From FreeBio

Core War Frequently Asked Questions


These are the Frequently Asked Questions (and answers) from the Usenet newsgroup REC.GAMES.COREWAR. A plain text version of this document is posted every two weeks. An old version is available at


What is Core War?

Core War is a game played by two or more programs (and vicariously by their authors) written in an assembly language called Redcode and run in a virtual computer called MARS (for Memory Array Redcode Simulator). The object of the game is to cause all processes of the opposing program to terminate, leaving your program in sole posession of the machine.

There are Core War systems available for most computer platforms. Redcode has been standardised by the ICWS in 1994, and is therefore transportable between all standard Core War systems.

The system in which the programs run is quite simple. The core (the memory of the simulated computer) is a continuous array of instructions, empty except for the competing programs. The core wraps around, so that after the last instruction comes the first one again.

There are no absolute addresses in Core War. That is, the address 0 doesn't mean the first instruction in the memory, but the instruction that contains the address 0. The next instruction is 1, and the previous one obviously -1. However, all numbers are treated as positive, and are in the range 0 to CORESIZE-1 where CORESIZE is the amount of memory locations in the core - this means that -1 would be treated as CORESIZE-1 in any arithmetic operations, eg. 3218 + 7856 = (3218 + 7856) mod CORESIZE. Many people get confused by this, and it is particularly important when using the SLT instruction. Note that the source code of a program can still contain negative numbers, but if you start using instructions like DIV #-2, #5 it is important to know what effect they will have when executed.

The basic unit of memory in Core War is one instruction. Each Redcode instruction contains three parts:

  * the opcode
  * the source address (a.k.a. the A-field)
  * the destination address (a.k.a. the B-field)

The execution of the programs is equally simple. The MARS executes one instruction at a time, and then proceeds to the next one in the memory, unless the instruction explicitly tells it to jump to another address. If there is more than one program running, (as is usual) the programs execute alternately, one instruction at a time. The execution of each instruction takes the same time, one cycle, whether it is MOV, DIV or even DAT (which kills the process).

Each program may have several processes running. These processes are stored in a task queue. When it is the program's turn to execute an instruction it dequeues a process and executes the corresponding instruction. Processes that are not killed during the execution of the instruction are put back into the task queue. Processes created by a SPL instruction are added to the task queue after the creating process is put back into the task queue.

Is it "Core War", "Core Wars" or "Corewar"

All three terms are used. Early references were to Core War or Core Wars. Lately, people seem to prefer "Corewar".

Where can I find more information about Core War?

Core War was first described in the Core War Guidelines of March, 1984 by D. G. Jones and A. K. Dewdney of the Department of Computer Science at The University of Western Ontario (Canada). Dewdney wrote several "Computer Recreations" articles in Scientific American which discussed Core War, starting with the May 1984 article. Those articles are contained in two anthologies:

                                                               Library of
 Author         Title         Published          ISBN           Congress
                                                               Call Number
          The Armchair
Dewdney,  Universe: An       New York: W.                     QA76.6 .D517
A. K.     Exploration of     H. Freeman �167-1939-8        1988
          Computer Worlds    1988
          The Magic                      0-7167-2125-2
Dewdney,  Machine: A         New York: W.(Hardcover),         QA76.6
A. K.     Handbook of        H. Freeman �167-2144-9        .D5173 1990
          Computer Sorcery   1990        (Paperback)

A.K. Dewdney's articles are still the most readable introduction to Core War, even though the Redcode dialect described in there is no longer current. For those who are interested, Dewdney has a home page at

Core War has changed since Dewdney's articles. Where do I get a copy of the current instruction set?

A draft of the official standard (ICWS'88) is available as This document is formatted awkwardly and contains ambiguous statements. For a more approachable intro to Redcode, take a look at Mark Durham's tutorials, and

Steven Morrell has prepared a more practically oriented Redcode tutorial that discusses different warrior classes with lots of example code. This and various other tutorials can be found at

Even though ICWS'88 is still the "official" standard, you will find that most people are playing by ICWS'94 draft rules and extensions.

