code: func (op *op) count() int {
  	switch op.typ {
  	case 0, 1:
  		return 1
  	case 2, 3:
  		return len(op.values)
  	default:
  		panic(fmt.Sprintf("unknown operation type: %d", op.typ))
  	}
  }
docs: // count returns the number of bits the operation mutates.