Re: Is detecting endianness at compile-time unworkable?

From: Michael <aixtools@felt.demon.nl>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: "brian m. carlson" <sandals@crustytoothpaste.net>,
	git@vger.kernel.org, Dan Shumow <shumow@gmail.com>,
	Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>
Subject: Re: Is detecting endianness at compile-time unworkable?
Date: Tue, 31 Jul 2018 22:06:14 +0200	[thread overview]
Message-ID: <325d1a6c-276a-9ffa-f9c5-72cbdecb6175@felt.demon.nl> (raw)
In-Reply-To: <87sh3ztrcb.fsf@evledraar.gmail.com>

On 31/07/2018 16:25, Ævar Arnfjörð Bjarmason wrote:
> ...the real trick is using these macros outside of GCC / glibc and on
> older GCC versions. See the github link above, you basically end up with
> a whitelist of how it looks on different systems / compilers. Sometimes
> both are defined, sometimes only both etc.
>
> It can be done, but as that code shows it's somewhat complex macro soup
> to get right.

FYI - the gcc I was using is 4.7.4.

And, the reason I suggest the test for both not being defined is so that 
'make' stops and whoever is running make just sets one or the other. Let 
them 'file a bug' When they come with a compiler that does not work - 
and find out what could be used.

For example, _AIX is the same as _BIG_ENDIAN. In the meantime, the code 
to test is simple.

Either one of _BIG_ENDIAN or _LITTLE_ENDIAN is provided by the compiler 
or the builder supplies one of the two using CFLAGS. I assume there is 
also a "undefine" flag, maybe -U - so hopefully a -U and a -D 
combination could be used for cross-compiling.

re: my mailer blocking things - it would only be for this list, as other 
lists come through with no extra work from me. At least I am not aware 
of anything special I could do.