What is ICWS'94? Which simulators support ICWS'94?

There is an ongoing discussion about future enhancements to the Redcode language. A proposed new standard, dubbed ICWS'94, is currently being evaluated. A major change is the addition of "instruction modifiers" that allow instructions to modify A-field, B-field or both. Also new is a new addressing modes and unrestricted opcode and addressing mode combination ("no illegal instructions"). ICWS'94 is backwards compatible; i.e. ICWS'88 warriors will run correctly on an ICWS'94 system. Take a look at the ICWS'94 draft at for more information. There is a HTML version of this document available at You can try out the new standard by submitting warriors to the '94 hills of the KotH servers. Two corewar systems currently support ICWS'94, pMARS (many platforms) and Redcoder (Mac), both available at Note that Redcoder only supports a subset of ICWS'94.

The two most popular MARS versions are pMARS (with binaries for windows):

and Corewin (Only for windows):

There are also several good MARS versions for evolving or for use under unix

Joonas Pihlaja wrote exhaust:

Martin Ankerl rewrote it as exmars:

Michal Janeczek wrote the current speed king, fmars:

What is the ICWS?

About one year after Core War first appeared in Scientific American, the "International Core Wars Society" (ICWS) was established. Since that time, the ICWS has been responsible for the creation and maintenance of Core War standards and the running of Core War tournaments. There have been six annual tournaments and two standards (ICWS'86 and ICWS'88). The ICWS is no longer active.

There are a few sites that have taken up the tasks of holding tournaments, continues to hold the "Redcoders Frenzy" ongoing corewars tournaments. As well, there are 30 minute IRC tournaments held on Sundays, at 7PM GMT on the #corewars channel at They run when there are enough people show up interested, and a willing host can be found.

What is Core Warrior?

Following in the tradition of The Core War Newsletter, Push Off, and The 94 Warrior, Core Warrior is a newsletter covering strategies and current standings in Corewar. Started in October 1995 by Beppe Bezzi and his team, back issues of Core Warrior (and the other newsletters) are available at:

The latest issue of Core Warrior is available at:

Many of the earlier issues contain useful information for beginners.

Where are the Core War archives?

Many documents such as the guidelines and the ICWS standards along with previous tournament Redcode entries and complete Core War systems are available via anonymous ftp from Also, most of past postings (including Redcode source listings) are archived there. Jon Blow ( is the archive administrator. When uploading to /pub/corewar/incoming, ask Jon to move your upload to the appropriate directory and announce it on the net.

This site is mirrored at:


The plain text version of this FAQ is automatically archived by news.answers (but this version is probably out-of-date).

Where can I find a Core War system for . . . ?

The two most popular MARS versions are pMARS (with binaries for windows):

(OS-X success has been reported with the pmars-sdl version.)

A full-featured, GUI-based Core War simulator for Windows:

A graphical MARS Emulator, incorporating a powerful debugger, which runs under Windows:

There are also several good MARS versions for evolving or for use under unix.

Joonas Pihlaja wrote exhaust:

Martin Ankerl rewrote it as exmars:

Michal Janeczek wrote the current speed king, fmars:

A redcode simulator that is (hopefully) easy to embed into your applications, as an alternative to pMARS:

It is heavily optimized to be as fast as possible:

Combines elements from Corewar and modern artificial life emulators:

Online MARS Java-Applet for ICWS '88

Where can I find warrior code?

Damien Doligez (a.k.a. Planar) has a well organized library of warriors: Convenient for U.S. users, this site is also mirrored at

How do I read the newsgroup for corewars?

The easiest way is to read it through google:

Alternately you can use any usenet news reader, or to receive articles by email, join the COREWAR-L list run on the Koth.Org list processor. To join, send the message...

