Re: Determine endianness in pure lua

[KHMan <keinhong@...>]

Jim Mellander wrote:
> I've been tinkering with ways to figure out a way to determine
> endianness of a system dynamically in pure lua.  This is what I came up,
> which is based on the bytecode format as documented with the below,
> which depends on examining the bytecode:
>
> function endian()
>         local function f() end
>         return string.byte(string.dump(f),7)
> end
>
> print(endian())
>
> I'm not happy with checking the header - is there something a bit less
> magic?

Looking at Perl and Python, if one does not use the available 
system configuration variable/info, we end up testing endianness 
using pack(). So, to get the same convenient feature, it's 
possible to add a custom 'system library' to Lua with the minimal 
of changes to the sources, in order to have our own 
'sys.byteorder'. But

function endian()
  # retrieve endian flag from a binary chunk header
  return string.byte(string.dump(function() end),7)
end

doesn't look too bad if one looks at it as the implementation of a 
primitive function... :-) To be perfectly safe though, note that 
the above is only guaranteed for major version bumps, I think.

--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia