  *
 * 7/27/92  Juan Pineda         Bug fix in SubBandSynthesis()         *
 *--------------------------------------------------------------------*
 * 6/14/92  Juan Pineda         Layer III decoding routines added.    *
 *          Amit Gulati         Follows CD 3-11172 rev2.  Contains    *
 *                              hacks deal with evolving available    *
 *                              layerIII bitstreams.  Some (minor)    *
 *                              modification of prior LI&II code.     *
 * 10/25/92 Amit Gulati         Updated layerIII routines. Added code *
 *                              for subblock_gain, switched block     *
 *                              modes, stereo pre-processing.         *
 *                              Corrected sign bits for huffman       *
 *                              decoding of quadruples region and     *
 *                              adjusted gain factor in III_dequant.  *
 * 11/21/92 Amit Gulati         Several layerIII bugs fixed.          *
 * 12/15/92 Amit Gulati         Corrected reordering (indexing)       *
 *          Stan Searing        within IMDCT routine.                 *
 *  8/24/93 Masahiro Iwadare    Included IS modification in Layer III.*
 *                              Changed for 1 pass decoding.          *
 *  9/07/93 Toshiyuki Ishino    Integrated Layer III with Ver 3.9.    *
 *--------------------------------------------------------------------*
 * 11/20/93 Masahiro Iwadare    Integrated Layer III with Ver 4.0.    *
 *--------------------------------------------------------------------*
 *  7/14/94 Juergen Koller      Bug fixes in Layer III code           *
 **********************************************************************/

#include        "common.h"
#include        "decoder.h"
#include        "huffman.h"

/***************************************************************
/*
/* This module contains the core of the decoder ie all the
/* computational routines. (Layer I and II only)
/* Functions are common to both layer unless
/* otherwise specified.
/*
/***************************************************************/

/*****************************************************************
/*
/* The following routines decode the system information
/*
/****************************************************************/

/************ Layer I, Layer II & Layer III ******************/

void decode_info(bs, fr_ps)
Bit_stream_struc *bs;
frame_params *fr_ps;
{
    layer *hdr = fr_ps->header;

    hdr->version = get1bit(bs);
    hdr->lay = 4-getbits(bs,2);
    hdr->error_protection = !get1bit(bs); /* error protect. TRUE/FALSE */
    hdr->bitrate_index = getbits(bs,4);
    hdr->sampling_frequency = getbits(bs,2);
    hdr->padding = get1bit(bs);
    hdr->extension = get1bit(bs);
    hdr->mode = getbits(bs,2);
    hdr->mode_ext = getbits(bs,2);
    hdr->copyright = get1bit(bs);
    hdr->original = get1bit(bs);
    hdr->emphasis = getbits(bs,2);
}

/*******************************************************************
/*
/* The bit allocation information is decoded. Layer I
/* has 4 bit per subband whereas Layer II is Ws and bit rate
/* dependent.
/*
/********************************************************************/

/**************************** Layer II *************/

void II_decode_bitalloc(bs, bit_alloc, fr_ps)
Bit_stream_struc *bs;
unsigned int bit_alloc[2][SBLIMIT];
frame_params *fr_ps;
{
    int i,j;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
    int jsbound = fr_ps->jsbound;
    al_table *alloc = fr_ps->alloc;

    for (i=0;i<jsbound;i++) for (j=0;j<stereo;j++)
        bit_alloc[j][i] = (char) getbits(bs,(*alloc)[i][0].bits);

    for (i=jsbound;i<sblimit;i++) /* expand to 2 channels */
        bit_alloc[0][i] = bit_alloc[1][i] =
            (char) getbits(bs,(*alloc)[i][0].bits);

    for (i=sblimit;i<SBLIMIT;i++) for (j=0;j<stereo;j++)
        bit_alloc[j][i] = 0;
}

