module Numeric.Combinatorics
( factorial
, choose
, doubleFactorial
, isPrime
) where
import Control.Composition
import Data.Word
import Foreign.C
foreign import ccall unsafe factorial_ats :: CInt -> CInt
foreign import ccall unsafe choose_ats :: CInt -> CInt -> CInt
foreign import ccall unsafe double_factorial :: CInt -> CInt
#if __GLASGOW_HASKELL__ >= 820
foreign import ccall unsafe is_prime_ats :: CInt -> CBool
#else
foreign import ccall unsafe is_prime_ats :: CInt -> CUChar
#endif
#if __GLASGOW_HASKELL__ >= 820
convertBool :: CBool -> Bool
#else
convertBool :: CUChar -> Bool
#endif
convertBool = go . fromIntegral
where
go :: Word8 -> Bool
go 0 = False
go 1 = True
go _ = False
isPrime :: Int -> Bool
isPrime = convertBool . is_prime_ats . fromIntegral
choose :: Int -> Int -> Int
choose = fromIntegral .* on choose_ats fromIntegral
doubleFactorial :: Int -> Int
doubleFactorial = fromIntegral . double_factorial . fromIntegral
factorial :: Int -> Int
factorial = fromIntegral . factorial_ats . fromIntegral