8 Bit Home Computer Benchmarks

Over the years I've collected quite a few 8 bit home computers. Out of curiosity I decided to write a simple prime sieve benchmark to compare their implementations of BASIC.

10 LET W=500:DIM F(W):LET P=1:LET A=3
20 LET F(P)=A:LET P=P+1:IF P>W THEN STOP
30 LET A=A+2:LET X=1
40 LET S=A/F(X):IF S=INT(S) THEN 30
50 LET X=X+1:IF X<P AND F(X)*F(X)<=A THEN 40
60 GOTO 20

Here are the results from a few of the machines I have to hand:

System	CPU	Time
Acorn Electron	2.0MHz 6502	138
Amstrad CPC464	4.0MHz Z80A	140
Commodore C64	1.0MHz 6510	254
Commodore Plus/4	1.0 MHz 8501	267
Tandy 64K CoCo 2	0.895MHz 6809E	271
Atari 800XL	1.8MHz 6502	316
Sinclair Spectrum +3	3.55MHz Z80A	388

Let me know how long it takes to run on your favourite classic computer. :-)

Secret Opcodes of the 8 Bit Processors

Undocumented instructions were common on early processors. A few would crash the computer (HCF - halt and catch fire) while others had strange but occasionally useful behaviour. Any self-respecting programmer would make use of these to squeeze out the last few cycles of performance.

The effect of undocumented opcodes would vary between different versions of some processors, no doubt leading to the classic excuse “it worked on my machine”. Here are a few examples I've found useful.

Secrets of the Z80

Zilog's Z80 was used in a number of popular 8 bit computers including the Sinclair Spectrum, Amstrad CPC, TRS-80 and MSX. There are a number of undocumented opcodes with the CB, DD, ED and FD prefix.

• CB30-CB37 - SLL reg shifts a register left, setting bit 0.
• DD - when used as a prefix to instructions which use H or L, either the high or low 8 bits of IX are used.
• FD - as DD, but the high or low 8 bits of IY will be used.
• ED70 - IN (C) reads from i/o port C, setting the flags and discarding the result.
• ED71 - OUT (C),0 outputs a zero to port C.

Secrets of the 8086/8088

Intel's 8088 was used in the original IBM PC and has spawned an entire family of processors.

• D6 - SALC sets the AL register to either 00 or FF depending on the carry flag. SALC was finally documented with the introduction of the Pentium Pro 27 years later.
• 0F - POP CS pops the CS register from the stack. Only works on 8086 processors.
• 0F05 - LOADALL loads all registers from memory location 0800. Only works on 80286 processors.

Which processors have you programmed and did you find any undocumented opcodes useful?

A History of Programming Games 1961-1989

In a programming game players write a program to complete a specific task, usually to wipe out all opponents. The contest takes place between either programs in the memory of a virtual computer or robots in an arena.

Darwin

In August 1961, Douglas McIlroy, Robert Morris and Victor Vyssotsky invented Darwin and the programming game genre. Programs written using IBM 7090 machine code competed to destroy all opponents and be the most prolific replicator. An Umpire provided three functions to probe memory for an opponent, to claim memory or kill an opponent.

RobotWar

RobotWar was written in the 1970s by Silas Warner for the PLATO computer system and published commercially for the Apple II by MUSE Software in 1981. Programs written in a proprietary high level language control robots which battle to eliminate all opponents in a virtual arena. In the early 1980s a society was formed and an annual tournament organised by Computer Gaming World.

Color Robot Battle

The Image Producers released Color Robot Battle in 1981 for the TRS-80 Color Computer. The game was played by writing programs in a simple hybrid of BASIC and Logo to control a battle robot. Programs faced each other in a one-on-one battle with the last robot standing being declared winner.

Core War

Alexander Dewdney described Core War in the May 1984 issue of Scientific American, introducing programming games to a wide audience for the first time. Core War became popular overnight. A society was formed, a newsletter published and regular tournaments held. Core War is played between assembly languages programs in the memory of a virtual computer. Each program attempts to eradicate all opponents. Core War can be played by email at KOTH.org or KOTH@SAL.

