[src/trunk]: src/sys/sys add __empty

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

details:   https://anonhg.NetBSD.org/src/rev/2ad68806604e
branches:  trunk
changeset: 821509:2ad68806604e
user:      christos <christos%NetBSD.org@localhost>
date:      Wed Feb 08 16:13:04 2017 +0000

description:
add __empty

diffstat:

 sys/sys/cdefs.h |  16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diffs (30 lines):

diff -r ffa99889eac9 -r 2ad68806604e sys/sys/cdefs.h
--- a/sys/sys/cdefs.h   Wed Feb 08 16:12:59 2017 +0000
+++ b/sys/sys/cdefs.h   Wed Feb 08 16:13:04 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cdefs.h,v 1.129 2016/12/27 21:52:01 christos Exp $     */
+/*     $NetBSD: cdefs.h,v 1.130 2017/02/08 16:13:04 christos Exp $     */
 
 /* * Copyright (c) 1991, 1993
  *     The Regents of the University of California.  All rights reserved.
@@ -306,6 +306,20 @@
 #define        __unreachable() do {} while (/*CONSTCOND*/0)
 #endif
 
+/*
+ * To be used when an empty body is required like:
+ *
+ * #ifdef DEBUG
+ * # define dprintf(a) printf(a)
+ * #else
+ * # define dprintf(a) __empty
+ * #endif
+ *
+ * We use ((void)0) instead of do {} while (/*CONSTCOND*/0) so that it
+ * works on , expressions.
+ */
+#define __empty        ((void)0)
+
 #if defined(__cplusplus)
 #define        __BEGIN_EXTERN_C        extern "C" {
 #define        __END_EXTERN_C          }