iteratebenchmark.hs

-- Compiled with GHC 7.4.1 under Debian Wheezy amd64 using the "-O2"
-- optimization, this takes 7.9 s on my Core2Duo@1.66GHz.
-- If GHCs LLVM backend is used the time goes down to 6.1 s.
-- It should be noted, that GHC automatically inlines 'logisticChaos' and
-- 'iterateN', because there are used only once.
--
-- The manually inlined C++ version needs 7.9 s to do the same (g++ 4.7 "-O2").
-- (see: http://kenta.blogspot.de/2013/07/abfsttwf-optimizing-iterate.html for the C++ code)

import Control.Exception (assert)

main = print $ iterateN (10^9) logisticChaos 0.5

logisticChaos :: Double -> Double
logisticChaos x = 3.57 * x * (1-x)

iterateN :: Int -> (a -> a) -> a -> a
iterateN n f = assert (n>=0) (go n) where
    go 0 result = result
    go n x = go (n-1) $! f x