blocks|key|143887|text|我选择了代数路线。测试一直很痛苦，因为很容易在强类型破坏执行的情况下获得溢出，PlayGround从toUInt函数返回负值，它一直崩溃或在进行双重转换时出现有趣的错误(我打开了一个错误报告)。无论如何，这是我最终得到的结果：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|143888|func+toUint(signed:+Int)+->+UInt+{

++++let+unsigned+=+signed+>=+0+?
++++++++UInt(signed)+:
++++++++UInt(signed++-+Int.min)+%2B+UInt(Int.max)+%2B+1

++++return+unsigned
}

func+toInt(unsigned:+UInt)+->+Int+{

++++let+signed+=+(unsigned+<=+UInt(Int.max))+?
++++++++Int(unsigned)+:
++++++++Int(unsigned+-+UInt(Int.max)+-+1)+%2B+Int.min

++++return+signed
}|code-block|syntax|javascript|143889|我用所有的极值(UInt.min、UInt.max、Int.min、Int.max)对它们进行了测试，当XCode没有变得疯狂时，它似乎可以工作，但它看起来过于复杂。非常奇怪的是，可以使用hashvalue属性简单地实现UInt到Int位的转换，如下所示：|143890|signed+=+UInt.max.hashValue+//+signed+is+-1|143891|但很明显，这并不能保证它总是有效的(它应该有效，但我不愿冒险)。|143892|任何其他的想法都将被感谢。|143893|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

I took the algebra route. Testing has been a pain because it is easy to get an overflow with the strong typing breaking the execution, PlayGround returned a negative value from the toUInt function, it kept crashing or gave funny errors doing a double casting (I opened a bug report). Anyway this is what I ended up with:

<pre><code>func toUint(signed: Int) -&gt; UInt {

 let unsigned = signed &gt;= 0 ?
 UInt(signed) :
 UInt(signed - Int.min) + UInt(Int.max) + 1

 return unsigned
}

func toInt(unsigned: UInt) -&gt; Int {

 let signed = (unsigned &lt;= UInt(Int.max)) ?
 Int(unsigned) :
 Int(unsigned - UInt(Int.max) - 1) + Int.min

 return signed
}
</code></pre>

I tested them with all extreme values (UInt.min, UInt.max, Int.min, Int.max) and when XCode doesn't go crazy it seems to work, but it looks overly complicated. Bizarre enough the UInt to Int bit casting could be simply achieved with the hashvalue property as in:

<pre><code>signed = UInt.max.hashValue // signed is -1
</code></pre>

But obviously it isn't guaranteed to always work (it should, but I'd rather not taking the chance). 

Any other idea will be appreciated.

blocks|key|146219|text|您可以执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|146220|let+unsigned+=+UInt8(bitPattern:+Int8(-1))+//+->+255
let+signed+++=+Int8(bitPattern:+UInt8(0xff))+//+->+-1|code-block|syntax|javascript|146221|存在许多类似的初始化器：|146222|extension+Int8+{
++++init(_+v:+UInt8)
++++init(_+v:+UInt16)
++++init(truncatingBitPattern:+UInt16)
++++init(_+v:+Int16)
++++init(truncatingBitPattern:+Int16)
++++init(_+v:+UInt32)
++++init(truncatingBitPattern:+UInt32)
++++init(_+v:+Int32)
++++init(truncatingBitPattern:+Int32)
++++init(_+v:+UInt64)
++++init(truncatingBitPattern:+UInt64)
++++init(_+v:+Int64)
++++init(truncatingBitPattern:+Int64)
++++init(_+v:+UInt)
++++init(truncatingBitPattern:+UInt)
++++init(_+v:+Int)
++++init(truncatingBitPattern:+Int)
++++init(bitPattern:+UInt8)
}|146223|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You can do:

<pre><code>let unsigned = UInt8(bitPattern: Int8(-1)) // -&gt; 255
let signed = Int8(bitPattern: UInt8(0xff)) // -&gt; -1
</code></pre>

Many similar initializers exist:

<pre><code>extension Int8 {
 init(_ v: UInt8)
 init(_ v: UInt16)
 init(truncatingBitPattern: UInt16)
 init(_ v: Int16)
 init(truncatingBitPattern: Int16)
 init(_ v: UInt32)
 init(truncatingBitPattern: UInt32)
 init(_ v: Int32)
 init(truncatingBitPattern: Int32)
 init(_ v: UInt64)
 init(truncatingBitPattern: UInt64)
 init(_ v: Int64)
 init(truncatingBitPattern: Int64)
 init(_ v: UInt)
 init(truncatingBitPattern: UInt)
 init(_ v: Int)
 init(truncatingBitPattern: Int)
 init(bitPattern: UInt8)
}
</code></pre>

blocks|key|2720115|text|numericCast(...)就是你要找的东西。它是一组泛型函数，可以在不同的数字类型之间进行相互转换。它根据其参数的类型和返回类型选择正确的实现。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2720116|entityMap^0|0|G|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

<code>numericCast(...)</code> is what you're looking for. It's a set of generic functions that converts from and to different number types. It picks the correct implementation based on the types of its argument and the return type.

I am looking for a direct way to bit cast the bit values of an Int to UInt and vice versa. For example (using the 8 bits integers for simplicity) I want to achieve the following:

<pre><code>let unsigned: UInt8 = toUInt8(-1) // unsigned is 255 or 0xff
let signed: Int8 = toInt8(0xff) // signed is -1 
</code></pre>

At first I came out with the following solution:

<pre><code>let unsigned = unsafeBitCast(Int8(-1), UInt8.self)
let signed = unsafeBitCast(UInt8(0xff), Int8.self)
</code></pre>

But Apple in the "unsafeBitCast()" documentation states the following:

<blockquote>
 .. Caution:: Breaks the guarantees of Swift's type system; use with
 extreme care. There's almost always a better way to do anything.
</blockquote>

Does anyone have the better way?

Int to UInt (and vice versa) bit casting in Swift

Swift

我正在寻找一种直接的方法来位转换为UInt的Int的位值，反之亦然。例如(为简单起见，使用8位整数)我希望实现以下目标：let unsigned: UInt8 = toUInt8(-1)  // unsigned is 255 or 0xfflet signed:   Int8  = toInt8(0xff) // s...

问Swift中Int到UInt (反之亦然)位转换
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