CU Amiga Super CD-ROM 23/CU Amiga - Super CD-ROM 23 (June 1998).iso/CUCD/Sound/PreludeAMP/src/layer3.c

C/C++ Source or Header | 1997-08-18 | 4.6 KB | 194 lines

/* this file is a part of amp software, (C) tomislav uzelac 1996,1997
*/

/* layer3.c  layer3 audio decoding
 *
 * Created by: tomislav uzelac  Mar  1 97
 * Last modified by:
 */
#include "amp.h"
#include "audio.h"
#include "dump.h"
#include "getbits.h"
#include "getdata.h"
#include "huffman.h"
#include "misc2.h"
#include "rtbuf.h"
#include "transform.h"

#define LAYER3
#include "layer3.h"

/* this function decodes one layer3 audio frame, except for the header decoding
 * which is done in main() [audio.c]. returns 0 if everything is ok.
 */
int layer3_frame(struct AUDIO_HEADER *header,int cnt)
{
static struct SIDE_INFO info;

int gr,ch,sb,i;
int mean_frame_size,bitrate,fs,hsize,ssize;

/* we need these later, hsize is the size of header+side_info
*/
    if (header->ID)
        if (header->mode==3) {
            nch=1;
            hsize=21;
        } else {
            nch=2;
            hsize=36;
        }
    else
        if (header->mode==3) {
            nch=1;
            hsize=13;
        } else {
            nch=2;
            hsize=21;
        }

/* crc increases hsize by 2
*/
    if (header->protection_bit==0) hsize+=2;


/* read layer3 specific side_info
*/
        getinfo(header,&info);


/* MPEG2 only has one granule
*/
    bitrate=t_bitrate[header->ID][3-header->layer][header->bitrate_index];
    fs=t_sampling_frequency[header->ID][header->sampling_frequency];
        if (header->ID) mean_frame_size=144000*bitrate/fs;
        else mean_frame_size=72000*bitrate/fs;


/* check if mdb is too big for the first few frames. this means that
 * a part of the stream could be missing. We must still fill the buffer
 *
 * don't forget to (re)initialise bclean_bytes to 0, and f_bdirty to FALSE!!!
 */
    if (f_bdirty)
        if (info.main_data_begin > bclean_bytes) {
            fillbfr(mean_frame_size + header->padding_bit - hsize);
            bclean_bytes+=mean_frame_size + header->padding_bit - hsize;
            /* warn(" frame %d discarded, incomplete main_data\n",cnt); */
            return 0;
        } else {
            /* re-initialise */
            f_bdirty=FALSE;
            bclean_bytes=0;
        }

/* now update the data 'pointer' (counting in bits) according to
 * the main_data_begin information
 */
        data = 8 * ((append - info.main_data_begin) & (BUFFER_SIZE-1));


/* read into the buffer all bytes up to the start of next header
*/
        fillbfr(mean_frame_size + header->padding_bit - hsize);


/* these two should go away
*/
    t_l=&t_b8_l[header->ID][header->sampling_frequency][0];
    t_s=&t_b8_s[header->ID][header->sampling_frequency][0];

/* debug/dump stuff
*/
    if (A_DUMP_BINARY) dump((int *)info.part2_3_length);

/* decode the scalefactors and huffman data
 * this part needs to be enhanced for error robustness
 */
    for (gr=0;gr < ((header->ID) ? 2 : 1);gr++) {
        for (ch=0;ch<nch;ch++) {
            ssize=decode_scalefactors(&info,header,gr,ch);
            decode_huffman_data(&info,gr,ch,ssize);
        }

    /* requantization, stereo processing, reordering(shortbl)
    */

        if (A_DOWNMIX && nch==2) requantize_downmix(gr,&info,header);
        else
            if (header->mode!=1 || (header->mode==1 && header->mode_extension==0))
                for (ch=0;ch<nch;ch++) requantize_mono(gr,ch,&info,header);
            else requantize_ms(gr,&info,header);

    /* just which window?
    */

    /* this is a very temporary, very ugly hack.
    */
        if (A_DOWNMIX) nch=1;

        for (ch=0; ch < (A_DOWNMIX ? 1:nch) ;ch++) {
        int win_type; /* same as in the standard, long=0, start=1 ,.... */
        int window_switching_flag = info.window_switching_flag[gr][ch];
        int block_type = info.block_type[gr][ch];
        int mixed_block_flag = info.mixed_block_flag[gr][ch];

        /* antialiasing butterflies
        */
            if (!(window_switching_flag &&
                  block_type==2))
                                alias_reduction(ch);

            if (window_switching_flag &&
                block_type==2 &&
                mixed_block_flag)
                win_type=0;
            else
                    if (!window_switching_flag) win_type=0;
                else win_type=block_type;

        /* imdct ...
        */
            for (sb=0;sb<2;sb++)
                imdct(win_type,sb,ch);

            if (window_switching_flag &&
                block_type==2 &&
                mixed_block_flag)
                win_type=2;

        /* no_of_imdcts tells us how many subbands from the top are all zero
         * it is set by the requantize functions in misc2.c
         */
            for (sb=2;sb<no_of_imdcts[ch];sb++)
                imdct(win_type,sb,ch);

            for (;sb<32;sb++)
                for (i=0;i<18;i++) {
                    res[sb][i]=s[ch][sb][i];
                    s[ch][sb][i]=0.0f;
                }

        /* polyphase filterbank
        */
            /* if (nch == 2) this was a bug, tomislav */
                    for (i=0;i<18;i++)
                        poly(ch,i);
        }

        printout();

        /* this is part2 of a particularily ugly hack. this should vanish as soon as nch isn't
           a global variable anymore
        */
        if (A_DOWNMIX && header->mode!=3) nch=2;

    }    /*  for (gr... */

    /* return status: 0 for ok, errors will be added
    */
    return 0;
}