Re: [FFmpeg-devel] [PATCH] avcodec/hevcdsp: Offset ff_hevc_.pel_filters to simplify addressing

[Nuo Mi <nuomi2021@gmail.com>]

On Sun, Feb 11, 2024 at 4:21 PM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> Besides simplifying address computations (it saves 432B of .text
> in hevcdsp.o alone here) it also fixes undefined behaviour that
> occurs if mx or my are 0 (happens when the filters are unused)
> because they lead to an array index of -1 in the old code.
> This happens in the checkasm-hevc_pel FATE-test.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
> The loongarch and mips parts of this are untested. Luckily we have a
> loongarch patchwork runner...
>
>  libavcodec/hevcdsp.c                    |   6 +-
>  libavcodec/hevcdsp.h                    |   5 +-
>  libavcodec/hevcdsp_template.c           |  38 ++--
>  libavcodec/loongarch/hevc_mc.S          | 224 +++++-------------------
>  libavcodec/loongarch/hevc_mc_bi_lsx.c   |   6 +-
>  libavcodec/loongarch/hevc_mc_uni_lsx.c  |   6 +-
>  libavcodec/loongarch/hevc_mc_uniw_lsx.c |   4 +-
>  libavcodec/loongarch/hevcdsp_lsx.c      |   6 +-
>  libavcodec/mips/hevc_mc_bi_msa.c        |   6 +-
>  libavcodec/mips/hevc_mc_biw_msa.c       |   6 +-
>  libavcodec/mips/hevc_mc_uni_msa.c       |   6 +-
>  libavcodec/mips/hevc_mc_uniw_msa.c      |   6 +-
>  libavcodec/mips/hevcdsp_mmi.c           |  20 +--
>  libavcodec/mips/hevcdsp_msa.c           |   6 +-
>  libavcodec/x86/hevcdsp_init.c           |   4 +-
>  15 files changed, 112 insertions(+), 237 deletions(-)
>
> diff --git a/libavcodec/hevcdsp.c b/libavcodec/hevcdsp.c
> index 2ca551df1d..630fdc012e 100644
> --- a/libavcodec/hevcdsp.c
> +++ b/libavcodec/hevcdsp.c
> @@ -91,7 +91,8 @@ static const int8_t transform[32][32] = {
>        90, -90,  88, -85,  82, -78,  73, -67,  61, -54,  46, -38,  31,
> -22,  13,  -4 },
>  };
>
> -DECLARE_ALIGNED(16, const int8_t, ff_hevc_epel_filters)[7][4] = {
> +DECLARE_ALIGNED(16, const int8_t, ff_hevc_epel_filters)[8][4] = {
> +    {  0 },
>      { -2, 58, 10, -2},
>      { -4, 54, 16, -2},
>      { -6, 46, 28, -4},
> @@ -101,7 +102,8 @@ DECLARE_ALIGNED(16, const int8_t,
> ff_hevc_epel_filters)[7][4] = {
>      { -2, 10, 58, -2},
>  };
>
> -DECLARE_ALIGNED(16, const int8_t, ff_hevc_qpel_filters)[3][16] = {
> +DECLARE_ALIGNED(16, const int8_t, ff_hevc_qpel_filters)[4][16] = {
>
Do you know why this is [4][16]? [4][8] should suffice.
If some architecture requires 16, we might need to update
VVC_INTER_LUMA_TAPS to 16 in the future.
Thank you

> +    { 0 },
>      { -1,  4,-10, 58, 17, -5,  1,  0, -1,  4,-10, 58, 17, -5,  1,  0},
>      { -1,  4,-11, 40, 40,-11,  4, -1, -1,  4,-11, 40, 40,-11,  4, -1},
>      {  0,  1, -5, 17, 58,-10,  4, -1,  0,  1, -5, 17, 58,-10,  4, -1}
> diff --git a/libavcodec/hevcdsp.h b/libavcodec/hevcdsp.h
> index 1b9c5bb6bc..a5933dcac4 100644
>
> --
> 2.34.1
>
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