mel

The story of Mel
Mel
Story of Mel
The story of Mel, a Real Programmer

   <programming, person> "The story of Mel, a Real Programmer",
   an 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 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
   Corporation}, 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-optimised 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 initialiser is optimised", he said proudly) he got
   a Change Request from the sales department.  The program used
   an elegant (optimised) 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 backward, 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."

   [Posted to USENET by its author, Ed Nather <utastro!nather>,
   on 1983-05-21].

   Was Mel, Mel Kaye? (http://foldoc.org/pub/misc/MelKaye.txt).

   [When did it happen?  Did Mel use hexadecimal or octal?]

   (2003-09-12)
    

MEL
       Maya Embedded Language (Maya)