bug: default RNG is quite terrible

[dragoncoder047]

Bug Description

kaplay's internal RNG is a linear congruential generator, which is known to be trash when you need to generate a random series of numbers, it's almost as bad as RANDU.

the CA example shared below shows some clear repeating diagonal patterns when the simulation stabilizes, which a good RNG would never produce. (and in fact I believe it is the same pattern every time, just shifted, which is even worse.)

Version

No response

Playground Link

https://play.kaplayjs.com/?code=eJyVVW1v2jAQ%2Fp5fceqHyhEhbTI%2BtElbqQPUTes6qWtVVQi1wRgSEWKUFyCa%2BO87vwRCk0pbhMjlnse%2B83Nn%2B%2BwM%2BkWW8yVkYTBlqbEIVnFQkj8G4DMJ6GKe8iKZenAyifHrxJLAKtqyeMCSLMpLD1xjZ%2FqGQXmS5fD4fD%2BEaxhJ3rmlf451sOWvBjtt8BgnjHkw%2FS3TIpJ%2BwnMa6AySIo6V9W4USTTj6RJmOCCH4m0TTfPQb7hDFs3DvOlPi5iNnAsRUbmEgyiTsiRnqaW5WbE0QUmjmSzDtZ7bvvRFMyBqANygs6JKOk%2BBREkOEfIvfXxdgXOB706nTqtmCSaZSoBE0IVLE%2F9k7CuwHVNH1YlHY38%2FfCetHbA4Y58FP1fBL%2F8l9n%2FGlf8py4s0EVzf2BnGmtEezNJgTtByYcUzC6RVrKXRA8pjjgpnwXIVs9QdQM62VV5I%2BKJrgJHFF0Fd%2FQOG2TWA%2FXKnW8S6ji%2BMq2uQxvGaD9SyopYVtWzKo9JBJqaIq2TugKBlifXRnBRr6Mi1afmmW%2FNMN6NuIDIthUs1ommadjqf%2BI0CiLSxTnB6KtNC0zxoQI%2F5stJChM4R1FIQoTXZE2SLq0ltIX6xtFPTaoXnCp5%2FAk8UPKnBji1NUzTA%2B%2BFk2GD67nnvwoJQW76xDlKgDn4ugwXrB8k6yMgGCaaG3FbImBUJzSOewCbKQ41RFLkqmArIRcS3hT2fbW1dBh4eXNV5IAbUWUJlW58hNUzRJVgfSe1pGmzIzGydiG%2Fa5%2BCh3B319PEMJCZc31QHjGhNocFWbVpsYVRK5wVtfSzIpSKXiqzzhJZWFkk%2FMuzaY7d4cI96qo%2BxtctaXatH5uDhod1AVMBWSG5zD2jIecbI6OXb96ehBV%2Fvb%2Fs%2FLHgcDiy4exwOH4TrGYH%2B6y3aP2%2Fvhg9Ptxa8Du%2Fvf72MPySzM5stvzvqjyxnK1Ktva62e6x2JYmGj0Wh0om5f1iWujK9o3upevQl40FTX30mePtyNsWqzgjkuLqKbSSxDz15437Q5aCKVqh6j0SbUXcsbmihAXXGshF5MhBdXJekVY42KQ79gld3V2VLzFqpMhqIPCUFw3cdje3qB7bo3tr91KsuKFVBX9b1L5orO4Y%3D&version=master

Extra information

a better one (I forget where this came from) can be pasted at the bottom of the kaplayground demo:

var seed = +new Date;

function bobrand() {
    seed &= 0xffffffff;
    seed = (seed + 0x7ed55d16 + (seed << 12)) & 0xffffffff;
    seed = (seed ^ 0xc761c23c ^ (seed >>> 19)) & 0xffffffff;
    seed = (seed + 0x165667b1 + (seed << 5)) & 0xffffffff;
    seed = ((seed + 0xd3a2646c) ^ (seed << 9)) & 0xffffffff;
    seed = (seed + 0xfd7046c5 + (seed << 3)) & 0xffffffff;
    seed = (seed ^ 0xb55a4f09 ^ (seed >>> 16)) & 0xffffffff;
    return seed / 0x100000000;
}

function choose(list) {
    return list[(bobrand() * list.length) | 0];
}

Summary

• Fixed in v4000
• Fixed in v3001

[mflerackers]

Or use this, which is faster, and used by many implementations

https://en.wikipedia.org/wiki/Xorshift
https://docs.unity3d.com/2022.3/Documentation//ScriptReference/Random.html

[Stanko]

I would consider Alea rng too, it should be around the same (or slightly faster) than xorshift with better statistical qualities. Unfortunately the site of the original author is no longer online.

The most popular implementation is seedrandom and it includes benchmarks. That said, the algorithm itself is very simple and can be extracted - I did it for my own purposes here.