2 files changed, 26 insertions, 6 deletions
diff --git a/src/Foreign/Ptr/Cast.hs b/src/Foreign/Ptr/Cast.hs
new file mode 100644
index 0000000..653604a
--- /dev/null
+++ b/src/Foreign/Ptr/Cast.hs
@@ -0,0 +1,21 @@
+-- Copyright 2018 Google LLC
+--
+-- Licensed under the Apache License, Version 2.0 (the "License"); you may not
+-- use this file except in compliance with the License. You may obtain a copy of
+-- the License at
+--
+--     https://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+-- License for the specific language governing permissions and limitations under
+-- the License.
+
+module Foreign.Ptr.Cast where
+
+import Foreign (Ptr)
+import Unsafe.Coerce (unsafeCoerce)
+
+asVoidPtr :: Ptr a -> Ptr ()
+asVoidPtr = unsafeCoerce
diff --git a/src/Foreign/Ptr/ConstantTimeEquals.hs b/src/Foreign/Ptr/ConstantTimeEquals.chs
index 0bd24e7..6b34e7b 100644
--- a/src/Foreign/Ptr/ConstantTimeEquals.hs
+++ b/src/Foreign/Ptr/ConstantTimeEquals.chs
@@ -12,20 +12,19 @@
 -- License for the specific language governing permissions and limitations under
 -- the License.
 
-{-# LANGUAGE ScopedTypeVariables #-}
-
 module Foreign.Ptr.ConstantTimeEquals where
 
 import Foreign (Ptr)
 import Foreign.C.Types
 
-foreign import ccall "openssl/mem.h CRYPTO_memcmp"
-  cryptoMemcmp :: Ptr a -> Ptr a -> CSize -> IO CInt
+import Foreign.Ptr.Cast (asVoidPtr)
+
+#include <openssl/mem.h>
 
 -- | Directly compares two buffers for equality. This operation takes an amount
 -- of time dependent on the specified size but independent of either buffer's
 -- contents.
 constantTimeEquals :: Ptr a -> Ptr a -> Int -> IO Bool
 constantTimeEquals a b size =
-  let size' = fromIntegral size :: CSize
-  in (== 0) <$> cryptoMemcmp a b size'
+  let size' = fromIntegral size :: CULong
+  in (== 0) <$> {#call CRYPTO_memcmp as ^#} (asVoidPtr a) (asVoidPtr b) size'