#2271: floor, ceiling, round :: Double -> Int are awesomely slow
------------------------------------------+---------------------------------
Reporter: dons | Owner: daniel.is.fischer
Type: bug | Status: patch
Priority: low | Milestone: 7.0.1
Component: libraries/base | Version: 7.1
Keywords: performance, math, double | Testcase:
Blockedby: | Difficulty: Unknown
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by michalt):
With the new patch GHC builds without any problems. I've run the testsuite
for
HEAD with and without the patch and the only difference is failure in
arith005
(more about it below). I haven't played with the QC tests, as quickcheck
apparently doesn't build with HEAD atm (maybe I'll do it when I have more
time).
Replying to [comment:17 daniel.is.fischer]:
> Oh, btw. due to the rewrite rules, in arith005, we get different
nonsense for
> the overflowing values with optimisations than a) before, b) without
> optimisations.
I think the difference that the tests were catching was the fact that
`-0.0` is
handled differently by `properFraction`:
{{{
module Main where
main = do
print $ (properFraction (-0.0) :: (Int,Float))
print $ (properFraction (-0.0) :: (Integer,Float))
print $ (properFraction (-0.0) :: (Int,Double))
print $ (properFraction (-0.0) :: (Integer,Double))
}}}
with the patch:
{{{
> ~/develop/ghc-mod/inplace/bin/ghc-stage2 --make -fforce-recomp Test
[1 of 1] Compiling Main ( Test.hs, Test.o )
Linking Test ...
> ./Test
(0,0.0)
(0,0.0)
(0,0.0)
(0,0.0)
> ~/develop/ghc-mod/inplace/bin/ghc-stage2 -O2 --make -fforce-recomp Test
[1 of 1] Compiling Main ( Test.hs, Test.o )
Linking Test ...
> ./Test
(0,-0.0)
(0,0.0)
(0,-0.0)
(0,0.0)
}}}
Without the patch the result is always `(0,0.0)`.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2271#comment:27>
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