/**************************** Layer I *************/

void I_decode_bitalloc(bs, bit_alloc, fr_ps)
Bit_stream_struc *bs;
unsigned int bit_alloc[2][SBLIMIT];
frame_params *fr_ps;
{
    int i,j;
    int stereo  = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
    int jsbound = fr_ps->jsbound;
    int b;

    for (i=0;i<jsbound;i++) for (j=0;j<stereo;j++)
        bit_alloc[j][i] = getbits(bs,4);
    for (i=jsbound;i<SBLIMIT;i++) {
        b = getbits(bs,4);
        for (j=0;j<stereo;j++)
            bit_alloc[j][i] = b;
    }
}

/*****************************************************************
/*
/* The following two functions implement the layer I and II
/* format of scale factor extraction. Layer I involves reading
/* 6 bit per subband as scale factor. Layer II requires reading
/* first the scfsi which in turn indicate the number of scale factors
/* transmitted.
/*    Layer I : I_decode_scale
/*   Layer II : II_decode_scale
/*
/****************************************************************/

/************************** Layer I stuff ************************/

void I_decode_scale(bs, bit_alloc, scale_index, fr_ps)
Bit_stream_struc *bs;
unsigned int bit_alloc[2][SBLIMIT], scale_index[2][3][SBLIMIT];
frame_params *fr_ps;
{
    int i,j;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;

    for (i=0;i<SBLIMIT;i++) for (j=0;j<stereo;j++)
        if (!bit_alloc[j][i])
            scale_index[j][0][i] = SCALE_RANGE-1;
        else                    /* 6 bit per scale factor */
            scale_index[j][0][i] =  getbits(bs,6);

}

/*************************** Layer II stuff ***************************/

void II_decode_scale(bs,scfsi, bit_alloc,scale_index, fr_ps)
Bit_stream_struc *bs;
unsigned int scfsi[2][SBLIMIT], bit_alloc[2][SBLIMIT],
             scale_index[2][3][SBLIMIT];
frame_params *fr_ps;
{
    int i,j;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
   
    for (i=0;i<sblimit;i++) for (j=0;j<stereo;j++) /* 2 bit scfsi */
        if (bit_alloc[j][i]) scfsi[j][i] = (char) getbits(bs,2);
    for (i=sblimit;i<SBLIMIT;i++) for (j=0;j<stereo;j++)   
        scfsi[j][i] = 0;

    for (i=0;i<sblimit;i++) for (j=0;j<stereo;j++) {
        if (bit_alloc[j][i])   
            switch (scfsi[j][i]) {
                /* all three scale factors transmitted */
             case 0 : scale_index[j][0][i] = getbits(bs,6);
                scale_index[j][1][i] = getbits(bs,6);
                scale_index[j][2][i] = getbits(bs,6);
                break;
                /* scale factor 1 & 3 transmitted */
             case 1 : scale_index[j][0][i] =
                 scale_index[j][1][i] = getbits(bs,6);
                scale_index[j][2][i] = getbits(bs,6);
                break;
                /* scale factor 1 & 2 transmitted */
             case 3 : scale_index[j][0][i] = getbits(bs,6);
                scale_index[j][1][i] =
                    scale_index[j][2][i] =  getbits(bs,6);
                break;
                /* only one scale factor transmitted */
             case 2 : scale_index[j][0][i] =
                 scale_index[j][1][i] =
                     scale_index[j][2][i] = getbits(bs,6);
                break;
                default : break;
            }
        else {
            scale_index[j][0][i] = scale_index[j][1][i] =
                scale_index[j][2][i] = SCALE_RANGE-1;
        }
    }
    for (i=sblimit;i<SBLIMIT;i++) for (j=0;j<stereo;j++) {
        scale_index[j][0][i] = scale_index[j][1][i] =
            scale_index[j][2][i] = SCALE_RANGE-1;
    }
}

/**************************************************************
/*
/*   The following two routines take care of reading the
/* compressed sample from the bit stream for both layer 1 and
/* layer 2. For layer 1, read the number of bits as indicated
/* by the bit_alloc information. For layer 2, if grouping is
/* indicated for a particular subband, then the sample size has
/* to be read from the bits_group and the merged samples has
/* to be decompose into the three distinct samples. Otherwise,
/* it is the same for as layer one.
/*
/**************************************************************/

