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Date: Wed, 17 Aug 2022 11:09:31 +0100 From: Valentin Schneider <vschneid@...hat.com> To: Yury Norov <yury.norov@...il.com> Cc: netdev@...r.kernel.org, linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Barry Song <song.bao.hua@...ilicon.com>, Heiko Carstens <hca@...ux.ibm.com>, Tony Luck <tony.luck@...el.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, Gal Pressman <gal@...dia.com>, Tariq Toukan <tariqt@...dia.com> Subject: Re: [PATCH 1/5] bitops: Introduce find_next_andnot_bit() On 16/08/22 15:13, Yury Norov wrote: > On Tue, Aug 16, 2022 at 07:07:23PM +0100, Valentin Schneider wrote: >> @@ -59,7 +63,9 @@ unsigned long _find_next_bit(const unsigned long *addr1, >> >> tmp = addr1[start / BITS_PER_LONG]; >> if (addr2) >> - tmp &= addr2[start / BITS_PER_LONG]; >> + tmp &= negate ? >> + ~addr2[start / BITS_PER_LONG] : >> + addr2[start / BITS_PER_LONG]; >> tmp ^= invert; >> } > > So it flips addr2 bits twice - first with new 'negate', and second > with the existing 'invert'. There is no such combination in the > existing code, but the pattern looks ugly, particularly because we use > different inverting approaches. Because of that, and because XOR trick > generates better code, I'd suggest something like this: > > tmp = addr1[start / BITS_PER_LONG] ^ invert1; > if (addr2) > tmp &= addr2[start / BITS_PER_LONG] ^ invert2; That does look much better, and also gets rid of the ternary. Thanks!
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