[Mesa-dev] [PATCH 2/2] util: Make CLAMP turn NaN into MIN.

[Marek Olšák]

On Tue, Jul 25, 2017 at 8:12 AM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 24.07.2017 um 11:44 schrieb Michel Dänzer:
>> On 14/07/17 10:01 PM, Marek Olšák wrote:
>>> Reviewed-by: Marek Olšák <marek.olsak at amd.com <mailto:marek.olsak at amd.com>>
>>
>> This change broke piglit spec at ext_texture_lod_bias@lodbias for me with
>> radeonsi (but not with llvmpipe).
>>
>>
>
> The S_FIXED function needs some fixing (for r600 too). The compiler
> takes full advantage of the fact that float to unsigned conversion is
> undefined for negative floats, apparently.
> The previous CLAMP would have used the state->lod_bias value if that was
> equal to the MIN value (-16) (so no way for the compiler to screw it up)
> whereas now it will use the -16 value.
> (This also means it was probably broken before, for values which were
> smaller than the min, albeit possibly noone cared as that would have
> been outside the advertized lod bias limits.)
> FWIW gcc generates a really terrible code for this (but that's not
> really dependent on the new or old macro...)
> (There's the same macro in mesa/main macros, but with signed numbers.)

https://patchwork.freedesktop.org/patch/168931/

Marek