Core Wars ST
Core Wars ST is an implementation of the program A. K.
Dewdney describes in the "Computer Recreations" column of
Scientific American in the May 1984, March 1985, and January 1987
issues. It includes the protect and split command. It also lets
you run up to 3 programs at once.
In Core Wars, each player writes a program with which they
attempt to destroy the other player's program. Each program is
placed at a random place in a 10,000 location circular area of
memory called core. The programs are written in a simple
language called REDCODE. Each instruction takes one location in
core. In Core wars there are no absolute memory locations;
everything is relative. For example, JMP 4 jumps forward 4
locations, not to location 4. A program dies if it tries to
execute a DAT statement. The REDCODE instructions are:
Instruction Mnemonic Arguments Explanation
Move MOV A B Move contents of address A to
address B.
Add ADD A B Add contents of address A to
address B.
Subtract SUB A B Subtracts contents of address A
from address B.
Jump JMP A Transfer control to address A.
Jump if zero JMZ A B Jump to A if the contents of
address B are 0.
Jump if JMG A B Jump to A if the contents of
greater than address B are greater than 0.
zero
Decrement: DJZ A B Subtract 1 from the contents
jump if zero of address B and jump to A if
B is now zero.
Decrement: DJN A B Subtract 1 from the contents
jump if not of address B and jump to A if
zero B is not zero.
Compare CMP A B Skip the next instruction if
the contents of address A
equal the contents of address
B.
Split SPL A Split execution to the next
instruction and address A.
Protect PCT A Protect address A against the
next MOV instruction
Data DAT B A nonexecutable statement
There are 4 different types of addressing modes:
The direct mode is the default mode, where the argument is taken
as an offset from the current address. For example, JMP -3 will
jump backwards 3 locations.
The indirect mode is denoted by the "@" symbol. The indicated
relative address contains another relative address in the B
argument. The DWARF program is a good example of the indirect
addressing mode.
DAT #-1
start ADD #5 -1
MOV #0 @-2
JMP -2
The DAT statement contains a pointer to where DWARF will
launch bombs. The program starts at the ADD #5 -1 command, which
makes the pointer equal to 4. The MOV #0 @-2 looks back 2
locations to the DAT statement, then moves a DAT #0 statement 4
addresses forward of the DAT statement (one beyond the JMP -2
command). It then jumps back to the ADD, and makes the pointer
9. Then it moves a DAT #0 9 addresses beyond the DAT statement,
etc.
Another indirect mode is denoted by the "<" symbol. This is like
the indirect mode, but it decrements the B argument of the
address pointed to before jumping. A good example of this is in
the MICE program which uses the "<" addressing mode to make
copies of itself.
DAT #0
start MOV #12 -1
MOV @-2 <5
DJN -1 -3
SPL @3
ADD #653 2
JMZ -5 -6
DAT #833
This program uses two pointers. The first, stored at the
beginning of the program keeps track of what statement it is
going to copy. The second, at the end of the program, keeps
track of where it is going to copy the statement. The program
starts off by putting a 12 in the first pointer. Then, it moves
the statement that the first pointer is pointing to (initially
DAT #833) to what is pointed to by the second pointer, but first
it subtracts 1 from the pointer. So, what it does is move the
DAT #833 statement 832 addresses beyond the DAT #833 statement,
and the DAT statement now holds 832. Then, the DJN command
subtracts 1 from the first pointer and if it is not zero(which it
isn't yet), it jumps backwards 1 command. This continues until
the entire program is copied. Once it is copied, it splits to
the new MICE, so it now has 2 running.
The immediate mode is denoted by the "#" sign, and will take the
number as an absolute number. SUB #2 -1 will subract 2 from the
B argument of the statement 1 before it. It cannot be used as an
address. For example, JMP #0 will not work, since you cannot use
absolute memory locations. When the immediate mode is used with
a MOV statement for the A argument(it cannot be used for the B
argument), it will move a DAT statement with that number as the B
argument to the correct address. Since the DAT statement is
unexecutable, this is a good way to kill enemy programs as DWARF
does.
The split command will allow you to run multiple programs at
once, but there is a drawback: you only get to execute one of
your programs for every one program your opponent executes. For
example, if you have 3 programs running (A1, A2, and A3) and your
opponent has programs B1 and B2, the order of execution would be
A1, B1, A2, B2, A3, B1, A1, B2, etc.
The protect command protects an instruction from being
written over. After an attempt has been made to write over a
protected address, it is no longer protected. For some
strategies to use with the protect instruction, see the March
1985 Scientific American. The protect command is not an official
Core War command. It was included because it was suggested in
the article.
The programs must be stored in standard text files. The can
be made with almost any editor, such as Micro Emacs. There can
be any number of spaces between the beginning of the line and the
instruction. There must be 1 and only 1 space between the
mnemonic and the A argument, and between the A argument and the B
argument. If the first line of the program to be executed is not
the first line in the program, the first line to be executed must
begin with "start". Notice: The DAT instruction does not use the
A argument, so you need 2 spaces between the DAT statement and
the argument.
Core Wars ST will let you select up to 3 programs. If you
want to run less than 3 programs, select Cancel on the file
selecter after you have loaded all of the programs you would
like. You are then asked how many turns you would like the
programs to run. You can the programs run up to 999,999 turns.
Next, you are shown the battle screen. On the bottom of the
screen, the number of programs each program is running is
displayed. This number will go up for a program when it splits,
and will go down when a program tries to execute a DAT statement.
If you want to abort early, hit one of the mouse buttons. Each
program has a different color (or pattern in monochrome mode). A
dot of the program's color will be put on the screen at the
address a program executes or moves something to.
The shortest program possible is called IMP:
MOV 0 1
It copies itself forward one location, then advances to the
next location etc. This program cannot win, because any other
program it overwrites will just become an IMP, but it is hard to
kill. An IMP GUN is:
SPL 2
JMP -1
MOV 0 1
This sends out a continuous stream of IMPs, which are very
hard to kill, but they move very slow. Take a look at the
included core wars programs for more examples. Also, if you can,
take a look at the Scientific American articles for more example
programs and strategies.
If you enjoy this program, please send me $5. If you would
like the source code, send me $10, and I'll send you a disk with
the source code. Send it to:
Dan Crevier
2536 Foothill Road
Santa Barbara, CA, 93015
If you have any questions or comments, contact me on GEnie
or on my Bulletin Board -- The Sanctuary (805) 687-1075
300/1200/2400.