Re: [boost] BOOST_BIG_ENDIAN

From: John Maddock (john_at_[hidden])
Date: 2004-07-24 05:57:50

> This macro (and its friend BOOST_LITTLE_ENDIAN) definition appears in
> boost/detail/limits.hpp.  However, that file is included only if
> boost/limits.hpp does not detect the standard <limits>.  Thus, it does
> not get defined for more standard compilers.
>
> The serialization library makes use of this macro (in a test), so I
> wonder how it works on standard compilers.
>
> I could use the ENDIAN macros in some of my code to provide compile time
> performance options (linux provides something similar).  Is it possible
> to move the ENDIAN macros into some other header so that they are more
> easily obtained, and also do not force including a limits workaround?
>
> I also imagine if they were actually included in more compilations, that
> they could get checked for correctness and the maintenance of newer
> platforms would increase.

I think this one has come up before: in general there is no way tell what
the endianness is without doing a runtime test, there's also the problem
that there are more than two orderings possible, for example
for 4 byte types the byte ordering could be any of:

1 2 3 4
4 3 2 1
2 1 4 3
3 4 1 2

throw in 8 or 16 byte types, plus floating point types, and things get
complicated :-(

BTW, if you need the endianness in a test, then it is much easier to
determine the byte ordering of a type at runtime than at compile time IMO.

Sorry to complicate things for you again!

John.