From 0a06817da12212b29cac740066fe51c89e1084af Mon Sep 17 00:00:00 2001
From: batt <batt@38d2e660-2303-0410-9eaa-f027e97ec537>
Date: Mon, 21 Feb 2011 22:27:21 +0000
Subject: [PATCH] Fix undefined behaviour.

In the expression:
(a) ^= (b) ^= (a) ^= (b)
'a' and 'b' are evaluated and assigned multiple times, and it is
not clear in which order operations are performed.
This patch re-write the XOR swap in a more canonical way.


git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4719 38d2e660-2303-0410-9eaa-f027e97ec537
---
 bertos/cpu/byteorder.h      |  2 +-
 bertos/cpu/byteorder_test.c | 71 +++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 bertos/cpu/byteorder_test.c

diff --git a/bertos/cpu/byteorder.h b/bertos/cpu/byteorder.h
index 721f81e5..37d7a841 100644
--- a/bertos/cpu/byteorder.h
+++ b/bertos/cpu/byteorder.h
@@ -132,7 +132,7 @@ INLINE float swab_float(float x)
 	/* Avoid breaking strict aliasing rules.  */
 	char *cx = (char *)(&x);
 	STATIC_ASSERT(sizeof(float) == 4);
-	#define BYTEORDER_SWAP(a, b) ((a) ^= (b) ^= (a) ^= (b))
+	#define BYTEORDER_SWAP(a, b) do { (a) ^= (b); (b) ^= (a); (a) ^= (b); } while(0)
 	BYTEORDER_SWAP(cx[0], cx[3]);
 	BYTEORDER_SWAP(cx[1], cx[2]);
 	#undef BYTEORDER_SWAP
diff --git a/bertos/cpu/byteorder_test.c b/bertos/cpu/byteorder_test.c
new file mode 100644
index 00000000..0064c621
--- /dev/null
+++ b/bertos/cpu/byteorder_test.c
@@ -0,0 +1,71 @@
+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2010 Develer S.r.l. (http://www.develer.com/)
+ *
+ * -->
+ *
+ * \brief byteorder.h macros test.
+ *
+ * \author Francesco Sacchi <batt@develer.com>
+ */
+
+#include <float.h>
+#include <cfg/debug.h>
+#include <cfg/test.h>
+
+#include "byteorder.h"
+
+int byteorder_testSetup(void)
+{
+	kdbg_init();
+	return 0;
+}
+
+int byteorder_testTearDown(void)
+{
+	return 0;
+}
+
+int byteorder_testRun(void)
+{
+	float a;
+	float b;
+	float c;
+
+	for (a = 0; a < 12345; a += 0.01)
+	{
+		b = swab_float(a);
+		c = swab_float(b);
+//		kprintf("a=%08lX, b=%08lX, c=%08lX\n", *((uint32_t *)&a), *((uint32_t *)&b), *((uint32_t *)&c));
+		ASSERT(a == c);
+	}
+	return 0;
+}
+
+TEST_MAIN(byteorder);
-- 
2.25.1