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/********************************************************************** 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<M; L++){ le = 1 << (M-L); le1 = le >> 1; w_real[0][L] = cos(PI/le1); w_imag[0][L] = -sin(PI/le1); } M = LOGBLKSIZE_S; for(L=0; L<M; L++){ le = 1 << (M-L); le1 = le >> 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<MM1; L++){ le = 1 << (M-L); le1 = le >> 1; u_real = 1; u_imag = 0; for(j=0; j<le1; j++){ for(i=j; i<N; i+=le){ ip = i + le1; t_real = x_real[i] + x_real[ip]; t_imag = x_imag[i] + x_imag[ip]; x_real[ip] = x_real[i] - x_real[ip]; x_imag[ip] = x_imag[i] - x_imag[ip]; x_real[i] = t_real; x_imag[i] = t_imag; t_real = x_real[ip]; x_real[ip] = x_real[ip]*u_real - x_imag[ip]*u_imag; x_imag[ip] = x_imag[ip]*u_real + t_real*u_imag; } t_real = u_real; u_real = u_real*w_real[MP][L] - u_imag*w_imag[MP][L]; u_imag = u_imag*w_real[MP][L] + t_real*w_imag[MP][L]; } } /* special case: L = M-1; all Wn = 1 */ for(i=0; i<N; i+=2){ ip = i + 1; t_real = x_real[i] + x_real[ip]; t_imag = x_imag[i] + x_imag[ip]; x_real[ip] = x_real[i] - x_real[ip]; x_imag[ip] = x_imag[i] - x_imag[ip]; x_real[i] = t_real; x_imag[i] = t_imag; energy[i] = x_real[i]*x_real[i] + x_imag[i]*x_imag[i]; if(energy[i] <= 0.0005){phi[i] = 0;energy[i] = 0.0005;} else phi[i] = atan2((double) x_imag[i],(double) x_real[i]); energy[ip] = x_real[ip]*x_real[ip] + x_imag[ip]*x_imag[ip]; if(energy[ip] == 0)phi[ip] = 0; else phi[ip] = atan2((double) x_imag[ip],(double) x_real[ip]); } /* this section reorders the data to the correct ordering */ j = 0; for(i=0; i<NM1; i++){ if(i<j){ /* use this section only if you need the FFT in complex number form * * (and in the correct ordering) */ t_real = x_real[j]; t_imag = x_imag[j]; x_real[j] = x_real[i]; x_imag[j] = x_imag[i]; x_real[i] = t_real; x_imag[i] = t_imag; /* reorder the energy and phase, phi */ t_real = energy[j]; energy[j] = energy[i]; energy[i] = t_real; t_real = phi[j]; phi[j] = phi[i]; phi[i] = t_real; } k=NV2; while(k<=j){ j = j-k; k = k >> 1; } j = j+k; } }
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