pns.c

AAC音频解码算法程序

/************************* MPEG-4 AAC Audio Decoder **************************
 *                                                                           *
"This software module was originally developed by 
AT&T, Dolby Laboratories, Fraunhofer Gesellschaft IIS in the course of 
development of the MPEG-2 AAC/MPEG-4 Audio standard ISO/IEC 13818-7, 
14496-1,2 and 3. This software module is an implementation of a part of one or more 
MPEG-2 AAC/MPEG-4 Audio tools as specified by the MPEG-2 AAC/MPEG-4 
Audio standard. ISO/IEC  gives users of the MPEG-2 AAC/MPEG-4 Audio 
standards free license to this software module or modifications thereof for use in 
hardware or software products claiming conformance to the MPEG-2 AAC/MPEG-4
Audio  standards. Those intending to use this software module in hardware or 
software products are advised that this use may infringe existing patents. 
The original developer of this software module and his/her company, the subsequent 
editors and their companies, and ISO/IEC have no liability for use of this software 
module or modifications thereof in an implementation. Copyright is not released for 
non MPEG-2 AAC/MPEG-4 Audio conforming products. The original developer
retains full right to use the code for his/her  own purpose, assign or donate the 
code to a third party and to inhibit third party from using the code for non 
MPEG-2 AAC/MPEG-4 Audio conforming products. This copyright notice must
be included in all copies or derivative works." 
Copyright(c)1996.
 *                                                                           *
 ****************************************************************************/
#include "all.h"


#define MEAN_NRG 1.5625e+18      /* Theory: (2^31)^2 / 3 = 1.537228e+18 */

long
random2( long *seed )
{
#if 0
	*seed = (*seed * 1103515245L) + 12345L;    /* VM */
#else
	*seed = (1664525L * *seed) + 1013904223L;  /* Numerical recipes */
#endif
	return(long)(*seed);
}


void
gen_rand_vector( float *spec, int size, long *state )  
/* Noise generator, generating vector with unity energy */
{
    int i;
    int mode = 2;

    if (mode==0)  {       /* Dummy 0:  zero vector */
		for (i=0; i<size; i++)
			spec[i] = 0.0;
    } else if (mode==1)  {  /* Dummy 1:  zero vector with one spectral component */
		for (i=0; i<size; i++)
			spec[i] = 0.0;
		spec[3] = 1.0;
    } else if (mode==2) {    /* Mode 2:  real random number generator */
		float s, norm, nrg= 0.0;

		norm = 1.0f / (float)sqrt( size * MEAN_NRG );

		for (i=0; i<size; i++) {
			spec[i] = (float)(random2( state ) * norm);   
			nrg += spec[i] * spec[i];
		}

		s = 1.0f / (float)sqrt( nrg );
		for (i=0; i<size; i++)
			spec[i] *= s;      
    }
}



/*
 * if (noise correlated) {
 *   restore saved left channel random generator state
 *   generate random values
 * } else {
 *   save current random generator state
 *   generate random values
 * }
 * scale according to scalefactor
 *
 * Important: needs to be called left channel, then right channel
 *            for each channel pair
 */

void pns(MC_Info *mip, Info *info, int widx, int ch,
		 byte *group, byte *cb_map, short *factors, 
		 int *lpflag, Float *coef[Chans] )
{
    Ch_Info *cip = &mip->ch_info[ch];
    Float   *spec, *fp, scale;
    int     cb, corr_flag, sfb, n, nn, b, bb, nband;
    short   *band;
    long    *nsp;

    static long    cur_noise_state;
    static long    noise_state_save[ MAXBANDS ];
    static int     lp_store[ MAXBANDS ];


    /* store original predictor flags when left channel of a channel pair */
    if ((cip->cpe  &&  cip->ch_is_left  &&  info->islong))
		for (sfb=0; sfb<info->sfb_per_sbk[0]; sfb++)
			lp_store[sfb+1] = lpflag[sfb+1];

	/* restore original predictor flags when right channel of a channel pair */
	if ((cip->cpe  &&  !cip->ch_is_left  &&  info->islong))
		for (sfb=0; sfb<info->sfb_per_sbk[0]; sfb++)
			lpflag[sfb+1] = lp_store[sfb+1];

	spec = coef[ ch ];
	nsp = noise_state_save;

    /* PNS goes by group */
    bb = 0;
    for (b = 0; b < info->nsbk; ) {
		nband = info->sfb_per_sbk[b];
		band = info->sbk_sfb_top[b];

		b = *group++;		/* b = index of last sbk in group */
		for (; bb < b; bb++) {	/* bb = sbk index */
			n = 0;
			for (sfb = 0; sfb < nband; sfb++){
				nn = band[sfb];	/* band is offset table, nn is last coef in band */
				cb = cb_map[sfb];
                if (cb == NOISE_HCB  ||  cb == NOISE_HCB+100) {
                    /* found noise  substitution code book */

					/* disable prediction (only important for long blocks) */
					if (info->islong)  lpflag[1+sfb] = 0;

                    /* determine left/right correlation */
					corr_flag = (cb != NOISE_HCB);

                    /* reconstruct noise substituted values */
                    /* generate random noise */
                    fp = spec + n;
                    if (corr_flag)  {
                        /* Start with stored state */
                        gen_rand_vector( fp, nn-n, nsp+sfb );
                    } else {
                        /* Store current state and go */
                        nsp[sfb] = cur_noise_state;
                        gen_rand_vector( fp, nn-n, &cur_noise_state );
                    }

                    /* scale to target energy */
                    scale = (float)pow( 2.0, 0.25*(factors[sfb]) );
					for (; n < nn; n++) {	/* n is coef index */
                        *fp++ *= scale;
					}
				}
				n = nn;
			}
            spec += info->bins_per_sbk[bb];
			factors += nband;
		}
        nsp += info->sfb_per_sbk[bb-1];
		cb_map += info->sfb_per_sbk[bb-1];
    }
}