{-2, -2, -4, true},

		{mostNegative, -1, 0, false},
		{mostNegative, 1, mostNegative + 1, true},
		{mostPositive, -1, mostPositive - 1, true},
		{mostPositive, 1, 0, false},

		{mostNegative, mostPositive, -1, true},
		{mostPositive, mostNegative, -1, true},
		{mostPositive, mostPositive, 0, false},
		{mostNegative, mostNegative, 0, false},

		{-mostPositive, mostNegative, 0, false},

)

const mostNegative = -(mostPositive + 1)
const mostPositive = 1<<63 - 1

// int64Add returns a+b, or false if that would overflow int64.
func int64Add(a, b int64) (int64, bool) {
	c := a + b
	switch {
	case a > 0 && b > 0:
		if c < 0 {
			return 0, false
		}
	case a < 0 && b < 0:
		if c > 0 {
			return 0, false
		}
		if a == mostNegative && b == mostNegative {
			return 0, false

		{int64Amount{value: mostNegative, scale: 0}, 1, int64Amount{value: mostNegative, scale: 0}, true},
		{int64Amount{value: mostNegative, scale: 1}, 0, int64Amount{value: 0, scale: 0}, true},
		{int64Amount{value: mostNegative, scale: 1}, 1, int64Amount{value: mostNegative, scale: 1}, false},
	} {
		c := test.a
		ok := c.Mul(test.b)
		if ok && !test.ok {

		{decQuantity(mostNegative/-2, 0, DecimalSI), -2, decQuantity(mostNegative, 0, DecimalSI), true},
		{decQuantity(mostNegative, 0, DecimalSI), 2,
			bigDecQuantity(big.NewInt(0).Mul(bigMostNegative, big.NewInt(2)), 0, DecimalSI), false},
		{decQuantity(mostNegative, 0, DecimalSI), 10, decQuantity(mostNegative, 1, DecimalSI), false},
		{decQuantity(mostNegative, 0, DecimalSI), -10,