View source for 1983-05-21 Lest a Whole New Generation of programmers Grow up in Ignorance of this Glorious Past...

==Introduction==
This essay was apparently posted to [[Usenet]] on May 21, 1983 by Ed Nather. It is presumably in the [[public domain]], as it is widely available on [[the internet]] (try Googling for any sentence in the essay to find other copies).

==Text==
REAL PROGRAMMERS


"Lest a Whole New Generation of programmers Grow up in Ignorance of this Glorious Past..."

by utastro!nather

May 21, 1983


A recent article devoted to the macho side of programming made the bald and unvarnished statement:

Real Programmers write in Fortran.

Maybe they do now, in this decadent era of Lite beer, hand calculators and "user-friendly" software,
but back in the Good Old Days, when computers were made out of drums and vacuum tubes, Real
Programmers wrote in machine code. Not Fortran. Not RATFOR. Not even assembly language.
Machine code. Raw, unadorned, inscrutable hexadecimal numbers. Directly.

Lest a whole new generation of programmers grow up in ignorance of this glorious past, I feel
duty-bound to describe, as best I can through the generation gap, how a Real Programmer wrote code.
I'll call him Mel, because that was his name.

I first met Mel when I went to work for Royal McBee Computer Corp., a now-defunct subsidiary of
the typewriter company. The firm manufactured the LGP-30, a small, cheap (by the standards of the
day) drum-memory computer, and had just started to manufacture the RPC-4000, a much improved,
bigger, better, faster drum-memory computer. Cores cost too much, and weren't here to stay, anyway.
(That's why you haven't heard of the company, or the computer.)

I had been hired to write a Fortran compiler for this new marvel and Mel was my guide to its wonders.
Mel didn't approve of compilers.

"If a program can't rewrite its own code,"he asked, "what good is it?"

Mel had written, in hexadecimal, the most popular computer program the company owned. It ran on
the LGP-30 and played blackjack with potential customers at computer shows. Its effect packed every
show, and the IBM salesmen stood around talking to each other. Whether or not this actually sold
computers was a question we never discussed.

Mel's job was to re-write the blackjack program for the RPC-4000. (Port? What does that mean?)
The new computer had a one-plus-one addressing scheme, in which each machine instruction, in
addition to the operation code and the address of the needed operand, had a second address that
indicated where, on the revolving drum, the next instruction was located. In modern parlance, every
single instruction was followed by a GO TO! Put that in Pascal's pipe and smoke it.

Mel loved the RPC-4000 because he could optimize his code: that is, locate instructions on the drum so
that just as one finished its job, the next would be just arriving at the "read head" and available for
immediate execution. There was a program to do that job, an "optimizing assembler", but Mel refused
to use it.

"You never know where its going to put things", he explained, "so you'd have to use separate
constants."

It was a long time before I understood that remark. Since Mel knew the numerical value of every
operation code, and assigned his own drum addresses, every instruction he wrote could also be
considered a numerical constant. He could pick up an earlier "add" instruction, say, and multiply by it, if
it had the right numeric value. His code was not easy for someone else to modify.

I compared Mel's hand-optimized programs with the same code massaged by the optimizing assembler
program, and Mel's always ran faster. That was because the "top-down" method of program design
hadn't been invented yet, and Mel wouldn't have used it anyway. He wrote the innermost parts of his
program loops first, so they would get first choice of the optimum address locations on the drum. The
optimizing assembler wasn't smart enough to do it that way.

Mel never wrote time-delay loops, either, even when the balky Flexowriter required a delay between
output characters to work right. He just located instructions on the drum so each successive one was
just past the read head when it was needed; the drum had to execute another complete revolution to
find the next instruction. He coined an unforgettable term for this procedure. Although "optimum" is an
absolute term, like "unique," it became common verbal practice to make it relative: "not quite optimum"
or "less optimum" or "not very optimum". Mel called the maximum time-delay locations the "most
pessimum."

After he finished the blackjack program and got it to run, ("Even the initializer is optimized," he said
proudly) he got a Change Request from the sales department. The program used an elegant (optimized)
random number generator to shuffle the cards and deal from the "deck", and some of the salesmen felt it
was too fair, since sometimes the customers lost. They wanted Mel to modify the program so, at the
setting of a sense switch on the console, they could change the odds and let the customer win.

Mel balked. He felt this was patently dishonest, which it was, and that it impinged on his personal
integrity as a programmer, which it did, so he refused to do it. The Head Salesman talked to Mel, as
did the Big Boss and, at the boss's urging, a few Fellow Programmers. Mel finally gave in and wrote the
code, but got the test backwards, and when the sense switch was turned on, the program would cheat,
winning every time. Mel was delighted with this, claiming his subconscious was uncontrollably ethical,
and adamantly refused to fix it.

Alter Mel had left the company for greener pa$ture$, the Big Boss asked me to look at the code and
see if I could find the test and reverse it. Somewhat reluctantly, I agreed to look. Tracking Mel's code
was a real adventure.

I have often felt that programming is an art form, whose real value can only be appreciated by another
versed in the same arcane art; there are lovely gems and brilliant coups hidden from human view and
admiration, sometimes forever, by the very nature of the process. You can learn a lot about an
individual just by reading through his code, even in hexadecimal. Mel was, I think an unsung genius.

Perhaps my greatest shock came when I found an innocent loop that had no test in it. No test. None.
Common sense said it had to be a closed loop, where the program would circle, forever, endlessly.
Program control passed right through it, however, and safely out the other side. It took me two weeks
to figure it out.

The RPC-4000 computer had a really modern facility called an index register. It allowed the
programmer to write a program loop that used an indexed instruction inside; each time through, the
number in the index register was added to the address of that instruction, so it would refer to the next
datum in a series. He had only to increment the index register each time through. Mel never used it.

Instead, he would pull the instruction into a machine register, add one to its address, and store it back.
He would then execute the modified instruction right from the register. The loop was written so this
additional execution time was taken into account -- just as this instruction finished, the next one was
right under the drum's read head, ready to go. But the loop had no test in it.

The vital clue came when I noticed the index register bit, the bit that lay between the address and the
operation code in the instruction word, was turned on--yet Mel never used the index register, leaving it
zero all the time.  When the light went on it nearly blinded me.

He had located the data he was working on near the top of memory -- the largest locations the
instructions could address -- so, after the last datum was handled, incrementing the instruction address
would make it overflow. The carry would add one to the operation code, changing it to the next one in
the instruction set: a jump instruction. Sure enough, the next program instruction was in address location
zero, and the program went happily on its way.

I haven't kept it touch with Mel, so I don't know if he ever gave in to the flood of changes that has
washed over programming techniques since those long-gone days. I like to think he didn't. In any event,
I was impressed enough that I quit looking for the offending test, telling the big Boss I couldn't find it.
He didn't seem surprised.

When I left the company, the blackjack program would still cheat if you turned on the right sense
switch, and I think that's how it should be. I didn't feel comfortable hacking up the code of a "Real
Programmer."