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Contents of the CROBOTS.DOC file

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(C) Copyright 1985, All rights reserved.

CROBOTS is copyrighted by:

Tom Poindexter
2903 Winchester Drive
Bloomington, Illinois 61701 USA

CROBOTS (C) Copyright 1985 by Tom Poindexter.

Table of Contents

1. License agreement and disclaimer of warranty...........2
2. Introduction
2-1. Description........................................3
2-2. Intended audience..................................3
2-3. Machine requirements...............................3
2-4. User interface.....................................3
3. Types of play
Single Play........................................4
Match Play.........................................4
4. Running CROBOTS
4-1. Command line options...............................4
4-2. Examples...........................................5
5. Game Parameters
5-1. Battlefield........................................5
5-2. Robot offense......................................5
5-3. Robot defense......................................6
5-4. Disabling robots...................................6
5-5. Sample display.....................................7
6. CROBOTS CPU............................................8
7. CROBOTS C Compiler
7-1. Description........................................8
7-2. Features missing from standard C...................8
7-3. CROBOTS language...................................9
7-4. Compiler limits...................................11
7-5. Error and warning messages........................11
8. CROBOTS C Intrinsic Function Library
loc_x(), loc_y()..................................14
sin(), cos(), tan(), atan().......................14
9. CROBOTS C Program Structure
9-1. Structure.........................................15
9-2. Sample: "sniper.r"................................15
10. CROBOTS CPU Architecture
10-1. Stack.............................................20
10-2. Link list.........................................21
10-3. Instruction set...................................22
10-4. Machine level debugging...........................23
11. Implementation Notes..................................24
12. Order Form............................................25

Page 1

CROBOTS (C) Copyright 1985 by Tom Poindexter.

1. License agreement:

You may make copies of this program, manual, and other files and
give it to your friends, upload it to bulletin boards, or include
it in the library of a non-profit computer club.

I expressly forbid any for-profit venture from selling this
software and manual, either separately or as part of a "library"

If you find this software has any value for you, please send a
contribution. For contributions of $20 or more, you will receive
the full source code to CROBOTS on diskette. Use the order form
at the end of the documentation. Your contribution will
encourage me to enhance the program, by expanding the CROBOTS C
compiler, adding graphics, sound, etc.

Whether or not you contribute, please share this software with



Page 2

CROBOTS (C) Copyright 1985 by Tom Poindexter.

2. Introduction

2-1. Description

CROBOTS ("see-robots") is a game based on computer programming.
Unlike arcade type games which require human inputs controlling
some object, all strategy in CROBOTS must be complete before the
actual game begins. Game strategy is condensed into a C language
program that you design and write. Your program controls a robot
whose mission is to seek out, track, and destroy other robots,
each running different programs. Each robot is equally equipped,
and up to four robots may compete at once. CROBOTS is best
played among several people, each refining their own robot
program, then matching program against program.

CROBOTS consists of a C compiler, a virtual computer, and
battlefield display (text graphics only, monochrome or color).
The CROBOTS compiler accecpts a limited (but useful) subset of
the C language. The C robot programs are aided by hardware
functions to scan for opponents, start and stop drive mechanisms,
fire cannons, etc. After the programs are compiled and loaded
into separate robots, the battle is observed. Robots moving,
missiles flying and exploding, and certain status information are
displayed on the screen, in real-time.

2-2. Intended audience

CROBOTS will most likely appeal to programmers (especially those
who think they can write the "best" programs), computer game
enthusiasts, people wishing to learn the C language, and those
who are interested in compiler design and virtual computer

2-3. Machine and software requirements

- IBM-PC, or other close MS-DOS computers that use INT 10H video
- 192k ram
- DOS 2.0 or higher
- One disk drive
- Monochrome or Color/Graphics display
- Text editor (PC-DOS Edlin, or your own favorite)

2-4. User interface

CROBOTS does not use menus, windows, pop-ups, or any other
user-friendly interface. Since the emphasis is on designing and
writing robot control programs, CROBOTS is started as a compiler
might be started, from the DOS command line.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

3. Types of play

CROBOTS can either run one match (single play), in which the full
screen, realtime battlefield display is used, or several matches
(match play), in which only the name of the winner is
printed after each match. Single play is the default. Match
play is intended to see how robot programs perform on the
average. Match play can consume several hours of computer
time depending on the number of matches and cpu cycle limit, and
can be run overnight.

