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Date: Thu, 14 Apr 2011 16:39:21 +0100
Message-ID: <BANLkTi=xrNTBgtB1Gykg0pSARoM+cdCRQA@mail.gmail.com>
From: Peter Maydell <peter.maydell@linaro.org>
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Subject: Re: [Qemu-devel] [PATCH 08/19] target-alpha: use new
 float64_unordered() function
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To: Richard Henderson <rth@twiddle.net>
Cc: qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>

On 14 April 2011 16:14, Richard Henderson <rth@twiddle.net> wrote:
> On 04/14/2011 02:14 AM, Peter Maydell wrote:
>> While we're on the subject of Alpha and flush-to-zero modes,
>> do you know what exception bits should get set when Alpha
>> flushes a denormal output (not input) to zero?
> ...
>> I think Alpha should set Inexact and not Underflow, but
>> I'm not sure -- can you confirm/deny?
>
> Deny.
>
> Page B-8, Add Sub Output Exceptions,
>
> =C2=A0Exponent underflow and disabled:
> =C2=A0 =C2=A0Supply +0, no exception delivered to user.
>
> =C2=A0Exponent underflow and enabled:
> =C2=A0 =C2=A0Supply +-MIN denorm, Underflow delivered to user.
>
> =C2=A0 =C2=A0Footnote 3, Overflow and Underflow have priority over Inexac=
t.

Thanks. Does "no exception delivered to user" mean also
"and do not set FPCR bit UNF" ?

The reason I thought it might set Inexact is that I was looking
at page 4-79, which says:

"If both the UNFD (underflow disable) bit and the UNDZ (underflow
 to zero) bit are set in the FPCR, the implementation sets the
 result of an underflow operation to a true zero result. The
 zeroing of a denormal result by UNDZ must also be treated as an
 inexact result."

-- PMM