From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <545B45E9.8070903@st.com> Date: Thu, 6 Nov 2014 10:56:57 +0100 From: Maxime Coquelin MIME-Version: 1.0 To: Peter Zijlstra Cc: Rasmus Villemoes , , Ingo Molnar , "Paul E. McKenney" , , , , , Subject: Re: [PATCH v3] bitops: Fix shift overflow in GENMASK macros References: <1415098697-16304-1-git-send-email-maxime.coquelin@st.com> <87vbmt52dm.fsf@rasmusvillemoes.dk> <545A4682.2080302@st.com> <20141105164454.GY3337@twins.programming.kicks-ass.net> In-Reply-To: <20141105164454.GY3337@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 11/05/2014 05:44 PM, Peter Zijlstra wrote: > 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 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. Thanks Peter, v4 just sent. Regards, Maxime