anchor.diff:      (setf (elt flags (- 15 6)) (flag :zf))
       (setf (elt flags (- 15 7)) (flag :sf))
       (when is-word
  +      (setf (elt flags (- 15 9)) (flag :if))
         (setf (elt flags (- 15 10)) (flag :df))
         (setf (elt flags (- 15 11)) (flag :of)))
       (bit-vector->integer flags)))
  
positive.code: (defun set-direction-flag ()
    (disasm-instr '("std")
      (setf (flag-p :df) t)))
  
  ;; One-byte opcodes on registers
  
  
negative.code:     ((= opcode #xf5) (complement-carry-flag))
      ((= opcode #xfc) (clear-direction-flag))
      ((= opcode #xfd) (set-direction-flag))
      ((= opcode #xfa) (clear-interrupt-flag))
      ((= opcode #xfb) (set-interrupt-flag))
      ((= opcode #x06) (push-segment :es))
      ((= opcode #x07) (pop-segment :es))
      ((= opcode #x0e) (push-segment :cs))
  