Bug 554687 patch 1: Add Swap() method for nsSMILValue. r=roc

content/smil/nsSMILValue.cpp

@@ -38,6 +38,7 @@
 
 #include "nsSMILValue.h"
 #include "nsDebug.h"
+#include "prlog.h"
 
 //----------------------------------------------------------------------
 // Public methods
@@ -84,6 +85,29 @@ nsSMILValue::operator==(const nsSMILValue& aVal) const
   return mType == aVal.mType && mType->IsEqual(*this, aVal);
 }
 
+static inline void
+CopyMemberData(nsSMILValue& aDest, const nsSMILValue& aSrc)
+{
+  aDest.mType = aSrc.mType;
+  aDest.mU.mUint = aSrc.mU.mUint;
+  // Make sure the above assignments accounted for all the bits in nsSMILValue
+  PR_STATIC_ASSERT(sizeof(aDest) ==
+                   sizeof(aDest.mType) + sizeof(aDest.mU.mUint));
+}
+
+void
+nsSMILValue::Swap(nsSMILValue& aOther)
+{
+  nsSMILValue tmp;
+  CopyMemberData(tmp, aOther);    // tmp    = aOther
+  CopyMemberData(aOther, *this);  // aOther = this
+  CopyMemberData(*this, tmp);     // this   = tmp
+
+  // |tmp| is about to die -- we need to clear its mType, so that its
+  // destructor doesn't muck with the data we just transferred out of it.
+  tmp.mType = &nsSMILNullType::sSingleton;
+}
+
 nsresult
 nsSMILValue::Add(const nsSMILValue& aValueToAdd, PRUint32 aCount)
 {

content/smil/nsSMILValue.h

@@ -68,6 +68,8 @@ public:
     return (mType == &nsSMILNullType::sSingleton);
   }
 
+  // Swaps the contents (mU & mType) of two nsSMILValue objects.
+  void     Swap(nsSMILValue& aOther);
   nsresult Add(const nsSMILValue& aValueToAdd, PRUint32 aCount = 1);
   nsresult SandwichAdd(const nsSMILValue& aValueToAdd);
   nsresult ComputeDistance(const nsSMILValue& aTo, double& aDistance) const;