[Mesa-dev] [PATCH] gallivm: unify sin and cos implementation

[Roland Mainz]

On Wed, Aug 21, 2013 at 1:45 AM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 21.08.2013 01:28, schrieb Roland Mainz:
>> On Wed, Aug 21, 2013 at 1:12 AM,  <sroland at vmware.com> wrote:
>>> From: Roland Scheidegger <sroland at vmware.com>
[snip]
>> Can you check whether the new code supports -nan correctly, please
>> (-nan is used by scientific software... we learned that the hard way
>> when we had to fix this in ksh93 for Sun) ?
>>
>
> This code is built to adhere to graphics apis, usually d3d10 (because it
> tends to be more strict than opengl/glsl).
> As such there's no rules (I think) as far as propagating "the right nan"
> concerns, and there's no distinction really between negative/positive
> QNaNs/SNaNs. The is_finite will catch all kind of nans (plus infs,
> obviously), but the output will always be the same NaN in this case,
> sign bits etc. will be lost (though IIRC sign bit, while possible with
> nan's, doesn't really have much meaning anyway).

Erm... the issue is (as Sun learned the hard way) that programmers may
use -nan and nan explicitly to pass error conditions down the
arithmetic chain without "littering" the "hot codepaths" with
if()/else (instead at the end the result is tested for -nan/nan to see
where the code approximately failed).

----

Bye,
Roland

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