+ -- | Create an 'Octet' from an 'Int'. The docs for Enum say we
+ -- should throw a runtime error on out-of-bounds, so we do.
+ toEnum x
+ | x < minBound || x > maxBound = error "octet out of bounds"
+ | otherwise = Octet a1 a2 a3 a4 a5 a6 a7 a8
+ where
+ a1 = if (x >= 128) then B.One else B.Zero
+ a2 = if ((x `mod` 128) >= 64) then B.One else B.Zero
+ a3 = if ((x `mod` 64) >= 32) then B.One else B.Zero
+ a4 = if ((x `mod` 32) >= 16) then B.One else B.Zero
+ a5 = if ((x `mod` 16) >= 8) then B.One else B.Zero
+ a6 = if ((x `mod` 8) >= 4) then B.One else B.Zero
+ a7 = if ((x `mod` 4) >= 2) then B.One else B.Zero
+ a8 = if ((x `mod` 2) == 1) then B.One else B.Zero
+
+ -- | Convert each bit to its integer value, and multiply by the
+ -- appropriate power of two. Sum them up, and we should get an integer
+ -- between 0 and 255.
+ fromEnum x =
+ 128 * (fromEnum (b1 x)) +
+ 64 * (fromEnum (b2 x)) +
+ 32 * (fromEnum (b3 x)) +
+ 16 * (fromEnum (b4 x)) +
+ 8 * (fromEnum (b5 x)) +
+ 4 * (fromEnum (b6 x)) +
+ 2 * (fromEnum (b7 x)) +
+ 1 * (fromEnum (b8 x))
+
+
+
+instance Read Octet where
+ readsPrec _ s =
+ case (reads s :: [(Int, String)]) of
+ [] -> []
+ (x,leftover):_ -> go x leftover
+ where
+ go :: Int -> String -> [(Octet, String)]
+ go x' leftover'
+ | x' < minBound || x' > maxBound = []
+ | otherwise = [(toEnum x', leftover')]
+
+
+-- Test lists.
+octet_tests :: Test
+octet_tests =
+ testGroup "Octet Tests" [
+ test_octet_from_int1,
+ test_octet_mask1,
+ test_octet_mask2 ]