Fungi-1.0: Math.hs

module Math (
    squareRoot
  ) where

-----------------------------------------------------------

-- The following code was aquired from:
-- http://www.haskell.org/haskellwiki/Generic_number_type#squareRoot

(^!) :: Num a => a -> Int -> a
(^!) x n = x^n
 
squareRoot :: Integer -> Integer
squareRoot 0 = 0
squareRoot 1 = 1
squareRoot n =
   let twopows = iterate (^!2) 2
       (lowerRoot, lowerN) =
          last $ takeWhile ((n>=) . snd) $ zip (1:twopows) twopows
       newtonStep x = div (x + div n x) 2
       iters = iterate newtonStep (squareRoot (div n lowerN) * lowerRoot)
       isRoot r  =  r^!2 <= n && n < (r+1)^!2
   in  head $ dropWhile (not . isRoot) iters