The Tao of Corewar

1
The Tao of Corewar

• by datagram
• (omghai2u)

2
Core-what?
3
History

• Created and extended by A. K. Dewdney in
  Scientific Americans Computer Recreations
  articles from 1984-1987.
• Two coding standards 88 and 94 rules
• Technically more exist, but these are the popular
  ones.
• Still popular mostly European players
• Currently supported on all platforms

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The Core

• Continuous, looping array of instructions.
• Basic unit of memory 1 instruction
• Execution is taken in turns between programs.
  (programs DO NOT compete for execution time)
• All instructions take 1 turn to execute.
• After executing, a process moves to the next
  instruction in the core, unless told to jump to
  another address or is killed.

5
Relative Addressing

• All addressing is relative either to
• The executing instruction itself
• An instruction that the executing instruction
  points to
• (not as complicated as it sounds)
• In a core of 8000 instructions, -1 7999, 10
  8010
• More on addressing methods and modifiers later.

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Anatomy of an Instruction

• OpCode A-field, B-Field
• Examples
• mov 0, 1
• spl _at_10, 0 (more on _at_, , etc. later)
• jmp 10

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The Instructions, Part 1

• MOV Move a-field instruction to b-field
  location.
• ADD Add a-field to b-field.
• SUB Subtract a-field from b-field.
• MUL Multiply a-field by b-field.
• DIV Divide a-field by b-field.
• MOD Modulus a-field by b-field.
• JMP Jump to a-field location.
• JMZ Jump to a-field location, if b-field is
  zero.
• JMN Jump to a-field location if b-field is not
  zero.
• DJN Jump to a-field location if b field is
  zero, but first PRE-DECREMENT b-field.
  (Complex!)
• SPL Split a new process to a-field location.

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The Instructions, Part 2

• CMP Same as SEQ but for 88 (compatible with
  94)
• SEQ Skip if a-field is equal to b-field
• SNE Skip if a-field is not equal to b-field
• SLT Skip if a-field is less than b-field
• Can be skip if greater than, too reverse the
  values.
• NOP No operation (do nothing)
• DAT Data. Illegal instruction kills the
  process.
• LDP Load from P-Space
• STP Store to P-Space
• More on P-Space in a while

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Deadly Instructions

• How do programs die?
• All processes in a program die.
• How do processes die?
• Executing illegal instructions.
• What are illegal instructions?
• Any DAT instruction dat 0, 0
• Modulus (MOD) by 0 mod 0, 1000
• Division (DIV) by 0 div -4569, 0

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Imp

• Our first warrior!
• What does Imp do?
• (shout it out, I dont give a shit)
• Note relative addressing.
• Lets look at Imp in the core (go go demo)

• redcode-94
• name Imp
• author datagram
• mov 0, 1
• end

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Dwarf

• Another warrior, except this time it has the
  potential for victory.
• Dwarf was the first bomber-type warrior.
• Note the use of advanced addressing methods.
• Dwarf in the core! Also, improved dwarf step
  sizes.

• redcode-94
• name Dwarf
• author datagram
• add 4, 3
• mov 2, _at_2
• jmp -2
• dat 0, 0
• end

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Dwarf, Step by Step 1

• Notes _at_ b-field indirect a literal
  number.
• Red Currently executing Bold Last
  instructions changes.
• --------------------------------------------------
  ------
• 0 add 4, 3 execution begins here
• 1 mov 2, _at_2 Add 4 to instruction 3s b-field
• 2 jmp -2
• 3 dat 0, 0
• --------------------------------------------------
  ------
• -1 add 4, 3
• 0 mov 2, _at_2 next instruction
• 1 jmp -2 Move the instruction at 2 to the
• 2 dat 0, 4 location pointed to be the 2s
  b-field
• --------------------------------------------------
  ------

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Dwarf, Step by Step 2

• Notes _at_ b-field indirect a literal
  number.
• Red Currently executing Bold Last
  instructions changes.
• --------------------------------------------------
  ------
• -2 add 4, 3 Jump back 2 instructions.
• -1 mov 2, _at_2 ?-,
• 0 jmp -2
• 1 dat 0, 4 ?---, The B-field of MOV points
  here.
• 2
• 3 4
• 4
• 5 dat 0, 4 ?--- The B-field of DAT points
  here.

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More complex, you say?

• Addressing Methods
• In Dwarf, you saw _at_, , etc. What do they mean?
• Methods are used to
• Modify code during and after execution
• Reference instructions indirectly
• Reference a/b fields of instruction indirectly

• Instruction Modifiers
• MOV moves one instruction to another location,
  right?
• Many instructions seem to have only one method of
  working, but can have appended modifiers.
• What if we want to move only a or b fields of
  instructions?
• What if we want to add or subtract something to
  an a-field of an instruction, not the default
  b-field?

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Addressing Methods

• - Direct. (The is optional.)
• - Immediate.
• - A-field indirect.
• - A-field indirect with pre-decrement.
• - A-field indirect with post-increment.
• _at_ - B-field indirect.
• lt - B-field indirect with pre-decrement.
• gt - B-field indirect with post-increment.

