这个随机函数有什么问题？

问题描述

我给它0和400，它返回我有时超过400的值。这是没有意义的。

I give it 0 and 400 and it returns me sometimes values above 400. That doesn't make sense.

- (float)randomValueBetween:(float)low andValue:(float)high {
    return (((float) arc4random() / RAND_MAX) * (high - low)) + low;
}

这实际上是我在网上找到的代码段。

that's actually a snippet I found on the net. Maybe someone can see the bug in there?

推荐答案

表示返回的值可以在 u int32 （即 0至（2 ** 32）-1 ）有效范围内的任何位置。这意味着你需要除以 0xFFFFFFFF ，而不是 RAND_MAX ，我想是更少

The manual page for arc4random indicates that the returned value can be anywhere in the range valid for u int32 (i.e. 0 to (2**32)-1). This means you'll want to divide by 0xFFFFFFFF, instead of RAND_MAX, which I would imagine is less (it is library dependant however, so you'll have to check exactly what it is).

您的函数应该成为：

- (float)randomValueBetween:(float)low andValue:(float)high {
    return (((float) arc4random() / 0xFFFFFFFFu) * (high - low)) + low;
}

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