Determining endianness in extconf.rb

ruby-talk
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 Patterson wrote:

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

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

[snip]

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

Thank you for the help!

--Aaron

···

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

4

Hi,

At Tue, 6 Dec 2005 04:21:37 +0900,
Daniel Berger 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.

···

--
Nobu Nakada

5

[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

···

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

6

[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__.

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.

···

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

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

Thanks for the help!

--Aaron