Re: [FFmpeg-devel] [PATCH 4/4] lavu/riscv: use Zbb CLZ/CTZ/CLZW/CTZW at run-time

[Lynne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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On 08/06/2024 13:37, Rémi Denis-Courmont wrote:
>           Zbb static    Zbb dynamic   I baseline
> clz       0.668032642   1.336072283   19.552376803
> clzl      0.668092643   1.336181786   26.110855571
> ctz       1.336208533   3.340209702   26.054869008
> ctzl      1.336247784   3.340362457   26.055266290
> (seconds for 1 billion iterations on a SiFive-U74 core)
> ---
>   libavutil/riscv/intmath.h | 101 ++++++++++++++++++++++++++++++++++++++
>   1 file changed, 101 insertions(+)
> 
> diff --git a/libavutil/riscv/intmath.h b/libavutil/riscv/intmath.h
> index 1f0afbc81d..3e7ab864c5 100644
> --- a/libavutil/riscv/intmath.h
> +++ b/libavutil/riscv/intmath.h
> @@ -73,6 +73,107 @@ static av_always_inline av_const int av_clip_intp2_rvi(int a, int p)
>   }
>   
>   #if defined (__GNUC__) || defined (__clang__)
> +static inline av_const int ff_ctz_rv(int x)
> +{
> +#if HAVE_RV && !defined(__riscv_zbb)
> +    if (!__builtin_constant_p(x) &&
> +        __builtin_expect(ff_rv_zbb_support(), true)) {
> +        int y;
> +
> +        __asm__ (
> +            ".option push\n"
> +            ".option arch, +zbb\n"
> +#if __riscv_xlen >= 64
> +            "ctzw    %0, %1\n"
> +#else
> +            "ctz     %0, %1\n"
> +#endif
> +            ".option pop" : "=r" (y) : "r" (x));
> +        if (y > 32)
> +            __builtin_unreachable();
> +        return y;
> +    }
> +#endif
> +    return __builtin_ctz(x);
> +}
> +#define ff_ctz ff_ctz_rv
> +
> +static inline av_const int ff_ctzll_rv(long long x)
> +{
> +#if HAVE_RV && !defined(__riscv_zbb) && __riscv_xlen == 64
> +    if (!__builtin_constant_p(x) &&
> +        __builtin_expect(ff_rv_zbb_support(), true)) {
> +        int y;
> +
> +        __asm__ (
> +            ".option push\n"
> +            ".option arch, +zbb\n"
> +            "ctz     %0, %1\n"
> +            ".option pop" : "=r" (y) : "r" (x));
> +        if (y > 64)
> +            __builtin_unreachable();
> +        return y;
> +    }
> +#endif
> +    return __builtin_ctzll(x);
> +}
> +#define ff_ctzll ff_ctzll_rv
> +
> +static inline av_const int ff_clz_rv(int x)
> +{
> +#if HAVE_RV && !defined(__riscv_zbb)
> +    if (!__builtin_constant_p(x) &&
> +        __builtin_expect(ff_rv_zbb_support(), true)) {
> +        int y;
> +
> +        __asm__ (
> +            ".option push\n"
> +            ".option arch, +zbb\n"
> +#if __riscv_xlen >= 64
> +            "clzw    %0, %1\n"
> +#else
> +            "clz     %0, %1\n"
> +#endif
> +            ".option pop" : "=r" (y) : "r" (x));
> +        if (y > 32)
> +            __builtin_unreachable();
> +        return y;
> +    }
> +#endif
> +    return __builtin_clz(x);
> +}
> +#define ff_clz ff_clz_rv
> +
> +#if __riscv_xlen == 64
> +static inline av_const int ff_clzll_rv(long long x)
> +{
> +#if HAVE_RV && !defined(__riscv_zbb)
> +    if (!__builtin_constant_p(x) &&
> +        __builtin_expect(ff_rv_zbb_support(), true)) {
> +        int y;
> +
> +        __asm__ (
> +            ".option push\n"
> +            ".option arch, +zbb\n"
> +            "clz     %0, %1\n"
> +            ".option pop" : "=r" (y) : "r" (x));
> +        if (y > 64)
> +            __builtin_unreachable();
> +        return y;
> +    }
> +#endif
> +    return __builtin_clzll(x);
> +}
> +#define ff_clz ff_clz_rv
> +#endif
> +
> +static inline av_const int ff_log2_rv(unsigned int x)
> +{
> +    return 31 - ff_clz_rv(x | 1);
> +}
> +#define ff_log2 ff_log2_rv
> +#define ff_log2_16bit ff_log2_rv
> +
>   static inline av_const int av_popcount_rv(unsigned int x)
>   {
>   #if HAVE_RV && !defined(__riscv_zbb)

Could you add a ./configure flag or a check for enabling non-dynamic Zbb?

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