Bug 551736: Add parens around right-shift, to fix compile warning and make sure we construct hash value correctly. r=sicking

content/smil/nsSMILCompositor.cpp

@@ -50,9 +50,12 @@ nsSMILCompositor::KeyEquals(KeyTypePointer aKey) const
 /*static*/ PLDHashNumber
 nsSMILCompositor::HashKey(KeyTypePointer aKey)
 {
-  // Combine the 3 values into one numeric value, which will be hashed
-  return NS_PTR_TO_UINT32(aKey->mElement.get()) >> 4 +
-    NS_PTR_TO_INT32(aKey->mAttributeName.get()) +
+  // Combine the 3 values into one numeric value, which will be hashed.
+  // NOTE: We right-shift one of the pointers by 2 to get some randomness in
+  // its 2 lowest-order bits. (Those shifted-off bits will always be 0 since
+  // our pointers will be word-aligned.)
+  return (NS_PTR_TO_UINT32(aKey->mElement.get()) >> 2) +
+    NS_PTR_TO_UINT32(aKey->mAttributeName.get()) +
     (aKey->mIsCSS ? 1 : 0);
 }