X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FFloat.lhs;h=5c3043910eaf4ef4d4ea6818655667ebc9714876;hb=073a40996177960147ef91988910c6131ef29cb3;hp=382ef645da810b45e8c675fb88ff4fc1409ce876;hpb=b706340c451952adf230b5b8daecad8a1f34d714;p=ghc-base.git

diff --git a/GHC/Float.lhs b/GHC/Float.lhs
index 382ef64..5c30439 100644
--- a/GHC/Float.lhs
+++ b/GHC/Float.lhs
@@ -98,7 +98,10 @@ class  (RealFrac a, Floating a) => RealFloat a  where
 %*********************************************************
 
 \begin{code}
+-- | Single-precision floating point numbers.
 data Float	= F# Float#
+
+-- | Double-precision floating point numbers.
 data Double	= D# Double#
 
 instance CCallable   Float
@@ -675,14 +678,18 @@ fromRat x = x'
 Now, here's Lennart's code (which works)
 
 \begin{code}
-{-# SPECIALISE fromRat :: 
-	Rational -> Double,
-	Rational -> Float #-}
+{-# SPECIALISE fromRat :: Rational -> Double,
+			  Rational -> Float #-}
 fromRat :: (RealFloat a) => Rational -> a
-fromRat x 
-  | x == 0    =  encodeFloat 0 0 		-- Handle exceptional cases
-  | x <  0    =  - fromRat' (-x)		-- first.
-  | otherwise =  fromRat' x
+
+-- Deal with special cases first, delegating the real work to fromRat'
+fromRat (n :% 0) | n > 0  =  1/0	-- +Infinity
+		 | n == 0 =  0/0	-- NaN
+		 | n < 0  = -1/0	-- -Infinity
+
+fromRat (n :% d) | n > 0  = fromRat' (n :% d)
+		 | n == 0 = encodeFloat 0 0 		-- Zero
+		 | n < 0  = - fromRat' ((-n) :% d)
 
 -- Conversion process:
 -- Scale the rational number by the RealFloat base until
@@ -693,6 +700,7 @@ fromRat x
 -- a first guess of the exponent.
 
 fromRat' :: (RealFloat a) => Rational -> a
+-- Invariant: argument is strictly positive
 fromRat' x = r
   where b = floatRadix r
         p = floatDigits r