| slovo | definícia |
the story of mel, a real programmer
(foldoc) | The story of Mel, a Real Programmer
Mel
Story of Mel
The story of Mel
An article about hacker Mel Kaye,
posted
to Usenet by its author, Ed Nather , on 1983-05-21.
(David *)Frenkiel's 2022-07-22 analysis, {Mel's Hack – The Missing
Bits
(https://melsloop.com/docs/mels-hack-the-missing-bits)} casts doubt
on some of the
details presented in the original story and offers some alternative
explanations.
Original Text
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 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."
{Jargon File
(http://www.catb.org/jargon/html/story-of-mel.html)}.
[{On the trail of a Real Programmer
(http://www.jamtronix.com/blog/2011/03/25/on-the-trail-of-a-real-programmer/)},
2011-03-25 blog post by "jonno" at Jamtronix]
[When did it happen? Did Mel use hexadecimal or octal?]
(2003-09-12)
|
| | podobné slovo | definícia |
the story of mel, a real programmer
(foldoc) | The story of Mel, a Real Programmer
Mel
Story of Mel
The story of Mel
An article about hacker Mel Kaye,
posted
to Usenet by its author, Ed Nather , on 1983-05-21.
(David *)Frenkiel's 2022-07-22 analysis, {Mel's Hack – The Missing
Bits
(https://melsloop.com/docs/mels-hack-the-missing-bits)} casts doubt
on some of the
details presented in the original story and offers some alternative
explanations.
Original Text
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 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."
{Jargon File
(http://www.catb.org/jargon/html/story-of-mel.html)}.
[{On the trail of a Real Programmer
(http://www.jamtronix.com/blog/2011/03/25/on-the-trail-of-a-real-programmer/)},
2011-03-25 blog post by "jonno" at Jamtronix]
[When did it happen? Did Mel use hexadecimal or octal?]
(2003-09-12)
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