[ot]

> Since nobody had figured out any downsides to PCG's yet, everyone shrugged and said "might as well just go with that then", and that is where, as of 2019, the art currently stands. The problem is solved, and life is good.

I wonder who "everyone" was, I'm not aware of many high-profile projects adopting PCG as a default. As of 2025, several high-profile runtimes (including all the major browsers) use xorshift variants [1]

Is there a list of users of PCG?

[1] See Adoption section in https://prng.di.unimi.it/

[vlovich123]

It kind of doesn’t matter if there are users - there are people still stupidly using Mersenne Twister. The point is that PCG is better than xorshift and related in that family. That other high profile applications haven’t switched is besides the point that PCG is objectively better:

> O'Neill proposes testing PRNGs by applying statistical tests to their reduced-size variants and determining the minimum number of internal state bits required to pass.[7] TestU01's BigCrush examines enough data to detect a period of 235, so even an ideal generator requires 36 bits of state to pass it. Some very poor generators can pass if given a large enough state;[8] passing despite a small state is a measure of an algorithm's quality, and shows how large a safety margin exists between that lower limit and the state size used in practical applications. PCG-RXS-M-XS (with 32-bit output) passes BigCrush with 36 bits of state (the minimum possible), PCG-XSH-RR (pcg32() above) requires 39, and PCG-XSH-RS (pcg32_fast() above) requires 49 bits of state. For comparison, xorshift*, one of the best of the alternatives, requires 40 bits of state,[5]: 19 and Mersenne twister fails despite 19937 bits of state.[9]

[ot]

> It kind of doesn’t matter if there are users [...] The point is that PCG is better

No that's not the point that the article makes and that I'm questioning, it says "everyone shrugged" which implies consensus, and I'm asking for evidence of that consensus, not of the objective quality of the two generators.

Also I don't think that that paragraph is even close to demonstrating "objectively better": the author of PCG pointed out one arbitrary metric, minimum state size, where PCG beats old variants of xorshift* on a statistical test suite, and in the meantime much better variants have come out. That metric is meaningless since everyone uses much bigger state anyway.

RNGs are a tricky subject, there isn't a singular measure of quality, statistical tests are necessary but not sufficient. The best testament to RNG quality is wide adoption, which builds confidence that there aren't undiscovered failure modes.

[adgjlsfhk1]

IMO there's plenty of reason to use Xoshiro over PCG. the quality differences between the best xoshiro and pcg differences are minimal (especially because most languages use a 256 bit state since it makes it easier to split/jump without worrying about duplicate streams), and Xoshiro generators tend to be easier to SIMD for when you need lots of random numbers.

[WarrenWeckesser]

The default bit generator in NumPy is PCG-64 [1].

[1] https://numpy.org/doc/stable/reference/random/bit_generators...

[aj_hackman]

Much like my beloved comb sort, I use xorshift because the implementation is small and it's Good Enough. God's Own 100 SLOC PRNG would have to be near-perfect and take three clock cycles to contemplate switching.

[camel-cdr]

> nobody had figured out any downsides to PCG's yet

BTW, people have broken PCG already: https://hal.science/hal-02700791/file/main.pdf

It takes up to 20000 CPU hours to break the seed from 512 output bits with an unknown state, increment and multiplier. (the multiplier is usually fixed constant)

[tptacek]

What does it mean to "break" PCG? It's not a secure random number generator.

[WalterGillman]

I wonder how much it would take to break mine.

https://github.com/waltergillman/xorshift_sbox

I have not been blessed by an education so I can't be eloquent and write proofs and papers and stuff but it passes PractRand for 4GB with only 32 bits of state.

Not very fast on modern computers, I will concede.