{-mostPositive, -mostPositive, 1, false},
	} {
		c, ok := int64Multiply(test.a, test.b)
		if c != test.c {
			t.Errorf("%v: unexpected result: %d", test, c)
		}
		if ok != test.ok {
			t.Errorf("%v: unexpected overflow: %t", test, ok)
		}
		// multiplication is commutative
		d, ok2 := int64Multiply(test.b, test.a)
		if c != d || ok != ok2 {
			t.Errorf("%v: not commutative: %d %t", test, d, ok2)

	case a < 0 && b < 0:
		if c > 0 {
			return 0, false
		}
		if a == mostNegative && b == mostNegative {
			return 0, false
		}
	}
	return c, true
}

// int64Multiply returns a*b, or false if that would overflow or underflow int64.
func int64Multiply(a, b int64) (int64, bool) {
	if a == 0 || b == 0 || a == 1 || b == 1 {
		return a * b, true
	}
	if a == mostNegative || b == mostNegative {
		return 0, false
	}

		a.scale = 0
		return true
	case a.scale == 0:
		c, ok := int64Multiply(a.value, b)
		if !ok {
			return false
		}
		a.value = c
	case a.scale > 0:
		c, ok := int64Multiply(a.value, b)
		if !ok {
			return false
		}
		if _, ok = positiveScaleInt64(c, a.scale); !ok {
			return false
		}
		a.value = c
	default:
		c, ok := int64Multiply(a.value, b)
		if !ok {
			return false
		}

		if scale >= int32(Nano) {
			shifted := num + denom

			var value int64
			value, err := strconv.ParseInt(shifted, 10, 64)
			if err != nil {
				return Quantity{}, ErrNumeric
			}
			if result, ok := int64Multiply(value, int64(mantissa)); ok {
				if !positive {
					result = -result
				}
				// if the number is in canonical form, reuse the string
				switch format {
				case BinarySI: