Self-Modifying and Machine-Generated Code

In a comment to my previous post, John Morales asked my opinion of self-modifying code.

Answering the question as asked

That’s an easy one:  it’s a maintenance nightmare.  Don’t do it.

More generally

Over the years, and I’m old enough to remember punching Hollerith cards1 and sticking them in sorting machines (wired boards were before my time), I’ve developed a very explicit coding style, principally because a week, a month, or a year from now, I don’t want to be wasting any time trying to puzzle out what the hell I was thinking about.  I always use meaningful identifiers (names of things that programmers make up), although I’ll break down and use abbreviations at block scope; and I avoid all the known anti-patterns (“magic numbers” come easily to mind).  When a function has more than one big thing to do, it’s time for refactoring.  I even prefer Allman-style curly brace placement precisely because it puts more white space in the code and so separates bits of code in ways that are immediately visible.

Back in my newbie days, I made all the newbie mistakes; I even thought that self-modifying code was Really Cool.  The only reason that I’m not still a newbie is that I learned from my mistakes (and I hope that I never stop learning).

Just for fun, I’ll put a cute little self-modifying PDP-8 program at the end of this post.

A related issue:  machine-generated code

This is a completely different thing and not particularly scary.  Programmers know how to write source code, which is just text; and they know how to write text to a file.  No big deal.  Indeed, the two programs that I wrote to generate simple Amtrak timetables and on-time performance statistics spit out complete Web pages2; and my timezone code comes with a couple of utilities that read Zoneinfo data and generate array initializers that get #included in other programs.  That’s all really simple stuff.

It could even be argued that this is what C++ templates are:  when you write a class template or function template, you’re telling the compiler how to write a class or a function for you.  Yes, really.  And if reflection makes its way into C++26, which is highly likely, we’ll have lots more compile-time code generation.3

1If I might stretch the meaning of “program” a bit beyond the breaking point for a moment, my first program was an 026 drum card.  That was back in the Viet Nam era when Sgt. Seymour was Base Fuels Accountant at March Air Force Base.  There was a very complicated daily report that got run overnight at 15th Air Force HQ; and it didn’t take me long to figure out that, in order to get the cards punched right the first time, I had to do it myself.

2It turns out that all I needed was good old HTML1 with no anchors or scripts…easy.

3But this kind of code generation is something that compiler authors do, not something that J. Random Coder like me does.  I know some compiler authors, and they’re way smarter than I am.  If those folks are the big leagues, I’m like an acceptable AAA baseball player when I’m having a good day.

Here’s a bit of machine-language PDP-8 code (not written by me) that sets all the bits in a memory field, including itself, to zero.

A PDP-8 field had 4096 12-bit words, so all the addresses and data are four octal digits.

ADDR  DATA  MNEMONIC
----  ----  --------
0004  1005  TAD 5
0005  3410  DCA I 10
0006  5004  JMP 4
0007  5404  JMP I 4
0010  0011  (data)
0011  2010  ISZ 10

TAD:  Two’s complement add.  Add the contents of the referenced location to the accumulator.

DCA:  Deposit and clear the accumulator.  Store the accumulator in the referenced location and set all the accumulator bits to zero.  The “I” in the mnemonic means “indirect”; and when absolute addresses 108 through 178 are used as indirect addresses, they pre-increment; so the first time the DCA I 10 instruction gets executed, it stores the accumulator in address 128, then 138, and so on.

JMP:  Jump to the referenced location.

ISZ:  Increment, skip if zero.  Add 1 to the referenced location and skip the next instruction if the sum is zero.

That first three-instruction loop just sticks 3410 all over memory until it finally wraps around to location 6 where we continue to location 7 and JMP I 4 to location 3410 and start executing 3410 instructions. 😎  Since DCA clears the accumulator, at this point we’re storing zeros all over memory.  0000 is an AND instruction:  load the bitwise AND of the referenced location and the accumulator into the accumulator.

I’ve forgotten what that final ISZ instruction is for, and I’m not in the mood to puzzle it out, so I’ll leave that as the dreaded exercise for the reader. 😎

You’ll notice that that program is not an algorithm because it doesn’t halt; it just keeps on executing AND 0 instructions.  When all the lights on the front panel stop flashing, you press the STOP switch. 😎

I’ve written a little paper about the PDP-8 if anybody is interested.

