调整XORShift发生器以返回最大值 [英] Adjusting XORShift generator to return a number within a maximum

问题描述

我需要在最大值内生成随机整数。由于性能至关重要，我决定使用XORShift生成器而不是Java的Random类。

I need to generate random integers within a maximum. Since performance is critical, I decided to use a XORShift generator instead of Java's Random class.

long seed = System.nanoTime();
seed ^= (seed << 21);
seed ^= (seed >>> 35);
seed ^= (seed << 4);

此实现 _（source） 给我一个长整数，但我真正想要的是0到最大值之间的整数。

This implementation _(source) gives me a long integer, but what I really want is an integer between 0 and a maximum.

public int random(int max){ /*...*/}

实现此方法的最有效方法是什么？

What it is the most efficient way to implement this method?

推荐答案

我对你的代码感兴趣并想出了这个：

I had some fun with your code and came up with this:

public class XORShiftRandom {

private long last;
private long inc;

public XORShiftRandom() {
    this(System.currentTimeMillis());
}

public XORShiftRandom(long seed) {
    this.last = seed | 1;
    inc = seed;
}

public int nextInt(int max) {
    last ^= (last << 21);
    last ^= (last >>> 35);
    last ^= (last << 4);
    inc += 123456789123456789L;
    int out = (int) ((last+inc) % max);     
    return (out < 0) ? -out : out;
}

}

我做了一个简单的测试，它是四倍于 java.util.Random

I did a simple test and it is about Four times as fast as the java.util.Random

如果你如果它有用，你可以阅读这个论文：

If you are intrested in how it works you can read this paper:

免责声明：

上述代码仅用于研究，而不是用于
替换股票Random或SecureRandom。

The code above is designed to be used for research only, and not as a replacement to the stock Random or SecureRandom.

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