Simplify copy_overlay.

* buffer.c (copy_overlay): Simplify, use build_marker.
* lisp.h (struct Lisp_Overlay): Restore comment with minor tweaks.

src/ChangeLog

+2012-07-24  Dmitry Antipov  <dmantipov@yandex.ru>
+
+	Simplify copy_overlay.
+	* buffer.c (copy_overlay): Simplify, use build_marker.
+	* lisp.h (struct Lisp_Overlay): Restore comment with minor tweaks.
+
 2012-07-23  Eli Zaretskii  <eliz@gnu.org>
 	* print.c (print_object): Don't crash when a frame's name is nil

src/buffer.c

@@ -410,32 +410,24 @@ even if it is dead.  The return value is never nil.  */)
 static struct Lisp_Overlay *
 copy_overlays (struct buffer *b, struct Lisp_Overlay *list)
 {
-  Lisp_Object buffer;
   struct Lisp_Overlay *result = NULL, *tail = NULL;
 
-  XSETBUFFER (buffer, b);
-
   for (; list; list = list->next)
     {
-      Lisp_Object overlay, start, end, old_overlay;
-      ptrdiff_t charpos;
-
-      XSETMISC (old_overlay, list);
-      charpos = marker_position (OVERLAY_START (old_overlay));
-      start = Fmake_marker ();
-      Fset_marker (start, make_number (charpos), buffer);
-      XMARKER (start)->insertion_type
-	= XMARKER (OVERLAY_START (old_overlay))->insertion_type;
+      Lisp_Object overlay, start, end;
+      struct Lisp_Marker *m;
 
-      charpos = marker_position (OVERLAY_END (old_overlay));
-      end = Fmake_marker ();
-      Fset_marker (end, make_number (charpos), buffer);
-      XMARKER (end)->insertion_type
-	= XMARKER (OVERLAY_END (old_overlay))->insertion_type;
+      eassert (MARKERP (list->start));
+      m = XMARKER (list->start);
+      start = build_marker (b, m->charpos, m->bytepos);
+      XMARKER (start)->insertion_type = m->insertion_type;
 
-      overlay = build_overlay
-	(start, end, Fcopy_sequence (OVERLAY_PLIST (old_overlay)));
+      eassert (MARKERP (list->end));
+      m = XMARKER (list->end);
+      end = build_marker (b, m->charpos, m->bytepos);
+      XMARKER (end)->insertion_type = m->insertion_type;
 
+      overlay = build_overlay (start, end, Fcopy_sequence (list->plist));
       if (tail)
 	tail = tail->next = XOVERLAY (overlay);
       else

src/lisp.h

@@ -1286,6 +1286,17 @@ struct Lisp_Marker
 /* START and END are markers in the overlay's buffer, and
    PLIST is the overlay's property list.  */
 struct Lisp_Overlay
+/* An overlay's real data content is:
+   - plist
+   - buffer (really there are two buffer pointers, one per marker,
+     and both points to the same buffer)
+   - insertion type of both ends (per-marker fields)
+   - start & start byte (of start marker)
+   - end & end byte (of end marker)
+   - next (singly linked list of overlays)
+   - next fields of start and end markers (singly linked list of markers).
+   I.e. 9words plus 2 bits, 3words of which are for external linked lists.
+*/
   {
     ENUM_BF (Lisp_Misc_Type) type : 16;	/* = Lisp_Misc_Overlay */
     unsigned gcmarkbit : 1;