File::Stat#readable?

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

#ifdef USE_GETEUID
    if (geteuid() == 0) return Qtrue;
#endif
#ifdef S_IRUSR
    if (rb_stat_owned(obj))
        return RBOOL(st->st_mode & S_IRUSR);
#endif
#ifdef S_IRGRP
    if (rb_stat_grpowned(obj))
        return RBOOL(st->st_mode & S_IRGRP);
#endif
#ifdef S_IROTH
    if (!(st->st_mode & S_IROTH)) return Qfalse;
#endif
    return Qtrue;
}