+(defmacro atomic-incf (place &optional (diff 1))
+ #!+sb-doc
+ "Atomically increments PLACE by DIFF, and returns the value of PLACE before
+the increment.
+
+The incrementation is done using word-size modular arithmetic: on 32 bit
+platforms ATOMIC-INCF of #xFFFFFFFF by one results in #x0 being stored in
+PLACE.
+
+PLACE must be an accessor form whose CAR is the name of a DEFSTRUCT accessor
+whose declared type is (UNSIGNED-BYTE 32) on 32 bit platforms,
+and (UNSIGNED-BYTE 64) on 64 bit platforms.
+
+DIFF defaults to 1, and must be a (SIGNED-BYTE 32) on 32 bit platforms,
+and (SIGNED-BYTE 64) on 64 bit platforms.
+
+EXPERIMENTAL: Interface subject to change."
+ (flet ((invalid-place ()
+ (error "Invalid first argument to ATOMIC-INCF: ~S" place)))
+ (unless (consp place)
+ (invalid-place))
+ (destructuring-bind (op &rest args) place
+ (when (cdr args)
+ (invalid-place))
+ (let ((dd (info :function :structure-accessor op)))
+ (if dd
+ (let* ((structure (dd-name dd))
+ (slotd (find op (dd-slots dd) :key #'dsd-accessor-name))
+ (index (dsd-index slotd))
+ (type (dsd-type slotd)))
+ (declare (ignorable structure index))
+ (unless (and (eq 'sb!vm:word (dsd-raw-type slotd))
+ (type= (specifier-type type) (specifier-type 'sb!vm:word)))
+ (error "ATOMIC-INCF requires a slot of type (UNSIGNED-BYTE ~S), not ~S: ~S"
+ sb!vm:n-word-bits type place))
+ (when (dsd-read-only slotd)
+ (error "Cannot use ATOMIC-INCF with structure accessor for a read-only slot: ~S"
+ place))
+ #!+(or x86 x86-64)
+ `(truly-the sb!vm:word
+ (%raw-instance-atomic-incf/word (the ,structure ,@args)
+ ,index
+ (the sb!vm:signed-word ,diff)))
+ ;; No threads outside x86 and x86-64 for now, so this is easy...
+ #!-(or x86 x86-64)
+ (with-unique-names (structure old)
+ `(sb!sys:without-interrupts
+ (let* ((,structure ,@args)
+ (,old (,op ,structure)))
+ (setf (,op ,structure) (logand #.(1- (ash 1 sb!vm:n-word-bits))
+ (+ ,old (the sb!vm:signed-word ,diff))))
+ ,old))))
+ (invalid-place))))))
+