linux-kernel - Re: [PATCH jiffies] Avoid undefined behavior from signed overflow

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Message-ID: <20130730000103.35524r83mpydvs7z@chicago.guarana.org>
Date:	Tue, 30 Jul 2013 00:01:03 +1000
From:	Kevin Easton <kevin@...rana.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, john.stultz@...aro.org,
	davem@...emloft.net, arnd@...db.de, mingo@...nel.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH jiffies] Avoid undefined behavior from signed overflow

Quoting "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>:

> On Mon, Jul 29, 2013 at 03:30:35PM +1000, caf@...rana.org wrote:
>> Quoting "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>:
>>
...
>> >
>> >Note that the C standard considers the cast from signed to
>> >unsigned to be implementation-defined, see 6.3.1.3p3.
...
>>
>> Don't worry, the case from signed to unsigned is actually well-defined -
>> the relevant part is 6.3.1.3p2 (in C99):
>>
>> >Otherwise, if the new type is unsigned, the value is converted by
>> >repeatedly adding or subtracting one more than the maximum value that
>> >can be represented in the new type until the value is in the range of
>> >the new type.
>
> Yep, but we are going in the other direction, from unsigned to signed.

Ahh, there's an error in the commit message (it says signed to unsigned).

     - Kevin

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