source: vendor/diffutils/2.8.1/m4/st_mtim.m4

#serial 5

dnl From Paul Eggert.

# Define ST_MTIM_NSEC to be the nanoseconds member of struct stat's st_mtim,
# if it exists.

AC_DEFUN([AC_STRUCT_ST_MTIM_NSEC],
 [AC_CACHE_CHECK([for nanoseconds member of struct stat.st_mtim],
   ac_cv_struct_st_mtim_nsec,
   [ac_save_CPPFLAGS="$CPPFLAGS"
    ac_cv_struct_st_mtim_nsec=no
    # tv_nsec -- the usual case
    # _tv_nsec -- Solaris 2.6, if
    #   (defined _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED == 1
    #    && !defined __EXTENSIONS__)
    # st__tim.tv_nsec -- UnixWare 2.1.2
    for ac_val in tv_nsec _tv_nsec st__tim.tv_nsec; do
      CPPFLAGS="$ac_save_CPPFLAGS -DST_MTIM_NSEC=$ac_val"
      AC_TRY_COMPILE([#include <sys/types.h>
#include <sys/stat.h>], [struct stat s; s.st_mtim.ST_MTIM_NSEC;],
        [ac_cv_struct_st_mtim_nsec=$ac_val; break])
    done
    CPPFLAGS="$ac_save_CPPFLAGS"])

  if test $ac_cv_struct_st_mtim_nsec != no; then
    AC_DEFINE_UNQUOTED(ST_MTIM_NSEC, $ac_cv_struct_st_mtim_nsec,
      [Define to be the nanoseconds member of struct stat's st_mtim,
   if it exists.])
  fi
 ]
)