# Crate num_bigint

source ·## Expand description

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

```
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.

## Structs

- A big signed integer type.
- A big unsigned integer type.
- The error type returned when a checked conversion regarding big integer fails.
- An iterator of
`u32`

digits representation of a`BigUint`

or`BigInt`

, ordered least significant digit first. - An iterator of
`u64`

digits representation of a`BigUint`

or`BigInt`

, ordered least significant digit first.

## Enums

- A Sign is a
`BigInt`

’s composing element.

## Traits

- 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`

. - A generic trait for converting a value to a
`BigUint`

.