linux-kernel - Re: [PATCH] libbpf: Fix is_pow_of

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Message-ID: <CAC1LvL0rZcEHe_ZHDcB38XD49FmdURg4+yKHP0O=J7=4Xx8M3Q@mail.gmail.com>
Date:   Tue, 21 Jun 2022 18:03:27 -0500
From:   Zvi Effron <zeffron@...tgames.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Ian Rogers <irogers@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yuze Chi <chiyuze@...gle.com>
Subject: Re: [PATCH] libbpf: Fix is_pow_of_2

On Sun, Jun 19, 2022 at 12:13 PM Pavel Machek <pavel@....cz> wrote:
>
> Hi!
>
> > From: Yuze Chi <chiyuze@...gle.com>
> >
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -4956,7 +4956,7 @@ static void bpf_map__destroy(struct bpf_map *map);
> >
> > static bool is_pow_of_2(size_t x)
> > {
> > - return x && (x & (x - 1));
> > + return x && !(x & (x - 1));
> > }
>
> I'm pretty sure we have this test in macro in includes somewhere... should we use
> that instead?

I went looking for a macro that provided this check and could not find one. I
did find the inlined static function is_power_of_2 in log2.h, though, that we
could use.

> Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html