    SUB COREWAR-L FirstName LastName You can send mail to to post even if you are not a member of the list. Responsible for the listserver is Scott J. Ellentuch (

Servers that allow you to post (but not receive) articles are available. Refer to the Accessing the Internet by E-Mail FAQ for more information.

Are there any Core War related WWW sites?

You bet. Each of the two KotH sites sport a world-wide web server. Stormking's Core War page is; pizza's is . Damien Doligez (a.k.a. Planar) has a web page that features convenient access to regular newsletters (Push Off, The '94 Warrior, Core Warrior) and a well organized library of warriors: Convenient for U.S. users, this site is also mirrored at

What is KotH? How do I enter?

King Of The Hill (KotH) is an ongoing Core War tournament available to anyone with email. You enter by submitting via email a Redcode program (warrior) with special comment lines. You will receive a reply indicating how well your program did against the current top programs "on the hill".

There are two styles of KotH tournaments, "classical" and "multi-warrior". The "classical" KotH is a one-on-one tournament, that is your warrior will play 100 battles against each of the 20 other programs currently on the Hill. You receive 3 points for each win and 1 point for each tie. (The existing programs do not replay each other, but their previous battles are recalled.) All scores are updated to reflect your battles and all 21 programs are ranked from high to low. If you are number 21 you are pushed off the Hill, if you are higher than 21 someone else is pushed off.

In "multi-warrior" KotH, all warriors on the hill fight each other at the same time. Score calculation is a bit more complex than for the one-on-one tournament. Briefly, points are awarded based on how many warriors survive until the end of a round. A warrior that survives by itself gets more points than a warrior that survives together with other warriors. Points are calculated from the formula (W*W-1)/S, where W is the total number of warriors and S the number of surviving warriors. The pMARS documentation has more information on multi-warrior scoring.

The idea for an email-based Core War server came from David Lee. The original KotH was developed and run by William Shubert at Intel starting in 1991, and discontinued after almost three years of service. Currently, KotHs based on Bill's UNIX scripts but offering a wider variety of hills are are running at two sites: is maintained by Scott J. Ellentuch ( and by Thomas H. Davies ( Up until May '95, the two sites provided overlapping services, i.e. the some of the hill types were offered by both "pizza" and "stormking". To conserve resources, the different hill types are now divided up among the sites. The way you submit warriors to both KotHs is pretty much the same. Therefore, the entry rules described below apply to both "pizza" and "stormking" unless otherwise noted.

Entry Rules for King of the Hill Corewar

  * Write a corewar program. KotH is fully ICWS '88 compatible, EXCEPT that
    a comma (",") is required between two arguments.
  * Put a line starting with ";redcode" (or ";redcode-94", etc., see below)
    at the top of your program. This MUST be the first line. Anything
    before it will be lost. If you wish to receive mail on every new
    entrant, use ";redcode verbose". Otherwise you will only receive mail
    if a challenger makes it onto the hill. Use ";redcode quiet" if you
    wish to receive mail only when you get shoved off the hill.
    Additionally, adding ";name <program name>" and ";author <your name>"
    will be helpful in the performance reports. Do NOT have a line
    beginning with ";address" in your code; this will confuse the mail
    daemon and you won't get mail back. Using ";name" is mandatory on the
    Pizza hills.
    In addition, it would be nice if you have lines beginning with
    ";strategy" that describe the algorithm you use.
    There are currently seven separate hills you can select by starting
    your program with ;redcode-94, ;redcode-b, ;redcode-lp, ;redcode-x,
    ;redcode, ;redcode-94x or ;redcode-94m. The former four run at "pizza",
    the latter three at "stormking". More information on these hills is
    listed below.
  * Mail this file to or "Pizza"
    requires a subject of "koth" (use the -s flag on most mailers).
  * Within a few minutes you should get mail back telling you whether your
    program assembled correctly or not. If it did assemble correctly, sit
    back and wait; if not, make the change required and re-submit.
  * In an hour or so you should get more mail telling you how your program
    performed against the current top 20 (or 10) programs. If no news
    arrives during that time, don't worry; entries are put in a queue and
    run through the tournament one at a time. A backlog may develop. Be

If your program makes it onto the hill, you will get mail every time a new program makes it onto the hill. If this is too much mail, you can use ";redcode[-??] quiet" when you first mail in your program; then you will only get mail when you make it on the top 25 list or when you are knocked off. Using ";redcode[-??] verbose" will give you even more mail; here you get mail every time a new challenger arrives, even if they don't make it onto the top 25 list.

