# Crate num_bigint [−] [src]

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));Run```

It's easy to generate large random numbers:

```extern crate rand;
extern crate num_bigint as bigint;

use bigint::{ToBigInt, RandBigInt};

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);
Run```

## Structs

 BigInt A big signed integer type. BigUint A big unsigned integer type.

## Enums

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

## Traits

 RandBigInt ToBigInt A generic trait for converting a value to a `BigInt`. ToBigUint A generic trait for converting a value to a `BigUint`.

## Type Definitions

 BigDigit A `BigDigit` is a `BigUint`'s composing element. DoubleBigDigit A `DoubleBigDigit` is the internal type used to do the computations. Its size is the double of the size of `BigDigit`.