From: David Laight <David.Laight@ACULAB.COM>
To: 'Alexei Starovoitov' <alexei.starovoitov@gmail.com>,
Yury Norov <yury.norov@gmail.com>
Cc: "Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Joe Perches" <joe@perches.com>,
"Julia Lawall" <Julia.Lawall@inria.fr>,
"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
"Nicholas Piggin" <npiggin@gmail.com>,
"Nicolas Palix" <nicolas.palix@imag.fr>,
"Peter Zijlstra" <peterz@infradead.org>,
"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
"Matti Vaittinen" <Matti.Vaittinen@fi.rohmeurope.com>,
LKML <linux-kernel@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Chris Zankel" <chris@zankel.net>,
"Christophe Leroy" <christophe.leroy@csgroup.eu>,
"Eric W . Biederman" <ebiederm@xmission.com>,
"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
"Max Filippov" <jcmvbkbc@gmail.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"linux-xtensa@linux-xtensa.org" <linux-xtensa@linux-xtensa.org>
Subject: RE: [PATCH 08/22] bitops: introduce MANY_BITS() macro
Date: Tue, 10 May 2022 17:54:13 +0000 [thread overview]
Message-ID: <3be064fe804845e4aeaca8b1d45ddf0a@AcuMS.aculab.com> (raw)
In-Reply-To: <CAADnVQKcX2xEWCHu-DX0Cy_mvCL6E0aE_BF1Wo+U-vy_Bi2-3w@mail.gmail.com>
From: Alexei Starovoitov
> Sent: 10 May 2022 17:51
...
> +/* Return: nonzero if 2 or more bits are set */
> +#define MANY_BITS(n) ((n) & ((n) - 1))
You can't have a macro that expands its argument twice.
...
> > static inline __attribute__((const))
> > bool is_power_of_2(unsigned long n)
> > {
> > - return (n != 0 && ((n & (n - 1)) == 0));
> > + return n != 0 && !MANY_BITS(n);
> > }
>
> Please don't. Open coded version is much easier to read.
Especially if you remove all the spare parenthesis.
return n && !(n & (n - 1));
I bet a lot of callers know the value is non-zero.
I suspect you'll find at least one caller that uses
is_power_of_2() assuming it is !(n & (n - 1)) and
so is wrong for zero.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-05-10 17:54 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 15:47 [PATCH 00/21] add coccinelle scripts for {bitmap,cpumask,nodes}_empty() Yury Norov
2022-05-10 15:47 ` [PATCH 01/22] introduce bitmap.cocci Yury Norov
2022-05-10 15:47 ` [PATCH 02/22] introduce cpumask.cocci Yury Norov
2022-05-10 15:47 ` [PATCH 03/22] introduce nodemask.cocci Yury Norov
2022-05-10 15:47 ` [PATCH 04/22] ice: use bitmap_empty() in ice_vf_has_no_qs_ena() Yury Norov
2022-05-10 15:47 ` [PATCH 05/22] iio: replace bitmap_weight with bitmap_weitght_{eq,le} where appropriate Yury Norov
2022-05-14 15:53 ` Jonathan Cameron
2022-05-14 16:31 ` Joe Perches
2022-05-15 16:40 ` Jonathan Cameron
2022-05-10 15:47 ` [PATCH 06/22] octeontx2: use bitmap_empty() instead of bitmap_weight() Yury Norov
2022-05-10 21:31 ` Jakub Kicinski
2022-05-10 15:47 ` [PATCH 07/22] risc-v: replace bitmap_weight with bitmap_empty in riscv_fill_hwcap() Yury Norov
2022-05-10 16:31 ` Anup Patel
2022-05-10 15:47 ` [PATCH 08/22] bitops: introduce MANY_BITS() macro Yury Norov
2022-05-10 16:50 ` Alexei Starovoitov
2022-05-10 17:54 ` David Laight [this message]
2022-05-10 19:11 ` Yury Norov
2022-05-11 10:59 ` Rasmus Villemoes
2022-05-10 17:57 ` Max Filippov
2022-05-10 19:16 ` Yury Norov
2022-05-11 4:55 ` Max Filippov
2022-05-10 15:47 ` [PATCH 09/22] qed: replace bitmap_weight() with MANY_BITS() Yury Norov
2022-05-10 15:47 ` [PATCH 10/22] net/mlx5e: simplify mlx5e_set_fecparam() Yury Norov
2022-05-10 15:47 ` [PATCH 11/22] KVM: x86: hyper-v: replace bitmap_weight() with hweight64() Yury Norov
2022-05-16 13:08 ` Vitaly Kuznetsov
2022-05-22 14:53 ` Guenter Roeck
2022-05-22 17:39 ` Yury Norov
2022-05-10 15:47 ` [PATCH 12/22] ia64: cleanup remove_siblinginfo() Yury Norov
2022-05-10 22:33 ` Andrew Morton
2022-05-10 15:47 ` [PATCH 13/22] x86: smp: move cpumask_weight() out of for-loop in remove_siblinginfo Yury Norov
2022-05-11 9:47 ` Thomas Gleixner
2022-05-10 15:47 ` [PATCH 14/22] x86: smp: use cpumask_weight_eq() " Yury Norov
2022-05-10 15:47 ` [PATCH 15/22] net/mlx5: use cpumask_weight_gt() in irq_pool_request_irq() Yury Norov
2022-05-10 15:47 ` [PATCH 16/22] x86/tsc: use cpumask_weight_gt() in loop_timeout() Yury Norov
2022-05-10 15:47 ` [PATCH 17/22] sched/core: fix opencoded cpumask_any_but() Yury Norov
2022-05-10 16:37 ` Peter Zijlstra
2022-05-10 17:21 ` Valentin Schneider
2022-05-10 15:47 ` [PATCH 18/22] sched/core: remove unneeded cpumask_weight() in sched_core_cpu_{starting,deactivate} Yury Norov
2022-05-10 15:47 ` [PATCH 19/22] sched/core: replace cpumask_weight() with cpumask_weight_eq() where appropriate Yury Norov
2022-05-10 15:47 ` [PATCH 20/22] sched/topology: " Yury Norov
2022-05-10 15:47 ` [PATCH 21/22] cpufreq: use cpumask_weight_gt() in policy_is_shared() Yury Norov
2022-05-11 3:16 ` Viresh Kumar
2022-05-10 15:47 ` [PATCH 22/22] clockevents: use cpumask_weight_eq() in tick_cleanup_dead_cpu() Yury Norov
2022-05-11 8:18 ` Thomas Gleixner
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