Historians Recreate Source Code of First 4004 Application

mcpublic writes "The team of 'digital archaeologists' who developed the technology behind the Intel Museum's 4004 microprocessor exhibit have done it again. 36 years after Intel introduced their first microprocessor on November 15, 1971, these computer historians have turned the spotlight on the first application software ever written for a general-purpose microprocessor: the Busicom 141-PF calculator. At the team's web site you can download and play with an authentic calculator simulator that sports a cool animated flowchart. Want to find out how Busicom's Masatoshi Shima compressed an entire four-function, printing calculator into only 1,024 bytes of ROM? Check out the newly recreated assembly language "source code," extensively analyzed, documented, and commented by the team's newest member: Hungary's Lajos Kintli. 'He is an amazing reverse-engineer,' recounts team leader Tim McNerney, 'We understood the disassembled calculator code well enough to simulate it, but Lajos really turned it into "source code" of the highest standards.'"

Comments

Those were fun

[certsoft]

Somewhere around 1975 or 1976 I wrote software for a 4004 (using a teletype connected to a modem connected to a mainframe someplace that had the assembler) to run a X-Y table. You would place a wafer with thick-film resistors on it and it would test each one to make sure it was within tolerance and if it wasn't it would mark it with magnetic ink. I think we were probably still using the infamous 1702 EPROMs but there might have been something newer at that time.

Commander Keen

[QuantumG]

I once reverse engineered the classic id software game Commander Keen. John Carmack did some cool stuff in that code.. each sprite had two function pointers in it, one was called when the sprite came into contact with another sprite, the other was called every frame to animate the sprite (he called it the "think" function). When you killed a monster the sprite was replaced with a "body" which was just like a sprite but had a few less fields (so it took up less memory). One of the neatest things he did was use this exact same framework of sprites and bodies to animate the "static" parts of the game. For example, the color coded doors that you have to get the key cards to open were sprites with a contact function that checked if the player had the right key card, at which time they would "die" and be replaced by a body that had a think function would make them slide out of the way.

For anyone who would like to take a look, I've put the re-engineered source code up.

Re:Commander Keen

[Cheesey]

Carmack's code is always interesting. Most famously, there's the infamous square root approximation from Quake. But I'm still impressed by the original Doom render loop, with it's self-modifying code.

The loop is drawing columns (vertical slivers of wall). It needs to interpolate between two things: the input wall texture, and the output part of the screen. Carmack uses something like Bresenham's line drawing algorithm to do this, but because the 386 has such a limited register set, he stores the fractional increment in an immediate attached to the "addl" instruction:

doubleloop:
    movl ecx,ebp // begin calculating third pixel
patch1:
    addl ebp,12345678h // advance frac pointer
    movb [edi],al // write first pixel
    shrl ecx,25 // finish calculation for third pixel
    movl edx,ebp // begin calculating fourth pixel
patch2:
    addl ebp,12345678h // advance frac pointer
    movl [edi+SCREENWIDTH],bl // write second pixel
    shrl edx,25 // finish calculation for fourth pixel
    movb al,[esi+ecx] // get third pixel
    addl edi,SCREENWIDTH*2 // advance to third pixel destination
    movb bl,[esi+edx] // get fourth pixel
    decl [loopcount] // done with loop?
    movb al,[eax] // color translate third pixel
    movb bl,[ebx] // color translate fourth pixel
    jnz doubleloop

and elsewhere... :)

movl ebx,[_dc_iscale]
    shll ebx,9
    movl eax,OFFSET patch1+2 // convice tasm to modify code...
    movl [eax],ebx

A similarly impressive trick is used to draw floors, where 3D interpolation is required because each texture needs to be crossed diagonally, not vertically. I never understood how Doom drew floors until I looked at the code, and I still think it's deep magic. And that's without even mentioning the BSP code!

Re:Amazing!

[dmonahan]

Sometime in the early 70s, a Honeywell division, one of our steady clients, called with a strange request. They had built a small number of special machines for the Navy. Now the Navy wanted more. Honeywell had the circuit drawings and the bootable tape (which they got from the Navy). They had no documentation (not even the instruction set). They asked us to rebuild the code. We did. Dick.

