Re: [boost] [endian] endian flip and endian domain

Subject: Re: [boost] [endian] endian flip and endian domain
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-06-08 13:14:23

Dave Handley wrote:
> Gottlob Frege wrote:
>
> > I think what I am saying is that, conceptually at least, the
> > endian-types come first, and the straight functions are built on top
> > of that (instead of the other way around as most are suggested).
> > Now, I wouldn't want that to impact performance, which is why I say
> > 'conceptually'.  We can specialize the heck out of
> > everything so that
> > performance wins, but I think the conceptual foundation is
> > important.
>
> I disagree.  If you have an endian type then I think you are
> coding in from the beginning a need for a copy in order to
> endian swap - even if the endian swap is a no-operation.

This discussion isn't necessarily intended to account for swap in place, which all have agreed is necessary.  Rather, I at least am thinking of this discussion as applying to the object-based approach and to the copy-based conversion functions.

> Unless I'm missing something here.  I also don't think this
> is bad.  Remember that endian swapping happens once at the
> boundary of the code.  It isn't something that is constantly
> changing type and we shouldn't be worried about the
> programmer losing track of what type the data is in imho.

This has been discussed repeatedly and there remain several in this discussion committed to the usefulness of the object-based approach, so you'll not convince them otherwise.  Instead, keep the two approaches distinctly in scope as you read the discussions.

> Of course, if someone can come up with a typed interface
> which doesn't enforce a copy then I may change my mind.

+1

> Next, on naming, I think we should be very careful that we
> don't over-think the naming question.  I'll ask a general
> question.  What term does everyone use when talking about
> endian swapping?  Certainly in my programming career I've
> never heard it called anything other than endian swapping.
> Also (and I know this shouldn't be taken as a definitive
> source) Wikipedia refers to the process of changing
> endianness as a byte swap.  Shouldn't we use swap because
> that is what everyone knows the process of changing
> endianness as?  That's my 2d, but I'm not wholly against
> another naming option.

While I sympathize with your position, it has been noted that "swap" is a very bad choice because of std::swap(), boost::swap(), etc.  Those functions have a distinct behavior and purpose that endianness conversion does not satisfy.  Considering that our work could be standardized in the future, can you imagine the committee accepting "swap" as the name?  I can't.  That implies the need to find another name.

_____
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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