From: Peter Zijlstra <peterz@infradead.org>
To: Maxime Coquelin <maxime.coquelin@st.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
gong.chen@linux.intel.com, 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, 5 Nov 2014 17:44:54 +0100 [thread overview]
Message-ID: <20141105164454.GY3337@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <545A4682.2080302@st.com>
On Wed, Nov 05, 2014 at 04:47:14PM +0100, Maxime Coquelin wrote:
>
> On 11/05/2014 12:10 PM, Rasmus Villemoes wrote:
> >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).
> That's a good point.
>
> Peter, what is your view?
I'm fine with that, feel free to post another version and I'll replace
v3.
next prev parent reply other threads:[~2014-11-05 16:44 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
2014-11-05 15:47 ` Maxime Coquelin
2014-11-05 16:44 ` Peter Zijlstra [this message]
2014-11-06 9:56 ` Maxime Coquelin
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