Monday, 8 December 2008

Corewar: Hostile Programming

Corewar is a game from the 1980's, played between computer programs written in Redcode, a language similar to assembly. The programmers design their battle programs to remove opponents from the memory of the MARS virtual computer by any means possible.

Some of the simpler techniques include blindly overwriting memory, searching for the opponent or spawning off new processes. These are commonly known as stone, scissors, paper after the popular playground game. Stone usually wins against scissors, scissors normally defeat paper, and paper mostly beats stone.

Here's an example of a typical Corewar program:

     org   wipe

step equ 5
first equ bomb-10

bomb:mov.i #1, -1

ptr: sub #step, #first
wipe:jmz.f ptr, @ptr

mov bomb, >ptr
djn.f wipe, {ptr-5


This simple example of scissors once held a 20 point lead over it's rivals. The first instruction is never executed, it's the bomb used to overwrite opponents. The next two instructions form a loop which looks through memory for an opponent, and the final two instructions actually overwrite it.

Corewar is still going strong, and celebrates it's 25th anniversary in 2009. If you'd like to discover more about Corewar, here are the top resources:

What are your experiences with Corewar, have you ever had any success?

John Metcalf

Corewar: Hostile Programming is a guest post written by John Metcalf.