[Mesa-dev] [PATCH 1/3] glsl: Add support for constant expression evaluation on round(), roundEven().

[Eric Anholt]

On Tue, 4 Oct 2011 04:42:55 +0200, Henri Verbeet <hverbeet at gmail.com> wrote:
> On 4 October 2011 00:41, Eric Anholt <eric at anholt.net> wrote:
> > They're both implemented the same in GLSL IR (since round() has
> > undefined behavior for n + 0.5).  The specification of the C function
> > in use here is a bit unclear: rint(3) says that nearbyint() is like
> > rint() in that it uses the current rounding direction from
> > fesetround(3).  fesetround(3) says behavior is according to
> > FLT_ROUNDS, which on this system is 1 ("Rounding is toward nearest
> > number"), but doesn't specify behavior for n + 0.5 in that case.
> > However, round(3) says that rint(3) has roundEven()'s behavior for n +
> > 0.5.
> >
> Does this depend on applications not touching the rounding mode?

Yeah, just like our existing IROUND calls used in glGet, glDrawPixels,
and more, as far as I can see.
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