Re: Your Emacs changes

[Dmitry Antipov <dmantipov@yandex.ru>]

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Richard Stallman wrote:

> Now that we have your papers, what changes should we install now?

Probably the thing described at http://lists.gnu.org/archive/html/emacs-devel/2007-07/msg00094.html.
Attached is the latest stuff on this.

Note the same optimization may be performed on sweeping floats.  But, since an amount of allocated
floats is too small in comparison with conses, an effect is expected to be very negligible.

Dmitry

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Index: alloc.c
===================================================================
RCS file: /sources/emacs/emacs/src/alloc.c,v
retrieving revision 1.414
diff -u -r1.414 alloc.c
--- alloc.c	19 Aug 2007 00:15:26 -0000	1.414
+++ alloc.c	21 Aug 2007 14:31:37 -0000
@@ -5974,23 +5974,53 @@
 
     for (cblk = cons_block; cblk; cblk = *cprev)
       {
-	register int i;
+	register int i = 0;
 	int this_free = 0;
-	for (i = 0; i < lim; i++)
-	  if (!CONS_MARKED_P (&cblk->conses[i]))
-	    {
-	      this_free++;
-	      cblk->conses[i].u.chain = cons_free_list;
-	      cons_free_list = &cblk->conses[i];
+
+	while (1)
+	  {
+	    if (cblk->gcmarkbits[i] == -1)
+	      {
+		/* Fast path - everything is marked.  */
+		cblk->gcmarkbits[i++] = 0;
+		num_used += BITS_PER_INT;
+	      }
+	    else
+	      {
+		/* Slow path - scan over each bit, from the beginning
+		   of current word to 'min (word boundary, LIM)'.  */
+		int start, stop;
+
+		start = i * BITS_PER_INT;
+		stop = lim - start;
+		if (stop > BITS_PER_INT)
+		  stop = BITS_PER_INT;
+		stop += start;
+
+		while (start < stop)
+		  {
+		    if (!CONS_MARKED_P (&cblk->conses[start]))
+		      {
+			this_free++;
+			cblk->conses[start].u.chain = cons_free_list;
+			cons_free_list = &cblk->conses[start];
 #if GC_MARK_STACK
-	      cons_free_list->car = Vdead;
+			cons_free_list->car = Vdead;
 #endif
-	    }
-	  else
-	    {
-	      num_used++;
-	      CONS_UNMARK (&cblk->conses[i]);
-	    }
+		      }
+		    else
+		      {
+			num_used++;
+			CONS_UNMARK (&cblk->conses[start]);
+		      }
+		    start++;
+		  }
+		if (stop < (++i) * BITS_PER_INT)
+		  /* Whole bitmap is scanned or LIM is reached.  */
+		  break;
+	      }
+	  }
+
 	lim = CONS_BLOCK_SIZE;
 	/* If this block contains only free conses and we have already
 	   seen more than two blocks worth of free conses then deallocate

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