From: "Jason A. Donenfeld" <Jason@zx2c4•com>
To: Kees Cook <keescook@chromium•org>
Cc: linux-kernel@vger•kernel.org, patches@lists•linux.dev,
"Greg Kroah-Hartman" <gregkh@linuxfoundation•org>,
"Jakub Kicinski" <kuba@kernel•org>,
"Russell King" <linux@armlinux•org.uk>,
"Catalin Marinas" <catalin.marinas@arm•com>,
"Thomas Bogendoerfer" <tsbogend@alpha•franken.de>,
"Heiko Carstens" <hca@linux•ibm.com>,
"Herbert Xu" <herbert@gondor•apana.org.au>,
"Christoph Böhmwalder" <christoph.boehmwalder@linbit•com>,
"Jani Nikula" <jani.nikula@linux•intel.com>,
"Jason Gunthorpe" <jgg@nvidia•com>,
"Sakari Ailus" <sakari.ailus@linux•intel.com>,
"Martin K . Petersen" <martin.petersen@oracle•com>,
"Theodore Ts'o" <tytso@mit•edu>,
"Andreas Dilger" <adilger.kernel@dilger•ca>,
"Jaegeuk Kim" <jaegeuk@kernel•org>,
"Richard Weinberger" <richard@nod•at>,
"Darrick J . Wong" <djwong@kernel•org>,
"SeongJae Park" <sj@kernel•org>,
"Thomas Gleixner" <tglx@linutronix•de>,
"Andrew Morton" <akpm@linux-foundation•org>,
"Michael Ellerman" <mpe@ellerman•id.au>,
"Helge Deller" <deller@gmx•de>,
netdev@vger•kernel.org, linux-crypto@vger•kernel.org,
linux-block@vger•kernel.org, linux-fsdevel@vger•kernel.org,
linux-media@vger•kernel.org,
linux-arm-kernel@lists•infradead.org, loongarch@lists•linux.dev,
linux-mips@vger•kernel.org, linuxppc-dev@lists•ozlabs.org,
linux-mmc@vger•kernel.org, linux-parisc@vger•kernel.org,
ydroneaud@opteya•com
Subject: Re: [PATCH v2 3/3] treewide: use get_random_u32_between() when possible
Date: Thu, 17 Nov 2022 00:55:47 +0100 [thread overview]
Message-ID: <Y3V4g8eorwiU++Y3@zx2c4.com> (raw)
In-Reply-To: <202211161436.A45AD719A@keescook>
On Wed, Nov 16, 2022 at 02:43:13PM -0800, Kees Cook wrote:
> On Mon, Nov 14, 2022 at 05:45:58PM +0100, Jason A. Donenfeld wrote:
> > - (get_random_u32_below(1024) + 1) * PAGE_SIZE;
> > + get_random_u32_between(1, 1024 + 1) * PAGE_SIZE;
>
> I really don't like "between". Can't this be named "inclusive" (and
> avoid adding 1 everywhere, which seems ugly), or at least named
> something less ambiguous?
>
> > - n = get_random_u32_below(100) + 1;
> > + n = get_random_u32_between(1, 101);
>
> Because I find this much less readable. "Below 100" is clear: 0-99
> inclusive, plus 1, so 1-100 inclusive. "Between 1 and 101" is not obvious
> to me to mean: 1-100 inclusive.
>
> These seem so much nicer:
> get_random_u32_inclusive(1, 1024)
> get_random_u32_inclusive(1, 100)
Yann pointed out something similar -- the half-closed interval being
confusing -- and while I was initially dismissive, I've warmed up to
doing this fully closed after sending a diff of that:
https://lore.kernel.org/lkml/Y3Qt8HiXj8giOnZy@zx2c4.com/
So okay, let's say that I'll implement the inclusive version instead. We
now have two problems to solve:
1) How/whether to make f(0, UR2_MAX) safe,
- without additional 64-bit arithmetic,
- minimizing the number of branches.
I have a few ideas I'll code golf for a bit.
2) What to call it:
- between I still like, because it mirrors "I'm thinking of a number
between 1 and 10 and..." that everybody knows,
- inclusive I guess works, but it's not a preposition,
- bikeshed color #3?
I think I can make progress with (1) alone by fiddling around with
godbolt enough, like usual. I could use some more ideas for (2) though.
Jason
next prev parent reply other threads:[~2022-11-16 23:56 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-14 16:45 [PATCH v2 0/3] convert tree to get_random_u32_{below,above,between}() Jason A. Donenfeld
2022-11-14 16:45 ` [PATCH v2 1/3] treewide: use get_random_u32_below() instead of deprecated function Jason A. Donenfeld
2022-11-14 17:35 ` Russell King (Oracle)
2022-11-14 16:45 ` [PATCH v2 2/3] treewide: use get_random_u32_{above,below}() instead of manual loop Jason A. Donenfeld
2022-11-14 16:45 ` [PATCH v2 3/3] treewide: use get_random_u32_between() when possible Jason A. Donenfeld
2022-11-16 22:43 ` Kees Cook
2022-11-16 23:55 ` Jason A. Donenfeld [this message]
2022-11-17 0:03 ` Jason A. Donenfeld
2022-11-17 0:31 ` Kees Cook
2022-11-17 0:43 ` Jason A. Donenfeld
2022-11-17 0:47 ` Kees Cook
2022-11-17 15:42 ` Theodore Ts'o
2022-11-17 16:19 ` Jason A. Donenfeld
2022-11-17 22:15 ` David Laight
2022-11-17 2:05 ` Jason A. Donenfeld
2022-11-17 10:32 ` Russell King (Oracle)
2022-11-17 20:29 ` [PATCH v3 0/3] convert tree to get_random_u32_{below,above,inclusive}() Jason A. Donenfeld
2022-11-17 20:29 ` [PATCH v3 1/3] treewide: use get_random_u32_below() instead of deprecated function Jason A. Donenfeld
2022-11-17 21:59 ` Kees Cook
2022-11-17 20:29 ` [PATCH v3 2/3] treewide: use get_random_u32_{above,below}() instead of manual loop Jason A. Donenfeld
2022-11-17 21:58 ` Kees Cook
2022-11-17 20:29 ` [PATCH v3 3/3] treewide: use get_random_u32_inclusive() when possible Jason A. Donenfeld
2022-11-17 21:57 ` Kees Cook
2022-11-17 22:10 ` Jason A. Donenfeld
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