[FFmpeg-devel] [PATCH] avcodec/x86/hevc: fix luma 12b overflow

[Henrik Gramner]

On Sun, Feb 25, 2024 at 5:42 PM Ronald S. Bultje <rsbultje at gmail.com> wrote:
> +    mova            m13, [pw_8]
> +    paddw           m10, m12, m12
> +    paddw           m12, m10 ; 9 * (q0 - p0) - 3 * ( q1 - p1 )
>      paddw           m12, m13; + 8

Memory operand

> +    paddw           m10, m13, m13
> +    paddw           m13, m10 ; abs(9 * (q0 - p0) - 3 * ( q1 - p1 ))
> +    paddw           m13, [pw_8]
[...]
> +    paddw           m13, m12, m12
> +    paddw           m13, m12 ; 3*abs(m12)
> +    paddw           m13, [pw_8]

Another minor improvement would be to reorder the adds like (x + x) +
(x + 8) instead of ((x + x) + x) + 8 to allow for more
instruction-level parallelism.