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-----Original Message-----
From: Kumar Gala [mailto:galak@kernel.crashing.org]=20
Sent: Wednesday, January 31, 2007 10:49 PM
To: Zhu Ebony-r57400
Cc: paulus@samba.org; linuxppc-dev@ozlabs.org
Subject: Re: [patch][0/5] powerpc: Add support to fully=20
comply with IEEE-754 standard
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quoted

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On Jan 29, 2007, at 4:00 AM, Zhu Ebony-r57400 wrote:

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Hi Kumar,

I think enabling SPEFSCR[FINXE] or SPEFSCR[FRMC]=3D0b10/0b11

to enable

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FP round interrupt will cause the exception occurring very often,=20
which will dramatically decrease the performance of SPE

instructions.

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Do you think putting an option in menuconfig to let user choose=20
whether to enable FP round simulation is a reasonable idea?

I don't see any issue with it, but I have to believe if=20

you want full=20

quoted

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IEEE results, you want full IEEE results for everything.

- k

Agreed, we need to fully comply with IEEE754. So let's talk=20

something=20

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about the handler.

The round exceptions can be put into 2 categories:

1. SPEFSCR[FRMC] =3D 0b10 or 0b11 (rounding toward +Inf and -Inf) We =

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need to handle this exception to comply with IEEE

2. SPEFSCR[FINXE] =3D 1
If we enable this, round exception will occurs when=20

inaccurate results=20

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are generated. However, I think we don't need to do so.=20

With FINXE=3D0,=20

quoted

if SPE data exception occurs, we can handle the exception=20

by existing=20

quoted

handler, which is fully IEEE complied, including rounding.=20

If no data=20

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exception occurs, HW can implement "round to nearest" and "round=20
toward zero" with IEEE complied, and "round toward=20

+Inf/-Inf" can be=20

quoted

handled by the handler of point 1.
So all
the situations are covered, we do have to enable FINXE.

Could you make some comments on this? Thanks!

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While I agree with most of what you're saying there is one=20
issue.  If the user want's an exception reported on inexact=20
results when the =20
rounding mode is set to "round to nearest" or "round towards zero".  =20
Of course we know when the user requests this and can=20
enable/disable this exception at that point if we want to.
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On a side node, wondering if you've come across this test suite:
http://www.jhauser.us/arithmetic/TestFloat.html
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- k

Thank  you for your comments and useful link. It seems quite good for
testing the handler.

B.R.
Ebony

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