    -- |
    -- Module      : Crypto.Internal.CompatPrim
    -- License     : BSD-style
    -- Maintainer  : Vincent Hanquez <vincent@snarc.org>
    -- Stability   : stable
    -- Portability : Compat
    --
    -- This module try to keep all the difference between versions of ghc primitive
    -- or other needed packages, so that modules don't need to use CPP.
    --
    -- Note that MagicHash and CPP conflicts in places, making it "more interesting"
    -- to write compat code for primitives
    --
    {-# LANGUAGE CPP #-}
    {-# LANGUAGE BangPatterns #-}
    {-# LANGUAGE MagicHash #-}
    {-# LANGUAGE UnboxedTuples #-}
    module Crypto.Internal.CompatPrim
        ( be32Prim
        , le32Prim
        , byteswap32Prim
        , booleanPrim
        , convert4To32
        ) where

    import GHC.Prim
    #if !defined(ARCH_IS_LITTLE_ENDIAN) && !defined(ARCH_IS_BIG_ENDIAN)
    import Data.Memory.Endian (getSystemEndianness, Endianness(..))
    #endif

    -- | byteswap Word# to or from Big Endian
    --
    -- on a big endian machine, this function is a nop.
    be32Prim :: Word# -> Word#
    #ifdef ARCH_IS_LITTLE_ENDIAN
    be32Prim = byteswap32Prim
    #elif defined(ARCH_IS_BIG_ENDIAN)
    be32Prim = id
    #else
    be32Prim w = if getSystemEndianness == LittleEndian then byteswap32Prim w else w
    #endif

    -- | byteswap Word# to or from Little Endian
    --
    -- on a little endian machine, this function is a nop.
    le32Prim :: Word# -> Word#
    #ifdef ARCH_IS_LITTLE_ENDIAN
    le32Prim w = w
    #elif defined(ARCH_IS_BIG_ENDIAN)
    le32Prim = byteswap32Prim
    #else
    le32Prim w = if getSystemEndianness == LittleEndian then w else byteswap32Prim w
    #endif

    -- | Simple compatibility for byteswap the lower 32 bits of a Word#
    -- at the primitive level
    byteswap32Prim :: Word# -> Word#
    #if __GLASGOW_HASKELL__ >= 708
    byteswap32Prim w = byteSwap32# w
    #else
    byteswap32Prim w =
        let !a =       uncheckedShiftL# w 24#
            !b = and# (uncheckedShiftL# w 8#) 0x00ff0000##
            !c = and# (uncheckedShiftRL# w 8#) 0x0000ff00##
            !d = and# (uncheckedShiftRL# w 24#) 0x000000ff##
         in or# a (or# b (or# c d))
    #endif

    -- | combine 4 word8 [a,b,c,d] to a word32 representing [a,b,c,d]
    convert4To32 :: Word# -> Word# -> Word# -> Word#
                 -> Word#
    convert4To32 a b c d = or# (or# c1 c2) (or# c3 c4)
      where
    #ifdef ARCH_IS_LITTLE_ENDIAN
            !c1 = uncheckedShiftL# a 24#
            !c2 = uncheckedShiftL# b 16#
            !c3 = uncheckedShiftL# c 8#
            !c4 = d
    #elif defined(ARCH_IS_BIG_ENDIAN)
            !c1 = uncheckedShiftL# d 24#
            !c2 = uncheckedShiftL# c 16#
            !c3 = uncheckedShiftL# b 8#
            !c4 = a
    #else
            !c1
                | getSystemEndianness == LittleEndian = uncheckedShiftL# a 24#
                | otherwise                           = uncheckedShiftL# d 24#
            !c2
                | getSystemEndianness == LittleEndian = uncheckedShiftL# b 16#
                | otherwise                           = uncheckedShiftL# c 16#
            !c3
                | getSystemEndianness == LittleEndian = uncheckedShiftL# c 8#
                | otherwise                           = uncheckedShiftL# b 8#
            !c4
                | getSystemEndianness == LittleEndian = d
                | otherwise                           = a
    #endif

    -- | Simple wrapper to handle pre 7.8 and future, where
    -- most comparaison functions don't returns a boolean
    -- anymore.
    #if __GLASGOW_HASKELL__ >= 708
    booleanPrim :: Int# -> Bool
    booleanPrim v = tagToEnum# v
    #else
    booleanPrim :: Bool -> Bool
    booleanPrim b = b
    #endif