A faster (^)-function.
|Reported by:||moonlite@…||Owned by:|
|Type of failure:||None/Unknown||Difficulty:||Unknown|
|Test Case:||Blocked By:|
This function performs better for me than the (^)-function in GHC. I seem to only be able to test it for the Integer type though and its only tested with ghc 6.6 (and ghc 6.6.1 by byorgey on #haskell).
I'm not sure if you really need this or if it is correct, but after discussion on #haskell i was asked to make a bug report so here it is! Enjoy. :)
module Pow (pow) where import Prelude hiding ((^)) pow = (^) (^) :: (Integral b, Num a) => a -> b -> a x ^ y | y < 0 = error "Negative exponent" | y == 0 = 1 | y == 1 = x | odd y = x * x^(y - 1) | otherwise = let x' = x^(y `div` 2) in x' * x'
-- TestData.hs module TestData where e = 10^8
-- mytest.hs import Pow import TestData main = print $ (2 `pow` e) `mod` 2
-- ghctest.hs import TestData main = print $ (2 ^ e) `mod` 2
Test results (performance)
$ time ./ghctest 0 real 0m11.744s user 0m11.449s sys 0m0.104s $ time ./mytest 0 real 0m6.794s user 0m6.696s sys 0m0.084s -}
-- qc.hs -- $ ./qc -- OK, passed 100 tests. import Test.QuickCheck import Pow main = quickCheck prop prop x y = y >= 0 ==> x `pow` y == x^y
Change History (14)
comment:4 Changed 6 years ago by guest
- Architecture changed from Unknown to x86
- Component changed from Compiler to Prelude
- Operating System changed from Unknown to Linux
comment:11 Changed 21 months ago by mihai.maruseac
- Cc mihai.maruseac@… added
- Type of failure set to None/Unknown