cw-bigint

This is a forked version of rust-num/num-bigint with float operations removed, so that it can be used in smart contracts.

lib.rs:

A Big integer (signed version: BigInt, unsigned version: BigUint).

A BigUint is represented as a vector of BigDigits. A BigInt is a combination of BigUint and Sign.

Common numerical operations are overloaded, so we can treat them the same way we treat other numbers.

Example

use num_bigint::BigUint;
use num_traits::{Zero, One};
use std::mem::replace;

// Calculate large fibonacci numbers.
fn fib(n: usize) -> BigUint {
    let mut f0: BigUint = Zero::zero();
    let mut f1: BigUint = One::one();
    for _ in 0..n {
        let f2 = f0 + &f1;
        // This is a low cost way of swapping f0 with f1 and f1 with f2.
        f0 = replace(&mut f1, f2);
    }
    f0
}

// This is a very large number.
println!("fib(1000) = {}", fib(1000));

It's easy to generate large random numbers:

use num_bigint::{ToBigInt, RandBigInt};

let mut rng = rand::thread_rng();
let a = rng.gen_bigint(1000);

let low = -10000.to_bigint().unwrap();
let high = 10000.to_bigint().unwrap();
let b = rng.gen_bigint_range(&low, &high);

// Probably an even larger number.
println!("{}", a * b);

See the "Features" section for instructions for enabling random number generation.

Features

The std crate feature is enabled by default, and is mandatory before Rust 1.36 and the stabilized alloc crate. If you depend on num-bigint with default-features = false, you must manually enable the std feature yourself if your compiler is not new enough.

Random Generation

num-bigint supports the generation of random big integers when the rand feature is enabled. To enable it include rand as

rand = "0.8"
num-bigint = { version = "0.4", features = ["rand"] }

Note that you must use the version of rand that num-bigint is compatible with: 0.8.

Compatibility

The num-bigint crate is tested for rustc 1.31 and greater.