Re: Determine endianness in pure lua

[Jim Mellander <jmellander@...>]

KHMan wrote:
> 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.
> 

Thanks, I got the idea from looking at your No Frills Intro to the Lua
instruction set - I appreciate it.

I suppose the lua version could be checked, as well, to address
versioning issues.



-- 
Jim Mellander
Incident Response Manager
Computer Protection Program
Lawrence Berkeley National Laboratory
(510) 486-7204

The reason you are having computer problems is:

The MGs ran out of gas.