4. Running CROBOTS

4-1. Command line options

CROBOTS is started from the DOS prompt:

A>crobots [options] robot-program-1 [robot-program-n] [>file]

Valid options and parameters are:

-c (opt) Compile only, and produce virtual machine
assembler code and symbol tables.

-d (opt) Compile one program, and invoke machine level
single step tracing.

-mxxx (opt) Run a series of matches, were "xxx" is the number
of matches. There should be no spaces between
"-m" and the number. If "-m" is not specified,
then the default is to run one match and display
the realtime battlefield.

-lxxx (opt) Limit the number of machine cpu cycles per match
when "-m" is specified. There should be no
spaces between "-l" and the number. The default
cycle limit is 500,000 when -m is specified

robot-programs (required)
The file name of the CROBOTS source program(s).
Up to four files may be specified. If
only one file is specified, it will be "cloned"
into another, so that two robots (running the
same program) will compete.
Any file name may be used, but for consistency
use '.r' as an extension.

>file (opt) Use DOS 2.0+ redirection to get a compile
listing ("-c" option) or to record matches ("-m"

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

4-2. Examples:

1) Watch three robots compete with full display:
A>crobots robot1.r robot2.r robot3.r

2) Compile one robot, and save the listing:
A>crobots -c robot1.r >robot1.lst

3) Debug a robot (first get an assembler code listing,
as in example 2:
A>crobots -d robot1.r

4) Run 50 matches, limiting total cpu cycles to 200,000,
and save results:
A>crobots -m50 -l200000 robot1.r robot2.r >save

5. Game parameters

5-1. Battlefield

The battlefield is a 1,000 by 1,000 meter square. A wall
surrounds the perimeter, so that a robot running into the wall
will incur damage.

The lower left corner has the coordinates x = 0, y = 0; the upper
right corner has the coordinated x = 999, y = 999.

The compass system is oriented so that due east (right) is 0
degrees, 90 is north, 180 is west, 270 is south. One degree
below due east is 359.

135 90 45
\ | /
\ | /
180 --- x --- 0
/ | \
/ | \
225 270 315

5-2. Robot offense

The main offensive weapons are the cannon and scanner. The
cannon has a range of 700 meters. There are an unlimited number
of missiles that can be fired, but a reloading factor limits the
number of missiles in the air at any one time to two. The cannon
is mounted on an independent turret, and therefore can fire any
direction, 0-359, regardless of robot heading.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

The scanner is an optical device that can instantly scan any
chosen heading, 0-359. The scanner has a maximum resolution of
+/- 10 degrees. This enables the robot to quickly scan the field
at a low resolution, then use maximum resolution to pinpoint an

5-3. Robot defense

The only defense available are the motor drive and status
registers. The motor can be engaged on any heading, 0-359, in
speeds from 0-100 percent of power. There are acceleration and
deacceleration factors. A speed of 0 stops the motor. Turns can
be negotiated at speeds of 50% and less, in any direction. Of
course, the motor drive can be engaged any time, and is necessary
on offense when a target is beyond the 700 meter range of the

Certain status registers provide feedback to the robot. The
primary registers indicate the percent of damage, and current x
and y locations on the battlefield. Another register provides
current drive speed.

5-4. Disabling opponents

A robot is considered dead when the damage reaches 100%. Percent
of damage is inflicted as follows:

2% - collision into another robot (both robots in a
collision receive damage) or into a wall. A
collision also causes the motor drive to disengage,
and speed is reduced to 0.

3% - a missile exploding within a 40 meter radius.

5% - a missile exploding within a 20 meter radius.

10% - a missile exploding within a 5 meter radius.

