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Date: Wed, 5 Nov 2014 16:47:14 +0100 From: Maxime Coquelin <maxime.coquelin@...com> To: Rasmus Villemoes <linux@...musvillemoes.dk> Cc: <gong.chen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, <tytso@....edu>, <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>, <kernel@...inux.com>, <eric.paire@...com> Subject: Re: [PATCH v3] bitops: Fix shift overflow in GENMASK macros On 11/05/2014 12:10 PM, Rasmus Villemoes wrote: > On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@...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? Kind regards, Maxime > > Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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