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Subject: Re: [boost] [boost::endian] Request for comments/interest
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-06-02 07:24:44

Terry Golubiewski wrote:
> Jonathan Franklin wrote:

Please clean up Outlook's quoting and attribution messes.

> > In addition to my network needs, I also have at least two image file
> > formats that have the option of storing the arbitrarily sized data on
> > disk in big- or little-endian format. A library that allows me to
> > slurp up the image data into memory and swap in place if needed is
> > terribly useful to me.
> In another post, I finally understood this use-case.
> Again (being the non-swap advocate) to address this, I would
> suggest...
> template<endian_t E1, class T, endian_t E2>
> endian<E2, T>* copy(const endian<E1, T>* first, const
> endian<E1, T>* last,
> endian<E2, T>* dest) {
> if (E1 == E2 && first == dest)
> return dest + distance(first, last);
> while (first != last)
> *dest++ = *first++;
> return dest;
> }

I assume you'd actually dispatch through a class template's static member function in order to get compile time detection of E1 == E2 via partial specialization.

The loop might well be as efficient as Tomas' swap_in_place().

> Assuming you just read a TCP stream of big-endian T's into
> memory at a location 'char* buf', then you could endian-
> convert the T's, if necessary, like this...
> const endian<big, T>* src = reinterpret_cast<const
> endian<big, T>*>(buf);
> endian<native, T>* dst = reinterpret_cast<endian<native, T>*>(buf);
> (void) copy(src, src+numTs, dst);

A call to swap_in_place() avoids the ugly reinterpret_casts and looks far simpler.

Thus far, I'm not convinced that there is any value in the endian types, but keep trying!

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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