The Meeting is Over

We finished the ISO standards committee meeting that I sponsored a bit before noon on Saturday, then some medical stuff got in the way of this post.  I’ll probably write about that tomorrow or Friday.

I was freaking out most of the week worried that everything would go well, in part because my hearing aids give me hardly anything but distortion when trying to listen to amplified sounds, so I spent most days working from home via Zoom.  That was OK because I have a box that I can plug into the headphone jack on my laptop that generates a bluetooth signal that feeds my hearing aids and gives me good enough quality to understand human speech.  I did check into the hotel Sunday night to help with the setup and to make sure I’d be there for the Monday morning plenary, and again Friday night to help with packing up and to be there for the Saturday plenary.

I guess I needn’t have worried so much because I got quite a few very nice thank-you notes from several movers and shakers on the committee.  Herb Sutter, the WG21 Convenor (the ISO word for chairperson), has a better post about the meeting than I could write on his own blog.  There’s a really good summary of the meeting at the beginning if anybody is wondering how this ISO committee works.  After that, it gets pretty technical and maybe not of much interest to folks who aren’t computer programmers.

I was fortunate to be able to give the committee a bit of payback for everything I’ve gotten from it over the years, but I don’t know that I’ll be able to do that again.

The next face-to-face meeting will be in Wrocław, Poland; and I’ve written about that already with a link to one possible itinerary.  We’ll see whether I’m able to attend.  All the trains I’d ride in the U.S. except the trains between New York and Boston have checked baggage service, all the stations where I’d be changing trains have red cap service (help with luggage), and I get wheelchair assistance at airports*; but I’d be lugging my luggage around on all the European trains.  A lot depends on whether I can get wheelchair assistance from the Frankfurt airport’s terminal two to the airport’s regional train station in terminal one.  The bus from terminal two to terminal one, which I’ve used before, would probably be a major hassle given my current mobility issues.  We’ll see…

Update:  2024-07-06:  I’ve found that I can indeed get wheelchair assistance between the two terminals in Frankfurt.

*I’ve found out that wheelchair assistance at airports gives me license to cut in line at security, immigration, and the boarding gates.  I’m not sure I deserve that; but I guess it makes sense to allow the folks pushing the wheelchairs to spend less time with me and so serve more customers.

By Their Fruits

It might seem strange for an atheist to quote the Bible; but from the stopped-clock-right-twice-a-day department…

Trump’s never-ending lies made me think of Matthew 7:15-20.  Near the end of the Sermon on the Mount, Jesus warns against false prophets.  He says that, just as you can’t expect to get grapes from thornbushes nor figs from thistles, so you can’t expect to get the truth from those who customarily lie.

Will “Bible believers” who “love Jesus” be moved by teaching that’s actually attributed to Jesus in a gospel?  A few might; but for the most part, nope, not a chance.  “Wherefore by their fruits ye shall know them.” (KJV)

That Horrible Debate

I still can’t process the “debate” that some of us endured on Thursday; but it’s clear that Biden’s awful performance is almost all of what the media want to talk about.  Trump’s Gish gallop of one bare-faced lie after another is hardly mentioned.

How can that be?  The only thing I can think of is that Biden’s performance was shocking, but Trump’s lies were unsurprising.

The Debate

I guess I’ll watch the big debate tonight.  I don’t expect to learn anything new about either Biden’s or Trump’s policies; but this boomer thinks it’s a civic duty…or something.  This time, it might be fun to see how Trump reacts to having his microphone cut off when it’s not his turn.

I don’t watch enough TV to justify getting cable; so I won’t be watching on CNN; but all of the usual five broadcast networks will air the debate beginning at 8:00pm central time (my time since I live in St. Louis).  Curiously, the online version of TV Guide shows FOX dumping out at 9:37 with all the others ending at 10:00.  I’m guessing that FOX is worried about having to find nice things to say about Trump in post-debate analysis. 😎  I’ll probably watch on PBS even though I’ll likely have to put up with Amy Walter making self-fulfulling prophecies about “electability” in the post-debate segment.

