# fastrand 2.0.2

A simple and fast random number generator
Documentation

# fastrand

A simple and fast random number generator.

The implementation uses Wyrand, a simple and fast generator but not cryptographically secure.

## Examples

Flip a coin:

``````if fastrand::bool() {
} else {
println!("tails");
}
``````

Generate a random `i32`:

``````let num = fastrand::i32(..);
``````

Choose a random element in an array:

``````let v = vec![1, 2, 3, 4, 5];
let i = fastrand::usize(..v.len());
let elem = v[i];
``````

Sample values from an array with `O(n)` complexity (`n` is the length of array):

``````fastrand::choose_multiple(vec![1, 4, 5].iter(), 2);
fastrand::choose_multiple(0..20, 12);
``````

Shuffle an array:

``````let mut v = vec![1, 2, 3, 4, 5];
fastrand::shuffle(&mut v);
``````

Generate a random `Vec` or `String`:

``````use std::iter::repeat_with;

let v: Vec<i32> = repeat_with(|| fastrand::i32(..)).take(10).collect();
let s: String = repeat_with(fastrand::alphanumeric).take(10).collect();
``````

To get reproducible results on every run, initialize the generator with a seed:

``````// Pick an arbitrary number as seed.
fastrand::seed(7);

// Now this prints the same number on every run:
println!("{}", fastrand::u32(..));
``````

To be more efficient, create a new `Rng` instance instead of using the thread-local generator:

``````use std::iter::repeat_with;

let rng = fastrand::Rng::new();
let mut bytes: Vec<u8> = repeat_with(|| rng.u8(..)).take(10_000).collect();
``````

This crate aims to expose a core set of useful randomness primitives. For more niche algorithms, consider using the `fastrand-contrib` crate alongside this one.

# Features

• `std` (enabled by default): Enables the `std` library. This is required for the global generator and global entropy. Without this feature, [`Rng`] can only be instantiated using the `with_seed` method.
• `js`: Assumes that WebAssembly targets are being run in a JavaScript environment.