From: Ian Lynagh <igloo@earth.li>
Date: Tue, 18 Mar 2008 00:30:17 +0000 (+0000)
Subject: Replace (^) with a faster variant (from trac #1687)
X-Git-Tag: 2008-05-28~30
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=fe3a8c9fa0c8a55e29a72e7f526984b201270c49;p=ghc-base.git

Replace (^) with a faster variant (from trac #1687)
---

diff --git a/GHC/Real.lhs b/GHC/Real.lhs
index f7e2eb2..17faed9 100644
--- a/GHC/Real.lhs
+++ b/GHC/Real.lhs
@@ -404,13 +404,12 @@ odd             =  not . even
         Integer -> Int -> Integer,
         Int -> Int -> Int #-}
 (^)             :: (Num a, Integral b) => a -> b -> a
-_ ^ 0           =  1
-x ^ n | n > 0   =  f x (n-1) x
-                   where f _ 0 y = y
-                         f a d y = g a d  where
-                                   g b i | even i  = g (b*b) (i `quot` 2)
-                                         | otherwise = f b (i-1) (b*y)
-_ ^ _           = error "Prelude.^: negative exponent"
+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'
 
 -- | raise a number to an integral power
 {-# SPECIALISE (^^) ::