got := f.int64()
		want := x &^ (1<<(63-prec) - 1) // cut off (round to zero) low 63-prec bits
		if got != want {
			t.Errorf("got %#x (%s); want %#x", got, f.Text('p', 0), want)
		}
	}
}

func TestFloatSetFloat64(t *testing.T) {
	for _, want := range []float64{
		0,
		1,
		2,
		12345,
		1e10,
		1e100,
		3.14159265e10,
		2.718281828e-123,
		1.0 / 3,
		math.MaxFloat32,
		math.MaxFloat64,