/******************************* Layer I stuff ******************/

void I_buffer_sample(bs, sample, bit_alloc, fr_ps)
unsigned int FAR sample[2][3][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
Bit_stream_struc *bs;
frame_params *fr_ps;
{
    int i,j,k;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
    int jsbound = fr_ps->jsbound;
    unsigned int s;

    for (i=0;i<jsbound;i++) for (j=0;j<stereo;j++)
        if ( (k = bit_alloc[j][i]) == 0)
            sample[j][0][i] = 0;
        else 
            sample[j][0][i] = (unsigned int) getbits(bs,k+1);
    for (i=jsbound;i<SBLIMIT;i++) {
        if ( (k = bit_alloc[0][i]) == 0)
            s = 0;
        else 
            s = (unsigned int)getbits(bs,k+1);
        for (j=0;j<stereo;j++)
            sample[j][0][i]    = s;
    }
}

/*************************** Layer II stuff ************************/

void II_buffer_sample(bs,sample,bit_alloc,fr_ps)
unsigned int FAR sample[2][3][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
Bit_stream_struc *bs;
frame_params *fr_ps;
{
    int i,j,k,m;
    int stereo = fr_ps->stereo;
    int sblimit = fr_ps->sblimit;
    int jsbound = fr_ps->jsbound;
    al_table *alloc = fr_ps->alloc;

    for (i=0;i<sblimit;i++) for (j=0;j<((i<jsbound)?stereo:1);j++) {
        if (bit_alloc[j][i]) {
            /* check for grouping in subband */
            if ((*alloc)[i][bit_alloc[j][i]].group==3)
                for (m=0;m<3;m++) {
                    k = (*alloc)[i][bit_alloc[j][i]].bits;
                    sample[j][m][i] = (unsigned int) getbits(bs,k);
                }         
            else {              /* bit_alloc = 3, 5, 9 */
                unsigned int nlevels, c=0;

                nlevels = (*alloc)[i][bit_alloc[j][i]].steps;
                k=(*alloc)[i][bit_alloc[j][i]].bits;
                c = (unsigned int) getbits(bs, k);
                for (k=0;k<3;k++) {
                    sample[j][k][i] = c % nlevels;
                    c /= nlevels;
                }
            }
        }
        else {                  /* for no sample transmitted */
            for (k=0;k<3;k++) sample[j][k][i] = 0;
        }
        if(stereo == 2 && i>= jsbound) /* joint stereo : copy L to R */
            for (k=0;k<3;k++) sample[1][k][i] = sample[0][k][i];
    }
    for (i=sblimit;i<SBLIMIT;i++) for (j=0;j<stereo;j++) for (k=0;k<3;k++)
        sample[j][k][i] = 0;
}      

/**************************************************************
/*
/*   Restore the compressed sample to a factional number.
/*   first complement the MSB of the sample
/*    for layer I :
/*    Use s = (s' + 2^(-nb+1) ) * 2^nb / (2^nb-1)
/*   for Layer II :
/*   Use the formula s = s' * c + d
/*
/**************************************************************/

static double c[17] = { 1.33333333333, 1.60000000000, 1.14285714286,
                        1.77777777777, 1.06666666666, 1.03225806452,
                        1.01587301587, 1.00787401575, 1.00392156863,
                        1.00195694716, 1.00097751711, 1.00048851979,
                        1.00024420024, 1.00012208522, 1.00006103888,
                        1.00003051851, 1.00001525902 };

static double d[17] = { 0.500000000, 0.500000000, 0.250000000, 0.500000000,
                        0.125000000, 0.062500000, 0.031250000, 0.015625000,
                        0.007812500, 0.003906250, 0.001953125, 0.0009765625,
                        0.00048828125, 0.00024414063, 0.00012207031,
                        0.00006103516, 0.00003051758 };

/************************** Layer II stuff ************************/