openmpi/config/c_get_alignment.m4

dnl -*- shell-script -*-
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# OPAL_C_GET_ALIGN(type, config_var)
# ----------------------------------
# Determine datatype alignment.
# First arg is type, 2nd arg is config var to define.
# Now that we require C99 compilers, we include stdbool.h
# in the alignment test so that we can find the definition
# of "bool" when we test for its alignment. We might be able
# to avoid this if we test for alignemtn of _Bool, but
# since we use "bool" in the code, let's be safe and check
# what we use. Yes, they should be the same - but "should" and
# "are" frequently differ
AC_DEFUN([OPAL_C_GET_ALIGNMENT],[
    AC_CACHE_CHECK([alignment of $1],
                   [AS_TR_SH([opal_cv_c_align_$1])],
		   [AC_RUN_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT
                                                    #include <stdbool.h> ],
[[
    struct foo { char c; $1 x; };
    struct foo *p = (struct foo *) malloc(sizeof(struct foo));
    int diff;
    FILE *f=fopen("conftestval", "w");
    if (!f) exit(1);
    diff = ((char *)&p->x) - ((char *)&p->c);
    free(p);
    fprintf(f, "%d\n", (diff >= 0) ? diff : -diff);
]])],                         [AS_TR_SH([opal_cv_c_align_$1])=`cat conftestval`],
                               [AC_MSG_WARN([*** Problem running configure test!])
                                AC_MSG_WARN([*** See config.log for details.])
                                AC_MSG_ERROR([*** Cannot continue.])],
                               [ # cross compile - do a non-executable test.  Trick
                                 # taken from the Autoconf 2.59c.  Switch to using
                                 # AC_CHECK_ALIGNOF when we can require Autoconf 2.60.
                                 _AC_COMPUTE_INT([(long int) offsetof (opal__type_alignof_, y)],
                                                 [AS_TR_SH([opal_cv_c_align_$1])],
                                                 [AC_INCLUDES_DEFAULT
#include <stdbool.h>

#ifndef offsetof
# define offsetof(type, member) ((char *) &((type *) 0)->member - (char *) 0)
#endif
typedef struct { char x; $1 y; } opal__type_alignof_;
],
                                                 [AC_MSG_WARN([*** Problem running configure test!])
                                                  AC_MSG_WARN([*** See config.log for details.])
                                                  AC_MSG_ERROR([*** Cannot continue.])])])])

AC_DEFINE_UNQUOTED([$2], [$AS_TR_SH([opal_cv_c_align_$1])], [Alignment of type $1])
eval "$2=$AS_TR_SH([opal_cv_c_align_$1])"

rm -rf conftest* ]) dnl