渐大的随机数在C / C ++ [英] Getting big random numbers in C/C++

问题描述

标准兰特（）函数提供的数字不够大对我来说：我需要无符号长长的。我们怎样才能达到真正的大的随机数？我试图改变一个简单的哈希函数，但它太的大的，需要很长时间才能运行，从来没有产生这是小于1E5！

Standard rand() function gives numbers not big enough for me: I need unsigned long long ones. How do we get really big random numbers? I tried modifying a simple hash function but it's too big, takes too long to run and never produces numbers which are less than 1e5!!

推荐答案

下面是返回一个随机的64位数字便携式C99的解决方案：

Here's a portable C99 solution that returns a random 64-bit number:

unsigned long long llrand() {
    unsigned long long r = 0;

    for (int i = 0; i < 5; ++i) {
        r = (r << 15) | (rand() & 0x7FFF);
    }

    return r & 0xFFFFFFFFFFFFFFFFULL;
}

说明：兰特（）返回范围0-2的整数 RAND_MAX 和 RAND_MAX 只能保证至少有32,767（15个随机位）。 长长都保证有64位，但可能较大。

Explanation: rand() returns integers in the range 0 to RAND_MAX and RAND_MAX is only guaranteed to be at least 32,767 (15 random bits). long long is guaranteed to have 64 bits but may be larger.

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