[Mesa-dev] [PATCH] gallium/util: fix p_atomic_dec_zero macros

[Michel Dänzer]

On 12.06.2014 17:00, Maarten Lankhorst wrote:
> I'm pretty sure that p_atomic_dec_zero should return 1 if the count
> drops to zero.
> 
> Cc: "10.2 10.1 10.0" <mesa-stable at lists.freedesktop.org>

I don't think the stable tag is justified: These bugs have been there
for more than four years. Nothing in Gallium can work properly if the
return value of p_atomic_dec_zero() is inverted, so if there was
significant use of the broken variants, we should have heard about it
long ago.


> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
> ---
> diff --git a/src/gallium/auxiliary/util/u_atomic.h
> b/src/gallium/auxiliary/util/u_atomic.h
> index 2f2b42b..08cadb4 100644
> --- a/src/gallium/auxiliary/util/u_atomic.h
> +++ b/src/gallium/auxiliary/util/u_atomic.h
> @@ -183,7 +183,7 @@ p_atomic_cmpxchg(int32_t *v, int32_t old, int32_t _new)
>  
>  #define p_atomic_set(_v, _i) (*(_v) = (_i))
>  #define p_atomic_read(_v) (*(_v))
> -#define p_atomic_dec_zero(_v) ((boolean) --(*(_v)))
> +#define p_atomic_dec_zero(_v) (!(boolean) --(*(_v)))

Will this compile (with the intended result) without another set of parens?


> @@ -324,7 +324,7 @@ p_atomic_dec_zero(int32_t *v)
>  {
>     uint32_t n = atomic_dec_32_nv((uint32_t *) v);
>  
> -   return n != 0;
> +   return n == 0;
>  }

This looks good, but there are more variants which look similarly broken?


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer