Real Programmers Don't Use PASCAL
Ed Post
Graphic Software Systems
P.O. Box 673
25117 S.W. Parkway
Wilsonville, OR 97070
Copyright (c) 1982
(decvax | ucbvax | cbosg | pur-ee | lbl-unix)!teklabs!ogcvax!gss1144!evp
Back in the good old days -- the "Golden Era" of computers, it was
easy to separate the men from the boys (sometimes called "Real Men" and
"Quiche Eaters" in the literature). During this period, the Real Men were
the ones that understood computer programming, and the Quiche Eaters were
the ones that didn't. A real computer programmer said things like "DO 10
I=1,10" and "ABEND" (they actually talked in capital letters, you under-
stand), and the rest of the world said things like "computers are too com-
plicated for me" and "I can't relate to computers -- they're so imper-
sonal". (A previous work [1] points out that Real Men don't "relate" to
anything, and aren't afraid of being impersonal.)
But, as usual, times change. We are faced today with a world in which
little old ladies can get computerized microwave ovens, 12 year old kids
can blow Real Men out of the water playing Asteroids and Pac-Man, and any-
one can buy and even understand their very own Personal Computer. The Real
Programmer is in danger of becoming extinct, of being replaced by high-
school students with TRASH-80s!
There is a clear need to point out the differences between the typical
high-school junior Pac-Man player and a Real Programmer. Understanding
these differences will give these kids something to aspire to -- a role
model, a Father Figure. It will also help employers of Real Programmers to
realize why it would be a mistake to replace the Real Programmers on their
staff with 12 year old Pac-Man players (at a considerable salary savings).
1. LANGUAGES
-------------
The easiest way to tell a Real Programmer from the crowd is by the
programming language he (or she) uses. Real Programmers use FORTRAN.
Quiche Eaters use PASCAL. Nicklaus Wirth, the designer of PASCAL, was once
asked, "How do you pronounce your name?". He replied "You can either call
me by name, pronouncing it 'Veert', or call me by value, 'Worth'." One can
tell immediately from this comment that Nicklaus Wirth is a Quiche Eater.
The only parameter passing mechanism endorsed by Real Programmers is call-
by-value-return, as implemented in the IBM/370 FORTRAN G and H compilers.
Real programmers don't need abstract concepts to get their jobs done: they
are perfectly happy with a keypunch, a FORTRAN IV compiler, and a beer.
* Real Programmers do List Processing in FORTRAN.
* Real Programmers do String Manipulation in FORTRAN.
* Real Programmers do Accounting (if they do it at all) in FORTRAN.
* Real Programmers do Artificial Intelligence programs in FORTRAN.
If you can't do it in FORTRAN, do it in assembly language. If you can't do
it in assembly language, it isn't worth doing.
2. STRUCTURED PROGRAMMING
--------------------------
Computer science academicians have gotten into the "structured pro-
gramming" rut over the past several years. They claim that programs are
more easily understood if the programmer uses some special language con-
structs and techniques. They don't all agree on exactly which constructs,
of course, and the examples they use to show their particular point of view
invariably fit on a single page of some obscure journal or another --
clearly not enough of an example to convince anyone. When I got out of
school, I thought I was the best programmer in the world. I could write an
unbeatable tic-tac-toe program, use five different computer languages, and
create 1000 line programs that WORKED. (Really!) Then I got out into the
Real World. My first task in the Real World was to read and understand a
200,000 line FORTRAN program, then speed it up by a factor of two. Any Real
Programmer will tell you that all the Structured Coding in the world won't
help you solve a problem like that -- it takes actual talent. Some quick
observations on Real Programmers and Structured Programming:
* Real Programmers aren't afraid to use GOTOs.
* Real Programmers can write five page long DO loops without getting
confused.
* Real Programmers enjoy Arithmetic IF statements because they make the
code more interesting.
* Real Programmers write self-modifying code, especially if it saves
them 20 nanoseconds in the middle of a tight loop.
* Real Programmers don't need comments: the code is obvious.
* Since FORTRAN doesn't have a structured IF, REPEAT ... UNTIL, or CASE
statement, Real Programmers don't have to worry about not using them.
Besides, they can be simulated when necessary using assigned GOTOs.
Data structures have also gotten a lot of press lately. Abstract Data
Types, Structures, Pointers, Lists, and Strings have become popular in cer-
tain circles. Wirth (the above-mentioned Quiche Eater) actually wrote an
entire book [2] contending that you could write a program based on data
structures, instead of the other way around. As all Real Programmers know,
the only useful data structure is the array. Strings, lists, structures,
sets -- these are all special cases of arrays and and can be treated that
way just as easily without messing up your programing language with all
sorts of complications. The worst thing about fancy data types is that you
have to declare them, and Real Programming Languages, as we all know,
have implicit typing based on the first letter of the (six character)
variable name.
3. OPERATING SYSTEMS
---------------------
What kind of operating system is used by a Real Programmer? CP/M? God
forbid -- CP/M, after all, is basically a toy operating system. Even lit-
tle old ladies and grade school students can understand and use CP/M.
Unix is a lot more complicated of course -- the typical Unix hacker
never can remember what the PRINT command is called this week -- but when
it gets right down to it, Unix is a glorified video game. People don't do
Serious Work on Unix systems: they send jokes around the world on USENET
and write adventure games and research papers.
No, your Real Programmer uses OS/370. A good programmer can find and
understand the description of the IJK305I error he just got in his JCL
manual. A great programmer can write JCL without referring to the manual
at all. A truly outstanding programmer can find bugs buried in a 6 megabyte
core dump without using a hex calculator. (I have actually seen this done.)
OS/370 is a truly remarkable operating system. It's possible to des-
troy days of work with a single misplaced space, so alertness in the pro-
gramming staff is encouraged. The best way to approach the system is
through a keypunch. Some people claim there is a Time Sharing system that
runs on OS/370, but after careful study I have come to the conclusion that
they are mistaken.
4. PROGRAMMING TOOLS
---------------------
What kind of tools does a Real Programmer use? In theory, a Real Pro-
grammer could run his programs by keying them into the front panel of the
computer. Back in the days when computers had front panels, this was actu-
ally done occasionally. Your typical Real Programmer knew the entire
bootstrap loader by memory in hex, and toggled it in whenever it got des-
troyed by his program. (Back then, memory was memory -- it didn't go away
when the power went off. Today, memory either forgets things when you don't
want it to, or remembers things long after they're better forgotten.)
Legend has it that Seymour Cray, inventor of the Cray I supercomputer and
most of Control Data's computers, actually toggled the first operating sys-
tem for the CDC7600 in on the front panel from memory when it was first
powered on. Seymour, needless to say, is a Real Programmer.
One of my favorite Real Programmers was a systems programmer for Texas
Instruments. One day, he got a long distance call from a user whose system
had crashed in the middle of some important work. Jim was able to repair
the damage over the phone, getting the user to toggle in disk I/O instruc-
tions at the front panel, repairing system tables in hex, reading register
contents back over the phone. The moral of this story: while a Real Pro-
grammer usually includes a keypunch and lineprinter in his toolkit, he can
get along with just a front panel and a telephone in emergencies.
In some companies, text editing no longer consists of ten engineers
standing in line to use an 029 keypunch. In fact, the building I work in
doesn't contain a single keypunch. The Real Programmer in this situation
has to do his work with a text editor program. Most systems supply several
text editors to select from, and the Real Programmer must be careful to
pick one that reflects his personal style. Many people believe that the
best text editors in the world were written at Xerox Palo Alto Research
Center for use on their Alto and Dorado computers [3]. Unfortunately, no
Real Programmer would ever use a computer whose operating system is called
SmallTalk, and would certainly not talk to the computer with a mouse.
Some of the concepts in these Xerox editors have been incorporated
into editors running on more reasonably named operating systems. EMACS and
VI are probably the most well known of this class of editors. The problem
with these editors is that Real Programmers consider "what you see is what
you get" to be just as bad a concept in text editors as it is in women. No,
the Real Programmer wants a "you asked for it, you got it" text editor --
complicated, cryptic, powerful, unforgiving, dangerous. TECO, to be pre-
cise.
It has been observed that a TECO command sequence more closely resem-
bles transmission line noise than readable text [4]. One of the more enter-
taining games to play with TECO is to type your name in as a command line
and try to guess what it does. Just about any possible typing error while
talking with TECO will probably destroy your program, or even worse --
introduce subtle and mysterious bugs in a once working subroutine.
For this reason, Real Programmers are reluctant to actually edit a
program that is close to working. They find it much easier to just patch
the binary object code directly, using a wonderful program called SUPERZAP
(or its equivalent on non-IBM machines). This works so well that many work-
ing programs on IBM systems bear no relation to the original FORTRAN code.
In many cases, the original source code is no longer available. When it
comes time to fix a program like this, no manager would even think of send-
ing anything less than a Real Programmer to do the job -- no Quiche Eating
structured programmer would even know where to start. This is called "job
security".
Some programming tools NOT used by Real Programmers:
* FORTRAN preprocessors like MORTRAN and RATFOR. The Cuisinarts of
programming -- great for making Quiche. See comments above on structured
programming.
* Source language debuggers. Real Programmers can read core dumps.
* Compilers with array bounds checking. They stifle creativity, destroy
most of the interesting uses for EQUIVALENCE, and make it impossible
to modify the operating system code with negative subscripts. Worst of
all, bounds checking is inefficient.
* Source code maintainance systems. A Real Programmer keeps his code
locked up in a card file, because it implies that its owner cannot
leave his important programs unguarded [5].
5. THE REAL PROGRAMMER AT WORK
-------------------------------
Where does the typical Real Programmer work? What kind of programs are
worthy of the efforts of so talented an individual? You can be sure that no
real Programmer would be caught dead writing accounts-receivable programs
in COBOL, or sorting mailing lists for People magazine. A Real Programmer
wants tasks of earth-shaking importance (literally!).
* Real Programmers work for Los Alamos National Laboratory, writing
atomic bomb simulations to run on Cray I supercomputers.
* Real Programmers work for the National Security Agency, decoding Rus-
sian transmissions.
* It was largely due to the efforts of thousands of Real Programmers
working for NASA that our boys got to the moon and back before the
cosmonauts.
* The computers in the Space Shuttle were programmed by Real Program-
mers.
* Real Programmers are at work for Boeing designing the operating sys-
tems for cruise missiles.
Some of the most awesome Real Programmers of all work at the Jet Pro-
pulsion Laboratory in California. Many of them know the entire operating
system of the Pioneer and Voyager spacecraft by heart. With a combination
of large ground-based FORTRAN programs and small spacecraft-based assembly
language programs, they can to do incredible feats of navigation and impro-
visation, such as hitting ten-kilometer wide windows at Saturn after six
years in space, and repairing or bypassing damaged sensor platforms,
radios, and batteries. Allegedly, one Real Programmer managed to tuck a
pattern-matching program into a few hundred bytes of unused memory in a
Voyager spacecraft that searched for, located, and photographed a new moon
of Jupiter.
One plan for the upcoming Galileo spacecraft mission is to use a grav-
ity assist trajectory past Mars on the way to Jupiter. This trajectory
passes within 80 +/- 3 kilometers of the surface of Mars. Nobody is going
to trust a PASCAL program (or PASCAL programmer) for navigation to these
tolerances.
As you can tell, many of the world's Real Programmers work for the
U.S. Government, mainly the Defense Department. Recently, however, a
black cloud has formed on the Real Programmer horizon. It seems that some
highly placed Quiche Eaters at the Defense Department decided that all
Defense programs should be written in some grand unified language called
"ADA" (registered trademark, DoD). For a while, it seemed that ADA was
destined to become a language that went against all the precepts of Real
Programming -- a language with structure, a language with data types, strong
typing, and semicolons. In short, a language designed to cripple the
creativity of the typical Real Programmer. Fortunately, the language adopted
by DoD has enough interesting features to make it approachable: it's
incredibly complex, includes methods for messing with the operating system
and rearranging memory, and Edsgar Dijkstra doesn't like it [6].
(Dijkstra, as I'm sure you know, was the author of "GoTos Considered Harmful" --
a landmark work in programming methodology, applauded by Pascal Programmers
and Quiche Eaters alike.) Besides, the determined Real Programmer can write
FORTRAN programs in any language.
The real programmer might compromise his principles and work on some-
thing slightly more trivial than the destruction of life as we know it,
providing there's enough money in it. There are several Real Programmers
building video games at Atari, for example. (But not playing them. A Real
Programmer knows how to beat the machine every time: no challange in that.)
Everyone working at LucasFilm is a Real Programmer. (It would be crazy to
turn down the money of 50 million Star Wars fans.) The proportion of Real
Programmers in Computer Graphics is somewhat lower than the norm, mostly
because nobody has found a use for Computer Graphics yet. On the other
hand, all Computer Graphics is done in FORTRAN, so there are a fair number
people doing Graphics in order to avoid having to write COBOL programs.
6. THE REAL PROGRAMMER AT PLAY
-------------------------------
Generally, the Real Programmer plays the same way he works -- with
computers. He is constantly amazed that his employer actually pays him to
do what he would be doing for fun anyway, although he is careful not to
express this opinion out loud. Occasionally, the Real Programmer does step
out of the office for a breath of fresh air and a beer or two. Some tips on
recognizing real programmers away from the computer room:
* At a party, the Real Programmers are the ones in the corner talking
about operating system security and how to get around it.
* At a football game, the Real Programmer is the one comparing the plays
against his simulations printed on 11 by 14 fanfold paper.
* At the beach, the Real Programmer is the one drawing flowcharts in the
sand.
* A Real Programmer goes to a disco to watch the light show.
* At a funeral, the Real Programmer is the one saying "Poor George. And
he almost had the sort routine working before the coronary."
* In a grocery store, the Real Programmer is the one who insists on run-
ning the cans past the laser checkout scanner himself, because he
never could trust keypunch operators to get it right the first time.
7. THE REAL PROGRAMMER'S NATURAL HABITAT
-----------------------------------------
What sort of environment does the Real Programmer function best in?
This is an important question for the managers of Real Programmers. Consid-
ering the amount of money it costs to keep one on the staff, it's best to
put him (or her) in an environment where he can get his work done.
The typical Real Programmer lives in front of a computer terminal.
Surrounding this terminal are:
* Listings of all programs the Real Programmer has ever worked on, piled
in roughly chronological order on every flat surface in the office.
* Some half-dozen or so partly filled cups of cold coffee. Occasionally,
there will be cigarette butts floating in the coffee. In some cases,
the cups will contain Orange Crush.
* Unless he is very good, there will be copies of the OS JCL manual and
the Principles of Operation open to some particularly interesting
pages.
* Taped to the wall is a line-printer Snoopy calender for the year 1969.
* Strewn about the floor are several wrappers for peanut butter filled
cheese bars (the type that are made stale at the bakery so they can't
get any worse while waiting in the vending machine).
* Hiding in the top left-hand drawer of the desk is a stash of double-
stuff Oreos for special occasions.
* Underneath the Oreos is a flow-charting template, left there by the
previous occupant of the office. (Real Programmers write programs, not
documentation. Leave that to the maintainence people.)
The Real Programmer is capable of working 30, 40, even 50 hours at a
stretch, under intense pressure. In fact, he prefers it that way. Bad
response time doesn't bother the Real Programmer -- it gives him a chance
to catch a little sleep between compiles. If there is not enough schedule
pressure on the Real Progl Programmer, he tendsto make things more challenging
by working on some small but interesting part of the problem for the first
nine weeks, then finishing the rest in the last week, in two or three 50-
hour marathons. This not only inpresses his manager, who was despairing of
ever getting the project done on time, but creates a convenient excuse for
not doing the documentation. In general:
* No Real Programmer works 9 to 5. (Unless it's 9 in the evening to 5 in
the morning.)
* Real Programmers don't wear neckties.
* Real Programmers don't wear high heeled shoes.
* Real Programmers arrive at work in time for lunch. [9]
* A Real Programmer might or might not know his wife's name. He does,
however, know the entire ASCII (or EBCDIC) code table.
* Real Programmers don't know how to cook. Grocery stores aren't often
open at 3 a.m., so they survive on Twinkies and coffee.
8. THE FUTURE
--------------
What of the future? It is a matter of some concern to Real Programmers
that the latest generation of computer programmers are not being brought up
with the same outlook on life as their elders. Many of them have never seen
a computer with a front panel. Hardly anyone graduating from school these
days can do hex arithmetic without a calculator. College graduates these
days are soft -- protected from the realities of programming by source
level debuggers, text editors that count parentheses, and user friendly
operating systems. Worst of all, some of these alleged computer scientists
manage to get degrees without ever learning FORTRAN! Are we destined to
become an industry of Unix hackers and Pascal programmers?
On the contrary. From my experience, I can only report that the
future is bright for Real Programmers everywhere. Neither OS/370 nor FOR-
TRAN show any signs of dying out, despite all the efforts of Pascal pro-
grammers the world over. Even more subtle tricks, like adding structured
coding constructs to FORTRAN have failed. Oh sure, some computer vendors
have come out with FORTRAN 77 compilers, but every one of them has a way of
converting itself back into a FORTRAN 66 compiler at the drop of an option
card -- to compile DO loops like God meant them to be.
Even Unix might not be as bad on Real Programmers as it once was. The
latest release of Unix has the potential of an operating system worthy of
any Real Programmer. It has two different and subtly incompatible user
interfaces, an arcane and complicated terminal driver, virtual memory. If
you ignore the fact that it's structured, even C programming can be appre-
ciated by the Real Programmer: after all, there's no type checking, vari-
able names are seven (ten? eight?) characters long, and the added bonus of
the Pointer data type is thrown in. It'slike having the best parts of FOR-
TRAN and assembly language in one place. (Not to mention some of the more
creative uses for #define.)
No, the future isn't all that bad. Why, in the past few years, the
popular press has even commented on the bright new crop of computer nerds
and hackers ([7] and [8]) leaving places like Stanford and M.I.T. for the
Real World. From all evidence, the spirit of Real Programming lives on in
these young men and women. As long as there are ill-defined goals, bizarre
bugs, and unrealistic schedules, there will be Real Programmers willing to
jump in and Solve The Problem, saving the documentation for later. Long
live FORTRAN!
9. ACKNOWLEGEMENT
------------------
I would like to thank Jan E., Dave S., Rich G., Rich E. for their help
in characterizing the Real Programmer, Heather B. for the illustration,
Kathy E. for putting up with it, and atd!avsdS:mark for the initial
inspriration.
REFERENCES
----------
[1] Feirstein, B., "Real Men Don't Eat Quiche", New York, Pocket Books,
1982.
[2] Wirth, N., "Algorithms + Data Structures = Programs", Prentice Hall,
1976.
[3] Ilson, R., "Recent Research in Text Processing", IEEE Trans. Prof.
Commun., Vol. PC-23, No. 4, Dec. 4, 1980
[4] Finseth, C., "Theory and Practice of Text Editors -- or -- a Cookbook
for an EMACS", B.S. thesis, MIT/LCS/TM-165, Massachusetts Institute of
Technology, May, 1980.
[5] Weinberg, G., "The Psychology of Computer Programming", New York, Van
Nostrand Reinhold, 1971, p. 110.
[6] Dijkstra, E., "On the GREEN language submitted to the DoD", Sigplan
Notices, Vol. 3 No. 10, Oct. 1978.
[7] Rose, Frank, "Joy of Hacking", Science 82, Vol. 3 No. 9, Nov. 82, pp.
58-66.
[8] "The Hacker Papers", Psychology Today, August, 1980.
[9] sdcarl!lin, "Real Programmers", USENET, Thu Oct 21 16:55:16 1982
August 18, 1984
From metheus!ogcvax!tektronix!uw-beaver!cornell!vax135!floyd!harpo!seismo!hao!ci
Real Programmers Don't Use Fortran, Either!
A recent article devoted to the *macho* side of programming
("Real Programmers Don't Use Pascal," by ucbvax!G:tut)
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 the term
"software" sounded funny and Real 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 was always dramatic. The LGP-30 booth
was packed at 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 assembly 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
he 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.
After 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 in touch with Mel, so I don't know if he ever gave in to the
flood of change 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.