* src/buffer.c (compare_overlays): Avoid qsort's instability.

Fixes: debbugs:6830

2 files changed, 17 insertions, 9 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index f623e9d46e7..b984064e26c 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2012-03-09  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * buffer.c (compare_overlays): Avoid qsort's instability (bug#6830).
+
 2012-03-08  Jan Djärv  <jan.h.d@swipnet.se>
 
         * gtkutil.c (x_wm_set_size_hint): Use one row in call to
@@ -201,8 +205,8 @@
 
 2012-02-04  Eli Zaretskii  <eliz@gnu.org>
 
-        * w32.c (get_emacs_configuration_options): Include
-        --enable-checking, if specified, in the return value.
+        * w32.c (get_emacs_configuration_options):
+        Include --enable-checking, if specified, in the return value.
 
 2012-02-04  Martin Rudalics  <rudalics@gmx.at>
 
@@ -308,8 +312,8 @@
 2012-01-19  Martin Rudalics  <rudalics@gmx.at>
 
         * window.c (save_window_save, Fcurrent_window_configuration)
-        (Vwindow_persistent_parameters): Do not use Qstate.  Rewrite
-        doc-strings.
+        (Vwindow_persistent_parameters): Do not use Qstate.
+        Rewrite doc-strings.
 
 2012-01-19  Kenichi Handa  <handa@m17n.org>
 
@@ -483,9 +487,9 @@
         * nsselect.m (CUT_BUFFER_SUPPORT): Remove define.
         (symbol_to_nsstring): Fix indentation.
         (ns_symbol_to_pb): New function.
-        (Fns_get_selection_internal): Renamed from Fns_get_cut_buffer_internal.
-        (Fns_rotate_cut_buffers_internal): Removed.
-        (Fns_store_selection_internal): Renamed from
+        (Fns_get_selection_internal): Rename from Fns_get_cut_buffer_internal.
+        (Fns_rotate_cut_buffers_internal): Remove.
+        (Fns_store_selection_internal): Rename from
         Fns_store_cut_buffer_internal.
         (ns_get_foreign_selection, Fx_own_selection_internal)
         (Fx_disown_selection_internal, Fx_selection_exists_p)
@@ -626,7 +630,7 @@
         (coding_set_destination): Return how many bytes
         coding->destination was relocated.
         (CODING_DECODE_CHAR, CODING_ENCODE_CHAR, CODING_CHAR_CHARSET)
-        (CODING_CHAR_CHARSET_P): Adjusted for the avove changes.
+        (CODING_CHAR_CHARSET_P): Adjust for the avove changes.
 
 2011-12-05  Kazuhiro Ito  <kzhr@d1.dion.ne.jp>  (tiny change)
 
diff --git a/src/buffer.c b/src/buffer.c
index 1577254d92a..efb9a80f35d 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2864,7 +2864,11 @@ compare_overlays (const void *v1, const void *v2)
     return s1->beg < s2->beg ? -1 : 1;
   if (s1->end != s2->end)
     return s2->end < s1->end ? -1 : 1;
-  return 0;
+  /* Avoid the non-determinism of qsort by choosing an arbitrary ordering
+     between "equal" overlays.  The result can still change between
+     invocations of Emacs, but it won't change in the middle of
+     `find_field' (bug#6830).  */
+  return XHASH (s1->overlay) < XHASH (s2->overlay) ? -1 : 1;
 }
 
 /* Sort an array of overlays by priority.  The array is modified in place.