rand()真的可以这么糟糕吗? [英] Can rand() really be this bad?

问题描述

以上是使用rand()获取随机坐标并在这些坐标处的像素值上添加常量的示例图像.这是经过数千次迭代后的样子.我正在Mac OS X Lion中使用stdlib.h中的rand()，并给它time(NULL)作为种子.

Above is an example image generated by using rand() to get random coordinates and add a constant to the pixel value at those coordinates. This is how it looks from a few thousand iterations. I'm using the rand() from stdlib.h in Mac OS X Lion, giving it time(NULL) as the seed.

您可以清楚地看到垂直线，好像具有x坐标奇数的竖线比具有x偶数坐标的竖线更高.

You can clearly see the vertical lines, as if the ones with an odd x-coordinate have higher values than those with even x-coordinates.

我将如何实现更好的算法，或者在哪里可以找到没有很多依赖性的算法呢? (我希望使用仅标头文件).

How would I implement a better algorithm, or where can I find one that doesn't have many dependencies? (I would prefer a header-only file).

这是代码(很抱歉，我花了这么长时间):

Here's the code (sorry it took me so long):

void generate(int iterations = 1) {
 for (unsigned int x = 0;x < (area * 4);++x) {
  map[rand() % area] += 1;
 }
 number a = min();
 number b = max();
 for (int i = 0;i < area;++i) {
  map[i] -= a;
  map[i] /= b;
 }
}

地图包含双精度浮点数，后来又变成了RGB值.

Map contains double-floats and is later turned into RGB values.

推荐答案

您是否尝试过

Have you tried arc4random()? It provides much stronger and more uniform random values than rand().

您还可以尝试 SecRandomCopyBytes() ，它是Security.framework的一部分.这基本上只是从/dev/random中读取.

You could also try SecRandomCopyBytes(), which is part of Security.framework. This basically just reads from /dev/random.

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