Damage is cumulative, and cannot be repaired. However, a robot
does not loose any mobility, fire potential, etc. at high damage
levels. In other words, a robot at 99% damage performs equally
as a robot with no damage.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

5-5. Sample display

(x=999,y=999) blocks)

+------------------------------------+ 1 fubar.r
| | D% 015 Sc 218
| \|/ 1 | Sp 000 Hd 090
| (missile exploding) -#- | ------------------
| /|\ | 2 snafu.r
(y | | D% 050 Sc 275
| + (missiles | Sp 100 Hd 180
a | + flying) | ------------------
x | 2 | 3 bimbo.r
i | | D% 000 Sc 045
s) | 3 | Sp 000 Hd 000
| / | ------------------
| (robots) ----\ | 4 kumquat.r
| 4 | D% 100 Sc 050
| | Sp 000 Hd 335
| |
| |
+------------------------------------+ CPU Cycle: 4500

(x=0,y=0) (x axis)

Each status block shows the file name of the robot, the damage
incurred, the current scan degrees, and the speed and heading.
Robots are represented on the field by '1', '2', etc., according
to the status block position. The number of elapsed robot cpu
cycles is shown at the bottom of the status blocks.

The CROBOTS program can be stopped at any time, by using

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CROBOTS (C) Copyright 1985 by Tom Poindexter.


The robot cpu is a simple stack-oriented computer. It operates
at very slow speeds (on a 4.77MHz 8088 PC with two robots
running, the average speed is 270 instructions per second, .00027
mips!!). The word size is 32 bits, allowing integer values from
-2,147,483,648 to 2,147,483,647. There are internal pointer
registers that manage stack usage, but are not accessable from a
robot program. The same is true for an implicit accumulator.

The maximum code space is 1,000 instructions. All instructions
are equal in length. The maximum stack size is 500 words, which
is used for data and function call/returns. The stack grows
upward for data usage, and downward (from the end) for function
call/returns. Three words are used for each function call, and
are release upon the function return. The data portion and
call/return portion are managed by separate internal stack

If the data stack pointer and call/return stack pointer collide,
a stack overflow occurs. In this case, the robot is restarted
at the 'main' function, with the stack reset to all zeroes.

For more information, see the section on machine instructions and

7. CROBOTS C compiler

7-1. Description

The CROBOTS compiler accepts a limited subset of the C language.
There is no provision for separate compilation, i.e., all modules
of a program must be in one file. No preprocessor is provided
for "#define", "#include", etc. Identifiers are significant to 7
characters, although any length may be used. The compiled
machine code is loaded into the robot cpu, and cannot be saved.

7-2. Features missing from standard C

Major language features missing from K&R are: floating point
variables, structures, unions, pointers, initializers, arrays,
character data, typedefs, for statment, do..while statement, statement, break, continue, gotos and labels,
ternary and comma operators, octal and hexadecimal constants, no
parameters to main(), and all preprocessor directives.
My apologies to "The C Programming Language" by Brian W.
Kernighan and Dennis M. Ritchie, Prenctice-Hall, 1978.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

7-3. CROBOTS language

The language features that are present are entirely suitable for
writing robot control programs. Basic programming constructs of
if..then..else, while, and function calls can be used freely.
Full expression evaluation is also provided, so that statements
such as:
if ((x = func1(y,1,++z,func2(c))) > 0)
a = 0;
a = x;
are perfectly legal. Ifs and whiles may be nested, and recursion
is supported. Variables declared outside a function definition
are global in scope, whereas variables declared inside a function
definition are local to that function.

