Determining endianness in extconf.rb


#1

Hi. Hopefully this is the right list for this question!

I am writing an extension for Ruby in C, and I need to determine
the endianness of the machine and set a flag when I compile. What is
the best way to go about this? I’ve seen examples of determining
endianness but I don’t know how to set the flag in extconf.rb

Any help would be greatly appreciated. Thank you!

–Aaron


#2

Aaron P. wrote:

Modify $CFLAGS or $CPPFLAGS directly:

extconf.rb

if [1].pack(“I”) == [1].pack(“N”)
$CFLAGS += " -DBIG_ENDIAN" # note the leading space
end

/* In your C code somewhere /
#ifdef BIG_ENDIAN
/
Do something */
#endif

Regards,

Dan


#3

On Tue, Dec 06, 2005 at 04:21:37AM +0900, Daniel B. wrote:

[snip]

#endif

Regards,

Dan

Thank you for the help!

–Aaron


#4

Hi,

At Tue, 6 Dec 2005 04:21:37 +0900,
Daniel B. wrote in [ruby-talk:168948]:

extconf.rb

if [1].pack(“I”) == [1].pack(“N”)
$CFLAGS += " -DBIG_ENDIAN" # note the leading space
end

It tells the endian of the running platform, but not of the
target platform. They can differ when cross-compiling.

Since config.h defines WORDS_BIGENDIAN for big-endian
platforms, you don’t have to test it in extconf.rb.


#5

On Tue, Dec 06, 2005 at 02:00:33PM +0900, nobuyoshi nakada wrote:
[snip]

Since config.h defines WORDS_BIGENDIAN for big-endian
platforms, you don’t have to test it in extconf.rb.


Nobu Nakada

I guess I don’t understand how I am supposed to set up my build
environment… As far as I can tell, config.h is generated while
building Ruby from source. The only config.h on my system is:

/usr/lib/ruby/1.8/i386-linux/config.h

Which does not have WORDS_BIGENDIAN listed in it. I did find
WORDS_BIGENDIAN in /usr/lib/ruby/1.8/i386-linux/defines.h but it just
says to look at BIG_ENDIAN.

Can you point me to a small project that I can model my build after, or
an example exconf.rb?

Thanks for the help!

–Aaron


#6

On Wed, 2005-12-07 at 07:22 +0900, Aaron P. wrote:

environment… As far as I can tell, config.h is generated while
building Ruby from source. The only config.h on my system is:

/usr/lib/ruby/1.8/i386-linux/config.h

Which does not have WORDS_BIGENDIAN listed in it. I did find
WORDS_BIGENDIAN in /usr/lib/ruby/1.8/i386-linux/defines.h but it just
says to look at BIG_ENDIAN.

That’s because you are on Intel, which is little endian.

Can you point me to a small project that I can model my build after, or
an example exconf.rb?

What he is saying is that you should not modify your extconf.rb file. In
your C code, just do:

#ifdef WORDS_BIGENDIAN
// Big endian code
#else
// Little endian code
#endif

Guillaume.