Re: [boost] [xint] Boost.XInt formal review

Subject: Re: [boost] [xint] Boost.XInt formal review
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-03-07 11:44:21

Chad Nelson wrote:
> "Stewart, Robert" <Robert.Stewart_at_[hidden]> wrote:
>
> >> I've located two: abs and negate. [...] Both involve changes to the
> >> sign bit only, and one only sometimes needs to alter it. [...]
> >
> > You can do the same, I should think, without COW.  All you
> > need is to make your algorithms less naive.  The algorithms
> > can manage the sign in a separate variable and refer to an
> > existing magnitude or make a copy, as needed, unless I'm much
> > mistaken.  That is a little less convenient, but should
> > obviate COW.
>
> Certainly it could be done without CoW. In an earlier iteration,
> I had a special subclass for that specific purpose, which kept a
> reference to an existing integer and a separate negate-the-sign
> Boolean. But if you work out the implementation, you'll see that
> it's essentially a poor-man's version of CoW anyway. Arguably
> less efficient, and definitely less aesthetically appealing, so
> I replaced it with a true CoW implementation.

The difference, as I see it, is that what I suggested is only used when it is needed and there is no reference counting involved.  With COW, you force the reference counting on all internals code.  There may be something about the algorithms I don't know, particularly since I haven't spent any time studying their code, but I think this will obviate the need for COW in the internals.

_____
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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