Re: [FFmpeg-devel] [PATCH 1/5] libswscale: Re-factor ff_shuffle_filter_coefficients.

[Michael Niedermayer <michael@niedermayer.cc>]

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On Wed, Feb 09, 2022 at 10:09:45AM +0100, Alan Kelly wrote:
> Make the code more readable and follow the style guide.
> ---
>  libswscale/utils.c | 64 +++++++++++++++++++++++++++-------------------
>  1 file changed, 37 insertions(+), 27 deletions(-)
> 
> diff --git a/libswscale/utils.c b/libswscale/utils.c
> index c5ea8853d5..1d919e863a 100644
> --- a/libswscale/utils.c
> +++ b/libswscale/utils.c
> @@ -278,39 +278,49 @@ static const FormatEntry format_entries[] = {
>      [AV_PIX_FMT_P416LE]      = { 1, 1 },
>  };
>  
> -void ff_shuffle_filter_coefficients(SwsContext *c, int *filterPos, int filterSize, int16_t *filter, int dstW){
> +void ff_shuffle_filter_coefficients(SwsContext *c, int *filterPos,
> +                                   int filterSize, int16_t *filter,
> +                                   int dstW)
> +{
>  #if ARCH_X86_64
> -    int i, j, k, l;
> +    int i, j, k;
>      int cpu_flags = av_get_cpu_flags();
> +    // avx2 hscale filter processes 16 pixel blocks.
> +    if (!filter || dstW % 16 != 0)
> +        return;
>      if (EXTERNAL_AVX2_FAST(cpu_flags) && !(cpu_flags & AV_CPU_FLAG_SLOW_GATHER)) {
> -        if ((c->srcBpc == 8) && (c->dstBpc <= 14)){
> -            if (dstW % 16 == 0){
> -                if (filter != NULL){
> -                    for (i = 0; i < dstW; i += 8){
> -                        FFSWAP(int, filterPos[i + 2], filterPos[i+4]);
> -                        FFSWAP(int, filterPos[i + 3], filterPos[i+5]);
> -                    }
> -                    if (filterSize > 4){
> -                        int16_t *tmp2 = av_malloc(dstW * filterSize * 2);
> -                        memcpy(tmp2, filter, dstW * filterSize * 2);
> -                        for (i = 0; i < dstW; i += 16){//pixel
> -                            for (k = 0; k < filterSize / 4; ++k){//fcoeff
> -                                for (j = 0; j < 16; ++j){//inner pixel
> -                                    for (l = 0; l < 4; ++l){//coeff
> -                                        int from = i * filterSize + j * filterSize + k * 4 + l;
> -                                        int to = (i) * filterSize + j * 4 + l + k * 64;
> -                                        filter[to] = tmp2[from];
> -                                    }
> -                                }
> -                            }
> -                        }
> -                        av_free(tmp2);
> -                    }
> -                }
> -            }
> +        if ((c->srcBpc == 8) && (c->dstBpc <= 14)) {
> +           int16_t *filterCopy = NULL;
> +           if (filterSize > 4) {

> +               if (!FF_ALLOC_TYPED_ARRAY(filterCopy, dstW * filterSize))
> +                   return;

this is not a matter of style, it changes a null pointer dereference on error
to simply returning with no error handling. I know the next patches
change this again but that makes it just more messy


> +               memcpy(filterCopy, filter, dstW * filterSize * sizeof(int16_t));
> +           }
> +           // Do not swap filterPos for pixels which won't be processed by
> +           // the main loop.
> +           for (i = 0; i + 8 <= dstW; i += 8) {
> +               FFSWAP(int, filterPos[i + 2], filterPos[i + 4]);
> +               FFSWAP(int, filterPos[i + 3], filterPos[i + 5]);
> +           }
> +           if (filterSize > 4) {
> +               // 16 pixels are processed at a time.
> +               for (i = 0; i + 16 <= dstW; i += 16) {
> +                   // 4 filter coeffs are processed at a time.
> +                   for (k = 0; k + 4 <= filterSize; k += 4) {
> +                       for (j = 0; j < 16; ++j) {
> +                           int from = (i + j) * filterSize + k;
> +                           int to = i * filterSize + j * 4 + k * 16;
> +                           memcpy(&filter[to], &filterCopy[from], 4 * sizeof(int16_t));
> +                       }
> +                   }
> +               }
> +           }

> +           if (filterCopy)
> +               av_free(filterCopy);

The null check is unneeded


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Does the universe only have a finite lifespan? No, its going to go on
forever, its just that you wont like living in it. -- Hiranya Peiri

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