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Addressing Methods, Examples

• 0 nop 0, gt1
• 1 nop 0, _at_5
• 2 nop 1, lt0
• 3 nop 4, 3
• 4 nop 1, 0
• 5 nop 0, 5
• 6 nop 0, 0
• end

• Line 0
• B-field of 1 (1) increases AFTER execution!
• Line 2
• A-field of 1 (3) decreases BEFORE execution!
• B-field of 0 (2) decreases BEFORE execution!
• Line 3
• A-field of 3 (6) increases AFTER execution.
• Line 4
• A-field of 0 (4) increases after execution.
• Easyright?

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Instruction Modifiers

• .A
• A-field of source into A-field of destination.
• .B
• B-field of source into B-field of destination.
• .AB
• A-field of source into B-field of destination.
• .BA
• B-field of source into A-field of destination.
• .F
• Both fields of source into same fields of
  destination.
• .X
• Both fields of source into opposite fields of
  destination.
• .I
• Moves the whole source instruction to destination.

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Instruction Modifiers, Examples

• mov.ba 0, 1 Move b-field of 0 to a-field of
  1
• nop 0, 0 lt- becomes nop 1, 0
• add.x 5, 1 Add, in reverse order, a and b
  fields to 1
• nop -1, -2 lt- becomes nop 0, 3
• Why does it add 5 and 1? Any n, when
  referenced directly, acts as a 0 address.
• mov.f 1, 2 Move both a and b fields of 1 to
  the
• dat 1, 7 same fields in line 2
• nop 3, 4 lt- becomes nop 1, 7
• Note It did NOT change the instruction

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Meet SPL

• Multi-tasking!
• SPL Create a new process executing at a-field
  location of SPL.
• SPL destination
• spl 1 spl 0 spl _at_0, 10 spl 1, lt1000
• Like JMP, but SPL jumps AND continues execution
  at the next instruction.
• Important
• Each program has its own process queue.
• Your program will split execution time between
  your processes.

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Process Queuing

• Program A 3 processes
• Program B 1 process.
• Program A, process 1,
• Program B, process 1,
• Program A, process 2,
• Program B, process 1,
• Program A, process 3,
• Program B, process 1,
• Program A, process 1,
• Program B, process 1,

• SPL in core example
• SPL 0 Process 1
• MOV 0, 1
• ------------------------------------
• SPL 0 Process 2
• MOV 0, 1 Process 1
• ------------------------------------
• SPL 0 Process 3
• MOV 0, 1 Process 2
• MOV 0, 1 Process 1

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P-Space

• A personal storage space that persists between
  rounds.
• Only numbers can be stored in p-space!
• STP Store a number in p-space.
• LDP Load a number from p-space.
• PIN Programs with the same PIN share p-space.
• P-warriors! Using p-space to store strategy
  information and switch strategies if they are
  losing repeatedly.
• Brainwashing! Getting enemies to execute STP
  instructions and trash their p-space with junk
  data. Can crash some p-warriors!
• Can be done by you if PIN numbers are identical.

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Rock, Paper, Scissors

• Very basic look at strategy
• Paper gt Rock gt Scissors gt Paper
• Paper Replicator (aka Silk)
• Rock Bomber (aka Stone)
• Scissors Scanners, Vampire
• Why does paper beat stone?
• Why does stone beat scanner?
• Why does scanner beat paper?

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Stones (Bombers)

• org sGo
• step EQU 551
• bomb dat 2667, lt5334
• sGo spl 0, step
• mov bomb, gt-1
• add.ab step, -2
• djn -2, lt-3

• How it works

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Papers (Replicators)

• pBoot spl 1, 1000
• spl 1, 2000
• spl 1, 3000
• pls mov plb, gt8
• plc mov pls, ltpln
• pln spl _at_pln, gt-1356
• mov plb, ltpln
• mov plb, lt-1000
• mov plb, gt200
• jmn.f _at_0, gtpls
• plb dat lt2667, lt5334

• How it works

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Scanners

• I cant write any simple scanners (
• Want to see my pimped out tournament submission?
• Complex, but shouldnt be too hard for the
  troopers in
• the audience whove followed the presentation so
  far.
• The basic idea goes
• compare two locations
• are these two locations different?
• if so, it is very likely that you found enemy
  code
• figure out which of the two you want to bomb
• bomb that bitch like Baghdad. (too racy?)

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Guerrilla Tactics

• Bootstrapping
• Copying away a piece of program code from your
  original code. Used to leave a large decoy for
  scanners to find, as well as create a smaller
  block of executing code to make it harder for
  scanners to find you.
• Core coloring
• Making bombs visible to scanners, so that
  scanners bomb useless locations.
• Dodging
• A program that looks for bombed locations and
  copies itself there. The idea is that bombers do
  not bomb the same location repeatedly in a short
  period of time, so this is a safe location.
• Q-Scanning
• A fast scan routine used as the start point of a
  warrior. Aims to get lucky and hit enemy code.
  Optimized q-scans can get 8-9 wins on their own.

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Any questions?
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The DC213 Tournament

• Given enough interestIll run a tournament.
• Make a warrior, standard settings
• Rounds 250
• Core size 8000
• Cycles 80000
• Processes 8000
• Code Length 100
• Min. Distance 100
• P-space Disabled
• All entries in by January 5th, 2006.

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More info

• http//corewar.info
• Christian Schmidts (Fizmo) Corewar page.
• Many great beginner links and guides.
• Information on evolving warriors.
• rec.games.corewar
• Google group with plenty of information.
• http//koth.org
• King of the Hill homepage.
• http//corewar.co.uk
• John Metcalfs Corewar page.

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The End.