func euclidExtGCD(a, b *Int) (g, x, y *Int) {
	A := new(Int).Set(a)
	B := new(Int).Set(b)

	// A = Ua*a + Va*b
	// B = Ub*a + Vb*b
	Ua := new(Int).SetInt64(1)
	Va := new(Int)

	Ub := new(Int)
	Vb := new(Int).SetInt64(1)

	q := new(Int)
	temp := new(Int)

	r := new(Int)
	for len(B.abs) > 0 {
		q, r = q.QuoRem(A, B, r)

		A, B, r = B, r, A

		// Ua, Ub = Ub, Ua-q*Ub

	}
}

func TestIssue6866(t *testing.T) {
	for _, prec := range precList {
		two := new(Float).SetPrec(prec).SetInt64(2)
		one := new(Float).SetPrec(prec).SetInt64(1)
		three := new(Float).SetPrec(prec).SetInt64(3)
		msix := new(Float).SetPrec(prec).SetInt64(-6)
		psix := new(Float).SetPrec(prec).SetInt64(+6)

		p := new(Float).SetPrec(prec)
		z1 := new(Float).SetPrec(prec)
		z2 := new(Float).SetPrec(prec)

		b1e9  = new(big.Int)
	)

	b1e9.SetInt64(1e9)

	testOne := func(ti, tns, di int64) bool {
		t.Helper()

		t0 := Unix(ti, tns).UTC()
		d := Duration(di)
		if d < 0 {
			d = -d
		}
		if d <= 0 {
			d = 1
		}

		// Compute bt = absolute nanoseconds.
		sec, nsec := abs(t0)
		bsec.SetInt64(sec)
		bnsec.SetInt64(nsec)
		bt.Mul(bsec, b1e9)
		bt.Add(bt, bnsec)