Re: [PATCH] block-sha1: Windows declares ntohl() in winsock2.h

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Aug 18, 2009, 15:40 UTC
Message-ID: <alpine.LFD.2.01.0908180836440.3162@localhost.localdomain>
In-Reply-To: <7v4os5gs0p.fsf@alter.siamese.dyndns.org>

On Tue, 18 Aug 2009, Junio C Hamano wrote:

Show 19 quoted lines

> Sebastian Schuberth <sschuberth@gmail.com> writes:
> 
> > On Tue, Aug 18, 2009 at 14:56, Artur Skawina<art.08.09@gmail.com> wrote:
> > ...
> >> I'd limit it to windows and any other ia32 platform that doesn't pick the
> >> bswaps itself; as is, it just adds an unnecessary hidden gcc dependency.
> >>
> >> Hmm, it's actually a gcc-4.3+ dependency, so it won't even build w/ gcc 4.2;
> >> something like this would be required: "(__GNUC__>=4 && __GNUC_MINOR__>=3)" .
> >
> > So, as you say the code makes no difference under Linux, would you be
> > OK with just testing for GCC 4.3+, and not for Windows? That would get
> > rid of the "hidden" GCC dependency and not make the preprocessor
> > checks overly complex. Moreover, limiting my patch to any "platform
> > that doesn't pick the bswaps itself" could possibly require
> > maintenance on compiler / CRT updates.
> 
> I would say that should be fine, but I'd let Linus and Nico to overrule me
> on this if they have any input.

I'd suggest not using a gcc builtin, since if you're using gcc you might as well just use inline asm that has been around forever (unlike the builtin).

Just do:

	#if defined(__GNUC__)
	#define htonl(x) ({ unsigned int __res; \
		__asm__("bswap %0":"=r" (__res):"0" (x)); \
		__res; })
	#define ntohl(x) htonl(x)
	#endif

or similar in the x86 section that does the rol/ror thing.

			Linus