64-Bit Bank Balances ‘Ought to Be Enough for Anybody’?

• 0.30000000000000004

  245 1,398 2.0 CSS

  Floating Point Math Examples

Surprisingly common values like 0.1 don't have a precise representation in binary for most formats, including standard floating point number formats. See https://0.30000000000000004.com/ for more detail than you can shake a stick at.

Also if the local tax code states using 5 decimal places for intermediate values when you will introduce “errors” using formats that give greater precision as well as those that give less precision. Having work on mortgage and pension calculations I can state that the (very) small errors seen at individual steps because of this can balloon significantly through repeated calculations.

Furthmore, the name floating point gives away the other issue. Floating point numbers are accurate to a given number of significant figures not decimal places. For large numbers any decimal places you have in the result are at best an estimate, and as above any rounding errors at each stage can compound into a much larger error by the end of a calculation.

• Joda-Money

  3 637 6.3 Java

  Java library to represent monetary amounts.

  

• InfluxDB

  www.influxdata.com sponsored

  Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.

  

• Chronicle-Core

  1 532 9.3 Java

  Low level access to native memory, JVM and OS.

  

You _can_ use floating point if you are very careful and know what you are doing and know about decimal normalization (see e.g. OpenHFT implementation for high-frequency trading: https://github.com/OpenHFT/Chronicle-Core/blob/ea/src/main/j...)

But if you are not an expert, you better stick to BigDecimal and absorb the performance costs.

• order-graph

  1 1 10.0 Haskell

  Matching engine + order routing for limit orders

This only puts currency codes in the type system; and uses rational numbers for amounts.

This is definitely useful because you can have the type system tell you if you've implemented e.g. exchange rate conversion incorrectly. But it's also a hassle because you need to reify currency values discovered at runtime as types, which isn't pretty [1].

[1] https://github.com/runeksvendsen/order-graph/blob/eef0006cba...

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