资料来源 : Free On-Line Dictionary of Computing

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 ,
        on 1983-05-21].
     
        {Was Mel, Mel Kaye? (http://www.foldoc.org/pub/MelKaye.txt)}.
     
        [When did it happen?  Did Mel use hexadecimal or octal?]
     
        (2003-09-12)