Often programmers want to try out slight variations in their programs. If you already have a program named "foo V1.0" on the hill, adding the line ";kill foo" to a new program will automatically bump foo 1.0 off the hill. Just ";kill" will remove all of your programs when you submit the new one. The server kills programs by assigning an impossibly low score; it may therefore take another successful challenge before a killed program is actually removed from the hill.

Sample Entry

name Dwarf
author A. K. Dewdney
strategy Throw DAT bombs around memory, hitting every 4th memory cell.
strategy This program was presented in the first Corewar article.

bomb DAT #0 dwarf ADD #4, bomb

     MOV   bomb, @bomb
     JMP   dwarf
     END   dwarf          ; Programs start at the first line unless
                          ; an "END start" pseudo-op appears to indicate
                          ; the first logical instruction.  Also, nothing
                          ; after the END instruction will be assembled.
                                         Duration  Max.
    Hill Name      Hill  Core    Max.     Before  Entry     Min.   Rounds   Instr.
                   Size  Size Processes                   Distance Fought    Set
                                           Tie    Length
Pizza's ICWS '94
Draft Hill                                                                 Extended
(Accessed with       25  8000       8000    80000    100       100     200 ICWS '94
";redcode-94")                                                             Draft
Pizza's Beginner's                                                         Extended
Hill (Accessed       25  8000       8000    80000    100       100     200 ICWS '94
with ";redcode-b")                                                         Draft
Experimental                                                               Extended
(Small) Hill         25   800        800     8000     20        20     200 ICWS '94
(Accessed with                                                             Draft
Pizza's Limited
Process (LP) Hill                                                          Extended
(Accessed with       25  8000          8    80000    200       200     200 ICWS '94
";redcode-lp")                                                             Draft
Stormking's ICWS
'88 Standard Hill
(Accessed with       20  8000       8000    80000    100       100     250 ICWS '88
Stormking's ICWS
'94 No Pspace Hill
(Accessed with       20  8000       8000    80000    100       100     250 ICWS '94
Stormking's ICWS
'94 Experimental                                                           Extended
(Big) Hill           20 55440      55440   500000    200       200     250 ICWS '94
(Accessed with                                                             Draft
Stormking's ICWS
'94 Multi-Warrior                                                          Extended
Hill (Accessed       10  8000       8000    80000    100       100     200 ICWS '94
with                                                                       Draft

Note: Warriors on the beginner's hill are retired at age 100.

If you just want to get a status report without actually challenging the hills, send email with ";status" as the message body (and don't forget "Subject: koth" for "pizza"). If you send mail to "pizza" with "Subject: koth help" you will receive instructions that may be more up to date than those contained in this document.

At "stormking", a message body with ";help" will return brief instructions. If you submit code containing a ";test" line, your warrior will be assembled but not actually pitted against the warriors on the hill.

At "pizza", you can use ";redcode[-??] test" to do a test challenge of the Hill without affecting the status of the Hill. These challenges can be used to see how well your warrior does against the current Hill warriors.

All hills run portable MARS (pMARS) version 0.8, a platform-independent Core War system available at

The '94 and '94x hills allow five experimental opcodes and three experimental addressing modes currently not covered in the ICWS'94 draft document:

  * LDP - Load P-Space
  * STP - Store P-Space
  * SEQ - Skip if EQual (synonym for CMP)
  * SNE - Skip if Not Equal
  * NOP - (No OPeration)
  * * - indirect using A-field as pointer
  * { - predecrement indirect using A-field
  * } - postincrement indirect using A-field

Is it DAT 0, 0 or DAT #0, #0? How do I compare to core?

