[Mesa-dev] [PATCH 16/28] Replace IROUND_POS with _mesa_roundevenf

[Dylan Baker]

Quoting Erik Faye-Lund (2018-11-13 01:34:53)
> On Mon, 2018-11-12 at 09:22 -0800, Dylan Baker wrote:
> > Quoting Erik Faye-Lund (2018-11-12 04:51:47)
> > > On Fri, 2018-11-09 at 10:40 -0800, Dylan Baker wrote:
> > > > Which has the same behavior.
> > > 
> > > Does it? I'm not so sure... IROUND_POS seems to round to nearest
> > > integer depending on the FPU rounding mode, _mesa_roundevenf rounds
> > > to
> > > the nearest *even* value regardless of the FPU rounding mode, no?
> > > 
> > > I'm not sure if it matters or not, but *at least* point that out in
> > > the
> > > commit message. Unless I'm missing something, of course...
> > 
> > I should put it in the commit message, but there is a comment in
> > rounding.h that
> > if you change the rounding mode you get to keep the pieces.
> 
> Well, this might regress performance pretty badly. Especially in the
> swrast code, this could be bad...
> 

Why? we have the assumption that you don't change the rounding mode already in
core mesa and many of the drivers.

For performance, I measured a simple 1000 loops of rounding, and found that the
only way the rounding.h function was slower is if you used the __SSE4_1__
path... (It was the same performance as the int cast +0.5 implementation)

Dylan
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