Two of the networks will have pre-debate analysis:  ABC News Special: Race for the White House from 7:00 to 8:00, andFOX News Special: Democracy '24 from 7:30 to 8:00.  I wouldn’t normally pay any attention to corporate media’s predictions of what will happen, preferring to see what actually happens; but the FOX show is only half an hour long; and it might be interesting to see whether they mindlessly repeat Trump’s claim that Biden will be using performance-enhancing drugs or something even more stupid.

In any event, I guess I’ll have to miss parts one and two of Planet of the Spiders on the Retro TV network.

Sentimental Value

PZ has a post about an old pocket watch that he inherited that includes:

Not particularly rare or valuable, but I didn’t expect much — it’s value is all sentimental to me.

I thought of adding a comment, but it wouldn’t have been about watches, so rather than hijack PZ’s comment thread, I decided to write a short post of my own.

Years ago, my maternal grandmother found an old sampler in a trunk; and she put it in a frame and hung it on her wall.  I was the only grandchild who stood up on a chair, pointed to each of the letters, and said, “A-B-C-D…”, so I inherited it.

About thirty years ago, I showed it to a woman (I can’t remember her name) who was the curator of fabrics at the St. Louis Art Museum.  As soon as she saw it, her face dropped.  It’s in a rather common style for the time, and it’s unfinished.

But I got her to clean it up as best she could and mount it on an acid-free backing.  That cost me way more than the object is worth by itself; but, yeah, it’s sentimental.

photo of sampler

The Next Treatment

I mentioned in a previous post that the cancer had returned and that I’d be getting yet another round of treatments.  The plan was to start four weeks of more aggressive radiation, twice a day for five days per week, and start another round of chemotherapy on radiation day 1.  That changed for some reason I don’t remember; so the current plan is to do just the chemo today, tomorrow and Wednesday, and then start the radiation and second session of three days of chemo on the 28th.

2024-05-06 13:30:

Here I sit getting my first of three days of chemotherapy.  I got started shortly after noon with some administrivia, three drugs administered from a syringe hooked up to the IV, and a bag of some drug that took about half an hour to drip.  Bag number two has started and will drip for about an hour; and then there will be maybe ten or fifteen minutes of more administrivia.  I hope to be out of here by 15:00.

Social Media and Me

I’ve never used social media*, so I’ve never been affected in any way by the problems Facebook, Xitter, etc.  Am I missing something?

I remember PZ trying to choose between Mastodon and BlueSky, and Mike the Mad Biologist recently mentioned a couple of things that he likes about BlueSky.  Should I try out one of those?  What will I be able to do that I can’t do now?

*OK, I guess blogs are a kind of social media; but aside from that…

I did create a LinkedIn account near its beginning, but I wound up never using it for anything.

Likely More Cancer

Back on the 12th of last month, as part of the study I’m in, I had a CT scan that showed what could be another bit of cancer in my lungs; and a PET scan about a week later confirmed that the lump was “hypermetabolic’.

Today, I had a bronchoscopy and a biopsy of the new lump.  Since that required general anesthesia and I have no one to drive me home and watch out for me overnight, I was admitted to the hospital for “observation”.  If my last two biopsies are any indication, nothing will be observed; and I’ll be on my way home by late morning or early afternoon.

I’m not sure when I’ll find out the results of the biopsy, but it’ll be tomorrow at the earliest, maybe not until Monday.  I have appointments with the radiation and chemo oncologists next Thursday when I’ll decide what to do.  At my age, there won’t be any thoracic surgery.

Update, Friday the 19th:  one thing I forgot to mention is that they put me in a private room, which was convenient.  Also, I brought my laptop with me along with my WiFi hotspot, so I was able to mitigate some of the boredom.

There was one interesting bit of news on NBC’s Today:  Israel, in response to the Iranian attack, refrained from cranking it up to eleven.  I was surprised by that.

Around 10:15 this morning, the doctor who had the authority to release me deigned to show up; and since, just like after the first two bronchoscopies, I had no unexpected, or even uncomfortable, symptoms; so I was out by about 10:30.  At 12:30 as I write this, I’ve returned home, unpacked, and checked my regular mail, e-mail, and the blogs I frequent; so I’m now ready to resume my normal life. 😎

I still haven’t seen any results from the biopsy, but I don’t really expect that until Monday.

