# Crate num_bigint

source · [−]## Expand description

Big Integer Types for Rust

- A
`BigUint`

is unsigned and represented as a vector of digits. - A
`BigInt`

is signed and 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};
// 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;
f0 = f1;
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.