Core is initialized to DAT 0, 0. This is an illegal instruction (in source code) under ICWS'88 rules and strictly compliant assemblers (such as KotH or pmars -8) will not let you have a DAT 0, 0 instruction in your source code - only DAT #0, #0. So this begs the question, how to compare something to see if it is empty core. The answer is, most likely the instruction before your first instruction and the instruction after your last instruction are both DAT 0, 0. You can use them, or any other likely unmodified instructions, for comparison. Note that under ICWS'94, DAT 0, 0 is a legal instruction.

How does SLT (Skip if Less Than) work?

SLT gives some people trouble because of the way modular arithmetic works. It is important to note that all negative numbers are converted to positive numbers before a battles begins. Example: -1 becomes M-1 where M is the memory size (core size).

Once you realize that all numbers are treated as positive, it is clear what is meant by "less than". It should also be clear that no number is less than zero.

What is the difference between in-register and in-memory evaluation?

These terms refer to the way instruction operands are evaluated. The '88 Redcode standard ICWS'88 is unclear about whether a simulator should "buffer" the result of A-operand evaluation before the B-operand is evaluated. Simulators that do buffer are said to use in-register evaluation, those that don't, in-memory evaluation. ICWS'94 clears this confusion by mandating in-register evaluation. Instructions that execute differently under these two forms of evaluation are MOV, ADD, SUB, MUL, DIV and MOD where the effective address of the A-operand is modified by evaluation of the B-operand. This is best illustrated by an example:

  L1  mov L2, <L2
  L2  dat #0, #1

Under in-register evaluation, the L2 instruction is saved in a buffer before the L2 memory location is decremented by evaluation of the B-operand of L1. The saved DAT #0,#1 instruction is then written to L2, leaving it unchanged.

Under in-memory evaluation, the L2 instruction is not buffered and thus decremented by evaluation of the B-operand. After execution of L1, L2 changes to DAT #0,#0.

What is P-space?

P-space is an area of memory which only your program's processes can access. The contents of each memory location are preserved between rounds in a multi-round match.

P-space is in many ways different from the core. First of all, each P-space location can only store one number, not a whole instruction. Also, the addressing in P-space is absolute, ie. the P-space address 1 is always 1 regardless of where in the core the instruction containing it is. And last but not least, P-space can only be accessed by two special instructions, LDP and STP.

The syntax of these two instructions is a bit unusual. STP, for example, has an ordinary value in the core as its source, which is put into the P-space field pointed to by the destination. So the P-space location isn't determined by the destination address, but by its value, ie. the value that would be overwritten if this were a MOV. So STP.AB #Q, #R would put the value Q into the P-space field R mod PSPACESIZE. Similarly,

       stp.b  2, 3
       dat    0, 0
       dat    0, 9
       dat    0, 7

would put the value 9 into the P-space field 7. LDP works the same way, except that now the source is a P-space field and the destination a core instruction. The P-space location 0 is a special location. It is initialised to a special value before each round. This value is:

  * -1 (or CORESIZE-1) at the beginning of the first round
  * 0 if the program died in the previous round
  * The number of surviving programs if the program did not die in the
    previous round

This means that for one-on-one matches, loss=0, win=1 and tie=2.

The default size of P-space is 1/16 of the core size. This size is the value of the predefined variable PSPACESIZE. The addresses in the P-space wrap around just like in the core, ie. you can store a value from 0 to CORESIZE-1 in each P-space location. All P-space values (except for location 0) are 0 initially.

What does "Missing ;assert .." in my message from KotH mean?

