[FFmpeg-devel] [PATCH] avcodec/rdft: reorder calculation

[Muhammad Faiz]

On Sat, Jul 22, 2017 at 6:57 AM, Muhammad Faiz <mfcc64 at gmail.com> wrote:
> old:
>  165188 decicycles in  rdft,   65536 runs,      0 skips
>  165865 decicycles in irdft,   65536 runs,      0 skips
> new:
>  142487 decicycles in  rdft,   65536 runs,      0 skips
>  141498 decicycles in irdft,   65536 runs,      0 skips
>
> Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
> ---
>  libavcodec/rdft.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/libavcodec/rdft.c b/libavcodec/rdft.c
> index 194e0bc4ee..6ba7484238 100644
> --- a/libavcodec/rdft.c
> +++ b/libavcodec/rdft.c
> @@ -35,7 +35,7 @@
>  static void rdft_calc_c(RDFTContext *s, FFTSample *data)
>  {
>      int i, i1, i2;
> -    FFTComplex ev, od;
> +    FFTComplex ev, od, odsum;
>      const int n = 1 << s->nbits;
>      const float k1 = 0.5;
>      const float k2 = 0.5 - s->inverse;
> @@ -58,14 +58,16 @@ static void rdft_calc_c(RDFTContext *s, FFTSample *data)
>          i2 = n-i1;                                                          \
>          /* Separate even and odd FFTs */                                    \
>          ev.re =  k1*(data[i1  ]+data[i2  ]);                                \
> -        od.im = -k2*(data[i1  ]-data[i2  ]);                                \
> +        od.im =  k2*(data[i2  ]-data[i1  ]);                                \
>          ev.im =  k1*(data[i1+1]-data[i2+1]);                                \
>          od.re =  k2*(data[i1+1]+data[i2+1]);                                \
>          /* Apply twiddle factors to the odd FFT and add to the even FFT */  \
> -        data[i1  ] =  ev.re + od.re*tcos[i] sign0 od.im*tsin[i];            \
> -        data[i1+1] =  ev.im + od.im*tcos[i] sign1 od.re*tsin[i];            \
> -        data[i2  ] =  ev.re - od.re*tcos[i] sign1 od.im*tsin[i];            \
> -        data[i2+1] = -ev.im + od.im*tcos[i] sign1 od.re*tsin[i];            \
> +        odsum.re = od.re*tcos[i] sign0 od.im*tsin[i];                       \
> +        odsum.im = od.im*tcos[i] sign1 od.re*tsin[i];                       \
> +        data[i1  ] =  ev.re + odsum.re;                                     \
> +        data[i1+1] =  ev.im + odsum.im;                                     \
> +        data[i2  ] =  ev.re - odsum.re;                                     \
> +        data[i2+1] =  odsum.im - ev.im;                                     \
>      }
>
>      if (s->negative_sin) {
> --
> 2.13.2
>

Applied.

Thank's.