    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE NoImplicitPrelude #-}

    -- ----------------------------------------------------------------------------
    --
    --  (c) The University of Glasgow 2006
    --
    -- Fingerprints for recompilation checking and ABI versioning, and
    -- implementing fast comparison of Typeable.
    --
    -- ----------------------------------------------------------------------------

    module GHC.Fingerprint.Type (Fingerprint(..)) where

    import GHC.Base
    import GHC.List (length, replicate)
    import GHC.Num
    import GHC.Show
    import GHC.Word
    import Numeric (showHex)

    -- Using 128-bit MD5 fingerprints for now.

    data Fingerprint = Fingerprint {-# UNPACK #-} !Word64 {-# UNPACK #-} !Word64
      deriving (Eq, Ord)

    instance Show Fingerprint where
      show (Fingerprint w1 w2) = hex16 w1 ++ hex16 w2
        where
          -- | Formats a 64 bit number as 16 digits hex.
          hex16 :: Word64 -> String
          hex16 i = let hex = showHex i ""
                     in replicate (16 - length hex) '0' ++ hex