Atomically compares and exchanges the value specified by the first
  argument (a 64-bit pointer).  This function maps to the
  cmpxchg4.acq instruction with appropriate setup.

  The value at *Destination is compared with the value specified by
  Comparand.  If they are equal, Newval is written to *Destination,
  and Oldval is returned.  The exchange will have taken place if the
  value returned is equal to the Comparand.  The following algorithm
  is used:

  ar.ccv = Comparand;
  Oldval = *Destination;         //Atomic
  if (ar.ccv == *Destination)    //Atomic
      *Destination = Newval;     //Atomic
  return Oldval;

  Those parts of the algorithm marked "Atomic" are performed
  atomically by the cmpxchg4.acq instruction.  This instruction has
  acquire ordering semantics; that is, the memory read/write is made
  visible prior to all subsequent data memory accesses of the
  Destination by other processors.

  Syntax:

       unsigned __int64 _InterlockedCompareExchange_acq (volatile
       unsigned int *Destination, unsigned __int64 Newval, unsigned
       __int64 Comparand);