FIX #1282: 64-bit unchecked shifts are not exported from base

[ghc-base.git] / Data / HashTable.hs

diff --git a/Data/HashTable.hs b/Data/HashTable.hs
index 8ea7909..391876f 100644 (file)
--- a/Data/HashTable.hs
+++ b/Data/HashTable.hs
@@ -189,13 +189,13 @@ golden :: Int32
 golden = -1640531527
 
 -- | A sample (and useful) hash function for Int and Int32,
--- implemented by extracting the uppermost 32 bits of the 64-bit
+-- implemented by extracting the lowermost 32 bits of the
 -- result of multiplying by a 32-bit constant.  The constant is from
 -- Knuth, derived from the golden ratio:
 --
 -- > golden = round ((sqrt 5 - 1) * 2^31) :: Int
 hashInt :: Int -> Int32
-hashInt x = mulHi (fromIntegral x) golden
+hashInt x = fromIntegral x * golden
 
 -- hi 32 bits of a x-bit * 32 bit -> 64-bit multiply
 mulHi :: Int32 -> Int32 -> Int32
@@ -207,14 +207,14 @@ mulHi a b = fromIntegral (r `shiftR` 32)
 -- golden ratio and adding.  The implementation is:
 --
 -- > hashString = foldl' f 0
--- >   where f m c = fromIntegral (ord c) + mulHi m golden
+-- >   where f m c = fromIntegral (fromEnum c + 1) * golden + mulHi m golden
 --
 -- Note that this has not been extensively tested for reasonability,
 -- but Knuth argues that repeated multiplication by the golden ratio
 -- will minimize gaps in the hash space.
 hashString :: String -> Int32
 hashString = foldl' f 0
-  where f m c = fromIntegral (ord c) + mulHi m golden
+  where f m c = fromIntegral (ord c + 1) * golden + mulHi m golden
 
 -- | A prime larger than the maximum hash table size
 prime :: Int32