[number] add further gmp optional compat

Crypto/Number/Compat.hs

@@ -18,6 +18,9 @@ module Crypto.Number.Compat
     , gmpInverse
     , gmpNextPrime
     , gmpTestPrimeMillerRabin
+    , gmpSizeInBytes
+    , gmpExportInteger
+    , gmpImportInteger
     ) where
 
 #ifndef MIN_VERSION_integer_gmp
@@ -29,6 +32,8 @@ import GHC.Integer.GMP.Internals
 import GHC.Base
 import GHC.Integer.Logarithms (integerLog2#)
 #endif
+import Data.Word
+import GHC.Ptr (Ptr(..))
 
 data GmpSupported a = GmpSupported a
                     | GmpUnsupported
@@ -94,3 +99,34 @@ gmpTestPrimeMillerRabin (I# tries) !n = GmpSupported $
 #else
 gmpTestPrimeMillerRabin _ _ = GmpUnsupported
 #endif
+
+gmpSizeInBytes :: Integer -> GmpSupported Int
+#if MIN_VERSION_integer_gmp(0,5,1)
+gmpSizeInBytes n = GmpSupported (I# (word2Int# (sizeInBaseInteger n 256#)))
+#else
+gmpSizeInBytes _ = GmpUnsupported
+#endif
+
+gmpExportInteger :: Integer -> Ptr Word8 -> GmpSupported (IO ())
+#if __GLASGOW_HASKELL__ >= 710
+gmpExportInteger n (Ptr addr) = GmpSupported $
+    _ <- exportIntegerToAddr n addr 1#
+    return ()
+#elif MIN_VERSION_integer_gmp(0,5,1)
+gmpExportInteger n (Ptr addr) = GmpSupported $ IO $ \s ->
+    case exportIntegerToAddr n addr 1# s of
+        (# s2, _ #) -> (# s2, () #)
+#else
+gmpExportInteger _ _ = GmpUnsupported
+#endif
+
+gmpImportInteger :: Int -> Ptr Word8 -> GmpSupported (IO Integer)
+#if __GLASGOW_HASKELL__ >= 710
+gmpImportInteger n (Ptr addr) = GmpSupported $
+    importIntegerFromAddr addr (int2Word# n) 1#
+#elif MIN_VERSION_integer_gmp(0,5,1)
+gmpImportInteger n (Ptr addr) = GmpSupported $ IO $ \s ->
+    importIntegerFromAddr addr (int2Word# n) 1# s
+#else
+gmpImportInteger _ _ = GmpUnsupported
+#endif