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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Florian La Roche <florian.laroche@googlemail.com>
Cc: Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Crt Mori <cmo@melexis.com>, Joe Perches <joe@perches.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Will Deacon <will.deacon@arm.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: fix int_sqrt() for very large numbers
Date: Mon, 21 Jan 2019 13:20:33 +1300	[thread overview]
Message-ID: <CAHk-=wjruxUdKWjn-PvZMOPn3pGO5yTcbc_J4hc4TrS0P15vaw@mail.gmail.com> (raw)
In-Reply-To: <20190119151450.26879-1-Florian.LaRoche@googlemail.com>

On Sun, Jan 20, 2019 at 4:15 AM Florian La Roche
<florian.laroche@googlemail.com> wrote:
>
> @@ -52,7 +52,7 @@ u32 int_sqrt64(u64 x)
>         if (x <= ULONG_MAX)
>                 return int_sqrt((unsigned long) x);
>
> -       m = 1ULL << (fls64(x) & ~1ULL);
> +       m = 1ULL << ((fls64(x) - 1) & ~1ULL);

I've applied this part of the patch as commit fbfaf851902c ("fix
int_sqrt64() for very large numbers") with slightly edited commit
log.

I still think there are some oddities in here in the types. I
mentioned the caller that unnecessarily does the int_sqrt64() twice,
even though the outer one doesn't actually take a 64-bit value.

But in the very line above, there's another type oddity: the "& ~1ULL"
is entirely the wrong type. The shift *count* shouldn't be an unsigned
long long, so that type doesn't make much sense. It should be just a
~1, or even just "62".

But I didn't actually start micro-editing the patch, and just did that
one-liner off-by-one fix.

             Linus

  parent reply	other threads:[~2019-01-21  7:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-19 15:14 fix int_sqrt() for very large numbers Florian La Roche
2019-01-20  0:01 ` Will Deacon
2019-01-20  3:48   ` Linus Torvalds
2019-01-20  5:03     ` Florian La Roche
2019-01-20  5:11       ` Linus Torvalds
2019-01-20  8:31     ` Crt Mori
2019-01-20  9:29       ` Crt Mori
2019-01-20 10:00         ` Linus Torvalds
2019-01-21  0:20 ` Linus Torvalds [this message]
2019-01-21 20:25   ` Crt Mori
2019-02-02  6:11 ` [LKP] 32bd07585d: kernel_selftests.lib.prime_numbers.sh.fail kernel test robot
2019-02-02 13:10   ` Florian La Roche

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