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Date: Wed, 03 Jul 2013 11:23:00 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: Bruce Evans <brde@optusnet.com.au>
Subject: Re: should_yield problem [Was: svn commit: r251322 - head/sys/kern]
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on 03/07/2013 07:40 Bruce Evans said the following:
> On Tue, 2 Jul 2013, Andriy Gapon wrote:
>> distance = (signed)( i1 - i2 )
> 
> With 2's complement and benign overflow, this is no different from
> 'distance = i1 - i2'.

Given the particular context I'd say that there is a difference.

> But signed counters are not wanted here.  A
> negative distance, or equivalently with 32-bit unsigned ints, an unsigned
> difference of >= 0x80000000 means overflow or an initialization error.
> Your bug is an initialization error.

Right.  But I'd rather produce a positive (unsigned) number than a negative
number when such an error happens (and is detectable).  Again, I am speaking
about the concrete context.

-- 
Andriy Gapon