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5687 :: interest in a decimal library

• JohnAD (orginal) [2019-12-14T20:34:27+01:00] view original

  I'm about to expand the BSON protocol library to support 128-bit decimal numbers. But, to do that, I would need to write a 128-decimal decimal number support into Nim.

  So, I could either:

  1. put the new data type directly into the BSON library, or
  2. create a seperate 128-bit decimal library and have BSON dependant on it, or
  3. put partial support into the BSON library and save/read using the arbitrary precision library at https://github.com/status-im/nim-decimal (which is not on nimble yet).

  Has there been much need for such decimal support?

  I know if Nim is ever used for financial work, some kind of decimal arithmetic would be needed to prevent rounding issues.

  If made it a separate library I would definitely put it on nimble.directory. Or, I could submit it to be part of the Nim language standard library if there was interest.

  Opinions?

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• JohnAD (orginal) [2019-12-14T20:35:24+01:00] view original

  other notes:

  1. The library would be written such that it conforms to the BSON spec:

  • https://github.com/mongodb/specifications/blob/master/source/bson-decimal128/decimal128.rst

  Which uses the IEEE 754 spec:

  • https://en.wikipedia.org/wiki/IEEE_754
  • https://en.wikipedia.org/wiki/Decimal128_floating-point_format
  • http://speleotrove.com/decimal/decbits.html

  2. Yes, there is another decimal library on nimble.directory, but it does not have high-enough precision.
  3. The arbitrary precision library by im-status has the benefit of near-infinite precision and uses Python's mpdecimal C library. In theory, the downside is performance, but that C library is pretty highly optimized.

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• mratsim (orginal) [2019-12-14T22:18:06+01:00] view original

  It's not on nimble because in the end we didn't use it so it's not tested.

  If someone is interested in adopting it, it can be forked and I can redirect to that repo.

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