[LCP]#defines to know Endianness

[Paul Gearon]

Greg Black wrote:
> You have two choices:
> 
>   1. Find something like I suggested that works on all the
>      platforms you care about; or
> 
>   2. Write your own macro and use that -- it's incredibly
>      trivial, after all.
> 
> You might also ask yourself why you're doing this at all.  It's
> rare for well-written code to need to know stuff like this.

I agree here.  It's normally only necessary for making data compatible 
across machines of different architectures.  This includes saved files 
and network communications.

If it's network communications that you're considering, then it's 
possible that you're operating at too low a level.  I'd recommend 
considering your options for using a higher level protocol.

Otherwise, the fact that networking needs this stuff provides a hint. 
You can use htonl and ntohl, which were both designed for this purpose. 
  They convert data into a common "network" format.  This can be useful 
for file use as well.

The nice thing about these functions is that they are normally 
implemented as macros.  On big endian platforms they do nothing (so the 
pre-compiler gets rid of it.  For non-macro implementations the 
optimizer can get rid of it), and on x86 (the predominant little endian 
platform) the macro is normally implemented with a bswap assembly 
instruction, which has less overhead than any macro you'd come up with.

In fact, have a look at netinet/in.h on Linux and you'll see that it 
does just this.  These functions/macros are available on all other 
platforms including Windows.

-- 
Regards,
Paul Gearon

Software Engineer                Telephone:   +61 7 3876 2188
Tucana Technologies              Fax:         +61 7 3876 4899
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