This means you have omitted an ";assert" line in your submission. ";assert" is used to specify which environments your code will work under or was designed for. For example, if your warrior was written for the '94 draft hill then you can put:

assert CORESIZE==8000

in your code, meaning that an error will occur if you attempt you compile the code for a different core size. If you don't want to use the features of ";assert" and you want to get rid of the annoying warning just put:

assert 1

in your code, which means it will compile unconditionally.

How should I format my code?

The way you format your code is really your own choice in the end. If you are new to the game then use the style you feel most comfortable with. However, using a common format helps others to understand your code quicker. Most players tend to use the following conventions when writing code:

  * use lower case for location names and opcode names
  * don't add opcode modifiers if you don't need to, eg. add.ab #1, #2 is
    the same as add #1, #2
  * use whitespace after every comma
  * use tabs to align the opcodes, the instruction field(s) and any
  * do not use $ (direct addressing mode) or : (suffix of some labels)

Evolvers use a slightly different ideal, to make the code easily parsed across several evolvers. The easiest format is the pmars processed format.

        ORG      START
 START  MOV.I  $    14, $  3207
        SPL.B  $     2, $     0
        SPL.B  $     1, $     0

Which consists of warriors in the format pmars displays when it compiles the warriors. It is a safe format that should be portable across all the evolving programs, and is easily programatically digested with regular expressions.

Are there any other Core War related resources I should know about?

Using genetic algorithms to generate warriors has been attempted by a number of people. There are a number of resources available for people who are interested in doing some experimentation:

  * There is a Core War genetic algorithms mailing list at The FTP site for this list is at The administrator is Martin
    Pedersen (
  * Jason's Core War project page
    ( contains a
    C program which can evolve warriors, along with some previously
    generated warriors.
  * Core Wars Genetics: The Evolution of Predation by John Perry can be
    found at
  * A recent paper on Core War evolution is by Ryan Coleman and can
    be found at
  * The most recent paper on Core War evolution can be found at:

Corewars evolving programs can be found at:

  * Barkley Vowk's CCAI and JNSL

  * Martin Ankel's YACE
  * Dave Hillis' RedRace
  * Loren Jamison's CRE
  * Wil Varfar's Species
  * The MicroGP research groups evolver
  * Terry Newtons's corewars Evolvers
  * Jason's corewars pages

What does (expression or term of your choice) mean?

Here is a selected glossary of terms. If you have a definition and/or term you wish to see here, please send it to me.

(References to an X-like program mean that the term X is derived from the specific program X and has become a generic term).

Binary launch

    One of several means to start an imp-spiral running. The fastest launch
    technique, but requires the most code. See also JMP/ADD Launch and
    Vector Launch.
        impsize   equ 2667
        example   spl 4               ; extend by adding spl 8, spl 16, etc.
                  spl 2
                  jmp imp+(0*impsize) ; jmp's execute in order
                  jmp imp+(1*impsize)
                  spl 2
                  jmp imp+(2*impsize)
                  jmp imp+(3*impsize)
        imp       mov 0, impsize      ; in '94 use -> mov.i #0, impsize


    Strategy of copying the active portion of the program away from the
    initial location, leaving a decoy behind and making the relocated
    program as small as possible.


    Scanners which only recognize non-zero B-fields.
        example   add #10, scan
        scan      jmz example, 10


    Measure of speed, equal to one location per cycle. Speed of light.


    A Scanner which uses a CMP instruction to look for opponents.
        example   add step, scan
        scan      cmp 10, 30
                  jmp attack
                  jmp example
        step      dat #20, #20


    Property of bombs making them visible to scanners, causing them to
    attack useless locations, thus slowing them down.
        example   dat #100


    Code that sequentially overwrites core with DAT instructions; usually
    the last part of a program.


    Bogus or unused instructions meant to slow down scanners. Typically,
    DATs with non-zero B-fields.

Decrement Resistant

    Property of warriors making them functional (or at least partially
    functional) when overrun by a DJN-stream.

