www.pudn.com > ampegsrc.zip > SUBS.C

/**********************************************************************
Copyright (c) 1991 MPEG/audio software simulation group, All Rights Reserved
subs.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   *
 *   Davis Pan, 508-493-2241, e-mail: pan@3d.enet.dec.com             *
 *                                                                    *
 * VERSION 3.9                                                        *
 *   changes made since last update:                                  *
 *   date   programmers         comment                               *
 * 2/25/91  Davis Pan           start of version 1.0 records          *
 * 5/10/91  W. Joseph Carter    Ported to Macintosh and Unix.         *
 * 7/10/91  Earle Jennings      Ported to MsDos from Macintosh        *
 *                              Replacement of one float with FLOAT   *
 * 2/11/92  W. Joseph Carter    Added type casting to memset() args.  *
 * 4/27/92  Masahiro Iwadare    Added 256 point version for Layer III *
 **********************************************************************/

#include "common.h"
#include "encoder.h"

/*****************************************************************************
 ************************** Start of Subroutines *****************************
 *****************************************************************************/

/*****************************************************************************
 * FFT computes fast fourier transform of BLKSIZE samples of data            *
 *   uses decimation-in-frequency algorithm described in "Digital            *
 *   Signal Processing" by Oppenheim and Schafer, refer to pages 304         *
 *   (flow graph) and 330-332 (Fortran program in problem 5)                 *
 *   to get the inverse fft, change line 20 from                             *
 *                 w_imag[L] = -sin(PI/le1);                                 *
 *                          to                                               *
 *                 w_imag[L] = sin(PI/le1);                                  *
 *                                                                           *
 *   required constants:                                                     *
 *         #define      PI          3.14159265358979                         *
 *         #define      BLKSIZE     1024                                     *
 *         #define      LOGBLKSIZE  10                                       *
 *         #define      BLKSIZE_S   256                                      *
 *         #define      LOGBLKSIZE_S 8                                       *
 *                                                                           *
 *****************************************************************************/
#define      BLKSIZE_S   256
#define      LOGBLKSIZE_S 8

void fft(x_real,x_imag, energy, phi, N)
FLOAT x_real[BLKSIZE], x_imag[BLKSIZE], energy[BLKSIZE], phi[BLKSIZE];
int	N;
{
 int     M,MM1;
 static int     init=0;
 int     NV2, NM1, MP;
 static double  w_real[2][LOGBLKSIZE], w_imag[2][LOGBLKSIZE];
 int            i,j,k,L;
 int            ip, le,le1;
 double         t_real, t_imag, u_real, u_imag;

 if(init==0) {
    memset((char *) w_real, 0, sizeof(w_real));  /* preset statics to 0 */
    memset((char *) w_imag, 0, sizeof(w_imag));  /* preset statics to 0 */
    M = LOGBLKSIZE;
    for(L=0; L> 1;
       w_real[0][L] = cos(PI/le1);
       w_imag[0][L] = -sin(PI/le1);
    }          
    M = LOGBLKSIZE_S;
    for(L=0; L> 1;
       w_real[1][L] = cos(PI/le1);
       w_imag[1][L] = -sin(PI/le1);
    }          
    init++;
 }
 switch(N) {
	case BLKSIZE:
			M = LOGBLKSIZE;
			MP = 0;
			break;
	case BLKSIZE_S:
			M = LOGBLKSIZE_S;
			MP = 1;
			break;
	default:	printf("Error: Bad FFT Size in subs.c\n");
			exit(-1);
 }
 MM1 = M-1;
 NV2 = N >> 1;
 NM1 = N - 1;
 for(L=0; L> 1;
    u_real = 1;
    u_imag = 0;
    for(j=0; j> 1;
    }
    j = j+k;
 }
}