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Date: Sat, 5 Jul 2014 06:26:07 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
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Sender: Al Viro <viro@ftp.linux.org.uk>
Subject: Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions
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To: Richard Henderson <rth@twiddle.net>
Cc: Peter Maydell <peter.maydell@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>

On Sat, Jul 05, 2014 at 02:40:55AM +0100, Al Viro wrote:
> d) at least on EV6 and EV67 DNOD *still* trips INV.  According to the
> manual suppression of INV by DNOD is optional.  And while their text
> might be interpreted as "INV is suppressed if operation with denorm
> wouldn't result in something unpleasant" (which would apply to
> sqrt(DBL_MIN/2)), the same behaviour happens on DBL_MIN/2 + DBL_MIN/2,
> where the result is a good finite value, so it really looks like DNOD
> doesn't suppress INV at all on these processors.
> 
> Does anybody have 21364 to run some tests on?

In fact, DNOD is simply not implemented on those guys - if you try to set it,
the bit still reads zero.  Worse, according to Compiler Writer's Guide for the
21264/21364, "Alpha architecture FPCR bit 47 (DNOD) is not implemented
by the 21264 or 21364".

In other words, it looks like FPCR.DNOD is something from (never-produced)
21464.