The following keywords are recognized:

"/* ... */" comments cannot be nested

any decimal digits, optionally preceeded with a '-'

"int" variable declare
"long" same as int
"auto" default storage scope, optional
"register" legal, but ignored, same as auto
"function (parms,.....)" function definition

logic control:
"if (expr) STMT else STMT"

"while (expr) STMT"

function return:
"return" return
"return expr" return a with value

assignment operators:
"=" assignment
">>=" assignment shift right
"<<=" assignment shift left
"+=" assignment addition
"-=" assignment subtraction
"*=" assignment multiplication
"/=" assignment division
"%=" assignment modulo
"&=" assignment and
"^=" assignment exclusive or
"|=" assignment inclusive or

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

bit-wise operators:
">>" shift right
"<<" shift left
"&" and
"!" unary not
"~" unary one's complement
"^" exclusive or
"|" inclusive or

increment/decrement operators:
"++" prefix increment, see derivations
"--" prefix decrement, see derivations

logical operators:
"&&" logical and
"||" logical or
"<=" logical less than or equal
">=" logical greater than or equal
"==" logical equal
"!=" logical not equal
"<" logical less than
">" logical greater than

arithmetic operators:
"-" subtraction or unary negation
"+" addition
"*" multiplication
"/" division
"%" modulo

";" statement terminator or null statement
"{ }" compound statement
"," parameter separator in function definition or call
"( )" expression or function definition or call

Precedence and order of evaluation are the same as in K&R.

Operator Associativity
() left to right
! ~ ++ -- - right to left
* / % left to right
+ - " " "
<< >> " " "
< <= => > " " "
== != " " "
& " " "
^ " " "
| " " "
&& " " "
|| " " "
= -= += etc. right to left

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

Major derivations from K&R:

-Local variables need not be declared before reference, i.e., any
undeclared variable will default to a local variable.

-Postfix increment and decrement ("var++" or "var--") are
recognized, but the result is the same as prefix
increment/decrement ("++var").

-Intrinsic function names are reserved.

7-4. Compiler limits

defined functions: 64
local variables per function: 64
external variables: 64
if nest level: 16
while nest level: 16

7-5. Complier error and warning messages:

The compiler has no error recovery and will stop on the first
error found. Sorry. Warning messages do not stop the compiler.

Error messages

"syntax error" - Any input that results in improper C syntax will
yield "syntax error", with an indicator pointing to the
unrecognizable input.

"instruction space exceeded" - compiler tried to generate more
than 1000 machine instructions.

"symbol pool exceeded" - the maximum local variable, external
variable, or function definition symbol table was exceeded.

"function referenced but not found" - a function was referenced
that was not defined in the input file or is not an intrinsic

"main not defined" - the input file did not define a 'main()'

"function definition same as intrinsic" - a function was defined
with the same name as an intrinsic function, which are reserved.

"if nest level exceeded" - more than 16 'if's were nested.

"while nest level exceeded" - more than 16 'while's were nested.

"yacc stack overflow" - the compiler's parser overflowed,
probably due to complex expressions and/or extreme nesting.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

Warning messages

These messages will not cause the compiler to fail, but may cause
the program to executed unexpectedly.

"unsupported initializer" - variable declares cannot include an
initializer. For future releases.

"unsupported break" - the 'break' statement was found and
ignored. For future releases.

"n postfix operators" - postfix increment or decrement
operators were used, and are coerced into prefix expressions.

"n undeclared variables" - one or more variables were implicitly

"code utilization: n%" - reports the capacity of machine
instructions generated.

8. CROBOTS C Intrinsic Function Library

The intrinsic function library provides machine level control and
certain arithmetic functions. These functions do not consume
any of the program code space or data stack, except for the three
words for call/return sequences. No explicit linking is required
to use any intrinsic function.

scan (degree,resolution)

The scan() function invokes the robot's scanner, at a specified
degree and resolution. scan() returns 0 if no robots are
within the scan range or a positive integer representing the
range to the closest robot. Degree should be within the range
0-359, otherwise degree is forced into 0-359 by a modulo 360
operation, and made positive if necessary. Resolution controls
the scanner's sensing resolution, up to +/- 10 degrees.
range = scan(45,0); /* scan 45, with no variance */
range = scan(365,10); /* scans the range from 355 to 15 */

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

cannon (degree,range)

