[Haskell-beginners] Performance of Idiomatic lazy Haskell
daniel.is.fischer at web.de
Mon Feb 1 08:52:41 EST 2010
Am Montag 01 Februar 2010 14:31:40 schrieb Markus Böhm:
> Daniel, with LuaJIT it needs 1.45 sec cpu-time on my machine with
> attached variant.
That's pretty fast.
> I compiled all our Haskell variants with ghc --make -O2.
Well, GHC isn't as good at loop-optimising as gcc is. Depending on the
loop, the via-C compiled binaries are between 1.4 and 2.3 times faster than
the NCG compiled.
> I don't know about -fvia-C, have to find out. I hope I didn't
> distract You with my Lua variant.
> In any case thank You very much for
> your advice. Markus.
Can you try the below with
ghc -O2 -fexcess-precision -fvia-C -optc-O3 -o luaLoop --make Whatever.hs
and run with
echo '0.00000001' | time ./luaLoop
It's a fairly direct translation of the Lua code, and it runs here more or
less equally fast as (gcc compiled) C-loops.
module Main (main) where
main :: IO ()
main = do
eps <- readLn :: IO Double
print $ 4*calcPi eps
calcPi :: Double -> Double
calcPi eps = go False 1 3
go bl p1 i
| 4*abs(p2-p1) < eps = p1
| otherwise = go (not bl) p2 (i+2)
p2 | bl = p1+1/i
| otherwise = p1-1/i
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