Crate shr3

SHR3: 3-shift register random number generator

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:

    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().

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.

Modules

prelude

Structs

Shr3

SHR3 generator register state.

Traits

BaseOps

Internal trait for basic operations on the output type.

Shr3Ops

Main operations for extracting bits from SHR3 generator.

Functions

shr3

One round of the SHR3 shuffle function.