ax_openmp

This macro tries to find out how to compile programs that use OpenMP a standard API and set of compiler directives for parallel programming (see http://www-unix.mcs/)

On success, it sets the OPENMP_CFLAGS/OPENMP_CXXFLAGS/OPENMP_F77FLAGS output variable to the flag (e.g. -omp) used both to compile *and* link OpenMP programs in the current language.

NOTE: You are assumed to not only compile your program with these flags, but also link it with them as well.

If you want to compile everything with OpenMP, you should set:

    CFLAGS="$CFLAGS $OPENMP_CFLAGS" 
    #OR#  CXXFLAGS="$CXXFLAGS $OPENMP_CXXFLAGS" 
    #OR#  FFLAGS="$FFLAGS $OPENMP_FFLAGS" 

(depending on the selected language).

The user can override the default choice by setting the corresponding environment variable (e.g. OPENMP_CFLAGS).

ACTION-IF-FOUND is a list of shell commands to run if an OpenMP flag is found, and ACTION-IF-NOT-FOUND is a list of commands to run it if it is not found. If ACTION-IF-FOUND is not specified, the default action will define HAVE_OPENMP.

AC_DEFUN([AX_OPENMP], [
AC_PREREQ(2.59) dnl for _AC_LANG_PREFIX

AC_CACHE_CHECK([for OpenMP flag of _AC_LANG compiler], ax_cv_[]_AC_LANG_ABBREV[]_openmp, [save[]_AC_LANG_PREFIX[]FLAGS=$[]_AC_LANG_PREFIX[]FLAGS
ax_cv_[]_AC_LANG_ABBREV[]_openmp=unknown
# Flags to try:  -fopenmp (gcc), -openmp (icc), -mp (SGI & PGI),
#                -xopenmp (Sun), -omp (Tru64), -qsmp=omp (AIX), none
ax_openmp_flags="-fopenmp -openmp -mp -xopenmp -omp -qsmp=omp none"
if test "x$OPENMP_[]_AC_LANG_PREFIX[]FLAGS" != x; then
  ax_openmp_flags="$OPENMP_[]_AC_LANG_PREFIX[]FLAGS $ax_openmp_flags"
fi
for ax_openmp_flag in $ax_openmp_flags; do
  case $ax_openmp_flag in
    none) []_AC_LANG_PREFIX[]FLAGS=$save[]_AC_LANG_PREFIX[] ;;
    *) []_AC_LANG_PREFIX[]FLAGS="$save[]_AC_LANG_PREFIX[]FLAGS $ax_openmp_flag" ;;
  esac
  AC_TRY_LINK_FUNC(omp_set_num_threads,
        [ax_cv_[]_AC_LANG_ABBREV[]_openmp=$ax_openmp_flag; break])
done
[]_AC_LANG_PREFIX[]FLAGS=$save[]_AC_LANG_PREFIX[]FLAGS
])
if test "x$ax_cv_[]_AC_LANG_ABBREV[]_openmp" = "xunknown"; then
  m4_default([$2],:)
else
  if test "x$ax_cv_[]_AC_LANG_ABBREV[]_openmp" != "xnone"; then
    OPENMP_[]_AC_LANG_PREFIX[]FLAGS=$ax_cv_[]_AC_LANG_ABBREV[]_openmp
  fi
  m4_default([$1], [AC_DEFINE(HAVE_OPENMP,1,[Define if OpenMP is enabled])])
fi
])dnl AX_OPENMP

Copyright © 2006 Steven G. Johnson <stevenj@alum.mit.edu>

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