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better, reduced mutliply in real fft

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This commit is contained in:
Mark Borgerding 2003-12-10 05:48:42 +00:00
parent b880c599ef
commit 8a992d0e98
3 changed files with 31 additions and 27 deletions
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7
fft.py
View File

@ -77,10 +77,11 @@ def real_fft( f,inv ):
F1k = Fp[k] + Fp[N-k].conjugate()
F2k = Fp[k] - Fp[N-k].conjugate()
F[k] = ( F1k + tw * F2k ) * .5
F2k *= tw
F[k] = ( F1k + F2k ) * .5
F[N-k] = ( F1k - F2k ).conjugate() * .5
#F[N-k] = ( F1kp + e ** ( -j*pi*(.5+float(N-k)/N ) ) * F2kp ) * .5
F[N-k] = ( F1k.conjugate() - tw.conjugate() * F2k.conjugate() ) * .5
#F[N-k] = ( F1k.conjugate() - tw.conjugate() * F2k.conjugate() ) * .5
F[N] = complex( Fp[0].real - Fp[0].imag , 0 )
return F

17
kiss_fftr.c
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@ -79,25 +79,30 @@ void kiss_fftr(const void * cfg,const kiss_fft_scalar *timedata,kiss_fft_cpx *fr
freqdata[0].r = st->tmpbuf[0].r + st->tmpbuf[0].i;
freqdata[0].i = 0;
for (k=1;k<N;++k) {
kiss_fft_cpx fpnk,fpk,f1k;
for (k=1;k <= N/2 ; ++k ) {
kiss_fft_cpx fpnk,fpk,f1k,f2k,tw;
fpk = st->tmpbuf[k];
fpnk.r = st->tmpbuf[N-k].r;
fpnk.i = -st->tmpbuf[N-k].i;
C_ADD( f1k, fpk , fpnk );
C_SUBFROM( fpk , fpnk );
C_MUL( freqdata[k], fpk , st->super_twiddles[k] );
C_ADDTO(freqdata[k],f1k);
C_SUB( f2k, fpk , fpnk );
C_MUL( tw , f2k , st->super_twiddles[k]);
C_ADD( freqdata[k] , f1k ,tw);
freqdata[k].r /= 2;
freqdata[k].i /= 2;
freqdata[N-k].r = f1k.r - tw.r;
freqdata[N-k].i = - (f1k.i - tw.i);
freqdata[N-k].r /= 2;
freqdata[N-k].i /= 2;
}
freqdata[N].r = st->tmpbuf[0].r - st->tmpbuf[0].i;
freqdata[N].i = 0;
}
void kiss_fftri(const void * cfg,const kiss_fft_cpx *freqdata,kiss_fft_scalar *timedata)
{
/* input buffer timedata is stored row-wise */

34
test/test_real.c
View File

@ -34,9 +34,7 @@ double snr_compare( kiss_fft_cpx * vec1,kiss_fft_cpx * vec2, int n)
printf( "\npoor snr, try a scaling factor %f\n" , scale );
return snr;
}
#define RANDOM
#ifndef RANDOM
#define NFFT 8
#else
@ -80,6 +78,22 @@ int main()
kiss_fftr(kiss_fftr_state,sin,sout);
printf( "nfft=%d, inverse=%d, snr=%g\n",
NFFT,0, snr_compare(cout,sout,(NFFT/2)+1) );
#ifdef RANDOM
ts = cputime();
for (i=0;i<NUMFFTS;++i) {
kiss_fft(kiss_fft_state,cin,cout);
}
tfft = cputime() - ts;
ts = cputime();
for (i=0;i<NUMFFTS;++i) {
kiss_fftr( kiss_fftr_state, sin, cout );
/* kiss_fftri(kiss_fftr_state,cout,sin); */
}
trfft = cputime() - ts;
printf("%d complex ffts took %gs, real took %gs\n",NUMFFTS,tfft,trfft);
#endif
free(kiss_fft_state);
free(kiss_fftr_state);
@ -99,22 +113,6 @@ int main()
printf( "nfft=%d, inverse=%d, snr=%g\n",
NFFT,1, snr_compare(cin,cin,NFFT/2) );
#ifdef RANDOM
ts = cputime();
for (i=0;i<NUMFFTS;++i) {
kiss_fft(kiss_fft_state,cin,cout);
}
tfft = cputime() - ts;
ts = cputime();
for (i=0;i<NUMFFTS;++i) {
/* kiss_fftr(kiss_fftr_state,sin,cout); */
kiss_fftri(kiss_fftr_state,cout,sin);
}
trfft = cputime() - ts;
printf("%d complex ffts took %gs, real took %gs\n",NUMFFTS,tfft,trfft);
#endif
free(kiss_fft_state);
free(kiss_fftr_state);