From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Maxime COQUELIN <maxime.coquelin@st.com>
Cc: gong.chen@linux.intel.com, Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
" Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
tytso@mit.edu, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, kernel@stlinux.com, eric.paire@st.com
Subject: Re: [PATCH v3] bitops: Fix shift overflow in GENMASK macros
Date: Wed, 05 Nov 2014 12:10:45 +0100 [thread overview]
Message-ID: <87vbmt52dm.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <1415098697-16304-1-git-send-email-maxime.coquelin@st.com> (Maxime COQUELIN's message of "Tue, 4 Nov 2014 11:58:17 +0100")
On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@st.com> wrote:
> -#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
> -#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))
> +#define GENMASK(h, l) \
> + ((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l))
> +
> +#define GENMASK_ULL(h, l) \
> + ((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l))
Slightly bikeshedding here, but may I suggest spelling it
(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
? This will ensure the arguments are expanded once each, and will, IMHO,
DTRT if/when l > h (namely, yield 0).
Rasmus
next prev parent reply other threads:[~2014-11-05 11:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-04 10:58 [PATCH v3] bitops: Fix shift overflow in GENMASK macros Maxime COQUELIN
2014-11-04 13:27 ` Peter Zijlstra
2014-11-05 11:10 ` Rasmus Villemoes [this message]
2014-11-05 15:47 ` Maxime Coquelin
2014-11-05 16:44 ` Peter Zijlstra
2014-11-06 9:56 ` Maxime Coquelin
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