done := make(chan bool)
	for i := 0; i < N; i++ {
		go func() {
			for j := 0; j < iter; j++ {
				f()
			}
			done <- true
		}()
	}
	for i := 0; i < N; i++ {
		<-done
	}
}

func TestXadduintptr(t *testing.T) {
	N := 20
	iter := 100000
	if testing.Short() {
		N = 10
		iter = 10000
	}
	inc := uintptr(100)
	total := uintptr(0)
	runParallel(N, iter, func() {
		atomic.Xadduintptr(&total, inc)

		}
	}
	if x.before != magic64 || x.after != magic64 {
		t.Fatalf("wrong magic: %#x _ %#x != %#x _ %#x", x.before, x.after, magic64, magic64)
	}
}

func TestAddUintptr(t *testing.T) {
	var x struct {
		before uintptr
		i      uintptr
		after  uintptr
	}
	var m uint64 = magic64
	magicptr := uintptr(m)
	x.before = magicptr
	x.after = magicptr
	var j uintptr