[PATCH] Avoid double argument evaluation in MIN and MAX macros

[Denys Vlasenko]

On Mon, Mar 31, 2014 at 12:08 AM, Bartosz Golaszewski
<bartekgola at gmail.com> wrote:
> Commit c3a27b0b fixes a double argument evaluation by modifying the
> macro invocation. What about preventing it on macro definition level?
>
> Signed-off-by: Bartosz Golaszewski <bartekgola at gmail.com>
> ---
>  include/libbb.h        | 22 +++++++++++++++-------
>  util-linux/swaponoff.c |  5 ++---
>  2 files changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/include/libbb.h b/include/libbb.h
> index 1cbe2c8..db75641 100644
> --- a/include/libbb.h
> +++ b/include/libbb.h
> @@ -265,13 +265,21 @@ struct BUG_off_t_size_is_misdetected {
>  #define SKIP   ((int) 2)
>
>  /* Macros for min/max.  */
> -#ifndef MIN
> -#define MIN(a,b) (((a)<(b))?(a):(b))
> -#endif
> -
> -#ifndef MAX
> -#define MAX(a,b) (((a)>(b))?(a):(b))
> -#endif
> +#undef MIN
> +#define MIN(a,b) \
> +       ({ \
> +               __typeof__(a) _a = (a); \
> +               __typeof__(b) _b = (b); \
> +               _a < _b ? _a : _b; \
> +       })
> +
> +#undef MAX
> +#define MAX(a,b) \
> +       ({ \
> +               __typeof__(a) _a = (a); \
> +               __typeof__(b) _b = (b); \
> +               _a > _b ? _a : _b; \
> +       })

typeof() is GCCism. I am wary of using it unless it's necessary.