The cannon() function fires a missile heading a specified range
and direction. cannon() returns 1 (true) if a missile was fired,
or 0 (false) if the cannon is reloading. Degree is forced into
the range 0-359 as in scan(). Range can be 0-700, with greater
ranges truncated to 700.
degree = 45; /* set a direction to test */
if ((range=scan(degree,2)) > 0) /* see if a target is there */
cannon(degree,range); /* fire a missile */

drive (degree,speed)

The drive() function activates the robot's drive mechanism, on a
specified heading and speed. Degree is forced into the range
0-359 as in scan(). Speed is expressed as a percent, with 100 as
maximum. A speed of 0 disengages the drive. Changes in
direction can be negotiated at speeds of less than 50 percent.
drive(0,100); /* head due east, at maximum speed */
drive(90,0); /* stop motion */


The damage() function returns the current amount of damage
incurred. damage() takes no arguments, and returns the percent
of damage, 0-99. (100 percent damage means the robot is
completely disabled, thus no longer running!)
d = damage(); /* save current state */
; ; ; /* other instructions */
if (d != damage()) /* compare current state to prior state */
drive(90,100); /* robot has been hit, start moving */
d = damage(); /* get current damage again */

speed ()

The speed() function returns the current speed of the robot.
speed() takes no arguments, and returns the percent of speed,
0-100. Note that speed() may not always be the same as the last
drive(), because of acceleration and deacceleration.
drive(270,100); /* start drive, due south */
; ; ; /* other instructions */
if (speed() == 0) /* check current speed */
drive(90,20); /* ran into the south wall, or another robot*/

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

loc_x ()
loc_y ()

The loc_x() function returns the robot's current x axis location.
loc_x() takes no arguments, and returns 0-999.
The loc_y() function is similar to loc_x(), but returns the
current y axis position.
drive (180,50); /* start heading for west wall */
while (loc_x() > 20)
; /* do nothing until we are close */
drive (180,0); /* stop drive */

rand (limit)

The rand() function returns a random number between 0 and limit,
up to 32767.
degree = rand(360); /* pick a random starting point */
range = scan(degree,0); /* and scan */

sqrt (number)

The sqrt() returns the square root of a number. Number is made
positive, if necessary.
x = x1 - x2; /* compute the classical distance formula */
y = y1 - y2; /* between two points (x1,y1) (x2,y2) */
distance = sqrt((x*x) - (y*y));

sin (degree)
cos (degree)
tan (degree)
atan (ratio)

These functions provide trigometric values. sin(), cos(),
and tan(), take a degree argument, 0-359, and returns the
trigometric value times 100,000. The scaling is necessary since
the CROBOT cpu is an integer only machine, and trig values are
between 0.0 and 1.0. atan() takes a ratio argument that has been
scaled up by 100,000, and returns a degree value, between -90 and
+90. The resulting calculation should not be scaled to the
actual value until the final operation, as not to lose accuracy.
See programming examples for usage.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

9. CROBOTS C Program Structure

9-1. Basic program structure

CROBOTS programs are not unlike other C programs. The minimum
CROBOTS program consist of a function named "main".
Additionally, other functions can be defined, along with external

9.2 "sniper.r"

The following CROBOTS program is provided as an example.

/* sniper */
/* strategy: since a scan of the entire battlefield can be done in 90 */
/* degrees from a corner, sniper can scan the field quickly. */

/* external variables, that can be used by any function */
int corner; /* current corner 0, 1, 2, or 2 */
int c1x, c1y; /* corner 1 x and y */
int c2x, c2y; /* " 2 " " " */
int c3x, c3y; /* " 3 " " " */
int c4x, c4y; /* " 4 " " " */
int s1, s2, s3, s4; /* starting scan position for corner 1 - 4 */
int sc; /* current scan start */
int d; /* last damage check */

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

/* main */
int closest; /* check for targets in range */
int range; /* range to target */
int dir; /* scan direction */

