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I once wrote some accounting software for a tiny team in an investment bank. The bosses decided that we should use our brand-new platform, which was cheap to de

I once wrote some accounting software for a tiny team in an investment bank. The bosses decided that we should use our brand-new platform, which was cheap to develop for, because most (normal) things could be done without code. All went well for a couple of months; then the customer reported that the system failed for currency conversions to and from Yen. There wasn't enough precision. We had to write an arbitrary-precision maths library, resulting in the project overrunning budget by a factor of three.

vlovich123 2y ago
There’s a world of difference between an arbitrary precision library like mpfr suited for financial applications, a fixed precision “Decimal” type that’s better suited for financial applications, and trying to roll your own thing. I don’t believe anywhere that I wrote that you should roll your own. All I said is that for financial stuff “Decimal”-like APIs are going to be easier to configure, manage and be better suited for financial applications.
- denton-scratch 2y ago
  Sure. This was the early eighties; we didn't really have "libraries", and even if we had, there was no way to plug them into this proprietary development system. > library like mpfr suited for financial applications, a fixed precision “Decimal” type that’s better suited for financial applications I don't know mpfr, but my guess is you meant to say that mpfr is better-suited for scientific applications?
  - vlovich123 2y ago
    Yeah, arbitrary precision is different from fixed point precision that financial institutions typically need. MPFR is arbitrary precision so if you’re doing stuff involving our solar system and beyond, you probably want to use mpfr and be very careful in setting up the equations you’re using. Financial transactions have different requirements though and the arbitrary precision is unnecessarily slow, uses unnecessary amounts of RAM, and I believe will probably difficult to configure correctly. That being said, I’ve never really used mpfr. More just relaying what I understand to be the lay of the land.
    - nullc 2y ago
      MPFR itself is pretty easy to use. Unfortunately, if your formula are ill conditioned you can get inaccurate results even using thousands of bits of precision... so there is no replacement for doing analysis and testing. Perhaps if there were some interval-math equivalent of MPFR you could at least tell when your code might be producing wrong results without extensive mathematical analysis.

vlovich123 2y ago

There’s a world of difference between an arbitrary precision library like mpfr suited for financial applications, a fixed precision “Decimal” type that’s better suited for financial applications, and trying to roll your own thing. I don’t believe anywhere that I wrote that you should roll your own. All I said is that for financial stuff “Decimal”-like APIs are going to be easier to configure, manage and be better suited for financial applications.

denton-scratch 2y ago
Sure. This was the early eighties; we didn't really have "libraries", and even if we had, there was no way to plug them into this proprietary development system. > library like mpfr suited for financial applications, a fixed precision “Decimal” type that’s better suited for financial applications I don't know mpfr, but my guess is you meant to say that mpfr is better-suited for scientific applications?
- vlovich123 2y ago
  Yeah, arbitrary precision is different from fixed point precision that financial institutions typically need. MPFR is arbitrary precision so if you’re doing stuff involving our solar system and beyond, you probably want to use mpfr and be very careful in setting up the equations you’re using. Financial transactions have different requirements though and the arbitrary precision is unnecessarily slow, uses unnecessary amounts of RAM, and I believe will probably difficult to configure correctly. That being said, I’ve never really used mpfr. More just relaying what I understand to be the lay of the land.
  - nullc 2y ago
    MPFR itself is pretty easy to use. Unfortunately, if your formula are ill conditioned you can get inaccurate results even using thousands of bits of precision... so there is no replacement for doing analysis and testing. Perhaps if there were some interval-math equivalent of MPFR you could at least tell when your code might be producing wrong results without extensive mathematical analysis.