anchor.diff:  		   (index-register index-register))
         memory-operand
       (or (and (not (null base-register))
  -	     (>= (code-number base-register) 8))
  +	     (>= base-register 8))
   	(and (not (null index-register))
  -	     (>= (code-number index-register) 8)))))
  +	     (>= index-register 8)))))
   
   (defun sib-byte-p (memory-operand)
     (with-accessors ((base-register base-register)
  
positive.code: 	  ;; If there is no index register, but there is a base
  	  ;; register, then there is a SIB byte only if the R/M field
  	  ;; is #b100.
  	  (not (member (code-number base-register) '(4 12)))))))
  
  (defun displacement-size (memory-operand)
    (with-accessors ((displacement displacement))
  
negative.code: 		(typep displacement '(signed-byte 8)))
  	   ;; We have a base register and an 8-bit displacement.
  	   (multiple-value-bind (rex.b r/m)
  	       (floor base-register 8)
  	     (if (= r/m 4)
  		 `(,rex.b
  		   #b01000100 ; ModR/M byte
  