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Core War Frequently Asked Questions (rec.games.corewar FAQ)


[ Usenet FAQs | Web FAQs | Documents | RFC Index | Houses ]
Archive-name: games/corewar-faq
Last-Modified: September 4, 1999
Version: 4.2
URL: http://homepages.paradise.net.nz/~anton/cw/corewar-faq.html
Copyright: (c) 1999 Anton Marsden
Maintainer: Anton Marsden <anton@paradise.net.nz>
Posting-Frequency: once every 2 weeks

See reader questions & answers on this topic! - Help others by sharing your knowledge
Core War Frequently Asked Questions

(rec.games.corewar FAQ)

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. The latest hypertext version is available at
http://homepages.paradise.net.nz/~anton/cw/corewar-faq.html and the latest
plain text version is available at
http://homepages.paradise.net.nz/~anton/cw/corewar-faq.txt.

This document is currently being maintained by Anton Marsden
(anton@paradise.net.nz).

Last modified: Sat Sep 4 00:22:22 NZST 1999
  ------------------------------------------------------------------------

To Do

   * Add the new No-PSpace '94 hill location
   * Add online location of Dewdney's articles
   * Make question 17 easier to understand. Add a state diagram?
   * Add info about infinite hills, related games (C-Robots, Tierra?, ...)
   * New question: How do I know if my warrior is any good? Refer to
     beginners' benchmarks, etc.
   * Add a Who's Who list?
   * Would very much like someone to compile a collection of the
     "revolutionary" warriors so that beginners can see how the game has
     developed over the years. Mail me if interested.

  ------------------------------------------------------------------------

What's New

   * Changed primary location of FAQ (again!)
   * Changed Philip Kendall's home page address.
   * Updated list server information
   * Changed primary location of FAQ
   * Vector-launching code was fixed thanks to Ting Hsu.
   * Changed the location of Ryan Coleman's paper (LaunchPad -> Launchpad)
   * Changed pauillac.inria.fr to para.inria.fr

  ------------------------------------------------------------------------

Table of Contents

  1. What is Core War
  2. Is it "Core War" or "Core Wars"?
  3. Where can I find more information about Core War?
  4. Core War has changed since Dewdney's articles. Where do I get a copy of
     the current instruction set?
  5. What is ICWS'94? Which simulators support ICWS'94?
  6. What is the ICWS?
  7. What is Core Warrior?
  8. Where are the Core War archives?
  9. Where can I find a Core War system for ...?
 10. Where can I find warrior code?
 11. I do not have FTP. How do I get all this great stuff?
 12. I do not have access to Usenet. How do I post and receive news?
 13. Are there any Core War related WWW sites?
 14. What is KotH? How do I enter?
 15. Is it DAT 0, 0 or DAT #0, #0? How do I compare to core?
 16. How does SLT (Skip if Less Than) work?
 17. What is the difference between in-register and in-memory evaluation?
 18. What is P-space?
 19. What does "Missing ;assert .." in my message from KotH mean?
 20. How should I format my code?
 21. Are there any other Core War related resources I should know about?
 22. What does (expression or term of your choice) mean?
 23. Other questions?

  ------------------------------------------------------------------------

1. 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, 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.

[ToC]
  ------------------------------------------------------------------------

2. Is it "Core War" or "Core Wars"?

Both terms are used. Early references were to Core War. Later references
seem to use Core Wars. I prefer "Core War" to refer to the game in general,
"core wars" to refer to more than one specific battle.

[ToC]
  ------------------------------------------------------------------------

3. 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 0-7167-1939-8        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 0-7167-2144-9        .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
http://www.csd.uwo.ca/faculty/akd/.

[ToC]
  ------------------------------------------------------------------------

4. 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
ftp://www.koth.org/corewar/documents/standards/redcode-icws-88.Z. This
document is formatted awkwardly and contains ambiguous statements. For a
more approachable intro to Redcode, take a look at Mark Durham's tutorials,
ftp://www.koth.org/corewar/documents/tutorial.1.Z and
ftp://www.koth.org/corewar/documents/tutorial.2.Z.

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 http://www.koth.org/papers.html.

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

[ToC]
  ------------------------------------------------------------------------

5. 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 ftp://www.koth.org/corewar/documents/icws94.0202.Z for more
information. There is a HTML version of this document available at
http://www.koth.org/info/icws94.html. 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 ftp://www.koth.org/corewar. Note that Redcoder only
supports a subset of ICWS'94.

[ToC]
  ------------------------------------------------------------------------

6. What is the ICWS?

About one year after Core War first appeared in Scientific American, the
"International Core War 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.

[ToC]
  ------------------------------------------------------------------------

7. What is Core Warrior?

Following in the tradition of the Core War News Letter, Push Off, and The 94
Warrior, Core Warrior is a newsletter about strategies and current standings
in Core War. Started in October 1995, back issues of Core Warrior (and the
other newsletters) are available at http://para.inria.fr/~doligez/corewar/.
There is also a Core Warrior index page at
http://www.kendalls.demon.co.uk/pak21/corewar/warrior.html which has a
summary of the contents of each issue of Core Warrior. Many of the earlier
issues contain useful information for beginners.

