Seeded random that has floats as input and output for possible recursion

Question

I am looking for a seeded solution to be able to reproduce results. I need a random float between 0 and 1 for each recursive run of my method, so I need to use the previous seed or float to produce a new random float or seed. So I am in need of a seeded seed generator or a seeded float generator where the seed is a float. Any ideas?

I hope this will help you https://stackoverflow.com/questions/686353/random-float-number-generation — Anurag Tomar, Sep 16 '19 at 09:26
It seems to focus on making a random from a pseudo-random, which is not what I am trying to do, thanks anyway :) — XGG, Sep 16 '19 at 09:38
Can you explain what application you are making that requires a generator you describe? — Peter O., Sep 16 '19 at 16:30
I am trying to visualize a tree and need a slight irregularity at each branch, and I need to be able to recreate the exact same tree with a seed — XGG, Sep 17 '19 at 08:58

Kamil Kiełczewski · Answer 1 · 2019-09-18T15:23:35.157

0

Try

// crypto-strong random num in rage [0,1)
let random = ()=> crypto.getRandomValues(new Uint32Array(1))[0]/2**32; 

function recursive(n,rand) {
  return n>0 ? recursive(n-1, rand/2) : rand;
}

console.log( recursive(5,random()) );

edited Sep 18 '19 at 15:23

answered Sep 16 '19 at 09:40

Kamil Kiełczewski

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score 0 · Answer 2 · answered Sep 19 '19 at 05:26

What you are asking for is just a seeded PRNG.

You just have to hard-code the seed and then call it in order.

// rewrite of https://gist.github.com/blixt/f17b47c62508be59987b
class Random {
  constructor( seed ) {
    this._seed = seed % 0x7fffffff;
    if (this._seed <= 0) { this._seed += 0x7ffffffe; }
  }
  next() {
    const next_int = this._seed =
      this._seed * 0x41a7 % 0x7fffffff;

    return ( next_int - 1 ) / 0x80000000;
  }
}

const my_seed = 42; // just hard-code this
const rand = new Random( my_seed );

let i = 0;
while( i++ < 5 ) {
  console.log( rand.next() );
}
/*
  0.000328707043081522
  0.524587101303041
  0.735423531383276
  0.2633055401965976
  0.37622397067025304
*/

If you ever wish to make it return the value at n-th iteration, then just create a new instance with the same seed and call it n times before getting the value.

// rewrite of https://gist.github.com/blixt/f17b47c62508be59987b
class Random {
  constructor( seed ) {
    this._seed = seed % 0x7fffffff;
    if (this._seed <= 0) { this._seed += 0x7ffffffe; }
  }
  next() {
    const next_int = this._seed =
      this._seed * 0x41a7 % 0x7fffffff;

    return ( next_int - 1 ) / 0x80000000;
  }
}

function getRandAtIndex( index = 0, seed ) {
  const gen = new Random( seed );
  let i = 0;
  while( i++ < index ) {
    gen.next();
  }
  return gen.next();
}

// this time we use a random seed
const my_seed = Math.random() * 0xFFFFFFFF;
const rand = new Random( my_seed );

// log the five first values
let i = 0;
while( i++ < 5 ) {
  console.log( rand.next() );
}

console.log( '\nthird value was', getRandAtIndex( 2, my_seed ) );

Seeded random that has floats as input and output for possible recursion

2 Answers2