anchor.diff:  	(multiple-value-bind (index-nr rex-x)
   	    (when index (encode-register index))
   	  (ecase class
  -            (:xmm)
  +            ((:xmm :mm))
   	    (:gpr-64 (assert (= *cpu-mode* 64) (*cpu-mode*)
   			"64-bit operand-size only supported in 64-bit mode.")
   		     (setf rex-w t))
  
positive.code:       (incf *current-address* (ecase class
  				((:gpr-64 :gpr-32) 4)
  				(:gpr-16 2)
  				(:gpr-8 1)))
        (generate-modrm class r/m opc-minor opc)
        (decf *current-address* (ecase class
  				((:gpr-64 :gpr-32) 4)
  				(:gpr-16 2)
  				(:gpr-8 1)))
        (emit-imm class imm-value)
        t)))
  
  
negative.code:   (when (and (eql (reg-class dst) :xmm)
               (or (eql (reg-class src) :gpr-32)
                   (consp src)))
      (emit #x66)
      (return-from instruction
        (generate-modrm :xmm src dst '(#x0F #x6E))))
    (when (and (eql (reg-class src) :xmm)
               (or (eql (reg-class dst) :gpr-32)
                   (consp dst)))
      (emit #x66)
      (return-from instruction
        (generate-modrm :xmm dst src '(#x0F #x7E))))
    (when (and (eql (reg-class dst) :mm)
               (or (eql (reg-class src) :gpr-32)
                   (consp src)))
      (return-from instruction
        (generate-modrm :mm src dst '(#x0F #x6E))))
    (when (and (eql (reg-class src) :mm)
               (or (eql (reg-class dst) :gpr-32)
                   (consp dst)))
      (return-from instruction
        (generate-modrm :mm dst src '(#x0F #x7E)))))
  
  (define-instruction movq (dst src)
    (when (and (eql (reg-class dst) :xmm)
               (or (eql (reg-class src) :gpr-32)
                   (consp src)))
      (emit #x66)
      (return-from instruction
        (generate-modrm :gpr-64 src dst '(#x0F #x6E))))
    (when (and (eql (reg-class src) :xmm)
               (or (eql (reg-class dst) :gpr-32)
                   (consp dst)))
      (emit #x66)
      (return-from instruction
        (generate-modrm :gpr-64 dst src '(#x0F #x7E))))
    (when (and (eql (reg-class dst) :mm)
               (or (eql (reg-class src) :gpr-32)
                   (consp src)))
      (return-from instruction
        (generate-modrm :gpr-64 src dst '(#x0F #x6E))))
    (when (and (eql (reg-class src) :mm)
               (or (eql (reg-class dst) :gpr-32)
                   (consp dst)))
      (return-from instruction
        (generate-modrm :gpr-64 dst src '(#x0F #x7E)))))
  
  (define-instruction ucomiss (lhs rhs)
    (modrm :xmm rhs lhs '(#x0F #x2E)))
  