需要对随机函数迅速进行解释 [英] Need explanation about random function swift

问题描述

有一个关于我的随机函数的问题:为什么会出现此错误?

Got a question about my random function: why is it giving this error?

'4294967295' is not exactly representable as 'Float'; it becomes '4294967296'

-

我的代码是

func random() ->CGFloat {
    return CGFloat(Float(arc4random()) / 0xFFFFFFFF)
}
func  random(min: CGFloat, max: CGFloat) -> CGFloat {
    return random() * (max - min) + min
}

它不会改变应用程序的功能，但它似乎无处不在.

it doesn't change the functionality of the application but it just appeared out of nowhere.

提前谢谢！

推荐答案

一个 IEEE 754 32位浮点数字的尾数有24个有效位，不足以精确存储10位整数:

A IEEE 754 32-bit floating point number has 24 significant bits for the mantissa, that is not enough to store a 10-digit integer exactly:

print(0xFFFFFFFF)             // 4294967295
print(Float(0xFFFFFFFF))      // 4.2949673e+09
print(Int(Float(0xFFFFFFFF))) // 4294967296

那不会影响您的代码，因为

That won't affect your code because

Float(arc4random()) / Float(0xFFFFFFFF)

仍然是0.0到1.0之间的浮点数.将计算更改为

is still a floating point number between 0.0 and 1.0. Changing the calculation to

return CGFloat(arc4random()) / 0xFFFFFFFF

将在64位平台上修复该警告:整数常量现在转换为(64位)Double.

will fix the warning on 64-bit platforms: The integer constant is now converted to a (64-bit) Double.

但是从Swift 4.2开始，您可以使用新的

But as of Swift 4.2 you can avoid the problem completely by using the new Random API:

func random(min: CGFloat, max: CGFloat) -> CGFloat {
    return CGFloat.random(in: min...max)
}

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