[FFmpeg-devel] [PATCH] vf_spp: only assign function pointers if permutation matches expectations.

[Michael Niedermayer]

On Wed, Jun 21, 2017 at 09:46:58AM -0400, Ronald S. Bultje wrote:
> ---
>  libavfilter/x86/vf_spp.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/libavfilter/x86/vf_spp.c b/libavfilter/x86/vf_spp.c
> index 45a9eb0..8e3c820 100644
> --- a/libavfilter/x86/vf_spp.c
> +++ b/libavfilter/x86/vf_spp.c
> @@ -217,6 +217,17 @@ static void store_slice_mmx(uint8_t *dst, const int16_t *src,
>  
>  #endif /* HAVE_MMX_INLINE */
>  
> +static const uint8_t simple_mmx_permutation[64] = {
> +    0x00, 0x08, 0x04, 0x09, 0x01, 0x0C, 0x05, 0x0D,
> +    0x10, 0x18, 0x14, 0x19, 0x11, 0x1C, 0x15, 0x1D,
> +    0x20, 0x28, 0x24, 0x29, 0x21, 0x2C, 0x25, 0x2D,
> +    0x12, 0x1A, 0x16, 0x1B, 0x13, 0x1E, 0x17, 0x1F,
> +    0x02, 0x0A, 0x06, 0x0B, 0x03, 0x0E, 0x07, 0x0F,
> +    0x30, 0x38, 0x34, 0x39, 0x31, 0x3C, 0x35, 0x3D,
> +    0x22, 0x2A, 0x26, 0x2B, 0x23, 0x2E, 0x27, 0x2F,
> +    0x32, 0x3A, 0x36, 0x3B, 0x33, 0x3E, 0x37, 0x3F,
> +};
> +
>  av_cold void ff_spp_init_x86(SPPContext *s)
>  {
>  #if HAVE_MMX_INLINE
> @@ -226,7 +237,9 @@ av_cold void ff_spp_init_x86(SPPContext *s)
>          int64_t bps;
>          s->store_slice = store_slice_mmx;
>          av_opt_get_int(s->dct, "bits_per_sample", 0, &bps);
> -        if (bps <= 8) {
> +        if (bps <= 8 &&
> +            !memcmp(s->dct->idct_permutation, simple_mmx_permutation,
> +                    sizeof(simple_mmx_permutation))) {

this would disable the SIMD code

also the memcmp() is a very ugly way to check the permutation

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
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