尴尬的 arc4 随机结果

发布于 2024-12-24 00:17:31 字数 549 浏览 0 评论 0原文

我正在使用此代码，其中“长度”值为“50”。

newX = (arc4random()%(lenght+1)) - (lenght/2);
newY = (arc4random()%(lenght+1)) - (lenght/2);
NSLog(@"Creature Move X:%f, Y:%f", newX, newY);

但在调试器中我得到这样的信息：

2012-01-02 21:10:50.794 Kipos[28833:207] Creature Move X:4294967296.000000, Y:4294967296.000000
2012-01-02 21:10:50.896 Kipos[28833:207] Creature Move X:4294967296.000000, Y:12.000000

发生了什么？

newX 和 newY 是浮点数：

float newX;
float newY;

原文

I'm using this code, where 'length' value is '50'.

newX = (arc4random()%(lenght+1)) - (lenght/2);
newY = (arc4random()%(lenght+1)) - (lenght/2);
NSLog(@"Creature Move X:%f, Y:%f", newX, newY);

But in the debugger I get things like:

2012-01-02 21:10:50.794 Kipos[28833:207] Creature Move X:4294967296.000000, Y:4294967296.000000
2012-01-02 21:10:50.896 Kipos[28833:207] Creature Move X:4294967296.000000, Y:12.000000

What is happening?

newX and newY are floats:

float newX;
float newY;

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焚却相思 2024-12-31 00:17:31

arc4random 返回一个无符号 int（并且可能 length 也是无符号的）。将代码更改为例如

newX = (float)((int)(arc4random() % (length + 1))) - (length / 2));

，以避免减法时溢出。

请注意，我还为结果添加了显式浮点转换，这并不是绝对必要的，但它使代码更加不言自明。

arc4random returns an unsigned int (and presumably length is also unsigned). Change your code to e.g.

newX = (float)((int)(arc4random() % (length + 1))) - (length / 2));

in order to avoid overflow when you subtract.

Note that I have also added an explicit float cast for the result, which is not strictly necessary but it makes the code a little more self-explanatory.

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