/* initialize the corner info */
/* x and y location of a corner, and starting scan degree */
c1x = 10; c1y = 10; s1 = 0;
c2x = 10; c2y = 990; s2 = 270;
c3x = 990; c3y = 990; s3 = 180;
c4x = 990; c4y = 10; s4 = 90;
closest = 9999;
new_corner(); /* start at a random corner */
d = damage(); /* get current damage */
dir = sc; /* starting scan direction */

while (1) { /* loop is executed forever */

while (dir < sc + 90) { /* scan through 90 degree range */
range = scan(dir,1); /* look at a direction */
if (range <= 700 && range > 0) {
while (range > 0) { /* keep firing while in range */
closest = range; /* set closest flag */
cannon(dir,range); /* fire! */
range = scan(dir,1); /* check target again */
if (d + 15 > damage()) /* sustained several hits, */
range = 0; /* goto new corner */
dir -= 10; /* back up scan, in case */

dir += 2; /* increment scan */
if (d != damage()) { /* check for damage incurred */
new_corner(); /* we're hit, move now */
d = damage();
dir = sc;

if (closest == 9999) { /* check for any targets in range */
new_corner(); /* nothing, move to new corner */
d = damage();
dir = sc;
} else /* targets in range, resume */
dir = sc;
closest = 9999;

} /* end of main */

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

/* new corner function to move to a different corner */
new_corner() {
int x, y;
int angle;
int new;

new = rand(4); /* pick a random corner */
if (new == corner) /* but make it different than the */
corner = (new + 1) % 4;/* current corner */
corner = new;
if (corner == 0) { /* set new x,y and scan start */
x = c1x;
y = c1y;
sc = s1;
if (corner == 1) {
x = c2x;
y = c2y;
sc = s2;
if (corner == 2) {
x = c3x;
y = c3y;
sc = s3;
if (corner == 3) {
x = c4x;
y = c4y;
sc = s4;

/* find the heading we need to get to the desired corner */
angle = plot_course(x,y);

/* start drive train, full speed */

/* keep traveling until we are within 100 meters */
/* speed is checked in case we run into wall, other robot */
/* not terribly great, since were are doing nothing while moving */

while (distance(loc_x(),loc_y(),x,y) > 100 && speed() > 0)

/* cut speed, and creep the rest of the way */

while (distance(loc_x(),loc_y(),x,y) > 10 && speed() > 0)

/* stop drive, should coast in the rest of the way */
} /* end of new_corner */

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

/* classical pythagorean distance formula */
int x1;
int y1;
int x2;
int y2;
int x, y;

x = x1 - x2;
y = y1 - y2;
d = sqrt((x*x) + (y*y));

/* plot course function, return degree heading to */
/* reach destination x, y; uses atan() trig function */
int xx, yy;
int d;
int x,y;
int scale;
int curx, cury;

scale = 100000; /* scale for trig functions */
curx = loc_x(); /* get current location */
cury = loc_y();
x = curx - xx;
y = cury - yy;

/* atan only returns -90 to +90, so figure out how to use */
/* the atan() value */

if (x == 0) { /* x is zero, we either move due north or south */
if (yy > cury)
d = 90; /* north */
d = 270; /* south */
} else {
if (yy < cury) {
if (xx > curx)
d = 360 + atan((scale * y) / x); /* south-east, quadrant 4 */
d = 180 + atan((scale * y) / x); /* south-west, quadrant 3 */
} else {
if (xx > curx)
d = atan((scale * y) / x); /* north-east, quadrant 1 */
d = 180 + atan((scale * y) / x); /* north-west, quadrant 2 */
return (d);

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

Notes: The distance() and plot_course() routines are
quite handy. Save them for your programs. Also, note that the
main scan routine will "back up" a few degrees after a target has
been found and fired upon. This should catch robots trying to
flee away from the direction you are scanning. If the target
moves the other way, the normal scan increment will find it.

See the other sample CROBOTS program files.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

10. CROBOTS CPU Architecture and Theory

This information is provided if you need to use the debug
facility, or are curious about the virtual machine interpreter.
Don't bother reading this section if you not so inclined; it is
not needed for normal play.

