// The maximum value we can represent milli-units for.
	// Compare with the return value of Quantity.Value() to
	// see if it's safe to use Quantity.MilliValue().
	MaxMilliValue = int64(((1 << 63) - 1) / 1000)
)

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) {