[Haskell-beginners] The cost of generality,
or how expensive is realToFrac?
daniel.is.fischer at web.de
Mon Sep 20 10:53:25 EDT 2010
On Monday 20 September 2010 05:09:16 you wrote:
> I'm building with the latest Haskell Platform. GHC 6.12.3 and OpenGL
So we can forget about rewrite rules, newtypes, unsafeCoerce and all that
In OpenGL-188.8.131.52, GLclampf (and GLfloat &c.) were not newtypes, they were
type GLclampf = Float
and so on.
So it's clear that GHC rewrites realToFrac to double2Float# in the
benchmark, since it's converting to Float (that also explains the absence
of casts in your core).
Then, if floatToFloat is faster than realToFrac in your programme (compiled
with optimisations), that probably means GHC doesn't spot an opportunity to
replace realToFrac with double2Float# because the types are still
polymorphic. Perhaps some type annotations would help.
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