10-1. Stack usage:

That stack is controlled implicitly by several pointers. Stack
pointers are not accessable through machine instructions. Most
instructions will either push data onto the stack, or pop data
off the stack. The stack is used from the bottom up (low memory)
for data and temporary storage, and is used from the top down
(high memory) for saving stack pointers and the program counter
on function call/return.

External (global) variables are allocated at the very bottom of
the stack, and the local mark pointer for 'main' starts just
after the externals. External variables are addressed from the
beginning of the stack, by offset.

When a function is called (including 'main'), the stack pointer
is marked (local mark) and is increased by the number of local
variables needed for that function. Local variables are
addressed relative to the local mark, by offsets. All
calculations, function calls, and constants are pushed on and
popped off the stack as needed (temporary mark or top of stack).

A function call also saves its current stack pointers (local
variable mark and frame mark) and program counter. This
return information grows from the top down.

Arguments are passed to functions by value. The first argument
in a function call becomes the first local variable for the
called function. Consider the following:

main() { /* main has three local variables: */
int a, b, c;
sub1 (a,b/2,c+1); /* call sub1, and pass arguments */

sub1 (x,y,z) /* sub1 takes three parameters and */
int x, y, z; { /* has one local variable */
int result;
result = x + y + z;
return (result);

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

The main() function allocates three local variables on the stack,
sets its local mark at 'a', and sets the temporary stack pointer
beyond the locals. Just before sub1() is called, the value of
'a' is pushed, followed by the result of 'b/2', and 'c+1'. When
sub1() is called, it sets its local mark where the value of 'a'
is, so that 'a' is know as 'x' in func1(), likewise 'b/2'
is known as 'y' and 'c+1' is known as 'z'. Sub1() also
allocates one more word for 'result', and sets the temporary mark
after the storage for 'result'.

The following diagram illustrates the stack usage:

+------------+ <-- end of stack, high memory
|main return | <-- return info for main
+------------+ (frame,ip,local mark)
|sub1 return | <-- return info for sub1
+------------+ (etc.)
| | |
| v | <-- additional function call return
| | info grow downwards
| |
| |
| |
| ^ | <-- additional function calls and
| | | expressions grow upwards
|expressions |
+------------+ <-- temporary mark (top of stack)
|sub1 locals |
+------------+ <-- local mark: sub1 function
|main locals |
+------------+ <-- local mark: main function
| |
| Externals |
| |
+------------+ <-- beginning of stack

10-2. Link list

The link list is a list built by the compiler that contains
the names and link information of the functions within the
program. The link information contains the starting location of
the function within the code, the number of parameters, and the
number of other local variables within the function. The link
list cannot be accessed by the user program.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

10-3. Instruction set

The CROBOTS cpu has 10 instructions. Each instruction occupies
the same amount of storage, with or without operands.

FETCH offset (external | local) - Fetch will retrieve a word from
either the external variable pool or the local variable pool and
push it onto the stack. The offset has its high-bit set (or'ed
with 0x8000) if it is an external (offset from the beginning of
the stack), otherwise it is a local (offset from the local
variable mark). See STORE.

STORE offset (external | local), opcode - Store pops the top two
items, applies the arithmetic opcode to the two operands,
pushes the result on the top of the stack and stores it in the
variable referenced by the offset. Offsets are either external
or local, according to the method described in Fetch. The result
of the opcode is left on the stack. See FETCH and BINOP.

CONST k - Const will push a constant onto the stack.

BINOP opcode - Binop will pop the top two items as top of stack =
y, next to top of stack as x, apply the arithmetic opcode as
(x opcode y), and push the result on the stack. Opcodes are
decimal representations of 'C' operators such as '+', '/',
'>=', etc. See STORE.

FCALL link-offset - Fcall performs a high level function call
facility. The link-offset operand specifies an entry in the link
list table. Fcall pushes its return information: the next
instruction counter and the current local variable mark. A new
local variable mark and temporary mark (top of stack pointer) is
set. The cpu then branches to the first instruction of the
function. See RETSUB and FRAME.

