Re: [boost] GSOC Boost BigInt design issues

Subject: Re: [boost] GSOC Boost BigInt design issues
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-03-30 06:51:41

swagat konchada wrote:

Please don't overquote.

> > Rob Stewart wrote
> > >
> > The usual idea is that BigInt would provide expression
> > templates and other optimizations to avoid calling the back
> > end engine inefficiently.  That may require an adapter layer
> > between the user-visible BigInt API and the computation
> > engine, like GMP, at the back end, to insulate the API from
> > differences in the back end engines.  (Then again, there may
> > be nothing left to a layer above the adapter layer; I'm not
> > saying there must be three layers.)
> >
> If we consider performance issues based on design, planning the
> BigInt architecture could be designed in two ways
>
> 1. 3 layers to allow optional binding to Boost's own bigint,
> GMP, or anyother bigint library, for the user during compile
> time.
>
> 2. 2 layers if we plan to limit Boost.Bigint's options to only
> itself and GMP.

[snip]

> This means doubling in the number of function calls.  Though I
> realize most of the time is spent inside the function rather
> than in calling the functions, does this result in an overhead
> we should worry about?

It is premature to think this way without a real, if test, implementation for comparison.  I expect the compiler to do much of the work, via expression templates, and much of the rest to be inlined, leaving relatively few real function calls to worry about.  Whether your expectation or mine is correct remains to be seen, but it shouldn't be an overarching consideration at this time.

What is important for a GSoC project is to design the interface well, provide the necessary points of customization to make the library appropriately flexible, produce correct results, and document the whole thing.  With that done, attention can then turn to reimplementing a Boost back end or otherwise optimizing the code.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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