[ToC]
  ------------------------------------------------------------------------

8. 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 ftp://ftp.csua.berkeley.edu/pub/corewar.
Also, most of past rec.games.corewar postings (including Redcode source
listings) are archived there. Jon Blow (blojo@csua.berkeley.edu) 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:

   * http://www.koth.org/corewar/
   * ftp://www.koth.org/corewar/
   * ftp://ftp.inria.fr/INRIA/Projects/para/doligez/cw/mirror

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

[ToC]
  ------------------------------------------------------------------------

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

Core War systems are available via anonymous FTP from www.koth.org in the
corewar/systems directory. Currently, there are UNIX, IBM PC-compatible,
Macintosh, and Amiga Core War systems available there. It is a good idea to
check ftp://www.koth.org/corewar/incoming for program updates first.

CAUTION! There are many, many Core War systems available which are NOT
ICWS'88 (or even ICWS'86) compatible available at various archive sites
other than www.koth.org. Generally, the older the program - the less likely
it will be ICWS compatible.

If you are looking for an ICWS'94 simulator, get pMARS, which is available
for many platforms and can be downloaded from:

   * ftp://ftp.csua.berkeley.edu/pub/corewar (original site)
   * ftp://www.koth.org/corewar (koth.org mirror)
   * ftp://ftp.inria.fr/INRIA/Projects/para/doligez/cw/mirror (Planar
     mirror)
   * http://www.nc5.infi.net/~wtnewton/corewar/ (Terry Newton)
   * ftp://members.aol.com/ofechner/corewar (Fechter)

Notes:

   * If you have trouble running pMARS with a graphical display under Win95
     then check out http://www.koth.org/pmars.html which should have a
     pointer to the latest compilation of pMARS for this environment.
   * RPMs for the Alpha, PowerPC, Sparc and i386 can be found at
     ftp://ftp.inria.fr/INRIA/Projects/para/doligez/cw/pmars-rpm/

Reviews of Core War systems would be greatly appreciated in the newsgroup
and in the newsletter.

Below is a not necessarily complete or up-to-date list of what's available
at www.koth.org:
MADgic41.lzh            corewar for the Amiga, v4.1
MAD4041.lzh             older version?
MAD50B.lha              corewar for the Amiga, beta version 5.0

Redcoder-21.hqx         corewar for the Mac, supports ICWS'88 and '94
                        (without extensions)
core-11.hqx             corewar for the Mac
core-wars-simulator.hqx same as core-11.hqx?

corewar_unix_x11.tar.Z  corewar for UNIX/X-windows, ICWS'86 but not ICWS'88
                        compatible

koth31.tar.Z            corewar for UNIX/X-windows. This program ran the
                        former KotH server at intel.com
koth.shar.Z             older version
kothpc.zip              port of older version of KotH to the PC

deluxe20c.tar.Z         corewar for UNIX (broken X-windows or curses) and
                        PC
mars.tar.Z              corewar for UNIX, likely not ICWS'88 compatible
icons.zip               corewar icons for MS-Windows
macrored.zip            a redcode macro-preprocessor (PC)
c88v49.zip              PC corewar, textmode display
mars88.zip              PC corewar, graphics mode display
corwp302.zip            PC corewar, textmode display, slowish
mercury2.zip            PC corewar written in assembly, fast!
mtourn11.zip            tournament scheduler for mercury (req. 4DOS)

pmars08s.zip            portable system, ICWS'88 and '94, runs on UNIX, PC,
                        Mac, Amiga. C source archive
pmars08s.tar.Z          same as above
pmars08.zip             PC executables with graphics display, req 386+

macpmars02.sit.hqx      pMARS executable for Mac (port of version 0.2)
                        buggy, no display
MacpMARS1.99a.cpt.hqx   port of v0.8 for the Mac, with display and debugger
MacpMARS1.0s.cpt.hqx    C source (MPW, ThinkC) for Mac frontend

pvms08.zip              pMARS v0.8 for VMS build files/help (req.
                        pmars08s.zip)
ApMARS03.lha            pMARS executable for Amiga (port of version 0.3.1)
wincor11.zip            MS-Windows system, shareware ($15)

[ToC]
  ------------------------------------------------------------------------

10. Where can I find warrior code?

To learn the game, it is a good idea to study previously posted warrior
code. The FTP archives have code in the ftp://www.koth.org/corewar/redcode
directory. A clearly organized on-line warrior collection is available at
the Core War web sites (see below).

[ToC]
  ------------------------------------------------------------------------

11. I do not have FTP. How do I get all this great stuff?

There is an FTP email server at bitftp@pucc.princeton.edu. This address may
no longer exist. I haven't tested it yet. Send email with a subject and body
text of "help" (without the quotes) for more information on its usage. Note
that many FTP email gateways are shutting down due to abuse. To get a
current list of FTP email servers, look at the Accessing the Internet by
E-mail FAQ posted to news.answers. If you don't have access to Usenet, you
can retrieve this FAQ one of the following ways:

   * Send mail to mail-server@rtfm.mit.edu with the body containing "send
     usenet/news.answers/internet-services/access-via-email".
   * Send mail to mailbase@mailbase.ac.uk with the body containing "send
     lis-iis e-access-inet.txt".

