On Thu, May 21, 2020 at 12:05:47PM -0700, Dale Curtis wrote: > On Thu, May 21, 2020 at 12:37 AM Michael Niedermayer <mich...@niedermayer.cc> > wrote: > > > gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0 > > used with ccache on a x86-64 > > > > Huh, I guess there's no early abort for conditionals in a preprocessor > statement with __has_builtin for some reason. I've added a AV_HAS_BUILTIN > macro to workaround this. > > - dale
> attributes.h | 6 ++++++
> common.h | 10 ++++++++++
> 2 files changed, 16 insertions(+)
> 0659f15ed4807d2db1fb07a77e74d33dc5ffb90a sat_math_builtin_v7.patch
> From 34b1e4e398d3f5af72adf6d7584008098614ea2c Mon Sep 17 00:00:00 2001
> From: Dale Curtis <dalecur...@chromium.org>
> Date: Fri, 1 May 2020 10:20:43 -0700
> Subject: [PATCH] Use gcc/clang builtins for av_sat_(add|sub)_64_c if
> available.
>
> Signed-off-by: Dale Curtis <dalecur...@chromium.org>
> ---
> libavutil/attributes.h | 6 ++++++
> libavutil/common.h | 10 ++++++++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/libavutil/attributes.h b/libavutil/attributes.h
> index ced108aa2c..ab2a1fdd0e 100644
> --- a/libavutil/attributes.h
> +++ b/libavutil/attributes.h
> @@ -34,6 +34,12 @@
> # define AV_GCC_VERSION_AT_MOST(x,y) 0
> #endif
>
> +#ifdef __has_builtin
> +# define AV_HAS_BUILTIN(x) __has_builtin(x)
> +#else
> +# define AV_HAS_BUILTIN(x) false
> +#endif
> +
> #ifndef av_always_inline
> #if AV_GCC_VERSION_AT_LEAST(3,1)
> # define av_always_inline __attribute__((always_inline)) inline
> diff --git a/libavutil/common.h b/libavutil/common.h
> index 7a774fc448..2777cea9f9 100644
> --- a/libavutil/common.h
> +++ b/libavutil/common.h
> @@ -299,11 +299,16 @@ static av_always_inline int av_sat_dsub32_c(int a, int
> b)
> * @return sum with signed saturation
> */
> static av_always_inline int64_t av_sat_add64_c(int64_t a, int64_t b) {
> +#if (!defined(__INTEL_COMPILER) && AV_GCC_VERSION_AT_LEAST(5,1)) ||
> AV_HAS_BUILTIN(__builtin_add_overflow)
> + int64_t tmp;
> + return !__builtin_add_overflow(a, b, &tmp) ? tmp : (tmp < 0 ? INT64_MAX
> : INT64_MIN);
> +#else
> if (b >= 0 && a >= INT64_MAX - b)
> return INT64_MAX;
> if (b <= 0 && a <= INT64_MIN - b)
> return INT64_MIN;
> return a + b;
> +#endif
> }
>
> /**
> @@ -314,11 +319,16 @@ static av_always_inline int64_t av_sat_add64_c(int64_t
> a, int64_t b) {
> * @return difference with signed saturation
> */
> static av_always_inline int64_t av_sat_sub64_c(int64_t a, int64_t b) {
> +#if (!defined(__INTEL_COMPILER) && AV_GCC_VERSION_AT_LEAST(5,1)) ||
> AV_HAS_BUILTIN(__builtin_sub_overflow)
> + int64_t tmp;
> + return !__builtin_sub_overflow(a, b, &tmp) ? tmp : (tmp < 0 ? INT64_MAX
> : INT64_MIN);
> +#else
> if (b <= 0 && a >= INT64_MAX + b)
> return INT64_MAX;
> if (b >= 0 && a <= INT64_MIN + b)
> return INT64_MIN;
> return a - b;
> +#endif
does this produce faster / better code ?
that is do compilers actually fail to optimize this from plain
clean C code ?
thanks
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
He who knows, does not speak. He who speaks, does not know. -- Lao Tsu
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