Re:Only 1024?

[TDRighteo]

Floating-point math doesn't fix itself. Let's not be hard on Microsoft when:

Python 2.5.1 (r251:54863, Oct 30 2007, 13:54:11)
[GCC 4.1.2 20070925 (Red Hat 4.1.2-33)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 10.1-10-0.1
-3.6082248300317588e-16

and...

$ perl
printf("%s\n", 10.1-10-0.1);
-3.60822483003176e-16

and...

$ php
<?php
echo (10.1-10-0.1);
?>
-3.6082248300318E-16

Note that the answers vary across languages too...

Asimov's The Feeling of Power

[drachenstern]

How has no one mentioned this yet? - Don't blame me too much, I just copied and pasted from: http://downlode.org/Etext/power.html

The Feeling Of Power
by Isaac Asimov

Jehan Shuman was used to dealing with the men in authority on long-embattled earth. He was only a civilian but he originated programming patterns that resulted in self-directing war computers of the highest sort. Generals, consequently listened to him. Heads of congressional committees too.

There was one of each in the special lounge of New Pentagon. General Weider was space-burned and had a small mouth puckered almost into a cipher. He smoked Denebian tobacco with the air of one whose patriotism was so notorious, he could be allowed such liberties.

Shuman, tall, distinguished, and Programmer-first-class, faced them fearlessly.

He said, "This, gentlemen, is Myron Aub."

"The one with the unusual gift that you discovered quite by accident," said Congressman Brant placidly. "Ah." He inspected the little man with the egg-bald head with amiable curiosity.

The little man, in return, twisted the fingers of his hands anxiously. He had never been near such great men before. He was only an aging low-grade technician who had long ago failed all tests designed to smoke out the gifted ones among mankind and had settled into the rut of unskilled labor. There was just this hobby of his that the great Programmer had found out about and was now making such a frightening fuss over.

General Weider said, "I find this atmosphere of mystery childish."

"You won't in a moment," said Shuman. "This is not something we can leak to the firstcomer. Aub!" There was something imperative about his manner of biting off that one-syllable name, but then he was a great Programmer speaking to a mere technician. "Aub! How much is nine times seven?"

Aub hesitated a moment. His pale eyes glimmered with a feeble anxiety.

"Sixty-three," he said.

Congressman Brant lifted his eyebrows. "Is that right?"

"Check it for yourself, Congressman."

The congressman took out his pocket computer, nudged the milled edges twice, looked at its face as it lay there in the palm of his hand, and put it back. He said, "Is this the gift you brought us here to demonstrate. An illusionist?"

"More than that, sir. Aub has memorized a few operations and with them he computes on paper."

"A paper computer?" said the general. He looked pained.

"No, sir," said Shuman patiently. "Not a paper computer. Simply a piece of paper. General, would you be so kind as to suggest a number?"

"Seventeen," said the general.

"And you, Congressman?"

"Twenty-three."

"Good! Aub, multiply those numbers, and please show the gentlemen your manner of doing it."

"Yes, Programmer," said Aub, ducking his head. He fished a small pad out of one shirt pocket and an artist's hairline stylus out of the other. His forehead corrugated as he made painstaking marks on the paper.

General Weider interrupted him sharply. "Let's see that."

Aub passed him the paper, and Weider said, "Well, it looks like the figure seventeen."

Congressman Brant nodded and said, "So it does, but I suppose anyone can copy figures off a computer. I think I could make a passable seventeen myself, even without practice."

"If you will let Aub continue, gentlemen," said Shuman without heat.

Aub continued, his hand trembling a little. Finally he said in a low voice, "The answer is three hundred and ninety-one."

Congressman Brant took out his computer a second time and flicked it. "By Godfrey, so it is. How did he guess?"

"No guess, Congressman," said Shuman. "He computed that result. He did it on this sheet of paper."

"Humbug," said the general impatiently. "A computer is one thing and marks on a paper are another."

"Explain, Aub," said Shuman.

"Yes, Programmer. Well, gentlemen, I write down seventeen, and just undernea