Re: [Qemu-devel] [PATCH] util: Fix MIN_NON_ZERO

[Stefan Hajnoczi]

On Tue, Jul 12, 2016 at 02:48:33PM +0800, Fam Zheng wrote:
> MIN_NON_ZERO(0, 1) is evaluated to 0. Rewrite the macro to fix it.

This is incorrect.  The actual results are:

MIN_NON_ZERO(0, 1) = 1
MIN_NON_ZERO(1, 0) = 0

The second case is the buggy one.

> 
> Reported-by: Miroslav Rezanina <address@hidden>
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  include/qemu/osdep.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index e63da28..e4c6ae6 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -151,7 +151,8 @@ extern int daemon(int, int);
>  /* Minimum function that returns zero only iff both values are zero.
>   * Intended for use with unsigned values only. */
>  #ifndef MIN_NON_ZERO
> -#define MIN_NON_ZERO(a, b) (((a) != 0 && (a) < (b)) ? (a) : (b))
> +#define MIN_NON_ZERO(a, b) ((a) == 0 ? (b) : \
> +                                ((b) == 0 ? (a) : (MIN(a, b))))
>  #endif
>  
>  /* Round number down to multiple */
> -- 
> 2.7.4
>

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