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From: Bob Friesenhahn
Subject: Re: AC_PROG_CC_C99 and AC_OPENMP
Date: Sun, 9 May 2010 11:49:21 -0500 (CDT)
User-agent: Alpine 2.01 (GSO 1266 2009-07-14)

On Sun, 9 May 2010, Ralf Wildenhues wrote:

I think Bob refers to different versions of the OpenMP standard,
as opposed to different versions of some library implementation.
Requiring one of those versions would make sense, similar to how
AC_PROG_CC_C99 requests the 1999 version of the ISO C standard
and not the 1989/90 one.  Of course, the actual test code could,
besides checking the value of _OPENMP, also test for actual features
of the respective standard version, similarly to how AC_PROG_CC_C99
works.  It could do runtime tests when not cross-compiling, and fall
back to link test/_OPENMP value otherwise.

Yes, exactly. My own OpenMP-dependent software is only expected to work with OpenMP 2.0 (2002 version) or later. Some other software might want to start with OpenMP 2.5 (2005 version) since that is the first one officially supported by GCC, or even OpenMP 3.0 (supported by GCC 4.4). Luckily, I have found OpenMP portability to good, and have only experienced failure with the SGI IRIX compiler.

At the moment, OpenMP feature tests don't seem to be very important since implementations should fully support the specification version they claim to support (and they seem to do so). The main issue that I have had to resolve outside of AC_OPENMP is determining the name of the OpenMP runtime library, since that is compiler/platform dependent.

Bob Friesenhahn
GraphicsMagick Maintainer,

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