From: Thomas Rast <trast@inf.ethz.ch>
Date: Wed, 23 May 2012 08:30:38 GMT
Subject: Re: [PATCH 2/3] xdiff: avoid more compiler warnings with XDL_FAST_HASH on 32-bit machines
Message-ID: <8762bn7101.fsf@thomas.inf.ethz.ch>
In-Reply-To: <4FBBF8D7.7050701@lsrfire.ath.cx>

René Scharfe <rene.scharfe@lsrfire.ath.cx> writes:

> Hide literals that can cause compiler warnings for 32-bit architectures in
> expressions that evaluate to small numbers there.  Some compilers warn that
> 0x0001020304050608 won't fit into a 32-bit long, others that shifting right
> by 56 bits clears a 32-bit value completely.
>
> The correct values are calculated in the 64-bit case, which is all that matters
> in this if-branch.
>
> Reported-by: Øyvind A. Holm <sunny@sunbase.org>
> Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>

Thanks for fixing this.  As far as logic and review goes, both patches

Acked-by: Thomas Rast <trast@student.ethz.ch>

I haven't checked whether it actually fixes the warnings, however.

> ---
>  xdiff/xutils.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/xdiff/xutils.c b/xdiff/xutils.c
> index 8580da7..78549e3 100644
> --- a/xdiff/xutils.c
> +++ b/xdiff/xutils.c
> @@ -272,7 +272,13 @@ static inline long count_masked_bytes(unsigned long mask)
>  		 * that works for the bytemasks without having to
>  		 * mask them first.
>  		 */
> -		return mask * 0x0001020304050608 >> 56;
> +		/*
> +		 * return mask * 0x0001020304050608 >> 56;
> +		 *
> +		 * Doing it like this avoids warnings on 32-bit machines.
> +		 */
> +		long a = (REPEAT_BYTE(0x01) / 0xff + 1);
> +		return mask * a >> (sizeof(long) * 7);
>  	} else {
>  		/*
>  		 * Modified Carl Chatfield G+ version for 32-bit *

-- 
Thomas Rast
trast@{inf,student}.ethz.ch