DJN-Stream (also DJN-Train)

    Using a DJN command to rapidly decrement core locations.
        example   ...
                  djn example, <4000


    The prototypical small bomber.

Gate-busting (also gate-crashing)

    technique to "interweave" a decrement-resistant imp-spiral (e.g. MOV 0,
    2668) with a standard one to overrun imp-gates.


    warriors that combine two or more of the basic strategies, either in
    sequence (e.g. stone->paper) or in parallel (e.g. imp/stone).


    Program which only uses the MOV instruction.
        example   mov 0, 1
        example   mov 0, 2
                  mov 0, 2


    A location in core which is bombed or decremented continuously so that
    an Imp can not pass. Also used to describe the program-code which
    maintains the gate.
        example   ...
                  spl 0, <example
                  dat <example, #0


    A minimal Imp-Spiral.
        D         EQU (CORESIZE+1)/3
        a         mov 0, D   ; copy self to b
        b         mov 0, D   ; copy self to c
        c         mov 0, D   ; copy self to a+1


    An Imp-like program with two or more processes supporting each other. A
    three-point spiral, with six processes running in this sequence:
        D         EQU (CORESIZE+1)/3
        a         mov 0, D   ; copy self to b
        b         mov 0, D   ; copy self to c
        c         mov 0, D   ; copy self to a+1
        a+1       mov 0, D   ; copy self to b+1
        b+1       mov 0, D   ; copy self to c+1
        c+1       mov 0, D   ; copy self to a+2

Incendiary Bomb

    A type of Stun bomb which creates a SPL 0 carpet.
    Here is an example of an incendiary bomb used in '88 warriors:
                  spl 0, 8
                  mov -1, <-1
    '94 warriors use somewhat different and a little better incendiary bombs. Here is one of them:
                  mov 1, }1
                  spl #1, 1
     This one is very good, because both of its instructions have "1"'s in their A and B fields, and therefore cause some problems for enemies using djn streams.

JMP/ADD Launch

    one of several means to start an imp-spiral running. The slowest launch
    technique, but requires the least code. See also Binary Launch and
    Vector Launch.
        IMPSIZE   EQU 2667
        example   spl 1               ; extend by adding more spl 1's
                  spl 1
                  spl 2
                  jmp @0, imp
                  add #IMPSIZE, -1    ; bump address by impsize after each jmp
                  dat #0, #0          ; excess processes must die!
        imp       mov 0, IMPSIZE      ; in '94 use -> mov.i #0,IMPSIZE


    see reflection.


    On-axis scanners compare two locations M/2 apart, where M is the memory
    size. Off-axis scanners use some other separation.

Optimal Constants

    (also optima-type constants) Bomb or scan increments chosen to cover
    core most effectively, i.e. leaving gaps of uniform size. Programs to
    calculate optimal constants and lists of optimal numbers are available


    A Paper-like program is one which replicates itself many times. Part of
    the Scissors (beats) Paper (beats) Stone (beats Scissors) analogy.


    A warrior which uses the results of previous round(s) in order to
    determine which strategy it will use.


    (also Slaver, Vampire). A program which enslaves another. Usually
    accomplished by bombing with JMPs to a SPL 0 pit with an optional
    core-clear routine.

Q^2 Scan

    A modern version of the Quick Scan where anything found is attacked
    almost immediately.

