# Crate fastrand

Expand description

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 mut 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. See the WebAssembly Notes section for more information.

## WebAssembly Notes

For non-WASI WASM targets, there is additional sublety to consider when utilizing the global RNG. By default, `std` targets will use entropy sources in the standard library to seed the global RNG. However, these sources are not available by default on WASM targets outside of WASI.

If the `js` feature is enabled, this crate will assume that it is running in a JavaScript environment. At this point, the `getrandom` crate will be used in order to access the available entropy sources and seed the global RNG. If the `js` feature is not enabled, the global RNG will use a predefined seed.

## Structs

• A random number generator.

## Functions

• alphabetic`std`
Generates a random `char` in ranges a-z and A-Z.
• alphanumeric`std`
Generates a random `char` in ranges a-z, A-Z and 0-9.
• bool`std`
Generates a random `bool`.
• char`std`
Generates a random `char` in the given range.
• choice`std`
Choose an item from an iterator at random.
• choose_multiple`std`
Collects `amount` values at random from the iterator into a vector.
• digit`std`
Generates a random digit in the given `base`.
• f32`std`
Generates a random `f32` in range `0..1`.
• f64`std`
Generates a random `f64` in range `0..1`.
• get_seed`std`
Gives back current seed that is being held by the thread-local generator.
• i8`std`
Generates a random `i8` in the given range.
• i16`std`
Generates a random `i16` in the given range.
• i32`std`
Generates a random `i32` in the given range.
• i64`std`
Generates a random `i64` in the given range.
• i128`std`
Generates a random `i128` in the given range.
• isize`std`
Generates a random `isize` in the given range.
• lowercase`std`
Generates a random `char` in range a-z.
• seed`std`
Initializes the thread-local generator with the given seed.
• shuffle`std`
Shuffles a slice randomly.
• u8`std`
Generates a random `u8` in the given range.
• u16`std`
Generates a random `u16` in the given range.
• u32`std`
Generates a random `u32` in the given range.
• u64`std`
Generates a random `u64` in the given range.
• u128`std`
Generates a random `u128` in the given range.
• uppercase`std`
Generates a random `char` in range A-Z.
• usize`std`
Generates a random `usize` in the given range.