Re: [FFmpeg-devel] [PATCH] lavc/rv34dsp: optimise R-V V idct_dc_add

["Rémi Denis-Courmont" <remi@remlab.net>]

Le 22 mai 2024 23:28:54 GMT+03:00, "Rémi Denis-Courmont" <remi@remlab.net> a écrit :
>This removes one stray LI and reworks the vector arithmetic to avoid
>changing the vector configuration. On K230, this takes the 46.5 cycle
>count down from 46.5 to 43.5.
>---
> libavcodec/riscv/rv34dsp_rvv.S | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
>diff --git a/libavcodec/riscv/rv34dsp_rvv.S b/libavcodec/riscv/rv34dsp_rvv.S
>index f1f6345012..e8aff7e570 100644
>--- a/libavcodec/riscv/rv34dsp_rvv.S
>+++ b/libavcodec/riscv/rv34dsp_rvv.S
>@@ -36,16 +36,15 @@ func ff_rv34_idct_dc_add_rvv, zve32x
>         vsetivli      zero, 4, e8, mf4, ta, ma
>         vlse32.v      v0, (a0), a1
>         li            t1, 169
>+        li            t2, 128
>         mul           t1, t1, a2
>-        li            a2, 255
>+        vsetivli      zero, 4*4, e8, m1, ta, ma
>+        vwsubu.vx     v2, v0, t2
>         addi          t1, t1, 512
>         srai          t1, t1, 10
>-        vsetivli      zero, 4*4, e16, m2, ta, ma
>-        vzext.vf2     v2, v0
>-        vadd.vx       v2, v2, t1
>-        vmax.vx       v2, v2, zero
>-        vsetvli       zero, zero, e8, m1, ta, ma
>-        vnclipu.wi    v0, v2, 0
>+        vwadd.wx      v2, v2, t1

Hmm, this should not work, as t1 has more than 8 bits. Maybe checkasm is sloppy here.

>+        vnclip.wi     v0, v2, 0
>+        vxor.vx       v0, v0, t2
>         vsetivli      zero, 4, e8, mf4, ta, ma
>         vsse32.v      v0, (a0), a1
> 
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