[Haskell-cafe] efficient chop
roma at ro-che.info
Wed Sep 14 09:11:46 CEST 2011
* Kazu Yamamoto <kazu at iij.ad.jp> [2011-09-14 15:59:05+0900]
> My friend reached the following version:
> chop :: String -> String
> chop = foldr go 
> go x xs
> | isSpace x && null xs = 
> | otherwise = x:xs
> This version is faster than the reverse version in most cases. The
> point is checking "isSpace" first and falling into "otherwise" in many
> cases, which is a natural co-recursion.
This was exactly my first attempt on rewriting your foldr version.
Unfortunately, it doesn't seem faster at all (foldr2 below).
The test input was replicate 100 'a' ++ replicate 100 ' '.
GHC 7, -O2.
mean: 2.808462 us, lb 2.807047 us, ub 2.810520 us, ci 0.950
std dev: 8.620822 ns, lb 6.535738 ns, ub 11.59552 ns, ci 0.950
mean: 4.128217 us, lb 4.125409 us, ub 4.134086 us, ci 0.950
std dev: 20.07591 ns, lb 11.47572 ns, ub 38.33738 ns, ci 0.950
mean: 6.701714 us, lb 6.692093 us, ub 6.711627 us, ci 0.950
std dev: 50.06638 ns, lb 42.25004 ns, ub 64.84223 ns, ci 0.950
Roman I. Cheplyaka :: http://ro-che.info/
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