code: func SubUintWithInt(a uint64, b int64) (uint64, error) {
  	if b < 0 {
  		return AddUint64(a, uint64(-b))
  	}
  	return SubUint64(a, uint64(b))
  }
docs: // SubUintWithInt subtracts uint64 a with int64 b and returns uint64 if no overflow error.