[Mesa-dev] [PATCH v2] mesa/main: Fix memset in formatquery.c

[Gustaw Smolarczyk]

27 mar 2017 08:47 "Alejandro Piñeiro" <apinheiro at igalia.com> napisał(a):

On 27/03/17 01:51, Edward O'Callaghan wrote:
> V.1:
> We memset number of elements without multiplication by the
> element size.

It is not usual to summarize v1. The idea is explain just the changes.
>
> V.2:
> We explicitly set each member to -1 over using a confusing
> memset().

Nitpick: usually, the info about version changes doesn't follow that
style (uppercase v, point, number => lowercase v, number).

>
> Signed-off-by: Edward O'Callaghan <funfunctor at folklore1984.net>
> ---
>  src/mesa/main/formatquery.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/mesa/main/formatquery.c b/src/mesa/main/formatquery.c
> index 598d34d..6aa57ec 100644
> --- a/src/mesa/main/formatquery.c
> +++ b/src/mesa/main/formatquery.c
> @@ -1564,7 +1564,7 @@ _mesa_GetInternalformati64v(GLenum target, GLenum
internalformat,
>      * no pname can return a negative value, we fill params32 with
negative
>      * values as reference values, that can be used to know what
copy-back to
>      * params */
> -   memset(params32, -1, 16);
> +   for (i = 0; i < realSize; i++) params32[i] = -1;

If you keep a loop, then what Brian already said.

But out of curiosity, as mentioned, the other alternative is filling
params32 with -1 when defining it:
     GLint params32[16] = { [0 ... 15] = -1 };

Any disadvantage over the loop?


If realSize < 16, this form will write more bytes. However if the fill size
is known at compile time, the compiler should be able to optimize the code
more, like using 4 sse writes without any loop instead of up-to-16 dword
ones in a loop.

Gustaw
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