[project @ 2002-07-04 16:22:02 by simonmar]

[ghc-base.git] / GHC / Float.lhs

diff --git a/GHC/Float.lhs b/GHC/Float.lhs
index d16ebeb..5c30439 100644 (file)
--- a/GHC/Float.lhs
+++ b/GHC/Float.lhs
@@ -1,23 +1,18 @@
-% ------------------------------------------------------------------------------
-% $Id: Float.lhs,v 1.5 2002/02/27 14:33:09 simonmar Exp $
-%
-% (c) The University of Glasgow, 1994-2000
-%
-
-\section[GHC.Num]{Module @GHC.Num@}
-
-The types
-
-       Float
-       Double
-
-and the classes
-
-       Floating
-       RealFloat
-
 \begin{code}
 {-# OPTIONS -fno-implicit-prelude #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.Float
+-- Copyright   :  (c) The University of Glasgow 1994-2002
+-- License     :  see libraries/base/LICENSE
+-- 
+-- Maintainer  :  cvs-ghc@haskell.org
+-- Stability   :  internal
+-- Portability :  non-portable (GHC Extensions)
+--
+-- The types 'Float' and 'Double', and the classes 'Floating' and 'RealFloat'.
+--
+-----------------------------------------------------------------------------
 
 #include "ieee-flpt.h"
 
@@ -103,7 +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
@@ -680,14 +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
@@ -698,6 +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