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