[FFmpeg-devel] [PATCH] lavc/aacenc_utils: unroll quantize_bands loop

[Michael Niedermayer]

On Fri, Mar 18, 2016 at 07:27:46PM -0700, Ganesh Ajjanagadde wrote:
> Yields speedup in quantize_bands, and non-negligible speedup in aac encoding overall.
> 
> Sample benchmark (Haswell, -march=native + GCC):
> new:
>     [...]
>     553 decicycles in quantize_bands, 2097136 runs,     16 skips9x
>     554 decicycles in quantize_bands, 4194266 runs,     38 skips8x
>     559 decicycles in quantize_bands, 8388534 runs,     74 skips7x
> 
> old:
>     [...]
>     711 decicycles in quantize_bands, 2097140 runs,     12 skips7x
>     713 decicycles in quantize_bands, 4194277 runs,     27 skips4x
>     715 decicycles in quantize_bands, 8388538 runs,     70 skips3x
> 
> old:
> ffmpeg -f lavfi -i anoisesrc -t 300 -y sin_new.aac  4.58s user 0.01s system 99% cpu 4.590 total
> 
> new:
> ffmpeg -f lavfi -i anoisesrc -t 300 -y sin_new.aac  4.54s user 0.02s system 99% cpu 4.566 total
> 
> Signed-off-by: Ganesh Ajjanagadde <gajjanag at gmail.com>
> ---
>  libavcodec/aacenc_utils.h | 33 +++++++++++++++++++++++++--------
>  1 file changed, 25 insertions(+), 8 deletions(-)
> 
> diff --git a/libavcodec/aacenc_utils.h b/libavcodec/aacenc_utils.h
> index 38636e5..0203b6e 100644
> --- a/libavcodec/aacenc_utils.h
> +++ b/libavcodec/aacenc_utils.h
> @@ -62,18 +62,35 @@ static inline int quant(float coef, const float Q, const float rounding)
>      return sqrtf(a * sqrtf(a)) + rounding;
>  }
>  
> +static inline float minf(float x, float y) {
> +    return x < y ? x : y;
> +}
> +
>  static inline void quantize_bands(int *out, const float *in, const float *scaled,
>                                    int size, float Q34, int is_signed, int maxval,
>                                    const float rounding)
>  {
> -    int i;
> -    for (i = 0; i < size; i++) {
[...]
> +    for (int i = 0; i < size; i+=4) {

iam not sure we still support a compiler that has a problem with
that int placement but its not done anywhere else

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA
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