Crate num_bigint 

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::One;

// Calculate large fibonacci numbers.
fn fib(n: usize) -> BigUint {
    let mut f0 = BigUint::ZERO;
    let mut f1 = BigUint::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 rand::{SeedableRng, rngs::SmallRng};
use num_bigint::{BigInt, BigRng010};

// This seed is just for demonstration, but in most cases
// you'll probably want a non-deterministic `rng`.
let mut rng = SmallRng::seed_from_u64(42);
let a = rng.random_bigint(1000);

let low = BigInt::from(-10000);
let high = BigInt::from(10000);
let b = rng.random_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, which enables [std::error::Error] implementations and some internal use of floating point approximations. This can be disabled by depending on num-bigint with default-features = false. Either way, the alloc crate is always required for heap allocation of the BigInt/BigUint digits.

Random Generation

num-bigint supports the generation of random big integers when either of the rand_0_9 or rand_0_10 features are enabled. The [BigRng09] and [BigRng010] traits provide extension methods for any rand_core RNG of their respective version, while the structs [RandomBits], [UniformBigInt], and [UniformBigUint] fulfill further functionality for random distributions in rand::distr.

For example, using rand v0.10 in your Cargo.toml may look like this:

rand = "0.10"
num-bigint = { version = "0.5", features = ["rand_0_10"] }

Note that you must use the same version of rand as the feature you enable in num-bigint. It’s also fine for multiple versions to be enabled at once – the random-distribution structs will be shared with trait implementations for each rand feature that is enabled, while the BigRng traits are distinct.

You can instead use rand_core_0_9 or rand_core_0_10 for a more restricted subset, with only the BigRng traits.

Arbitrary Big Integers

num-bigint supports arbitrary and quickcheck features to implement [arbitrary::Arbitrary] and [quickcheck::Arbitrary], respectively, for both BigInt and BigUint. These are useful for fuzzing and other forms of randomized testing.

Serialization

The serde feature adds implementations of [Serialize][serde::Serialize] and [Deserialize][serde::Deserialize] for both BigInt and BigUint. Their serialized data is generated portably, regardless of platform differences like the internal digit size.

Compatibility

The num-bigint crate is tested for rustc 1.60 and greater.

Structs

BigInt

A big signed integer type.

BigUint

A big unsigned integer type.

ParseBigIntError

TryFromBigIntError

The error type returned when a checked conversion regarding big integer fails.

U32Digits

An iterator of u32 digits representation of a BigUint or BigInt, ordered least significant digit first.

U64Digits

An iterator of u64 digits representation of a BigUint or BigInt, ordered least significant digit first.

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.