Unroll exponentation uo to 5 for inlining.

Author: axman6

Statistics/Sample/Fold.hs

@@ -139,7 +139,11 @@ import Prelude hiding ((^), sum)
 
 -- (^) operator from Prelude is just slow.
 (^) :: Double -> Int -> Double
-x ^ 1 = x
+!x ^ 1 = x
+x ^ 2 = x * x
+x ^ 3 = x * x * x
+x ^ 4 = (x * x) * (x * x)
+x ^ 5 = (x * x) * x * (x * x)
 -- x ^ n = x * (x ^ (n-1))
 x0 ^ n0 = go (n0-1) x0 where
     go 0 !acc = acc