src/IPv4Address.hs: convert Int to Word32 before doing math in toEnum.

[hath.git] / src / IPv4Address.hs

diff --git a/src/IPv4Address.hs b/src/IPv4Address.hs
index 7e502125722cbfb354a53d517acd206a3fe678ad..85d86616023b19f3cc936ac2f69f1b65020df880 100644 (file)
--- a/src/IPv4Address.hs
+++ b/src/IPv4Address.hs
@@ -5,6 +5,7 @@ module IPv4Address(
   most_sig_bit_different )
 where
 
+import Data.Word (Word32)
 
 import Test.Tasty ( TestTree, testGroup )
 import Test.Tasty.HUnit ( (@?=), testCase )
@@ -188,18 +189,26 @@ instance Enum IPv4Address where
   -- | Convert an 'Int' @x@ to an 'IPv4Address'. Each octet of @x@ is
   --   right-shifted by the appropriate number of bits, and the fractional
   --   part is dropped.
-  toEnum x =
+  toEnum y =
     IPv4Address oct1 oct2 oct3 oct4
     where
+      -- Convert the input Int to a Word32 before we proceed. On x86,
+      -- the Int that we get could be negative (half of all IP
+      -- addresses correspond to negative numbers), and then the magic
+      -- below doesn't work. The Word32 type is unsigned, so we do the
+      -- math on that and then convert everything back to Int later on
+      -- once we have four much-smaller non-negative numbers.
+      x = fromIntegral y :: Word32
+
       -- Chop off the higher octets. x1 = x `mod` 2^32, would be
       -- redundant.
       x2 = x `mod` 2^(24 :: Integer)
       x3 = x `mod` 2^(16 :: Integer)
-      x4 = x `mod` 2^(8  :: Integer)
+      x4 = (fromIntegral $ x `mod` 2^(8  :: Integer)) :: Int
       -- Perform right-shifts. x4 doesn't need a shift.
-      shifted_x1 = x `quot` 2^(24 :: Integer)
-      shifted_x2 = x2 `quot` 2^(16 :: Integer)
-      shifted_x3 = x3 `quot` 2^(8 :: Integer)
+      shifted_x1 = (fromIntegral $ x `quot` 2^(24 :: Integer)) :: Int
+      shifted_x2 = (fromIntegral $ x2 `quot` 2^(16 :: Integer)) :: Int
+      shifted_x3 = fromIntegral $ x3 `quot` 2^(8 :: Integer) :: Int
       oct1 = toEnum shifted_x1 :: Octet
       oct2 = toEnum shifted_x2 :: Octet
       oct3 = toEnum shifted_x3 :: Octet
@@ -432,7 +441,11 @@ test_to_enum =
   where
     desc     = "192.168.0.0 in base-10 is 3232235520"
     expected = mk_testaddr 192 168 0 0
-    actual   = toEnum 3232235520 :: IPv4Address
+    -- We declare the big number as Word32 because otherwise, on x86,
+    -- we get a warning that it's too big to fit in a 32-bit integer.
+    -- Ultimately we convert it to a (negative) Int on those systems
+    -- anyway, but the gymnastics declare our intent to the compiler.
+    actual   = toEnum (fromIntegral (3232235520 :: Word32)) :: IPv4Address
 
 
 test_ord_instance1 :: TestTree