Math.random（）何时开始重复？ [英] When does Math.random() start repeating?

问题描述

我在nodejs中进行了这个简单的测试，我让它在一夜之间运行，无法重复Math.random（）。我意识到迟早价值（甚至整个序列）都会重复，但对于什么时候会有什么合理的预期呢？

I have this simple test in nodejs, I left it running overnight and could not get Math.random() to repeat. I realize that sooner or later the values (or even the whole sequence) will repeat, but is there any reasonable expectancy as to when it is going to happen?

let v = {};
for (let i = 0;; i++) {
  let r = Math.random();
  if (r in v) break;
  v[r] = r;
}
console.log(i);

推荐答案

这是浏览器特定的：

https：// www.ecma-international.org/ecma-262/6.0/#sec-math.random

20.2 .2.27
Math.random（）返回一个带有正号的数字值，大于或等于0但小于1，随机选择或伪
随机选择，在该范围内大致均匀分布，
使用依赖于实现的算法或策略。此函数
不带参数。

20.2.2.27 Math.random ( ) Returns a Number value with positive sign, greater than or equal to 0 but less than 1, chosen randomly or pseudo randomly with approximately uniform distribution over that range, using an implementation-dependent algorithm or strategy. This function takes no arguments.

为不同的代码创建的每个Math.random函数必须
从连续调用生成不同的值序列。

Each Math.random function created for distinct code Realms must produce a distinct sequence of values from successive calls.

此处的要求只是伪随机且均匀分布。

The requirement here is just pseudo-random with uniform distribution.

这是来自V8（Chrome和NodeJs的Javascript引擎）的博客文章。

Here's a blog post from V8 (Chrome and NodeJs's Javascript Engine).

https://v8.dev/blog / math-random

他们说他们在使用 xorshift128 + ，其最大周期为 2 ^ 128 -1 。

Where they say they are using xorshift128+, which has a maximal period of 2^128 -1.

这篇关于Math.random（）何时开始重复？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！