Integer overflow: Difference between revisions

Revision as of 13:44, 10 August 2010

Revision as of 13:45, 10 August 2010

Line 15:

: 128 bits: maximum representable value 2¹²⁸ − 1 = 340,282,366,920,938,463,463,374,607,431,768,211,455

Since an arithmetic operation may produce a result larger than the maximum representable value, a potential error condition may result. In the [[C (programming language)|C programming language]], signed integer overflow causes [[undefined behavior]], while unsigned integer overflow causes the number to be reduced [[modular arithmetic|modulo a power of two]], meaning that unsigned integers "wrap around" on overflow. This "wrap around" is the cause of the famous "[[kill screen|Split Screen]]" in Pac-Man.<ref>{{cite web|url=http://home.comcast.net/~jpittman2/pacman/pacmandossier.html#Chapter 5|title=The Pac-Man Dossier|author=Pittman, Jamey}}</ref>

A "wrap around" corresponds to the fact, that e.g. if the addition of two positive integers produces an overflow, it may result in a negative number. In counting, one just starts over again from the bottom.

Example: 16 bit signed integer: 30000 + 30000 = −5536.