Is there a thing like a flexible number data type?

[AjiBuster499]

I'm writing a calculator, and currently implementing factorial functionality. The calculator uses f64 as the primary data type, because decimals are pretty crucial to calculators, but this is incompatible with factorials for two reasons:

1. You can't calculate the factorial of a float.
2. f64 is unlikely to be able to hold larger factorials.

For this reason, I want to use an i128 for factorials, and factorials only. Of course, it is difficult to switch between floats and integers while maintaining precision, so I wanted to ask if there was a way/crate with a data type that can flex between an integer and a float, or simplifies conversion between the two while maintaining precision.

Alternatively are there crates that allow much larger floating types, so I can simply store an integer as a float for these calculations?

[2e71828]

@AjiBuster499

Alternatively are there crates that allow much larger floating types, so I can simply store an integer as a float for these calculations?

A quick search of crates.io finds astro_float, which looks like it fits the bill. I don’t have any experience with it, though.

[simonbuchan]

F64 can precisely hold integers up to 2**53, so it's not a terrible option... but you sound like you're looking for an arbitrary precision number library.

Start with num-bigint — Rust math library // Lib.rs there, and you can use num-rational — Rust math library // Lib.rs to represent fractions. That doesn't cover everything, but really high quality calculators are actually quite tricky, you shouldn't expect a simple answer.

[H2CO3]

@AjiBuster499

You can't calculate the factorial of a float.

Well, actually.

[AjiBuster499]

Thank you, this ended up letting me do the job.

[lambda-fairy]

As an aside, note that equality of trigonometric expressions is undecidable (Richardson's theorem). Any calculator that has them will need to deal with that uncertainty – whether via rounding or otherwise.