Re: [boost] floating point FUD

Subject: Re: [boost] floating point FUD
From: Barend Gehrels (barend_at_[hidden])
Date: 2010-01-24 13:56:29

>
> This looks like fixed-point support will really become "mainstream" soon. How is this related to C++ and the idea of a Boost fixed-point library?
>
>   

John Maddock wrote:
>> FP algorithms are all about accumulation of error, aren't they? Would be
>> nice to have some kind of debugging facility (integrated with the code),
>> that somehow keeps track of all kinds of error bounds/measures you're
>> interested in.
>
> I've experimented with that - a "dual precision" type - basically a 
> class that evaluates every expression it's subject to at two different 
> precisions - say double and with an arbitrary precision type, and then 
> optionally prints out the accumulated error.  The idea is one can then 
> step through code, or else set a break when the accumulated error 
> reaches some threshold, and see where the error is coming from in the 
> algorithm.  That's the theory anyway, in practice I've found good old 
> fashioned pen and paper analysis of the algorithm is often as good...
>

I encountered the TTMath library recently, http://www.ttmath.org/ttmath. 
Is it already discussed within the context of Boost? It is a templated 
library, head-only where mantissa and exponent of a big-number-library 
can be set as template parameters, it is almost like a Boost library...

I used TTmath figuring out a problem within segment intersection, all 
numeric types gave me different results, including Excel and spatial 
databases, and I didn't have any clue of what the real real result 
should look like (even GMP and CLN differed...). But this library helped me.

Regards, Barend