func byteSliceArithmeticUint16(m *mutator, b []byte) []byte {
	if len(b) < 2 {
		return nil
	}
	v := uint16(m.rand(35) + 1)
	if m.r.bool() {
		v = 0 - v
	}
	pos := m.rand(len(b) - 1)
	enc := m.randByteOrder()
	enc.PutUint16(b[pos:], enc.Uint16(b[pos:])+v)
	return b
}

// byteSliceArithmeticUint32 adds/subtracts from a random uint32 in b.
func byteSliceArithmeticUint32(m *mutator, b []byte) []byte {

}

func newMutator() *mutator {
	return &mutator{r: newPcgRand()}
}

func (m *mutator) rand(n int) int {
	return m.r.intn(n)
}

func (m *mutator) randByteOrder() binary.ByteOrder {
	if m.r.bool() {
		return binary.LittleEndian
	}
	return binary.BigEndian
}

// chooseLen chooses length of range mutation in range [1,n]. It gives
// preference to shorter ranges.