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# SHR3: 3-shift register random number generator
[https://bues.ch/](https://bues.ch/)
[Git repository](https://bues.ch/cgit/shr3rs.git/)
The SHR3 generator can be used to generate non-crypto random bits with only very few computations.
It is suitable for running on very small and restricted hardware (e.g. small 8 bit microcontrollers).
The SHR3 function is evaluated once per extracted random bit. The LSB of the SHR3 state is extracted as output.
The generator has a cycle of approximately `4_000_000_000` bits.
Do not use it to extract large amounts of random bits (more than a hundred MiB or so),
unless you can tolerate looping back to the beginning of the random stream.
It will loop back to the beginning after `2**32 - 1` iterations.
This generator is *not* cryptographically secure! Do not use it for cryptographic applications.
# Example usage:
use shr3::prelude::*;
let mut shr3 = Shr3::new(); // SHR3 with default seed (1).
let x: u8 = shr3.get(); // Extract 8 bits from shr3.
let y: u16 = shr3.get_bits(10); // Extract 10 bits from shr3 and store in lower bits of y.
assert_eq!(x, 0xF8); // Extracted random value.
assert_eq!(y, 0x2CC); // Extracted random value.
let mut shr3 = Shr3::new_state(42); // SHR3 with custom seed (42).
let mut shr3: Shr3 = Default::default(); // Alternative to Shr::new().
# Example Cargo.toml dependencies
Add this to your Cargo.toml:
[dependencies]
shr3 = "1"
# no_std
This crate does not require the Rust std library. It does not link to std.
# Optimized implementation
This crate includes an optimized implementation for AVR 8-bit.
All other architectures use the generic implementation.
On most architectures, this generic implementation will be compiled to rather efficient code.
# License
Copyright (c) 2022 Michael Buesch <m@bues.ch>
Licensed under the Apache License version 2.0 or the MIT license, at your option.
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