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Topic: forcing intel floating registers to use 64-bit arithmetic
Replies: 5   Last Post: Feb 3, 2013 10:48 PM

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Gordon Sande

Posts: 119
Registered: 5/13/10
Re: forcing intel floating registers to use 64-bit arithmetic
Posted: Jan 11, 2013 4:07 PM
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On 2013-01-11 16:46:58 -0400, Tom Stockfisch said:

> I need to force all double precision calculations to proceed strictly
> in 64-bit -- no 80-bit
> intel register arithmetic. Can someone tell me the current function calls or
> command line settings to achieve this on both MacOS and linux?
>
> I need this to be able to track down platform-dependent differences in
> numerical code.


This would seem to be rather compiler dependent. Good old RTFM would seem to be
a possible source of enlightenment. Different languages have different
conventions.

Such options tend to have names like fast arithmetic or safe
arithmetic. It gets
confused with forcing all intermediates into storage. There is also the issue
of fused add-multiplies. Even when all that is sorted out you can still have
differing evaluation orders as complex expressions are assembled. And check
the quality of input/output conversions as full bit accuracy is not always
present.

In other words, over precision of intermediates is not the only source of
differences between various supposedly similar implementations.

Happy reading the arcane back sections of whatever compiler you are using.





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