From: Daniel Fischer <daniel.is.fischer@web.de>
Date: Thu, 21 Oct 2010 09:32:46 +0000 (+0000)
Subject: FIX #4336
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=b2f76d1e62488565e470ffc24551090c83f66ee5;p=ghc-base.git

FIX #4336
Avoid superfluous gcd calculation in recip for Ratio a because numerator
and denominator are known to be coprime.
---

diff --git a/GHC/Real.lhs b/GHC/Real.lhs
index 971f276..4c2ed45 100644
--- a/GHC/Real.lhs
+++ b/GHC/Real.lhs
@@ -331,7 +331,10 @@ instance  (Integral a)  => Num (Ratio a)  where
 instance  (Integral a)  => Fractional (Ratio a)  where
     {-# SPECIALIZE instance Fractional Rational #-}
     (x:%y) / (x':%y')   =  (x*y') % (y*x')
-    recip (x:%y)        =  y % x
+    recip (0:%_)        = error "Ratio.%: zero denominator"
+    recip (x:%y)
+        | x < 0         = negate y :% negate x
+        | otherwise     = y :% x
     fromRational (x:%y) =  fromInteger x :% fromInteger y
 
 instance  (Integral a)  => Real (Ratio a)  where