let seed = 9385;

  let myRandom = function() {

    seed = (seed * seed).toString();

    while (seed.length < 8) {

      seed = '0'+seed;

    }

    seed = seed.substr(2, 4);

    seed = parseInt(seed);

    return seed / 10000;

  }

  return myRandom;

}

​

function middleSquare6() {

  var seed = 987654;

  let myRandom = function() {

    seed = (seed * seed).toString();

    while (seed.length < 10) {

      seed = '0'+seed;

    }

    seed = seed.substr(2, 6);

    seed = parseInt(seed);

    return seed / 1000000;

  };

  return myRandom;

}

​

function lfsr() {

  var value = 0x8988;

  var tap1bit = 1;

  var tap2bit = 9;

  let myRandom = function() {

    // taken from https://github.com/kirbysayshi/tetris-prng

    var tap1val = (value >> tap1bit) & 1;

    var tap2val = (value >> tap2bit) & 1;

    var leftmostBit = tap1val ^ tap2val;

    value = ((leftmostBit << 15) | (value >>> 1)) >>> 0;

    return value / (2 ** 16);

  };

  return myRandom;

}

​

function logisticMap() {

  var p = 0.1;

  var r = 3.5;

  let myRandom = function() {

    p = r * p * (1 - p);

    if (r < 3.96995) {

      r += 0.00005;

    }

    return p;

  };

  return myRandom;

}

​

function xorshift() {

  var state = 1;

  let myRandom = function() {

    // adapted from http://excamera.com/sphinx/article-xorshift.html

    state ^= state << 13;

    state ^= state >> 17;

    state ^= state << 5;

    // javascript numbers overflow as negative, so map output to modulo

    // plus 0.5

    var ret = ((state % 100) / 200) + 0.5;

    return ret;

  }

  return myRandom;

}

​

function jsBuiltin() {

  return Math.random;

}

​

function p5jsBuiltin() {

  return random;

}

​

// ---

// try to keep the code below unchanged (unless you have a really

// clever idea).

// ---

let currentRandom;

let sampleCount = 0;

let statusP;

let rselect;

let funcMap = {

  'middle square 4': middleSquare4,

  'middle square 6': middleSquare6,

  'linear feedback shift register': lfsr,

  'logistic map': logisticMap,

  'xorshift': xorshift,

  'Math.random()': jsBuiltin,

  'p5js random()': p5jsBuiltin

}

​

function setup() { 

  createCanvas(400, 400);

  background(0);

  statusP = createP();

  rselect = createSelect();

  for (let key in funcMap) {

    if (funcMap.hasOwnProperty(key)) {

      rselect.option(key);

    }

  }

  rselect.changed(function() {

    currentRandom = funcMap[rselect.value()]();

    sampleCount = 0;

    background(0);

  });

  currentRandom = middleSquare4();

} 

​

function draw() {

  let xpos = currentRandom() * width;

  let ypos = currentRandom() * height;

  noStroke();

  fill(255, 240);

  ellipse(xpos, ypos, 10, 10);

  fill(255);

  statusP.html("samples: " + sampleCount);

  sampleCount++;

}

​

​