PHP 的 shuffle 函数有多随机?
有谁知道 PHP 的 shuffle() 函数的随机性是什么?它取决于操作系统吗?它是否使用 PHP 自己的播种机?
Does anyone know what's the randomness of PHP's shuffle() function? Does it depend on the operating system?
Does it use PHP's own seeder?
是否可以使用 mt_rand() 作为生成器?
Is it possible to use mt_rand() as generator?
推荐答案
shuffle() 函数基于与 rand() 相同的生成器，也就是系统基于线性同余算法的生成器.这是一个快速生成器，但或多或少具有随机性.自 PHP 4.2.0 起，随机生成器会自动播种，但您可以根据需要使用 srand() 函数来播种.
shuffle() function is based on the same generator as rand(), which is the system generator based on linear congruential algorithm. This is a fast generator, but with more or less randomness. Since PHP 4.2.0, the random generator is seeded automatically, but you can use srand() function to seed it if you want.
mtrand() 基于 Mersenne Twister 算法，其中是最好的伪随机算法之一.要使用该生成器对数组进行混洗，您需要编写自己的 shuffle 函数.例如，您可以查看 Fisher-Yates 算法.编写自己的 shuffle 函数会产生更好的随机性，但会比内置的 shuffle 函数慢.
mtrand() is based on Mersenne Twister algorithm, which is one of the best pseudo-random algorithms available. To shuffle an array using that generator, you'd need to write you own shuffle function. You can look for example at Fisher-Yates algorithm. Writing you own shuffle function will yield to better randomness, but will be slower than the builtin shuffle function.
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