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# fastrand
[](
https://github.com/smol-rs/fastrand/actions)
[](
https://github.com/smol-rs/fastrand)
[](
https://crates.io/crates/fastrand)
[](
https://docs.rs/fastrand)
A simple and fast random number generator.
The implementation uses [Wyrand](https://github.com/wangyi-fudan/wyhash), a simple and fast
generator but **not** cryptographically secure.
## Examples
Flip a coin:
```rust
if fastrand::bool() {
println!("heads");
} else {
println!("tails");
}
```
Generate a random `i32`:
```rust
let num = fastrand::i32(..);
```
Choose a random element in an array:
```rust
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):
```rust
fastrand::choose_multiple([1, 4, 5], 2);
fastrand::choose_multiple(0..20, 12);
```
Shuffle an array:
```rust
let mut v = vec![1, 2, 3, 4, 5];
fastrand::shuffle(&mut v);
```
Generate a random `Vec` or `String`:
```rust
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:
```rust
// 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:
```rust
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`](https://docs.rs/fastrand/latest/fastrand/struct.Rng.html#method.with_seed) method.
- `js`: Assumes that WebAssembly targets are being run in a JavaScript environment.
[`fastrand-contrib`]: https://crates.io/crates/fastrand-contrib
## License
Licensed under either of
* Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
#### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.
|
