robojeb/pcg_rand

pcg_rand's Issues

Set up CI integration

It would be nice to have CI integration to run build and tests.

Port to rand_core 0.2

I'm working on updating pcg_rand to use rand_core 0.2 (which corresponds to Rand 0.5) instead of Rand 0.4. Unfortunately, I ran into a compiler bug (rust-lang/rust#43408). I'm not sure yet how to work around it.

First return from gen() on new_unseeded() is 0

Here's a program:

extern crate rand;
extern crate pcg_rand;

use rand::Rng;
use rand::XorShiftRng;
use pcg_rand::Pcg32;

pub fn main() {
    let mut xorshift = XorShiftRng::new_unseeded();
    let mut pcg = Pcg32::new_unseeded();
    let xv: u32 = xorshift.gen();
    let pv: u32 = pcg.gen();
    println!("{} {}", xv, pv);
}

And here's its output (at least on my box):

3690029583 0

While the pcg output is technically ok — the generator is unseeded, and so can start the sequence where it likes — I'd strongly prefer that the first output of an unseeded generator still "look random" as with xorshift. Fix should be as easy as a call to gen() inside new_unseeded().

PCG extension mechanism

About a month ago I started implementing the PCG extension mechanism in a repository where I compare small RNG's. But when I realized how complex it was it did not seem like a good fit.

I you are still interested in working on the extension mechanism, it may be a good starting point:
https://github.com/pitdicker/small-rngs/blob/master/src/pcg_ext.rs
And an overview of how I think it is supposed to work: dhardy/rand#52 (comment)

Cannot use pcg_rand 0.9.2 without nightly

886f854 added a #![feature(tool_lints)] which requires nightly to work, making it not possible to use 0.9.2 on beta or stable

pcg_rand/src/lib.rs

Line 121 in 93ff7d3

#![feature(tool_lints)]

The tool_lints warning has been canceled by rust-lang/rust#54358 on the current 1.30 beta channel, so writing #[allow(needless_pass_by_value)] should be fine.

BTW, the feature has been stabilized by rust-lang/rust#54870 on the current 1.31 nightly channel meaning you don't need #![feature(tool_lints)] to write #[allow(clippy::needless_pass_by_value)] either.

128-bit integers are available in nightly Rust

u128 and i128 were added in rust-lang/rust/pull/38482. They're currently behind the i128_type feature gate.

How to resume a PRNG, at a later time deterministically?

How can I access and save the state in a way, that I can resume the pseudo random number generator at a later time?