V8 Engine 的 Math.random() 在新版被重寫了...

先前在「V8 的 Math.random() 亂度不足的問題」提到 Math.random() 因為使用 MWC1616 (Fast random number generation using 128 bit multimedia extension registers on Pentium class machines) 而不夠亂的問題。

這個問題在新版 V8 Engine 提出改善了:「There's Math.random(), and then there's Math.random()」。

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新實作的方法是 xorshift128+,擁有極長的 period length:

This has been pointed out to us, and having understood the problem and after some research, we decided to reimplement Math.random based on an algorithm called xorshift128+. It uses 128 bits of internal state, has a period length of 2128 - 1, and passes all tests from the TestU01 suite.

將會在 Google Chrome 49 (目前是 47) 引入:

The new implementation landed in V8 within a few days of us becoming aware of the issue. It will become available with Chrome 49. Both Firefox and Safari switched to xorshift128+ as well.

同時還是再次提醒,這不是 CSPRNG,要用在密碼學相關應用還是要用專門的 library 來產生 pseudo random number:

Make no mistake however: even though xorshift128+ is a huge improvement over MWC1616, it still is not cryptographically secure.