[Mesa-stable] [Mesa-dev] [PATCH 1/5] st/nine: Clamp RCP when 0*inf!=0

[Roland Scheidegger]

Am 12.09.2018 um 23:43 schrieb Roland Scheidegger:
> Am 12.09.2018 um 08:31 schrieb Axel Davy:
>> On 9/12/18 8:17 AM, Axel Davy wrote:
>>>
>>> The goal is to catch inf and -inf and replace them by FLT_MAX and
>>> -FLT_MAX.
>>>
>>> Without, the NaN would appear when doing mul or mad.
> Ah I somehow completely missed this (but indeed this code will replace
> nans with flt_max, I guess though it's fine as long as you try to avoid
> getting nans as inputs there in the first place).
> 
> 
>>>
>>> Axel
>>>
>>>
>>>
>> I small precision I want to add: This is not the only place clamping
>> makes a difference.
>>
>> Indeed else MUL_ZERO_WINS would be safe to use and remove all the clamping.
>>
>>
>> The rasterizers can produce NaN when given Inf in the vertex shader on
>> some devices for example,
>>
>> and I think on some devices inf and FLT_MAX give different color in the
>> pixel shader.
>>
>>
>> Thus why I want to test carefully what do the other vendors for all the
>> shader versions (we know already there are
>>
>> behaviour changes for some) and check with the behaviours mentionned
>> above, before removing the clamps when MUL_ZERO_WINS.
> Yes it's all quite a mess. d3d9 rules are awkward (if they are even
> documented), whereas gl may do whatever (personally I would consider at
> least for core contexts everything not following ieee754 rules a bug,
> well maybe not for gles...).
Forgot to mention, of course unless forced with things like mul_zero_wins.

Roland


> 
> Roland
> 
> 
>>
>>
>>
>> Axel
>>
>