diff -rN -u old-mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/Base.hsc mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/Base.hsc
--- old-mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/Base.hsc	2008-10-16 11:01:29.000000000 +0200
+++ mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/Base.hsc	2008-10-16 11:01:29.000000000 +0200
@@ -48,6 +48,9 @@
 foreign import ccall unsafe "mix_bits"
     c_mix_word64 :: Word64 -> Word64
 
+foreign import ccall unsafe "double_from_long_long"
+    c_double_from_long_long :: Word64 -> Double
+
 foreign import ccall unsafe "seed_genrand64_block"
     c_seed_genrand64_block :: Ptr a -> Word64 -> IO ()
 
diff -rN -u old-mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/MTBlock.hs mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/MTBlock.hs
--- old-mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/MTBlock.hs	2008-10-16 11:01:29.000000000 +0200
+++ mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64/MTBlock.hs	2008-10-16 11:01:29.000000000 +0200
@@ -27,6 +27,7 @@
     -- * Misc functions
     blockLen,
     mixWord64,
+    word64ToDouble,
 ) where
 
 import GHC.Exts
@@ -92,3 +93,8 @@
   in
     W64# x4
 -}
+
+word64ToDouble :: Word64 -> Double
+word64ToDouble = c_double_from_long_long
+
+-- word64ToDouble i = fromIntegral (i `div` 2048) / 9007199254740992
diff -rN -u old-mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64.hs mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64.hs
--- old-mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64.hs	2008-10-16 11:01:29.000000000 +0200
+++ mersenne-random-pure64-0.2.0.2/System/Random/Mersenne/Pure64.hs	2008-10-16 11:01:29.000000000 +0200
@@ -98,7 +98,7 @@
 
 -- | Efficiently yield a new 53-bit precise 'Double' value, and a new generator.
 randomDouble :: PureMT -> (Double,PureMT)
-randomDouble g = (fromIntegral (i `div` 2048) / 9007199254740992, g')
+randomDouble g = (word64ToDouble i, g')
         where (i, g') = randomWord64 g
 {-# INLINE randomDouble #-}
 
diff -rN -u old-mersenne-random-pure64-0.2.0.2/cbits/mt19937-64-block.c mersenne-random-pure64-0.2.0.2/cbits/mt19937-64-block.c
--- old-mersenne-random-pure64-0.2.0.2/cbits/mt19937-64-block.c	2008-10-16 11:01:29.000000000 +0200
+++ mersenne-random-pure64-0.2.0.2/cbits/mt19937-64-block.c	2008-10-16 11:01:29.000000000 +0200
@@ -97,3 +97,8 @@
     x ^= (x >> 43);
     return x;
 }
+
+double double_from_long_long(unsigned long long x)
+{
+    return (x >> 11) * (1.0L/9007199254740992.0);
+}
diff -rN -u old-mersenne-random-pure64-0.2.0.2/include/mt19937-64-block.h mersenne-random-pure64-0.2.0.2/include/mt19937-64-block.h
--- old-mersenne-random-pure64-0.2.0.2/include/mt19937-64-block.h	2008-10-16 11:01:29.000000000 +0200
+++ mersenne-random-pure64-0.2.0.2/include/mt19937-64-block.h	2008-10-16 11:01:29.000000000 +0200
@@ -71,3 +71,5 @@
 void next_genrand64_block(mt_block st, mt_block newst);
 
 unsigned long long mix_bits(unsigned long long x);
+
+double double_from_long_long(unsigned long long x);