Subject: Re: [PATCH v2] Net: mac802154: comparision issue of type cast, finding by EXTRA_CFLAGS=-W

From: Chen Gang <[email-masked]>
Date: Tue, 23 Apr 2013 19:22:57 +0800

I will send patch v3 for properly capitalizing my comments' sentences
and subject.

On 2013年04月23日 10:54, Chen Gang wrote:
> 
> 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]
> 
> 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 <[email-masked]>
> ---
>  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;
> 

-- 
Chen Gang

Asianux Corporation