X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=Data%2FBits.hs;h=88f707affd6f8e5fcf0638dfd98669f9e1d3e013;hb=74bc2d04fdbae494bcf4839c4ec5e6ec1d0bf600;hp=25bc9a1f9b645ce91d467a66febf9e77ca55b3a8;hpb=58251b3e59d8cabbeaf8a2f4679ac17012b8b0d3;p=haskell-directory.git

diff --git a/Data/Bits.hs b/Data/Bits.hs
index 25bc9a1..88f707a 100644
--- a/Data/Bits.hs
+++ b/Data/Bits.hs
@@ -1,4 +1,4 @@
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -fno-implicit-prelude #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Bits
@@ -9,11 +9,11 @@
 -- Stability   :  experimental
 -- Portability :  portable
 --
---  This module defines bitwise operations for signed and unsigned
---  integers.  Instances of the class 'Bits' for the 'Int' and
---  'Integer' types are available from this module, and instances for
---  explicitly sized integral types are available from the
---  "Data.Int" and "Data.Word" modules.
+-- This module defines bitwise operations for signed and unsigned
+-- integers.  Instances of the class 'Bits' for the 'Int' and
+-- 'Integer' types are available from this module, and instances for
+-- explicitly sized integral types are available from the
+-- "Data.Int" and "Data.Word" modules.
 --
 -----------------------------------------------------------------------------
 
@@ -66,6 +66,10 @@ The 'Bits' class defines bitwise operations over integral types.
 
 * Bits are numbered from 0 with bit 0 being the least
   significant bit.
+
+Minimal complete definition: '.&.', '.|.', 'xor', 'complement',
+('shift' or ('shiftL' and 'shiftR')), ('rotate' or ('rotateL' and 'rotateR')),
+'bitSize' and 'isSigned'.
 -}
 class Num a => Bits a where
     -- | Bitwise \"and\"
@@ -80,8 +84,11 @@ class Num a => Bits a where
     {-| Reverse all the bits in the argument -}
     complement        :: a -> a
 
-    {-| Shift the argument left by the specified number of bits.
-	Right shifts (signed) are specified by giving a negative value.
+    {-| @'shift' x i@ shifts @x@ left by @i@ bits if @i@ is positive,
+	or right by @-i@ bits otherwise.
+	Right shifts perform sign extension on signed number types;
+	i.e. they fill the top bits with 1 if the @x@ is negative
+	and with 0 otherwise.
 
 	An instance can define either this unified 'shift' or 'shiftL' and
 	'shiftR', depending on which is more convenient for the type in
@@ -92,8 +99,8 @@ class Num a => Bits a where
                   | i==0 = x
                   | i>0  = x `shiftL` i
 
-    {-| Rotate the argument left by the specified number of bits.
-	Right rotates are specified by giving a negative value.
+    {-| @'rotate' x i@ rotates @x@ left by @i@ bits if @i@ is positive,
+	or right by @-i@ bits otherwise.
 
         For unbounded types like 'Integer', 'rotate' is equivalent to 'shift'.
 
@@ -160,8 +167,11 @@ class Num a => Bits a where
     shiftL            :: a -> Int -> a
     x `shiftL`  i = x `shift`  i
 
-    {-| Shift the argument right (signed) by the specified number of bits
+    {-| Shift the first argument right by the specified number of bits
 	(which must be non-negative).
+	Right shifts perform sign extension on signed number types;
+	i.e. they fill the top bits with 1 if the @x@ is negative
+	and with 0 otherwise.
 
 	An instance can define either this and 'shiftL' or the unified
 	'shift', depending on which is more convenient for the type in
@@ -188,6 +198,8 @@ class Num a => Bits a where
     x `rotateR` i = x `rotate` (-i)
 
 instance Bits Int where
+    {-# INLINE shift #-}
+
 #ifdef __GLASGOW_HASKELL__
     (I# x#) .&.   (I# y#)  = I# (word2Int# (int2Word# x# `and#` int2Word# y#))
     (I# x#) .|.   (I# y#)  = I# (word2Int# (int2Word# x# `or#`  int2Word# y#))
@@ -197,8 +209,8 @@ instance Bits Int where
         | i# >=# 0#        = I# (x# `iShiftL#` i#)
         | otherwise        = I# (x# `iShiftRA#` negateInt# i#)
     (I# x#) `rotate` (I# i#) =
-        I# (word2Int# ((x'# `shiftL#` i'#) `or#`
-                       (x'# `shiftRL#` (wsib -# i'#))))
+        I# (word2Int# ((x'# `uncheckedShiftL#` i'#) `or#`
+                       (x'# `uncheckedShiftRL#` (wsib -# i'#))))
         where
         x'# = int2Word# x#
         i'# = word2Int# (int2Word# i# `and#` int2Word# (wsib -# 1#))