code: def PXOR(cpu, dest, src):
          
          res = dest.write(dest.read() ^ src.read())
docs: Logical exclusive OR.
  
          Performs a bitwise logical exclusive-OR (XOR) operation on the quadword
          source (second) and destination (first) operands and stores the result
          in the destination operand location. The source operand can be an MMX(TM)
          technology register or a quadword memory location; the destination operand
          must be an MMX register. Each bit of the result is 1 if the corresponding
          bits of the two operands are different; each bit is 0 if the corresponding
          bits of the operands are the same::
  
              DEST  =  DEST XOR SRC;
  
          :param cpu: current CPU.
          :param dest: destination operand.
          :param src: quadword source operand.