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added optimization for radix 2

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### testing SNR for  1024 point FFTs
#### DOUBLE
snr_t2f = 296.29
snr_f2t = 314.48
#### FLOAT
snr_t2f = 146.48
snr_f2t = 143.03
#### SHORT
snr_t2f = -30.269
snr_f2t = -60.442

#### timing 10000 x 1024 point FFTs
#### DOUBLE
Elapsed:0:02.77 user:2.22 sys:0.13
#### FLOAT
Elapsed:0:01.65 user:1.35 sys:0.07
#### SHORT
Elapsed:0:02.44 user:2.00 sys:0.06
This commit is contained in:
Mark Borgerding 2003-10-14 00:38:58 +00:00
parent 0d6d61cfce
commit 8460f1f8f5
1 changed files with 58 additions and 5 deletions
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63
kiss_fft.c
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@ -64,7 +64,49 @@ kiss_fft_cpx cexp(double phase)
return x; return x;
} }
static
void fft_work(
kiss_fft_cpx * Fout,
const kiss_fft_cpx * f,
int fstride,
int * factors,
const kiss_fft_state * st
);
// the heart of the fft // the heart of the fft
static
void fft2work(
kiss_fft_cpx * Fout,
const kiss_fft_cpx * f,
int fstride,
int * factors,
const kiss_fft_state * st,
int m
)
{
int u;
kiss_fft_cpx t;
//kiss_fft_cpx * scratch = st->scratch;
kiss_fft_cpx * twiddles = st->twiddles;
//int Norig = st->nfft;
if (m==1) {
Fout[0] = f[0];
Fout[1] = f[fstride];
} else {
fft_work( Fout , f, fstride*2,factors,st);
fft_work( Fout + m, f+fstride, fstride*2,factors,st);
}
for ( u=0; u<m; ++u ) {
C_MUL (t, Fout[ u +m ] , twiddles[fstride * u]);
Fout[u+m].r = Fout[u].r - t.r;
Fout[u+m].i = Fout[u].i - t.i;
Fout[u].r += t.r;
Fout[u].i += t.i;
}
}
static static
void fft_work( void fft_work(
kiss_fft_cpx * Fout, kiss_fft_cpx * Fout,
@ -74,21 +116,31 @@ void fft_work(
const kiss_fft_state * st const kiss_fft_state * st
) )
{ {
int m,p=0,q,q1,u,k; int m,p,q,q1,u,k;
kiss_fft_cpx t; kiss_fft_cpx t;
kiss_fft_cpx * scratch = st->scratch; kiss_fft_cpx * scratch = st->scratch;
kiss_fft_cpx * twiddles = st->twiddles; kiss_fft_cpx * twiddles = st->twiddles;
int Norig = st->nfft; int Norig = st->nfft;
p=*factors++; p=*factors++;
m=*factors++;//m = n/p; m=*factors++;
#if 1
switch (*factors) {
case 2:
fft2work(Fout,f,fstride,factors,st,m);
return;
default:
break;
}
#endif
for (q=0;q<p;++q) { for (q=0;q<p;++q) {
// TODO f+= fstride; instead of offset below
if (m==1) if (m==1)
*(Fout + m*q) = *(f+q*fstride); Fout[q] = *f;
else else
fft_work( Fout + m*q, f+q*fstride, fstride*p,factors,st); fft_work( Fout + m*q, f, fstride*p,factors,st);
f+= fstride;
} }
for ( u=0; u<m; ++u ) { for ( u=0; u<m; ++u ) {
@ -169,6 +221,7 @@ void * kiss_fft_alloc(int nfft,int inverse_fft)
p = primes[i]; p = primes[i];
break; break;
} }
++i;
} }
st->factors[2*nstages] = p; st->factors[2*nstages] = p;
nfft /= p; nfft /= p;