What actually happens when a Byte overflows?

Question

What actually happens when a Byte overflows?

Say we have

byte byte1 = 150; // 10010110  
byte byte2 = 199; // 11000111

If we now do this addition

byte byte3 = byte1 + byte2;

I think we'll end up with byte3 = 94 but what actually happens? Did I overwrite some other memory somehow or is this totally harmless?

Solution 1

It's quite simple. It just does the addition and comes off at a number with more than 8 bits. The ninth bit (being one) just 'falls off' and you are left with the remaining 8 bits which form the number 94.

(yes it's harmless)

Solution 2

The top bits will be truncated. It is not harmful to any other memory, it is only harmful in terms of unintended results.

Solution 3

In C# if you have

 checked { byte byte3 = byte1 + byte2; }

It will throw an overflow exception. Code is compiled unchecked by default. As the other answers are saying, the value will 'wrap around'. ie, byte3 = (byte1 + byte2) & 0xFF;

Solution 4

Typically (and the exact behaviour will depend on the language and platform), the result will be taken modulo-256. i.e. 150+199 = 349. 349 mod 256 = 93.

This shouldn't affect any other storage.

Solution 5

The carry flag gets set... but besides the result not being what you expect, there should be no ill effects.

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