Crate num_bigint

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

extern crate num_bigint;
extern crate num_traits;

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:

extern crate rand;
extern crate num_bigint as bigint;

use 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 mandatory and enabled by default. If you depend on num-bigint with default-features = false, you must manually enable the std feature yourself. In the future, we hope to support #![no_std] with the alloc crate when std is not enabled.

Implementations for i128 and u128 are only available with Rust 1.26 and later. The build script automatically detects this, but you can make it mandatory by enabling the i128 crate feature.

Random Generation

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

rand = "0.5"
num-bigint = { version = "0.2", features = ["rand"] }

Note that you must use the version of rand that num-bigint is compatible with: 0.5.

Compatibility

The num-bigint crate is tested for rustc 1.15 and greater.

Structs

BigInt

A big signed integer type.

BigUint

A big unsigned integer type.

ParseBigIntError

Enums

Sign

A Sign is a BigInt’s composing element.

Traits

ToBigInt

A generic trait for converting a value to a BigInt. This may return None when converting from f32 or f64, and will always succeed when converting from any integer or unsigned primitive, or BigUint.

ToBigUint

A generic trait for converting a value to a BigUint.