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movq
www.uninformativ.de
 (25w ago)

I did a “lecture”/“workshop” about this at work today. 16-bit DOS, real mode. 💾 Pretty cool and the audience (devs and sysadmins) seemed quite interested. 🥳

  • People used the Intel docs to figure out the instruction encodings.
  • Then they wrote a little DOS program that exits with a return code and they used uhex in DOSBox to do that. Yes, we wrote a COM file manually, no Assembler involved. (Many of them had never used DOS before.)
  • DEBUG from FreeDOS was used to single-step through the program, showing what it does.
  • This gets tedious rather quickly, so we switched to SVED from SvarDOS for writing the rest of the program in Assembly language. nasm worked great for us.
  • At the end, we switched to BIOS calls instead of DOS syscalls to demonstrate that the same binary COM file works on another OS. Also a good opportunity to talk about bootloaders a little bit.
  • (I think they even understood the basics of segmentation in the end.)

The 8086 / 16-bit real-mode DOS is a great platform to explain a lot of the fundamentals without having to deal with OS semantics or executable file formats.

Now that was a lot of fun. 🥳 It’s very rare that we do something like this, sadly. I love doing this kind of low-level stuff.

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movq
www.uninformativ.de
 (25w ago)

Saw this on Mastodon:

https://racingbunny.com/@mookie/114718466149264471

18 rules of Software Engineering

  1. You will regret complexity when on-call
  2. Stop falling in love with your own code
  3. Everything is a trade-off. There’s no “best” 3. Every line of code you write is a liability 4. Document your decisions and designs
  4. Everyone hates code they didn’t write
  5. Don’t use unnecessary dependencies
  6. Coding standards prevent arguments
  7. Write meaningful commit messages
  8. Don’t ever stop learning new things
  9. Code reviews spread knowledge
  10. Always build for maintainability
  11. Ask for help when you’re stuck
  12. Fix root causes, not symptoms
  13. Software is never completed
  14. Estimates are not promises
  15. Ship early, iterate often
  16. Keep. It. Simple.

Solid list, even though 14 is up for debate in my opinion: Software can be completed. You have a use case / problem, you solve that problem, done. Your software is completed now. There might still be bugs and they should be fixed – but this doesn’t “add” to the program. Don’t use “software is never done” as an excuse to keep adding and adding stuff to your code.

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movq
www.uninformativ.de
 (25w ago)

Okay, here’s a thing I like about Rust: Returning things as Option and error handling. (Or the more complex Result, but it’s easier to explain with Option.)

fn mydiv(num: f64, denom: f64) -> Option<f64> {
    // (Let’s ignore precision issues for a second.)
    if denom == 0.0 {
        return None;
    } else {
        return Some(num / denom);
    }
}

fn main() {
    // Explicit, verbose version:
    let num: f64 = 123.0;
    let denom: f64 = 456.0;
    let wrapped_res = mydiv(num, denom);
    if wrapped_res.is_some() {
        println!("Unwrapped result: {}", wrapped_res.unwrap());
    }

    // Shorter version using "if let":
    if let Some(res) = mydiv(123.0, 456.0) {
        println!("Here’s a result: {}", res);
    }

    if let Some(res) = mydiv(123.0, 0.0) {
        println!("Huh, we divided by zero? This never happens. {}", res);
    }
}

You can’t divide by zero, so the function returns an “error” in that case. (Option isn’t really used for errors, IIUC, but the basic idea is the same for Result.)

Option is an enum. It can have the value Some or None. In the case of Some, you can attach additional data to the enum. In this case, we are attaching a floating point value.

The caller then has to decide: Is the value None or Some? Did the function succeed or not? If it is Some, the caller can do .unwrap() on this enum to get the inner value (the floating point value). If you do .unwrap() on a None value, the program will panic and die.

The if let version using destructuring is much shorter and, once you got used to it, actually quite nice.

Now the trick is that you must somehow handle these two cases. You must either call something like .unwrap() or do destructuring or something, otherwise you can’t access the attached value at all. As I understand it, it is impossible to just completely ignore error cases. And the compiler enforces it.

(In case of Result, the compiler would warn you if you ignore the return value entirely. So something like doing write() and then ignoring the return value would be caught as well.)

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bender
twtxt.net
 (26w ago)
↳ In-reply-to » @movq why Gopher to babble, and not just HTTP? I mean, may as well just write plain text files on your machine, and leave them there, right?

@prologic@twtxt.net I am finding writing my Notes very therapeutic. Just create a markdown file and commit, push, and it’s live. Whatever comes to mind, whatever I want to keep as relevant. Silly things, more like a dump.

If I feel like it, I do. If not, I don’t. Not social, not intended for anyone to see them. I am enjoying it!

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bender
twtxt.net
 (26w ago)
↳ In-reply-to » @bender Both Gopher and Mastodon are a way for me to “babble”. 😅 I basically shut down Gopher in favor of Mastodon/Fedi last year. But the Fediverse doesn’t really work for me. It’s too focused on people (I prefer topics) and I dislike the addictive nature of likes and boosts (I’m not disciplined enough to ignore them). Self-hosting some Fedi thing is also out of the question (the minimalistic daemons don’t really support following hashtags, which is a must-have for me).

@movq@www.uninformativ.de why Gopher to babble, and not just HTTP? I mean, may as well just write plain text files on your machine, and leave them there, right?

Gopher and Mastodon are two completely different things. That’s where my confusion comes from.

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lobste_rs
feeds.twtxt.net
 (27w ago)

How can one write blazing fast yet useful compilers (for lazy pure functional languages)?
I’ve decided enough is enough and I want to write my own compiler (seems I caught a bug and lobste.rs is definitely not discouraging it). The language I have in mind is a basic (lazy?) statically-typed pure functional programming language with do notation and records (i.e. mostly Haskell-lite).

I have other ideas I’d like to explore as well, but mainly, I want the compiler to be so fast (w/ optimisations) that … ⌘ Read more

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osnews
feeds.twtxt.net
 (27w ago)

A critical look at NetBSD’s installer
NetBSD is an OS that I installed only a couple of times over the years, so I’m not very familiar with its installer, sysinst. This fact was actually what led to this article (or the whole series rather): Talking to a NetBSD developer at EuroBSDcon 2023, I mentioned my impression that NetBSD was harder to install than it needed to be. He was interested in my perspective as a relative newcomer, and so I promised to take a closer look and write about it. While … ⌘ Read more

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