From: Andrew Morton <akpm@linux-foundation.org>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Guenter Roeck <linux@roeck-us.net>,
Sowmini Varadhan <sowmini.varadhan@oracle.com>,
linux-kernel@vger.kernel.org, benh@kernel.crashing.org,
davem@davemloft.net
Subject: Re: [PATCH] iommu-common: Do not use 64 bit constant 0xffffffffffffffffl for computing align_mask
Date: Mon, 20 Jul 2015 16:28:00 -0700 [thread overview]
Message-ID: <20150720162800.734632f4e05ffae173cff527@linux-foundation.org> (raw)
In-Reply-To: <87oaj6ogox.fsf@rasmusvillemoes.dk>
On Mon, 20 Jul 2015 19:57:18 +0200 Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:
> On Mon, Jul 20 2015, Guenter Roeck <linux@roeck-us.net> wrote:
>
> > So either case ~0l appears to be wrong; it should be ~0ul.
>
> Yes, right-shifting -1 of any type is probably always wrong, as it will
> always give -1 again.
Not for unsigned types.
The kernel uses "-1UL" and "-1ULL" quite a lot - it's a convenient way
of saying "all ones, regardless of size". Also, assigning plain old
"-1" to an unsigned variable will make that variable all-ones
regardless of size.
In this case I expect we could do
align_mask = -1UL >> (64 - align_order);
but I don't know about that 64. Maybe it should be BITS_PER_LONG?
next prev parent reply other threads:[~2015-07-20 23:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-19 12:20 Sowmini Varadhan
2015-07-19 15:27 ` Guenter Roeck
2015-07-19 20:25 ` Rasmus Villemoes
2015-07-19 20:41 ` Sowmini Varadhan
2015-07-20 1:58 ` Guenter Roeck
2015-07-20 17:57 ` Rasmus Villemoes
2015-07-20 19:25 ` Sowmini Varadhan
2015-07-20 23:28 ` Andrew Morton [this message]
2015-07-21 0:26 ` Guenter Roeck
2015-07-20 14:44 ` Sowmini Varadhan
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