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Re: [Qemu-devel] [PATCH 08/19] target-alpha: use new float64_unordered()

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 08/19] target-alpha: use new float64_unordered() function
Date: Thu, 14 Apr 2011 16:39:21 +0100

On 14 April 2011 16:14, Richard Henderson <address@hidden> 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,
>  Exponent underflow and disabled:
>    Supply +0, no exception delivered to user.
>  Exponent underflow and enabled:
>    Supply +-MIN denorm, Underflow delivered to user.
>    Footnote 3, Overflow and Underflow have priority over Inexact.

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

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