Learn Core War.
Twelve lessons, zero install.

Memory is a ring of cells

The battlefield is called the core: 8000 cells in the standard game. Every cell holds one instruction, and the end wraps around to the start, so cell 8000 is cell 0 again.

Addresses are relative: 0 means this cell, 1 the next one, -1 the previous one. Neither warrior knows where it was loaded.

Empty cells hold DAT 0, 0. A program that executes a DAT dies. Make every enemy process hit a DAT and you win. If nobody dies within 80,000 cycles, it's a tie.

Your first warrior: the Imp

This program copies itself into the next cell. The next cell is exactly where it runs next, so it crawls through memory forever.

The Imp almost never wins, but it is very hard to kill. It mostly ends in ties.

Bombing: the Dwarf

bomb is a DAT whose B-field works as a target pointer. Each loop adds 4 to the target, then copies the bomb to wherever the pointer says (that's what @ means).

It covers every 4th cell. The Dwarf itself is 4 cells long, so its own bombs miss it.

Addressing modes

The symbol in front of a number says how to use it:

More processes: SPL

SPL starts a new process. A warrior gets one instruction per turn however many processes it has, so more processes doesn't mean more speed. It means the warrior is harder to kill.

A replicator like this one copies itself across the core faster than most bombers can hit it.

Look before you shoot: scanners

SNE compares two cells. If they differ, one of them isn't empty memory, so something is there. The scanner bombs both cells and keeps looking.

When the scan finishes, it wipes every cell of the core except its own.

Rock, paper, scissors

Most warriors are one of three kinds:

Stones (bombers like the Dwarf) are small and fast. Papers (replicators) make copies faster than stones can bomb them. Scissors (scanners) find papers and cut them down, but stones are too small for them to find in time.

Paper beats stone, scissors beat paper, stone beats scissors, roughly. Good warriors mix two kinds.

Safety in numbers: imp rings

Three imps, spaced (CORESIZE+1)/3 cells apart, take turns: each one copies itself onto the spot the next one is about to run. Together they advance one cell per round, like a single fat imp.

SPL 1 followed by MOV -1, 0 is a classic trick for getting exactly three processes. Bombers struggle to kill all three in time.

Clearing the core

SPL #0 creates an endless stream of processes, and each one wipes one cell and moves the pointer on. Eventually every cell gets a DAT, including the ones the enemy is hiding in.

The trick: when the pointer wraps all the way around and hits itself, the bomb that lands there resets it to 4, so the Broom never sweeps away its own code. It's one of the few things that reliably kills an Imp.

Traps: make them work for you

A DAT bomb kills one process. Against a replicator running thousands of them, that's hopeless. So instead of killing, trap: plant a JMP on the enemy that leads into an SPL 0 loop.

Trapped processes multiply uselessly instead of copying or bombing, and a final DAT clear wipes them all out. That's how Mousetrap beats Mice nine times out of ten.

Small cores: Tiny and Nano

Same game, less room. Tiny has 800 cells and allows 20 instructions. Nano has 80 cells and only 5 instructions. Warriors start just a few cells apart and battles are over in a blink.

Long, clever warriors don't fit, so there are fewer tricks to learn. A beginner, an evolutionary algorithm or an AI has a real chance against experienced players here. Write numbers in terms of CORESIZE and the same warrior works on all three.

Your turn

Open the template in the arena, change something, and press Test Warrior 1 against every built-in. Or go straight for the challenges. Your score is points per 100 rounds: 3 for a win, 1 for a tie, so the maximum is 300.

Getting above 150 takes some real thought. Getting above 200 means you've found something clever.