RETSUB - Retsub returns from a function, leaving the return value
on the top of the stack. Retsub restores the previous local
variable pool, the next instruction counter, and re-adjusts the
stack frame to the point just before the call. The C
compiler generates code to return a dummy value if the
function does not explicitly return one. See FCALL and FRAME.

BRANCH instruction - Branch pops the top of the stack and
branches to the instruction if the value is zero. The next
sequential instruction is executed if the value is
anything other than zero.

CHOP - Chop discards the top of the stack by popping it into

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

FRAME - Frame facilitates fcall/retsub by saving the current top
of stack pointer (temporary mark) in anticipation of a fcall
statement. The top of stack pointer is saved in the call/return
stack as a frame marker. See FCALL and RETSUB.

NOP - No operation. Is used as a mark indicating the end of

10-4. Machine level debugging

Debug mode is used to trace by single stepping machine
instructions. Use this only if you need to see your program
execute, or are just curious.

First, get a listing on paper of a compile with full information
by using the '-c' option:
A>crobots -c yourpgm.r >prn:

Next, start CROBOTS again with the '-d' flag:
A>crobots -d yourprm.r

Your robot will be placed randomly in the field, and a target
robot will be placed at the center of the field (x=500,y=500)
so your robot program can find and shoot at a target.

The virtual machine interpreter will single step through your
program (machine instructions, that is). At every instruction,
an machine instruction is disassembled, and the top of stack
pointer and value are printed. The top of stack and value are
after the results of the instruction. Other information may
also be printed, such as function calls searching the link list,

On every step, you are prompted "d,h,q,:". Entering 'd' will
dump external and local variable pools, as well as vital
information of your robot: coordinates, heading, speed, damage,
etc., and the status of any missiles your robot may have fired.
Entering 'h' will simulate your robot taking a 10% damage hit, so
you can check damage detection, etc. Entering 'q' will quit the
program immediately, and return you to DOS. A carriage return
alone will continue the stepping process. All responses
('d','h', or 'q') should be in lower case only. You should refer
to the compile listing for offsets into the external and local
variable pools, C code, etc.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

11. Implemetation notes

CROBOTS is written entirely in 'C'. The compiler section was
developed with the aid of the Unix* (TM) programs 'yacc' and
'lex'. Yacc (yet another compiler-compiler) accepts a 'grammar',
which describes the CROBOTS 'C' language. Yacc produces a 'C'
function known as a parser. The parser is the heart of the
compiler, recognizing vaild 'C' constructs. Lex (lexical
analyzer) accepts a list of token combinations, and produces a
'C' function to scan the compiler input for the tokens. The yacc
generated parser, yyparse(), repeatedly calls the lex generated
analyzer, yylex(), to process the source program. The initial
screen display routines were developed with the 'curses' screen

The 'C' source code was then ported to MS-DOS** (TM), and
recompiled using the Lattice*** (TM) 2.15E compiler, using the
'small' memory model. The screen display functions were
modified to use 'int86()', accessing the rom INT 10H cursor
postitioning functions in the IBM-PC bios.

* Unix is a trademark of Bell Telephone Laboratories.
** MS-DOS is a trademark of Microsoft, Inc.
*** Lattice is a trademark of Lattice, Inc.
**** IBM is a trademark of International Business Machines, Inc.

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CROBOTS (C) Copyright 1985 by Tom Poindexter.

CROBOTS Order Form:

| 1. Complete and sign the source code license. |
| |
| 2. Send this completed form along with $20 check or |
| money order to: |
| |
| Tom Poindexter |
| 2903 Winchester Drive |
| Bloomington, Illinois 61701 |
| |
| -For orders outside the U.S., add an additional $5, and |
| enclose an international money order, payable in |
| U.S. currency. |
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| ______________________ ________ ____________ |
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| Source code license: |
| Source code to CROBOTS is provided for personal use only. |
| You may incorporate portions of CROBOTS into your own |
| programs. |
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| I agree not to distribute CROBOTS source code to anyone |
| without prior written permission from the copyright |
| holder, whether a fee is charged or not. |
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CROBOTS (C) Copyright 1985 by Tom Poindexter.

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