BigNum

A library that allows the creation of incredibly large numbers, but with a low memory/runtime footprint (relative to arbitrary-precision libraries). It accomplishes this by only storing up to 64 bits in the significand (similar to the floating point standard).

Inspiration/Why Did I Make This?

The inspiration for this library was looking into idle/incremental games. These games almost always have some sort of exponential growth function and as a result often have to limit the number of items/buildings you can own to avoid overflowing the f64 they store the value in. I want to be able to ignore this limit, hence this library. It's perfect for situations where you need to store an extremely large number but without the overhead of an arbitrary-precision library.

Goals

My ultimate goal is to make this as close to a u64 stand-in as possible. The user should be able to create them at the beginning of the program (or whenever they're needed), and then use them as if it was a standard u64 price/score/etc. value.

As an addendum to the above I want it to be lightweight and performant. Users should be able to modify, create, and delete them at will without notable performance hits (to the extent that's possible).

Usage

Bases 2, 8, 10, and 16 are all pre-defined, and aliased to BigNumBin, BigNumOct, BigNumDec, BigNumHex. As an example, to create a binary BigNum to represent the formula 1234123223468 * 2^123422235, do BigNumBin::new(1234123223468, 123422235). Then you can freely apply any of the 4 standard math operations between this value and a u64 or another BigNumBin. For more examples check the page on docs.rs and the test code.

Performance

Here are a couple of results from benchmarking the current version. TL;DR it's probably fast enough for anything but performance-critical applications.

Each test involved running 10k of the listed operations, code is in benches/multi.rs

Features

Random

I've added an implementation to generate random-ish BigNum values for testing. It is not actually correct (values won't appear at the frequency you'd expect and the bounds are not expected). But it will do for peformance testing and whatnot.