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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: Fix ptimer_get_count overflow.
Date: Tue, 31 Mar 2009 14:38:26 +0000
References: <200902121733.43146.vladimir@codesourcery.com>
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To: qemu-devel@nongnu.org
Cc: Vladimir Prus <vladimir@codesourcery.com>

On Wednesday 04 March 2009, Vladimir Prus wrote:
> Vladimir Prus wrote:
> > At present, ptimers have a slight inaccuracy that can lead to
> > overflow. The period is stored as 64.32 fixed point number.
> > ptimer_reload uses both integer and fractional part of the perion
> > when computing when the next event should happen. ptimer_get_count,
> > however, uses only integer part of the period. Therefore, when
> > ptimer_get_count is called very soon after ptimer_reload the value
> > returned may be greater than the value ptimer_reload has set.
> > And if the counter was 0xFFFFFFFF, this may result in overflow.

I think your patch has problems with out of range shift counts, so I applied a 
slightly different version.

Paul