#2306: The (^) operator sometimes uses one (*) more than needed.
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Reporter: guest | Owner: igloo
Type: bug | Status: closed
Priority: normal | Milestone: 6.8.3
Component: Prelude | Version: 6.8.2
Severity: minor | Resolution: fixed
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Changes (by igloo):
* status: new => closed
* resolution: => fixed
Comment:
It's now
{{{
(^) :: (Num a, Integral b) => a -> b -> a
x0 ^ y0 | y0 < 0 = error "Negative exponent"
| y0 == 0 = 1
| otherwise = f x0 y0
where -- f : x0 ^ y0 = x ^ y
f x y | even y = f (x * x) (y `quot` 2)
| y == 1 = x
| otherwise = g (x * x) ((y - 1) `quot` 2) x
-- g : x0 ^ y0 = (x ^ y) * z
g x y z | even y = g (x * x) (y `quot` 2) z
| y == 1 = x * z
| otherwise = g (x * x) ((y - 1) `quot` 2) (x * z)
}}}
in the HEAD and 6.8 branch.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2306#comment:2>
GHC <http://www.haskell.org/ghc/>
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