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Re: Excess precision problem on IA-64

From: Andreas Schwab <schwab at suse dot de>
To: Geert Bosch <bosch at adacore dot com>
Cc: Eric Botcazou <ebotcazou at adacore dot com>,Andrew Pinski <pinskia at physics dot uc dot edu>, gcc at gcc dot gnu dot org
Date: Thu, 27 Oct 2005 23:19:24 +0200
Subject: Re: Excess precision problem on IA-64
References: <200510271751.j9RHppOd012284@earth.phy.uc.edu><200510272012.16194.ebotcazou@adacore.com><4E7B8AEB-26DF-4017-BCF2-92A4B8EAB9DC@adacore.com>

Geert Bosch <bosch@adacore.com> writes:

> On Oct 27, 2005, at 14:12, Eric Botcazou wrote:
>> I'm under the impression that it's worse on IA-64 because of the
>> "infinite
>> precision", but I might be wrong.
>
> Fused multiply-add always uses "infinite precision" in the intermediate
> result. Only a single rounding is performed at the end. We really should
> have a way to express situations where operations may or may not be
> contracted, instead of having to do this on a whole-compilation level.

I think this is what the FP_CONTRACT pragma is supposed to provide.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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"And now for something completely different."

Follow-Ups:
- Re: Excess precision problem on IA-64
  - From: Geert Bosch

References:
- Re: Excess precision problem on IA-64
  - From: Andrew Pinski
- Re: Excess precision problem on IA-64
  - From: Eric Botcazou
- Re: Excess precision problem on IA-64
  - From: Geert Bosch

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