func (z *Int128) SetInt64(x int64) *Int128 {
	z.lo = uint64(x)
	if x < 0 {
		z.hi = -1
	} else {
		z.hi = 0
	}
	return z
}
SetInt64 sets z to x and returns z.
package decimal
type Int128 struct {
	lo uint64
	hi int64
}
var (
	intOne = &Int128{1, 0}
	intTen = &Int128{10, 0}
)
func overflow() {
	panic("Arithmetic overflow")
}