X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FBits.hs;h=88f707affd6f8e5fcf0638dfd98669f9e1d3e013;hb=42acd5eac493493748281da8240ec6e98c9dbee9;hp=eb8ace1bd90a8e4ff044fb123fa5730a1f440d75;hpb=3a540635e558efbd275ae8bfa4326f5adfa96208;p=ghc-base.git

diff --git a/Data/Bits.hs b/Data/Bits.hs
index eb8ace1..88f707a 100644
--- a/Data/Bits.hs
+++ b/Data/Bits.hs
@@ -84,8 +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
@@ -96,8 +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'.
 
@@ -164,8 +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
@@ -203,8 +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#))