DROID

Inspired by RobotWar, DROID was developed at Reichhold Chemicals as a teaching aid in December 1984. Programs to control robots are written in the D-code assembly language and attempt to exterminate all adversaries in the virtual arena. DROID can be played by Telnet on the Empire HPe3000 server.

CROBOTS

Tom Poindexter published CROBOTS as shareware in December 1985 after being inspired by RobotWar. A subset of C is used to control battle robots. As usual, the aim of the game is to destroy all opponents in a virtual arena. A king of the hill tournament is organised by Maurizio Camangi.

P-Robots

In 1988 David Malmberg released P-Robots, a robot battle game based on a subset of the Pascal programming language and inspired by CROBOTS. Later versions introduced a variety of optional extras for robots, teams and obstacles.

OMEGA

OMEGA is a programming game written by Stuart Marks and published by Origin Systems in 1989. The object of the game is to program a tank to defeat a series of increasingly more powerful enemies. Each opponent defeated unlocks a higher security clearance and increased budget.

Unfortunately there's very little information about some of these games online. Do you remember playing any of the above? Which is your favourite programming game and why?

#songsincode - Lyrics for Programmers

#songsincode are small pseudo-programs which display a song title or part of the lyrics. The more refined examples use conditional code and control stuctures to define the song.

The tag was first used on twitter a couple of weeks ago. After a sudden burst of popularity, #songsincode has slowed to about 20 tweets a day. Here's an example by testydonkey:

if(Door.Color == System.Color.Red)
{ Door.Color = System.Color.Black; }

This is Paint it Black by the Rolling Stones, “I see a red door and I want it painted black”.

Here's the top 25 countdown of the very finest #songsincode. Can you identify all 25? Is your favourite missing? Let me know :-)

anurse:

var s = new Submarine(Color.Yellow);
s.Residents.Add(Us); for(int i=0;i<2;i++)
{Assert.IsTrue(s.Color == Color.Yellow);}

darrennisbett:

h=new hotel(); h.name="california";
h.guest.addEvent("checkout");
h.guest.removeEvent("leave")

royvanrijn:

if(grass=="green" && girls == "pretty")
{ takeMe(paradiseCity); }

injenierobarsa:

for (int i = 1; i <= 99; i++)
{ redBalloons[i].goBy() }

3d0:

if(my.sexyness>shirt.sexyness) pain();

phikachu:

me.color = 0x0000FF;
me.text = “Da Ba Dee Da Ba Di”;

Borisson:

($horse_name == false ? $location = desert : ' ');

plaxdan:

self.vehicle = new CombineHarvester();
you.setKey(vehicle.getKey());

cargoweasel:

SubwayWalls.write(words_of_the_prophets());

Leadhyena:

I.send("...---...",world);
I.send("...---...",world);
while(!(someone.receive(bottle)&&
bottle.contains(message)){I.hope()}

antallan:

substring("the tiger",6,1)

pitsk:

void shootPeople() { shootSherif; return;
shootDeputy; }

sbruchmann:

if ($angelsDeserveToDie) { iCry(); }

royvanrijn:

while( !me.like(mondays) ) { tellWhy(me); }

Levistica:

cuts.firstElement().deepness = max;

uberTof:

final--;

plaxdan:

while (thing != that) { doForLove(thing);

numptygeek:

jumpWithDirection(left); stepWithDirection(right);

CarstenHagemann:

$jealous_sky[$sun] = $you->tell()
if ($we->walk($fields_of_gold));

numptygeek:

if(somethingStrange==true && location ==
neighborhood){ ghostbusters();
printf("I ain't afraid of no ghost");}

draconum:

//roxanne.putOnLight('#ff0000');
commented out, was not necessary

brozow:

video$ kill -9 `ps -ef | grep radio*`

rennyhernandez:

stuff={'red door','a line of cars', 'my heart'}
stuff.each do |it| it.setColor('#000000') end

codepo8:

.clowns{float:left;}.jokers{float:right};
#me_you{position:fixed;margin:0 auto;width:100%}

royvanrijn:

for(Leaf leaf:leafs)
{ leaf.setColor(new Color(139,69,19)); }
sky.setColor(Color.GRAY);

#moviesincode, #tvincode, #booksincode!

