    -- |
    -- Module      : Crypto.Random.Entropy.RDRand
    -- License     : BSD-style
    -- Maintainer  : Vincent Hanquez <vincent@snarc.org>
    -- Stability   : experimental
    -- Portability : Good
    --
    {-# LANGUAGE ForeignFunctionInterface #-}
    module Crypto.Random.Entropy.RDRand
        ( RDRand
        ) where

    import Foreign.Ptr
    import Foreign.C.Types
    import Data.Word (Word8)
    import Crypto.Random.Entropy.Source

    foreign import ccall unsafe "cryptonite_cpu_has_rdrand"
       c_cpu_has_rdrand :: IO CInt

    foreign import ccall unsafe "cryptonite_get_rand_bytes"
      c_get_rand_bytes :: Ptr Word8 -> CInt -> IO CInt

    -- | fake handle to Intel RDRand entropy cpu instruction
    data RDRand = RDRand

    instance EntropySource RDRand where
        entropyOpen     = rdrandGrab
        entropyGather _ = rdrandGetBytes
        entropyClose  _ = return ()

    rdrandGrab :: IO (Maybe RDRand)
    rdrandGrab = supported `fmap` c_cpu_has_rdrand
      where supported 0 = Nothing
            supported _ = Just RDRand

    rdrandGetBytes :: Ptr Word8 -> Int -> IO Int
    rdrandGetBytes ptr sz = fromIntegral `fmap` c_get_rand_bytes ptr (fromIntegral sz)