www.pudn.com > ampegsrc.zip > SUBS.C
/**********************************************************************
Copyright (c) 1991 ISO/IEC JTC1 SC29 WG1, 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, 708-538-5671, e-mail: pan@ukraine.corp.mot.com *
* *
* VERSION 4.3 *
* 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;
}
}