netdev - [PATCH v3] net: mac802154: comparision issue of type cast, finding by EXTRA

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Date:	Tue, 23 Apr 2013 19:24:36 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	alex.bluesman.smirnov@...il.com, dbaryshkov@...il.com,
	David Miller <davem@...emloft.net>,
	linux-zigbee-devel@...ts.sourceforge.net,
	netdev <netdev@...r.kernel.org>
Subject: [PATCH v3] net: mac802154: comparision issue of type cast, finding
 by EXTRA_CFLAGS=-W


Need change ~(u8)0 to 0xff, or in mac802154_wpan_xmit(), "u8 chan"
will never == MAC802154_CHAN_NONE.

The related warning:
  net/mac802154/wpan.c:325:2: warning: comparison is always false
  due to limited range of data type [-Wtype-limits]

The related unit test:
  cc -Wall -O2 -o test test.c
  ./test
  will output 'different'

  (after use '0xff' instead of '~(u8)0', it will output 'equal')

-----------------------test code begin--------------------------------

#include <stdio.h>

typedef unsigned char u8;

int main()
{
	u8 uc = 0xff;

	if (uc == ~(u8)0)
		printf("\nequal\n");
	else
		printf("\ndifferent\n");

	return 0;
}

-----------------------test code end----------------------------------


Signed-off-by: Chen Gang <gang.chen@...anux.com>
---
 net/mac802154/mac802154.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/mac802154/mac802154.h b/net/mac802154/mac802154.h
index 5c9e021..d48422e 100644
--- a/net/mac802154/mac802154.h
+++ b/net/mac802154/mac802154.h
@@ -88,7 +88,7 @@ struct mac802154_sub_if_data {
 
 #define mac802154_to_priv(_hw)	container_of(_hw, struct mac802154_priv, hw)
 
-#define MAC802154_CHAN_NONE		(~(u8)0) /* No channel is assigned */
+#define MAC802154_CHAN_NONE		0xff /* No channel is assigned */
 
 extern struct ieee802154_reduced_mlme_ops mac802154_mlme_reduced;
 extern struct ieee802154_mlme_ops mac802154_mlme_wpan;
-- 
1.7.7.6
--
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