如何在swift中屏蔽或转换Int32到Int16

Question

Data loss is no problem for me.

var temp1:Int32 = 45058 
var temp2:Int32 = -20345 
var temp3:Int32 = -40345

var temp4:Int16 =  Int16(temp1)//overflow
var temp5:Int16 =  Int16(temp2)//return wrog value
var temp6:Int16 =  Int16(temp3)//overflow

Also tried this, but it is also returning wrong value, it is not what I want.

temp4 = Int16(temp1 & 0x0000ffff)//overflow  

In my C code, there is no any issue because c compiler does this by self.

Answer 1

This is actually very simple, you just have to say explicitly what you want to do:

var temp4: Int16 =  Int16(truncatingIfNeeded: temp1) // -20478
var temp5: Int16 =  Int16(truncatingIfNeeded: temp2) // -20345
var temp6: Int16 =  Int16(truncatingIfNeeded: temp3) // 25191

(the method is called truncatingBitPattern: in Swift 3)

truncatingIfNeeded will reinterpret the lower 16 bits as Int16 .

Note that & 0xffff won't work in this case. The default initializer is trying to convert the numeric value , not the bit value and unfortunately 45058 , or 0xB002 will be unchanged through & 0xffff and it won't fit Int16 . That would work for unsigned integers though.