[FFmpeg-devel] [PATCH v3] avcodec/fft_template: improve performance of the ff_fft_init in fft_template

[Steven Liu]

Steven Liu <lq at chinaffmpeg.org> 于2018年12月26日周三 下午4:15写道：
>
> Before patch:
> init nbits = 17, get 10000 samples, average cost: 16175 us
> After patch:
> init nbits = 17, get 10000 samples, average cost: 14989 us
>
> Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
> ---
>  libavcodec/fft_template.c | 46 +++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 35 insertions(+), 11 deletions(-)
>
> diff --git a/libavcodec/fft_template.c b/libavcodec/fft_template.c
> index 762c014bc8..20a62e4290 100644
> --- a/libavcodec/fft_template.c
> +++ b/libavcodec/fft_template.c
> @@ -261,17 +261,41 @@ av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
>      if (s->fft_permutation == FF_FFT_PERM_AVX) {
>          fft_perm_avx(s);
>      } else {
> -        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);
> -            if (s->revtab)
> -                s->revtab[k] = j;
> -            if (s->revtab32)
> -                s->revtab32[k] = j;
> -        }
> +#define PROCESS_FFT_PERM_SWAP_LSBS(num) do {\
> +    for(i = 0; i < n; i++) {\
> +        int k;\
> +        j = i;\
> +        j = (j & ~3) | ((j >> 1) & 1) | ((j << 1) & 2);\
> +        k = -split_radix_permutation(i, n, s->inverse) & (n - 1);\
> +        s->revtab##num[k] = j;\
> +    } \
> +} while(0);
> +
> +#define PROCESS_FFT_PERM_DEFAULT(num) do {\
> +    for(i = 0; i < n; i++) {\
> +        int k;\
> +        j = i;\
> +        k = -split_radix_permutation(i, n, s->inverse) & (n - 1);\
> +        s->revtab##num[k] = j;\
> +    } \
> +} while(0);
> +
> +#define SPLIT_RADIX_PERMUTATION(num) do { \
> +    if (s->fft_permutation == FF_FFT_PERM_SWAP_LSBS) {\
> +        PROCESS_FFT_PERM_SWAP_LSBS(num) \
> +    } else {\
> +        PROCESS_FFT_PERM_DEFAULT(num) \
> +    }\
> +} while(0);
> +
> +    if (s->revtab)
> +        SPLIT_RADIX_PERMUTATION()
> +    if (s->revtab32)
> +        SPLIT_RADIX_PERMUTATION(32)
> +
> +#undef PROCESS_FFT_PERM_DEFAULT
> +#undef PROCESS_FFT_PERM_SWAP_LSBS
> +#undef SPLIT_RADIX_PERMUTATION
>      }
>
>      return 0;
> --
> 2.15.2 (Apple Git-101.1)
>
>
>
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