Update, 2024-04-25:  it’s definitely small-cell cancer that has shown up again, so the chemo routine will be mostly what I had before, the same drugs that I had no horrible response to; although they won’t be able to treat the low white blood cell side effect in the same way, so I might be also taking antibiotics to help guard against infection.  The chemo doctor also mentioned the possibility of immunotherapy, but they’ll wait on that depending on how the first round of chemo goes.

I’ll be getting lots more radiation, though:  twice a day, five days per week, for three weeks, starting on the 6th, a week from Monday.  I’ll probably get the first three-day round of chemo that first week; and it’s because of the radiation happening on the same days that they won’t be able to give me the Neulasta with the drugs that goose my bone marrow to counter the white blood cell deficiency.

I’ll know more when it actually happens, but I don’t expect any of the awful side effects of chemo since I tolerated it easily the last time.  I’ll be getting lots more radiation, but still low doses.  I think I remember being told that the dose is similar to what you get with a dental x-ray.

If my reaction to the chemo is no worse than it was the last time, the worst part of the business will likely be the drive to and from the hospital twice a day for three weeks.  One way takes me about half an hour on the best days; and since they want at least six hours between the first and second radiation treatments on each day, it’ll necessarily be scheduled to put me in rush-hour traffic to the hospital in the morning and home in the afternoon.  On the three chemo days, I’ll probably just hang around at the hospital all day; I’l take my laptop with me and be happy as a clam.  I’m not sure what I’ll do the other days.

I’ll keep readers informed about what goes on.  I’m not looking for sympathy (which, as I’ve said before, I don’t deserve); but maybe some folks might like to know what they might be up against (although I’m a statistic of one, of course, so YMMV).

My Next Excuse for Riding Trains

I won’t be blogging about riding trains until November when I’ll be traveling to Wrocław, Poland to attend a meeting of the ISO C++ standards committee, but I’m starting to think about it, and I’ve worked up a possible itinerary that includes a three-day conference in Berlin the week before and a one-day conference in Wrocław afterwards.

As I’ve said before, I like to fly Icelandair across the Pond because I like to get off the plane and stretch my legs in Keflavík.  Also, because travel to these meetings is the only thing I spend my fun money on, I’m fortunate to be able to afford Icelandair’s Saga class if I don’t try to afford other stuff that I don’t really want that much anyway.  (Business class on other airlines would probably be out of my price range; and besides, I wouldn’t want to sit in an airplane long enough to get all the way to Europe in one fell swoop.)

Unfortunately, Icelandair serves Berlin only five days per week, so the eastbound trip doesn’t work well.  I’m currently thinking about going a day late and missing almost all of the first day of Meeting C++.  I could fly into Frankfurt instead and take an ICE directly from the airport to Berlin; but then I’d have to return from Frankfurt to get the round-trip air fare; and getting from Wrocław to Frankfurt by train doesn’t look easy.

Update 2024-04-20:  I think I’ve found a way to get from Wrocław to the Frankfurt airport by train, and I like that better.  The link above is to the new version.  The version flying into and out of Berlin is still available here.

Nokia will be sponsoring a one-day conference called code:dive that’s still not officially announced, so I don’t know when or where it’ll be.  My rough itinerary assumes that it’ll be in the same hotel the Monday after the ISO meeting, which could be wrong; so the westbound trip is still subject to change.

Update, 2024-04-17:  I’ve added another option for the first leg that saves a long layover in Chicago.  That train originates in Kansas City and is often delayed on the former MoPac west of St. Louis, so I’m a bit leery about counting on it:  missing the very first connection would likely destroy the whole trip.

I checked out train 318’s arrival times in Chicago and the likelihood of making my connection back to the 1st of October, and it doesn’t look too dangerous; but I’m still not sure I’d want to chance it.  (If I look only at Mondays, which is the weekday I’ll be traveling, I never miss the connection on any of the 29 days; but it’s not clear whether the weekday actually has any effect.)  I probably won’t be making any reservations until the end of July or so, so I’ll check again then.  I’ll probably just stick with the Texas Eagle in any event since that will allow checking a bag all the way to New York.  (The Missouri-Illinois corridor trains don’t have checked baggage service.)

I’ve also been told that Nokia’s code:dive conference will definitely be on Monday, November 25th, but not at the Double Tree where the WG21 meeting will be.