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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [git pull] timer fix
Date: Wed, 4 Feb 2009 14:16:23 -0800 (PST)	[thread overview]
Message-ID: <alpine.LFD.2.00.0902041412420.3247@localhost.localdomain> (raw)
In-Reply-To: <alpine.LFD.2.00.0902041400100.3247@localhost.localdomain>



On Wed, 4 Feb 2009, Linus Torvalds wrote:
> 
> Either cast the result of the subtract to "s32" (or "int", whatever), or 
> cast _both_ of them to (s32) so that the subtract is done in a signed 
> type, and then the expansion to (long) will still be right - but 
> unnecessary - in the sign.

Btw, doing it with a nice helper macro or function is also perhaps a good 
idea, at least if these "compare hpet values" things happen more than 
once. 

Look at "time_after()" in <linux/jiffies.h> to see how to do these kinds 
of "comparisons of things that may overflow" really carefully. You 
absolutely need to do the compare in a size that is no larger than the 
size of the actual values (and in the case of HPET, it's 32-bit, at least 
the way we do things now - I guess HPET's _could_ be 64-bit, but we don't 
read more than 32 bits or whatever).

So <linux/jiffies.h> does the cast to "(long)", but it does so because the 
incoming values really have type "unsigned long" and are valid in all 
bits.

			Linus

  reply	other threads:[~2009-02-04 22:17 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-02-04 19:25 [git pull] timer fix Ingo Molnar
2009-02-04 22:11 ` Linus Torvalds
2009-02-04 22:16   ` Linus Torvalds [this message]
2009-02-04 22:25   ` Ingo Molnar
2009-02-04 22:58   ` Ingo Molnar
2009-02-04 23:13     ` H. Peter Anvin
2009-02-05  0:04       ` Ingo Molnar
2009-02-05  7:51     ` Kirill Korotaev
2009-02-05  9:58       ` Pavel Emelyanov
2009-02-05 14:30         ` Ingo Molnar
2009-02-05 16:04         ` Ray Lee
2009-02-17 16:38 Ingo Molnar
2009-06-20 16:55 [GIT PULL] " Ingo Molnar
2009-08-04 19:04 Ingo Molnar
2009-08-09 16:09 Ingo Molnar
2009-09-26 12:27 Ingo Molnar
2009-10-02 12:38 Ingo Molnar
2010-01-31 17:26 Ingo Molnar
2011-02-15 17:06 Ingo Molnar
2011-02-28 17:39 Ingo Molnar
2011-04-29 18:11 Ingo Molnar
2011-10-17  1:39 Linux 3.1-rc9 Linus Torvalds
2011-10-17 10:34 ` Peter Zijlstra
2011-10-17 14:57   ` Linus Torvalds
2011-10-17 17:54     ` Peter Zijlstra
2011-10-17 18:31       ` Linus Torvalds
2011-10-17 19:23         ` Peter Zijlstra
2011-10-17 21:00           ` Thomas Gleixner
2011-10-18  8:39             ` Thomas Gleixner
2011-10-18  9:05               ` Peter Zijlstra
2011-10-18 14:59                 ` Linus Torvalds
2011-10-18 18:14                   ` [GIT PULL] timer fix Ingo Molnar
2013-09-18 16:22 Ingo Molnar
2013-10-26 12:27 Ingo Molnar
2014-01-15 18:27 Ingo Molnar
2014-03-29 18:44 Ingo Molnar
2015-02-06 18:38 Ingo Molnar
2015-07-18  3:06 Ingo Molnar
2015-08-14  7:13 Ingo Molnar
2016-04-23 11:34 Ingo Molnar
2016-07-13 12:58 Ingo Molnar
2016-10-18 11:18 Ingo Molnar
2016-12-23 22:53 Ingo Molnar
2017-01-18  9:37 Ingo Molnar
2017-05-12  7:35 Ingo Molnar
2017-07-21 10:21 Ingo Molnar
2017-08-26  7:17 Ingo Molnar
2017-09-24 11:25 Ingo Molnar
2018-03-25  9:00 Ingo Molnar
2018-12-21 12:34 Ingo Molnar
2018-12-21 19:30 ` pr-tracker-bot
2018-12-23 19:29 ` Heiko Carstens
2019-01-17  9:51   ` Ingo Molnar
2019-01-17 15:58     ` Heiko Carstens
2019-01-17 16:57       ` Thomas Gleixner
2019-04-12 13:09 Ingo Molnar
2019-04-13  4:05 ` pr-tracker-bot
2019-09-26 20:18 Ingo Molnar
2019-09-26 23:00 ` pr-tracker-bot
2019-10-02 22:06 Ingo Molnar
2019-10-02 23:00 ` pr-tracker-bot
2019-11-16 21:38 Ingo Molnar
2019-11-17  0:35 ` pr-tracker-bot
2020-04-25 10:16 Ingo Molnar
2020-04-25 19:30 ` pr-tracker-bot
2020-06-28 18:39 Ingo Molnar
2020-06-28 22:05 ` pr-tracker-bot
2024-05-10 11:12 Ingo Molnar
2024-05-10 17:29 ` pr-tracker-bot

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