CODEWITHSUNDEEP
swift
D.Moses
D.Moses

Reputation: 59

Using an overflow operator in Swift 3

I am new to Swift, and I am reading The Big Nerd Ranch Guide. I came across this example:

He wants me to get the value of z 

let y: Int8 = 120 
let z = y &+ 10 
print ("120 &+ 10 is \(z)")

He mentioned that the result of overflow-adding 120 + 10 and storing the result into an Int8 is -126

I don't understand the logic of this result. I tried to read more resources about the overflow operators, but I got more confused. I'd greatly appreciate your help.

Upvotes: 1

Views: 627

Answers (1)

Scott Thompson
Scott Thompson

Reputation: 23701

In binary, the value of y, 120 is:

01111000

If you add 10 to that (which is 1010 in binary) you get:

10000010

If you take that binary pattern and interpret it as a signed 8 bit integer, you note that the high bit is 1 (which means the number is negative) and the value of the negative number is the twos complement of the pattern (0000010) which is (1111101 + 1) or (1111110) which is 126

Therefore the result is -126

Upvotes: 2

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