id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
1687	A faster (^)-function.	moonlite@…		"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'
}}}

Tests

{{{
-- 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

-}
}}}

QuickCheck test
{{{
-- 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
}}}"	bug	new	normal	_|_	Prelude	6.6.1			mihai.maruseac@…	Linux	x86	None/Unknown	Unknown