utils/alea.js

   1 // https://stackoverflow.com/a/47593316/12660887
   2 function mulberry32(a) {
   3     return function() {
   4         let t = a += 0x6D2B79F5;
   5         t = Math.imul(t ^ t >>> 15, t | 1);
   6         t ^= t + Math.imul(t ^ t >>> 7, t | 61);
   7         return ((t ^ t >>> 14) >>> 0) / 4294967296;
   8     }
   9 }
  10
  11 export const Random = {
  12
  13   rand: null,
  14
  15   setSeed: function(a) {
  16     Random.rand = mulberry32(a);
  17   },
  18
  19   randInt: function(min, max) {
  20     if (!max) {
  21       max = min;
  22       min = 0;
  23     }
  24     if (!Random.rand)
  25       Random.setSeed(Math.floor(Math.random() * 19840));
  26     return Math.floor(Random.rand() * (max - min)) + min;
  27   },
  28
  29   randBool: function() {
  30     return Random.randInt(0, 2) == 0;
  31   },
  32
  33   // Inspired by https://github.com/jashkenas/underscore
  34   sample: function(arr, n) {
  35     n = n || 1;
  36     let cpArr = arr.map(e => e);
  37     for (let index = 0; index < n; index++) {
  38       const rand = Random.randInt(index, arr.length);
  39       [ cpArr[index], cpArr[rand] ] = [ cpArr[rand], cpArr[index] ];
  40     }
  41     const res = cpArr.slice(0, n);
  42     return (n >= 2 ? res : res[0]);
  43   },
  44
  45   shuffle: function(arr) {
  46     return Random.sample(arr, arr.length);
  47   }
  48
  49 };