Julia EvansApr 13, 2023

today I'm thinking about the "don't use floating point for money" advice I hear all the time. It obviously has a lot of truth to it.

But -- Excel/Google Sheets uses floating point for all of its calculations, people use spreadsheets for money calculations all the time, and it generally seems to work just fine -- the results get rounded for display.

So I'm trying to figure out if there's a more nuanced guideline than "never use floating point for money".

Show threadJulia EvansApr 13, 2023

thinking about trying to define a "safe zone" and a "danger zone" for floating point. maybe something like:

safe zone:
* all integer values (like 1.0, 234.0) behave 100% exactly the way you'd expect, UNLESS (!!!) they're more than 2^52. You can check for equality, it's fine.
* adding up ~100 numbers and rounding the result to 4 decimal places or so is going to work fine, as long as the numbers are roughly the same size

Show threadbigblen
@b0rk this paper has some great pictures (and words) about the "badlands" of some FP functions https://jeapostrophe.github.io/home/static/tm-cise2014.pdf
Apr 14, 2023 at 11:26amWeb