Amounts

Financial amounts must be kept exactly, but float and double types are susceptible to rounding errors. Also, both prices and volumes trade in discrete increments, sometimes in half- or quarter- units. So Coin Trader has an Amount base class which has basic arithmatic operations on it, and two subclasses DecimalAmount and DiscreteAmount which have different numerical representations. DecimalAmount is backed by a BigDecimal with MathContext.DECIMAL128 rounding for fine-grained (continuous) number representation. The DiscreteAmount class represents numbers using a two-number representation: a count and a basis. The basis is the smallest increment in the counting system, like pennies are the smallest unit for US dollars. Swiss Francs are rounded to the nearest nickel, and are represented in a DiscreteAmount with a basis of 0.05. The count is the number of increments in the value. For Bitcoin, the count is the number of Satoshis, and the basis is 1e-8. To avoid float rounding, DiscreteAmount actually stores 1/basis as a long. This "inverted basis" is the number of increments in a whole unit. Most of the Amount methods are accessible from the base class, but DiscreteAmount additionally offers increment() and decrement() which are useful for bidding one pip higher or lower than a target price.