+
+(defun toggle-word-width (chunk inst stream dstate)
+ (declare (ignore chunk inst stream))
+ (let ((word-width (or (sb!disassem:dstate-get-prop dstate 'word-width)
+ +default-operand-size+)))
+ (setf (sb!disassem:dstate-get-prop dstate 'word-width)
+ (ecase word-width
+ (:word :dword)
+ (:dword :word)))))
+
+;;; This is a "prefix" instruction, which means that it modifies the
+;;; following instruction in some way without having an actual
+;;; mnemonic of its own.
+(define-instruction operand-size-prefix (segment)
+ (:printer byte ((op +operand-size-prefix-byte+))
+ nil ; don't actually print it
+ :control #'toggle-word-width))