File::Stat#executable_real?

static VALUE
rb_stat_X(VALUE obj)
{
    struct stat *st = get_stat(obj);

#ifdef USE_GETEUID
    if (getuid() == 0) {
        return RBOOL(st->st_mode & S_IXUGO);
    }
#endif
#ifdef S_IXUSR
    if (rb_stat_rowned(obj))
        return RBOOL(st->st_mode & S_IXUSR);
#endif
#ifdef S_IXGRP
    if (rb_group_member(get_stat(obj)->st_gid))
        return RBOOL(st->st_mode & S_IXGRP);
#endif
#ifdef S_IXOTH
    if (!(st->st_mode & S_IXOTH)) return Qfalse;
#endif
    return Qtrue;
}