# [−][src]Crate num_bigint

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

A `BigUint` is represented as a vector of `BigDigit`s. 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 RandomBits A random distribution for `BigUint` and `BigInt` values of a particular bit size. UniformBigInt The back-end implementing rand's `UniformSampler` for `BigInt`. UniformBigUint The back-end implementing rand's `UniformSampler` for `BigUint`.

## Enums

 Sign A Sign is a `BigInt`'s composing element.

## Traits

 RandBigInt A trait for sampling random big integers. 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`.