Hello!

I wish to present you the format of the EMC files.
I've been working on Dune2 code for few months (trying to understand
how strategy game works) and finally found the part which is
responsible on executing EMC script. Yes - script because it looks like
a tiny programming language.

First of all let's say what's the purpose of this "script". It is used
to control several things of object lifetime (object stand for unit, building
or team). Each type of object has its own script so the harvester has its own script as do refinery, windtrap etc. What is to be done usually depends on objects state. The script can have condition codes, loops and even subroutines!
It can execute some external routines.

For example let's get refinery: after the initiation (which contains
build-up animation) the script goes into infinite loop and checks from
time to time if there's a harvester docken in. If so it gets money from it
until it's empty. Then calls carry-all to the refinery or if there's no
one left releases the harvester. That's all. See below for more details.

Now let's describe the script.
There is given to you a stack (upto 16 values) and 5 local variables (named 0-4)
and about 18 commands.
Here’s a brief list of commands:
Number in brackets is the hex number of command.
After the command name is the argument - if it's constant it must
be set as argument for this command to work.

(0) Go to line %arg - goes to specified line (can be subroutine)
(1) Set return code %arg - sets return code of the subroutine
(2) Push return code 0 - pushes return code on stack
(2) Push record 1 - pushes stack pointer and frame pointer on
stack (used to call subroutine)
(3,4) Push %arg - pushes a number on stack
(5) Push var %arg - pushes specified variable on stack
(6) Push frame (-) %arg - pushes value taken from frame ptr - %arg
frame pointer is the same as stack pointer
on the begining of the routine and don't
change within routine
(7) Push frame (+) %arg - similiar to above but from frame ptr + %arg
(8) Pop return code 0 - pops a number from the stack and saves
as return code
(8) Pop record 1 - returns from subroutine
(9) Pop var %arg - pops a value and saves to variable %arg
(A) Pop frame (-) %arg - pops value from the stack and saves to
frame ptr - %arg
(B) Pop frame (+) %arg - similiar to above but to frame ptr + %arg
functions (+) are used to operate on
routine arguments and functions (-) are used
to operate on additional local variables.
(C) Add to SP %arg - adds %arg to stack pointer
(D) Sub from SP %arg - subtracts %arg from stack pointer
(E) Execute %arg - executes external routine indexed with %arg
(F) If not go to %arg - continues only if the value on stack is
different from zero. else jumps to %arg
it does pop value from stack!
(10) Negate 0 - performs an action on value on the stack
this does something like "!expression" in C
(10) Negate 1 - this does arithmetic negation
(10) Negate 2 - this does bitwise negation
(11) Evaluate %arg - performs arithmetic or boolean action on last
two values on stack. result saves on stack.
the operations are: &&, ||, ==, !=, >,
>=, <, <=, +, -, *, /, >>, <<, &, |, %, XOR.
(12) Return - this does return from subroutine but seems
to be obsolete (is not used)

The script is stored in DATA chunk. The ORDR chunk stores line numbers
from which to begin executing script for appropriate object types.
Note that the line number is the index in WORD array (not command array).

One command is stored in one or two words. 3 last bits of the first byte
are something like control bits. They are mutual exclusive so only one
bit should be set (or none).
7th bit - this performs Go to line %arg command, but the argument
is stored in word (higher byte preceeding!)
e.g.
0x819B - jumps to line 0x19B

6th bit - this is most used: the first byte is the command number and the
second is argument.
e.g.
0x4404 - push 0x4 on stack

5th bit - mostly used in "If not go to". the first byte is the command
number, the second byte is unused, but the next WORD is used
as argument (always positive!)
e.g.
0x2F00819B - if condition is false jumps to 0x19B

If none bit is set the argument is set to zero.

Besides normal commands you can execute external routines.
At the moment I know only few BUILD.EMC routines.
They are for example: Delay() which delays execution of the script
for some time, CallCarryAll() which calls carryall to the structure,
GetState(), SetState() related to the state of the structure,
RafineSpice() which takes 1% of harvester's cargo.

Here is the build-up animation of the initiation code:
...
10 Push 24
11 Execute Delay() - delays some time
12 Add SP 1
13 Push -1
14 Execute SetState() - draws "construction" frame
15 Add SP 1
16 Push 15
17 Execute Delay() - delays some less time
18 Add SP 1
19 Push 0
1A Execute SetState() - draws normal frame
etc.
...

Here are the parts of the code for Refinery:

111 Execute Reveal() - reveals fog of war around structure
...
115 Execute GetState() - returns state of the structure..
116 Push return code - ..and pushes it on stack
117 Push 2
118 Evaluate (==) - checks if the state is equal to 2..
119 Else go 12F - ..if so there's harvester in refinery
11B Execute RafineSpice() - get 1% of spice
11C Push return code - check if the harvester still has spice
11D Else go 120 - if not exit loop
11F Go to 11B - if so continue
...
121 Push var 4 - VAR 4 is nonzero if the carry-all is attached
122 Negate 0
123 Else go 12F - continue if there is NO carry-all attached
...
126 Execute CallCarryAll()- try to attach carry-all
...
128 Push return code
129 Pop var 4 - save carryall (or zero) to VAR 4
12A Push var 4
12B Negate 0
12C Else go C - continue if couldn't attach carryall
12E Execute Deploy() - deploy harvester on the ground
12F Push 60
130 Execute Delay() - delay script for 60 frames
131 Add SP 1 - restore stack space
132 Go to 112

If the refinery is surrounded CallCarryAll() will create new carry-all!

Ok. I hope this will give some important info about the format.
I know that it is has very limited use and is very hard to modify.
Recently I patched one thing: you don't need to surround repair
facility in order to get your units back on the battle-field - it works!

If You wish some more explanation or „decompiler” please feel free to write.