Re: [Boost-users] Ann: Floating Point Utilities Review starts today

From: Robert Kindred (RKindred_at_[hidden])
Date: 2008-03-04 10:35:50

"Johan Råde" <rade_at_[hidden]> wrote in message 
news:fqh5ob$l9m$1_at_ger.gmane.org...
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>>> http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm
[]
>> Why don't you write code for this and submit to Boost?
>>
>> --Johan
>
> Thanks, Johan, are you suggesting I add this to your library?  If so, I
> would use your traits mechanism.
>
> Robert Kindred

Of course you can do that.

I'm not sure what the formal procedure is,
but we could find out.

Could you give a brief explanation of exactly what it is you want to add?
I looked at the link, and there they discussed several different problems.

--Johan

We have software we wrote in-house to run engine stands to perform data 
acquisition and control, according to tests specified by the Society of 
Automotive Engineers.

Oops, I am already not brief.  The short of it is that, in the real world, 
floating point numbers are almost never equal, even when you think they 
should be.  Even if I convert a floating point number to a string and back 
again, there is a good chance the 'before' and the 'after' differ bitwise. 
We are using the absolute-value-epsilon approach now, but we have, I think 3 
different epsilons that we use, depending on what we predict the magnitude 
of the compared values will be.  I am looking into this Sign-Magnitude 
comparison routine for high-speed floating point compares.  One caveat is 
that it would only work on IEEE floating point numbers.  This seemed like a 
floating point utility to me, so the name of your library caught my eye.

Robert Kindred