A pseudo random number generator using the algorithm Romu for the programing language Rust.
This pseudo random number generator (PRNG) is not intended for cryptographic purposes. This crate only implements the 64-bit "RomuTrio" generator, since it's the recommended generator by the original author.
Romu is a non-linear random number generator. That means that the period is probabilistic and is based on the seed. The bigger the needed period is, the higher the chance it is that the actual period is "too small".
Following formula is given by the author:
P(|cycle contains x<= 2^k|) = 2^k-s+7
k is size of random numbers needed + 1.
s is the state size.
Example chances for getting a "too small" period: * When 2^62 * 64-bit numbers are needed (32 EiB) -> 2^-122 chance * When 2^39 * 64-bit numbers are needed (4 TiB) -> 2^-146 chance * When 2^36 * 64-bit numbers are needed (512 GiB) -> 2^-149 chance
You can read more about the theory behind Romu in the official paper and it's unique selling points on the official website of the original author.
When the user calls the new() or default() functions of a generator, the implementation
tries to use the best available randomness source to seed the generator (in the following order):
1. The crate getrandom to seed from a high quality randomness source of the operating system.
The feature getrandom must be activated for this.
2. Use the functionality of the standard library to create a low quality randomness seed (using
the current time, the thread ID and a memory address).
The feature std must be activated for this.
3. Use a memory address as a very low randomness seed. If Address Space Layout Randomization
(ASLR) is supported by the operating system, this should be a pretty "random" value.
It is highly recommended using the no_std compatible getrandom feature to get high quality
randomness seeds.
The user can always create / update a generator with a user provided seed value.
If the tls feature is used, the user should call the seed() function to seed the TLS
before creating the first random numbers, since the TLS instance is instantiated with a fixed
value.
The crate currently provides three fallback generators that try to use auto vectorization to speed up the generation for large amount of random numbers. They should provide good results for SIMD extensions of their same size:
Rng128 - Generator with a width of 128-bit.Rng256 - Generator with a width of 256-bit.Rng512 - Generator with a width of 512-bit.Suggested generators for certain CPU SIMD extensions:
* AVX2: Rng512
* NEON: Rng128
* SSE2: Rng128
AVX2 has special hand-written implementations. With AVX2 enabled and using the Rng512 generator we reached 28 GiB/s
on an AMD Ryzen 9 5950X.
The nightly only feature unstable_simd uses the core::simd create to implement the SIMD generators.
The crate is no_std compatible.
std - If getrandom is not used or returns an error, the generator will use the thread name and the current
instance time to create a seed value. Enabled by default.tls - Creates static functions that use a thread local version of the generator. Enabled by default.getrandom - Uses the getrandom crate to create a seed of high randomness. Enabled by default.unstable_tls - Uses the unstable thread_local feature of Rust nightly. Improves the call times to the
thread local functions greatly. unstable_simd - Uses the unstable std::simd crate of Rust nightly to provide the SIMD versions of the generators.Licensed under Apache License, Version 2.0, (LICENSE or http://www.apache.org/licenses/LICENSE-2.0).
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license without any additional terms or conditions.