[FFmpeg-devel] [PATCH 6/6] lavc/takdsp: R-V V decorrelate_sm

[Rémi Denis-Courmont]

Le perjantaina 22. joulukuuta 2023, 3.34.39 EET flow gg a écrit :
> func ff_decorrelate_sm_rvv, zve32x
> 1:
>         vsetvli  t0, a2, e32, m8, ta, ma
>         vle32.v  v8, (a1)
>         sub a2,  a2, t0
>         vle32.v  v0, (a0)
>         vssra.vi  v8, v8, 1
>         vsub.vv  v16, v0, v8
>         vse32.v  v16, (a0)
>         sh2add   a0, t0, a0
>         vadd.vv  v16, v0, v8
>         vse32.v  v16, (a1)
>         sh2add   a1, t0, a1
>         bnez     a2, 1b
>         ret
> endfunc
> 
> Is this way? In this situation, or when using vsra, there will be some
> tests that fail, and the result value differs by 1. I'm not sure where the
> problem..

No, I meant something like this, but it turns out slightly slower anyway. 
Saving the data dependency is not worth adding an instruction.

func ff_decorrelate_sm_rvv, zve32x
        csrwi   vxrm, 0
1:
        vsetvli t0, a2, e32, m8, ta, ma
        vle32.v v8, (a1)
        sub     a2, a2, t0
        vle32.v v0, (a0)
        vsra.vi v16, v8, 1
        vssra.vi v8, v8, 1
        vsub.vv v16, v0, v16
        vadd.vv v8, v0, v8
        vse32.v v16, (a0)
        sh2add  a0, t0, a0
        vse32.v v8, (a1)
        sh2add  a1, t0, a1
        bnez    a2, 1b

        ret
endfunc

-- 
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