[FFmpeg-devel] [PATCH] avutil/mem: use GCC builtins to check for overflow in av_size_mult()

[Carl Eugen Hoyos]

Am Do., 27. Mai 2021 um 17:08 Uhr schrieb James Almer <jamrial at gmail.com>:
>
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavutil/mem.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/libavutil/mem.h b/libavutil/mem.h
> index e21a1feaae..c876111afb 100644
> --- a/libavutil/mem.h
> +++ b/libavutil/mem.h
> @@ -674,11 +674,18 @@ void *av_dynarray2_add(void **tab_ptr, int *nb_ptr, size_t elem_size,
>   */
>  static inline int av_size_mult(size_t a, size_t b, size_t *r)
>  {
> -    size_t t = a * b;
> +    size_t t;
> +
> +#if (!defined(__INTEL_COMPILER) && AV_GCC_VERSION_AT_LEAST(5,1)) || AV_HAS_BUILTIN(__builtin_mul_overflow)
> +    if (__builtin_mul_overflow(a, b, &t))
> +        return AVERROR(EINVAL);
> +#else
> +    t = a * b;
>      /* Hack inspired from glibc: don't try the division if nelem and elsize
>       * are both less than sqrt(SIZE_MAX). */
>      if ((a | b) >= ((size_t)1 << (sizeof(size_t) * 4)) && a && t / a != b)
>          return AVERROR(EINVAL);
> +#endif

The commit message appears to be missing a hint about the performance
difference.

Carl Eugen