+
+ /* Exchange charstarts between current_frame and new_frame. */
+ temp1 = desired_frame->charstarts[vpos];
+ desired_frame->charstarts[vpos] = current_frame->charstarts[vpos];
+ current_frame->charstarts[vpos] = temp1;
+}
+\f
+/* A vector of size >= NFRAMES + 3 * NBUFFERS + 1, containing the session's
+ frames, buffers, buffer-read-only flags, and buffer-modified-flags,
+ and a trailing sentinel (so we don't need to add length checks). */
+static Lisp_Object frame_and_buffer_state;
+
+DEFUN ("frame-or-buffer-changed-p", Fframe_or_buffer_changed_p,
+ Sframe_or_buffer_changed_p, 0, 0, 0,
+ "Return non-nil if the frame and buffer state appears to have changed.\n\
+The state variable is an internal vector containing all frames and buffers,\n\
+along with the buffers' read-only and modified flags, which allows a fast\n\
+check to see whether the menu bars might need to be recomputed.\n\
+If this function returns non-nil, it updates the internal vector to reflect\n\
+the current state.\n")
+ ()
+{
+ Lisp_Object tail, frame, buf;
+ Lisp_Object *vecp;
+ int n;
+ vecp = XVECTOR (frame_and_buffer_state)->contents;
+ FOR_EACH_FRAME (tail, frame)
+ if (!EQ (*vecp++, frame))
+ goto changed;
+ for (tail = Vbuffer_alist; CONSP (tail); tail = XCONS (tail)->cdr)
+ {
+ buf = XCONS (XCONS (tail)->car)->cdr;
+ if (!EQ (*vecp++, buf))
+ goto changed;
+ if (!EQ (*vecp++, XBUFFER (buf)->read_only))
+ goto changed;
+ if (!EQ (*vecp++, Fbuffer_modified_p (buf)))
+ goto changed;
+ }
+ return Qnil;
+ changed:
+ n = 1;
+ FOR_EACH_FRAME (tail, frame)
+ n++;
+ for (tail = Vbuffer_alist; CONSP (tail); tail = XCONS (tail)->cdr)
+ n += 3;
+ /* Reallocate the vector if it's grown, or if it's shrunk a lot. */
+ if (n > XVECTOR (frame_and_buffer_state)->size
+ || n < XVECTOR (frame_and_buffer_state)->size / 2)
+ frame_and_buffer_state = Fmake_vector (make_number (n), Qlambda);
+ vecp = XVECTOR (frame_and_buffer_state)->contents;
+ FOR_EACH_FRAME (tail, frame)
+ *vecp++ = frame;
+ for (tail = Vbuffer_alist; CONSP (tail); tail = XCONS (tail)->cdr)
+ {
+ buf = XCONS (XCONS (tail)->car)->cdr;
+ *vecp++ = buf;
+ *vecp++ = XBUFFER (buf)->read_only;
+ *vecp++ = Fbuffer_modified_p (buf);
+ }
+ /* If we left any slack in the vector, fill it up now. */
+ for (; n < XVECTOR (frame_and_buffer_state)->size; ++n)
+ *vecp++ = Qlambda;
+ return Qt;