Byte Order Swapping Function

[Jonathan M Davis]

On Sunday 17 July 2011 01:48:37 Jonathan M Davis wrote:
> On Sunday 17 July 2011 09:40:06 Alix Pexton wrote:
> > On 17/07/2011 07:42, Jonathan M Davis wrote:
> > > On Saturday 16 July 2011 23:31:09 Andrew Wiley wrote:
> > [snip]
> > 
> > >> Take a look at http://www.dmh2000.com/cpp/dswap.shtml . It made
> > >> the
> > >> odd
> > >> behavior make a lot more sense to me.
> > > 
> > > Okay. Good to know. In other words, we can't have swapEndian work
> > > with
> > > floating point values like that. It can generate a byte array from
> > > them
> > > (or maybe an integral value of the same size), but it can't generate
> > > another floating point value. Bleh. Okay. Floating point values with
> > > have to use an entirely different overload then. Thanks for the
> > > info.
> > > 
> > > - Jonathan M Davis
> > 
> > I find myself wanting to address this issue by using types, as the FP
> > example demonstrates that when the endieness of a value changes, its
> > type should too.
> > 
> > using double as an example, I'd like to be able to write code something
> > like this.
> > 
> > > auto v0 = 0.1;
> > > auto v1 = nbo!double(v0); // nbo = network byte order, your names
> > > may
> > > vary auto v2 = to!double(v1);
> > > assert(v0 == v2);
> > 
> > I would, of course, expect aliases for those occasions when one wants to
> > state endieness explicitly (I just can't think of any >< ), and for
> > non-conversions (when nbo == hbo) to be no-ops.
> > 
> > Or am I missing something?
> > 
> > A...
> 
> I suppose that you _could_ do something like that, though I'm not sure that
> there's much point. You can swap integers with impunity. Having a separate
> type would actually be a problem, because then you'd have to translate to an
> integer again anyway to do anything with it. In the case of a floating
> point value, you essentially have to convert to either an integral value or
> an array of ubytes. You could wrap that in a struct or somesuch, but I'm
> not sure how much point there is in that. Just like with integers, you'd
> have to convert it over to a prmitive type before doing anything with it
> like sending it via the network.
> 
> So, sure you _could_ make such types, but I don't think that there's much
> point to it. And if someone wants to do that in their own code, it wouldn't
> be all that hard. The hard part is the actual byte swapping.

Actually, having a value in little endian vs big endian or native vs host 
order is a prime example of what the original hungarian notation was for 
(rather than what it became once the systems group at Microsoft got their 
hands on it and misunderstood the explanation on it due to the poor usage of 
the word type). By putting an appropriate prefix on the variables, it makes it 
clear. e.g.

auto netValue = hostToNet(hostValue);

It's too bad that the basic concept of hungarian notation was misunderstood 
and became what it is today. The original concept is quite good (check out 
http://www.joelonsoftware.com/articles/Wrong.html for more details).

- Jonathan M Davis