add booleanPrim to compat.

Crypto/Internal/Compat.hs

@@ -9,15 +9,20 @@
 -- or other needed packages, so that modules don't need to use CPP
 --
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE MagicHash #-}
 module Crypto.Internal.Compat
     ( unsafeDoIO
     , popCount
     , byteSwap64
+    , booleanPrim
     ) where
 
 import System.IO.Unsafe
 import Data.Word
 import Data.Bits
+#if __GLASGOW_HASKELL__ >= 708
+import GHC.Prim
+#endif
 
 -- | perform io for hashes that do allocation and ffi.
 -- unsafeDupablePerformIO is used when possible as the
@@ -46,3 +51,11 @@ byteSwap64 w =
     .|. ((w `shiftR` 24) .&. 0xff0000)   .|. ((w .&. 0xff0000) `shiftL` 24)
     .|. ((w `shiftR` 8)  .&. 0xff000000) .|. ((w .&. 0xff000000) `shiftL` 8)
 #endif
+
+#if __GLASGOW_HASKELL__ >= 708
+booleanPrim :: Int# -> Bool
+booleanPrim v = tagToEnum# v
+#else
+booleanPrim :: Bool -> Bool
+booleanPrim b = b
+#endif