[ToC]
  ------------------------------------------------------------------------

12. I do not have access to Usenet. How do I post and receive news?

To receive rec.games.corewar 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

to listproc@koth.org. You can send mail to corewar-l@koth.org to post even
if you are not a member of the list. Responsible for the listserver is Scott
J. Ellentuch (ttsg@ttsg.com).

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.

[ToC]
  ------------------------------------------------------------------------

13. 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 http://www.koth.org; pizza's is
http://www.ecst.csuchico.edu/~pizza/koth . 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: http://para.inria.fr/~doligez/corewar/. Convenient for U.S. users,
this site is also mirrored at koth.org.

[ToC]
  ------------------------------------------------------------------------

14. 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: koth@koth.org is maintained by Scott J. Ellentuch
(tuc@ttsg.com) and pizza@ecst.csuchico.edu by Thomas H. Davies
(sd@ecst.csuchico.edu). 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 koth@koth.org or pizza@ecst.csuchico.edu. "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
     patient.

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

;redcode
;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
 Pizza's
 Experimental                                                               Extended
 (Small) Hill         25   800        800     8000     20        20     200 ICWS '94
 (Accessed with                                                             Draft
 ";redcode-x")
 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
 ";redcode")
 Stormking's ICWS
 '94 No Pspace Hill
 (Accessed with       20  8000       8000    80000    100       100     250 ICWS '94
 ";redcode-94nop")
 Stormking's ICWS
 '94 Experimental                                                           Extended
 (Big) Hill           20 55440      55440   500000    200       200     250 ICWS '94
 (Accessed with                                                             Draft
 ";redcode-94x")
 Stormking's ICWS
 '94 Multi-Warrior                                                          Extended
 Hill (Accessed       10  8000       8000    80000    100       100     200 ICWS '94
 with                                                                       Draft
 ";redcode-94m")

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 www.koth.org.

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

[ToC]
  ------------------------------------------------------------------------

15. 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.

[ToC]
  ------------------------------------------------------------------------

16. 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.

[ToC]
  ------------------------------------------------------------------------

17. 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.

[ToC]
  ------------------------------------------------------------------------

18. 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.

[ToC]
  ------------------------------------------------------------------------

19. 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.

[ToC]
  ------------------------------------------------------------------------

20. 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
     comments
   * do not use $ (direct addressing mode) or : (suffix of some labels)

[ToC]
  ------------------------------------------------------------------------

21. 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
     corewar-ga-request@sunsite.auc.dk. The FTP site for this list is at
     ftp://sunsite.auc.dk/pub/local/corewar/. The administrator is Martin
     Pedersen (martin.pedersen@person.dk).
   * Jason's Core War project page
     (http://www.avalon.net/~jboer/projects/corewar/corewar.html) 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 http://www.koth.org/evolving_warriors.html.
   * The most recent paper on Core War evolution is by Ryan Coleman and can
     be found at
     http://www.geocities.com/CapeCanaveral/Launchpad/6898/paper.html.

[ToC]
  ------------------------------------------------------------------------

22. 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

Bootstrapping
     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.

B-Scanners
     Scanners which only recognize non-zero B-fields.

         example   add #10, scan
         scan      jmz example, 10

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

CMP-Scanner
     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

Colour
     Property of bombs making them visible to scanners, causing them to
     attack useless locations, thus slowing them down.

         example   dat #100

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

Decoys
     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

Dwarf
     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.

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

Imp
     Program which only uses the MOV instruction.

         example   mov 0, 1

     or

         example   mov 0, 2
                   mov 0, 2

Imp-Gate
     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

Imp-Ring
     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

Imp-Spiral
     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.

         example   spl 0, 8
                   mov -1, <-1

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

Mirror
     see reflection.

On-axis/off-axis
     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
     at www.koth.org.

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

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

Pit-Trapper
     (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.

     Example:

          start
          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
          rof
                 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
          rof
          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
     opcode:

          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
          rof
                 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
          rof
          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

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

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

Self-Splitting
     Strategy of amplifying the number of processes executing a piece of
     code.

         example    spl 0
         loop       add #10, example
                    mov example, @example
                    jmp loop

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

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

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

Silk
     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

Slaver
     see Pit-Trapper.

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

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

Stun
     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
     variations.

Vampire
     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

[ToC]
  ------------------------------------------------------------------------

23. Other questions?

Just ask in the rec.games.corewar newsgroup or contact me. If you are shy,
check out the Core War archives first to see if your question has been
answered before.

[ToC]
  ------------------------------------------------------------------------

Credits

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 (wrote the original version of the FAQ)
   * Paul Kline
   * Randy Graham
   * Stefan Strack (maintained a recent version of the FAQ)

  ------------------------------------------------------------------------

Copyright  1999 Anton Marsden.

Verbatim copying and distribution of this entire article is permitted in any
medium, provided this notice is preserved.
  ------------------------------------------------------------------------

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Last Update March 27 2014 @ 02:11 PM