On Sun, Dec 16, 2018 at 21:19:17 +0800, Steven Liu wrote:
> move the two if condition out of the loop, that can less n-1 times than
> condition
> in loop.
[...]
> k = -split_radix_permutation(i, n, s->inverse) & (n-1);
> - if (s->revtab)
> s->revtab[k] = j;
> - if (s->revtab32)
> - s->revtab32[k] = j;
> }
Does this really improve performance? You only save one if-check per
loop (as only one of s->revtab and s->revtab32 is defined). Benchmarks?
> + if (s->revtab32) {
> + for(i=0; i<n; i++) {
> + int k;
> + j = i;
> + if (s->fft_permutation == FF_FFT_PERM_SWAP_LSBS)
> + j = (j&~3) | ((j>>1)&1) | ((j<<1)&2);
> + k = -split_radix_permutation(i, n, s->inverse) &
> (n-1);
> + s->revtab32[k] = j;
> + }
> + }
On the other hand, all the code is duplicated. Is there a more elegant
way to do this?
Moritz
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