[src/trunk]: src/sys/kern Signed overflow is undefined behavior, and one vers...

[pooka <pooka%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/548d6f64b647
branches:  trunk
changeset: 783243:548d6f64b647
user:      pooka <pooka%NetBSD.org@localhost>
date:      Wed Dec 12 11:10:56 2012 +0000

description:
Signed overflow is undefined behavior, and one version of gcc
clearly tells us:

        kern_rate.c:98: warning: assuming signed overflow does not
        occur when assuming that (X + c) > X is always true

Check value against INT_MAX instead.  Also, for good measure throw
in a __predict() to flag the assumed common case.

diffstat:

 sys/kern/kern_rate.c |  6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diffs (27 lines):

diff -r b393ff14af55 -r 548d6f64b647 sys/kern/kern_rate.c
--- a/sys/kern/kern_rate.c      Wed Dec 12 09:20:35 2012 +0000
+++ b/sys/kern/kern_rate.c      Wed Dec 12 11:10:56 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_rate.c,v 1.1 2008/09/25 17:17:10 pooka Exp $      */
+/*     $NetBSD: kern_rate.c,v 1.2 2012/12/12 11:10:56 pooka Exp $      */
 
 /*-
  * Copyright (c) 2000, 2004, 2005, 2007, 2008 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_rate.c,v 1.1 2008/09/25 17:17:10 pooka Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_rate.c,v 1.2 2012/12/12 11:10:56 pooka Exp $");
 
 #include <sys/param.h>
 #include <sys/time.h>
@@ -95,7 +95,7 @@
 
 #if 1 /*DIAGNOSTIC?*/
        /* be careful about wrap-around */
-       if (*curpps + 1 > *curpps)
+       if (__predict_true(*curpps != INT_MAX))
                *curpps = *curpps + 1;
 #else
        /*