Quick Scan

    2c scan of a set group of core locations with bombing if anything is
    found. Both of the following codes snips scan 16 locations and check
    for a find. If anything is found, it is attacked, otherwise 16 more
    locations are scanned.
         s1 for 8    ;'88 scan
                cmp  start+100*s1, start+100*s1+4000 ;check two locations
                mov  #start+100*s1-found, found      ;they differ so set pointer
                jmn  attack,   found    ;if we have something, get it
         s2 for 8
                cmp  start+100*(s2+6), start+100*(s2+6)+4000
                mov  #start+100*(s2+6)-found, found
         found  jmz  moveme,  #0        ;skip attack if qscan found nothing
         attack cmp  @found,  start-1   ;does found points to empty space?
                add  #4000,   found     ;no, so point to correct location
                mov  start-1, @found    ;move a bomb
         moveme jmp  0,       0
    In ICWS'94, the quick scan code is more compact because of the SNE
         start       ;'94 scan
         s1 for 4
                sne  start+400*s1, start+400*s1+100     ;check two locations
                seq  start+400*s1+200, start+400*s1+300 ;check two locations
                mov  #start+400*s1-found, found       ;they differ so set pointer
                jmn  which,   found     ;if we have something, get it
         s2 for 4
                sne  start+400*(s2+4), start+400*(s2+4)+100
                seq  start+400*(s2+4)+200, start+400*(s2+4)+300
                mov  #start+400*(s2+4)-found-100, found
         found  jmz  moveme,  #0        ;skip attack if qscan found nothing
                add  #100,    -1        ;increment pointer till we get the
         which  jmn  -1,      @found    ;right place
                mov  start-1, @found    ;move a bomb
         moveme jmp  0,       0


    Copy of a program or program part, positioned to make the active
    program invisible to a CMP-scanner.


    Generic for Paper. A program which makes many copies of itself, each
    copy also making copies.


    Strategy of amplifying the number of processes executing a piece of
        example    spl 0
        loop       add #10, example
                   mov example, @example
                   jmp loop


    A program which searches through core for an opponent rather than
    bombing blindly.


    A program designed to beat replicators, usually a (B-field scanning)
    vampire. Part of the Paper-Scissors-Stone analogy.


    Ability of a program to fix it's own code after attack.


    A replicator which splits off a process to each new copy before
    actually copying the code. This allows it to replicate extremely
    quickly. This technique is only possible under the '94 draft, because
    it requires post-increment indirect addressing. Example:
                spl   1
                mov   -1, 0
                spl   1                ;generate 6 consecutive processes
        silk    spl   3620,   #0       ;split to new copy
                mov   >-1, }-1      ;copy self to new location
                mov   bomb,   >2000 ;linear bombing
                mov   bomb,   }2042    ;A-indirect bombing for anti-vamp
                jmp   silk,   {silk    ;reset source pointer, make new copy
        bomb    dat   >2667,  >5334  ;anti-imp bomb


    see Pit-Trapper.


    Property of programs, or program parts, which are invisible to
    scanners, accomplished by using zero B-fields and reflections.


    A Stone-like program designed to be a small bomber. Part of the
    Paper-Scissors-Stone analogy.


    A type of bomb which makes the opponent multiply useless processes,
    thus slowing it down. Example is referred to as a SPL-JMP bomb.
        example    spl   0
                   jmp   -1

Two-Pass Core-Clear (also SPL/DAT Core-Clear)

    core clear that fills core first with SPL instructions, then with DATs.
    This is very effective in killing paper and certain imp-spiral


    see Pit-Trapper.

Vector Launch

    one of several means to start an imp-spiral running. As fast as Binary
    Launch, but requiring much less code. See also JMP/ADD Launch and
    Binary Launch. This example is one form of a Vector Launch:
        sz      EQU   2667
                spl   1
                spl   1
                jmp   @vt, }0
        vt      dat   #0, imp+0*sz ; start of vector table
                dat   #0, imp+1*sz
                dat   #0, imp+2*sz
                dat   #0, imp+3*sz ; end of vector table
        imp     mov.i #0, sz

Other questions?

Just ask in the newsgroup, #corewars on, or contact any of the contributors to this faq.

If you are shy, check out the Core War archives first to see if your question has been answered before.


Additions, corrections, etc. to this document are solicited. Thanks in particular to the following people who have contributed major portions of this document:

  * Mark Durham 
  * Paul Kline
  * Randy Graham
  * Stefan Strack 
  * Anton Marsden
  * Barkley Vowk