#songsincode has inspired three new tags. Can you see #moviesincode, #tvincode or #booksincode catching on? :-)

sijmen:

TypeError: Result of expression this.spoon'
[undefined] is not an object

rhizomecowboy:

trace(isNAN(prisoner));

nail7:

var i = count(MonteChristo);

My Two Greatest Programming Sins

My programming sins are too numerous to count, but there are two which keep coming back to haunt me over and over:

• version control - while developing a program I create multiple versions. Development may split into multiple paths or be backtracked. Without proper version control, confusion is inevitable.
• illegible code - I make frequent tweaks and changes, use irrelevant names for labels and functions and fail to comment code. It's unlikely I'll understand the program if I return to it a few weeks later.

Earlier this week I posted an example of ugly code. By examining the program, the magic numbers or output for sample input, three readers identified the code as an implementation of parallel bit counting. Here's how the bit counter ought to have been implemented:

: (COUNTBITS) ( u1 u2 u3 -- u4 )
( u1 = partial count )
( u2 = power )
( u3 = mask )
( u4 = new partial count )
ROT 2DUP AND >R ROT / AND R> +
;

: COUNTBITS ( u1 -- u2 ) ( parallel count )
( u2 = number of 1 bits in u1 )
2   %101010101010101 (COUNTBITS)
4   %011001100110011 (COUNTBITS)
16  %000011100000111 (COUNTBITS)
256 %000000000001111 (COUNTBITS)
;

To increase code legibility, the following changes have been made:

• function name now represents the word's behaviour
• word factored into two simpler words
• documented the word's stack activity
• represented the bit masks in binary

It's also worth considering what countbits will be used for (any suggestions?). Do we really need a fast bit twiddling algorithm? A simple iterated count or sparse ones algorithm will probably suffice:

: COUNTBITS ( u1 -- u2 )( iterated count )
( u2 = number of 1 bits in u1 )
0 SWAP
BEGIN
2 /MOD >R + R>
?DUP 0=
UNTIL
;

: COUNTBITS ( u1 -- u2 ) ( sparse ones )
( u2 = number of 1 bits in u1 )
0 SWAP
BEGIN
?DUP
WHILE
DUP 1- AND >R 1+ R>
REPEAT
;

Now I've identified a couple of faults with my coding technique, I'm hoping to correct my shortcomings while tackling my next programming project. What is your greatest coding sin and how do you plan to deal with it?

Impenetrable Code

However elegant a programming language, some fool will always find a way to write ugly code.

Here's a word I recently implemented in Forth:

: C
>R
256 15 16 1799
4 13107 2 21845
R>
4 0 DO
TUCK OVER AND -ROT
INVERT AND ROT / +
LOOP
;

Although I didn't set out to intentionally create something hideous, I'm appalled by how difficult to understand the code is. How can I make the word easier to comprehend and can you remind me what it's supposed to do?

Perverse Code: Deviant Forth

The Forth programming language has a set of functions (or words) called primitives. These are traditionally written in the language of the host machine to keep the system as simple and efficient as possible. Typically the primitives required no more than about five machine instructions each to implement.

Deviant Forth explores the possibility of using Forth to implement some of the primitives. Warning, prolonged exposure to this code may cause permanent damage to your eyes!

As a exercise, let's implement NIP in Forth:

: NIP SWAP DROP ;

Standard stuff so far. Now lets try to implement SWAP and DROP!

: DROP DUP - + ;

: SWAP OVER >R >R DROP R> R> ;

Things are beginning to look ugly. On most systems DROP can be implemented in one machine instruction and SWAP in four. It's also possible to implement DUP, + and OVER in Forth:

: DUP >R R@ R> ;

: + >R DUP DUP - R> - - ;

: OVER >R DUP DUP R@ - DUP >R - R> R> + ;

I'm no Forth purist, but I feel repelled by the abomination I've programmed. Despite this, it's interesting to discover so many Forth words can be implemented with just >R, R>, R@ and -, however unnatural it might be.

As an afront to the very nature of Forth I challenge you to implement ROT using only >R, R>, R@ and -. If you can in less than 50 words I'd love to see your solution, however unpleasant :-)