(Fframe_or_buffer_changed_p): Calculate vector size right.

Add hysteresis when making it larger.  Fill it up reliably
and check at the end for overflowing it.
(syms_of_display): Make frame_and_buffer_state initially with 20 elts.

1 files changed, 13 insertions, 6 deletions

diff --git a/src/dispnew.c b/src/dispnew.c
index a1240cb7c6b..a09d9273e61 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -1953,13 +1953,14 @@ the current state.\n")
   /* Start with 1 so there is room for at least one lambda at the end.  */
   n = 1;
   FOR_EACH_FRAME (tail, frame)
-    n++;
+    n += 2;
   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);
+      || n + 20 < XVECTOR (frame_and_buffer_state)->size / 2)
+    /* Add 20 extra so we grow it less often.  */
+    frame_and_buffer_state = Fmake_vector (make_number (n + 20), Qlambda);
   vecp = XVECTOR (frame_and_buffer_state)->contents;
   FOR_EACH_FRAME (tail, frame)
     {
@@ -1976,9 +1977,15 @@ the current state.\n")
       *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)
+  /* Fill up the vector with lambdas (always at least one).  */
+  *vecp++ = Qlambda;
+  while  (vecp - XVECTOR (frame_and_buffer_state)->contents
+          < XVECTOR (frame_and_buffer_state)->size)
     *vecp++ = Qlambda;
+  /* Make sure we didn't overflow the vector.  */
+  if (vecp - XVECTOR (frame_and_buffer_state)->contents
+      > XVECTOR (frame_and_buffer_state)->size)
+    abort ();
   return Qt;
 }
 
@@ -2545,7 +2552,7 @@ syms_of_display ()
   defsubr (&Ssleep_for);
   defsubr (&Ssend_string_to_terminal);
 
-  frame_and_buffer_state = Fmake_vector (make_number (1), Qlambda);
+  frame_and_buffer_state = Fmake_vector (make_number (20), Qlambda);
   staticpro (&frame_and_buffer_state);
 
   DEFVAR_INT ("baud-rate", &baud_rate,