{-# 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  -- ^ @since 4.4.0.0
           , Ord -- ^ @since 4.4.0.0
           )

-- | @since 4.7.0.0
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
