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Adventures in Advent of Code

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Re: Adventures in Advent of Code

#21

Post by smcl »

stareatgoats wrote: post #2

When your code fails it's never the fault of the language. It's always ones own fault, a typo, some error in the logic, or something. Debugging always reveals that with a stone face. Always. Except > "It turns out, there was a bug in Set.intersection(_:), but it had only been discovered this past June, and the fix hasn’t made it into a public version of Swift yet. "

As someone who worked on C compilers for DSPs for a few years, I was conditioned for a while to think "compilers are broken, libraries are broken - you have no hope" for a while, when all I dealt with was our software. Obviously that's heavily influenced by what I was actually dealing with day to day and not by normal software development, but still :)

One of the guys in my team handled a frantic support request from a Formula 1 team because they required reproducible builds or else they got some fine from the FIA, and they somehow hit a situation where our compiler was outputting different code depending on time of day. Wild.

Re: Adventures in Advent of Code

#22

Post by forrestthewoods »

sokoloff wrote: post #12
mtlmtlmtlmtl wrote: post #9

I'll be doing AoC in C this year. And I've decided to do that every year as I enjoy doing it in C and trying to get the entire calendar, all 50 parts to run in less than one second on a single core, which it turns out is quite doable, but only with a much deeper understanding of the problems. I end up learning a lot more computer science this way. I also like it since I don't do any work or even side projects in C th…

Hat tip if you did 2021:14:2 under this constraint. I didn’t find the trick to allow that type of performance.

Is that the right day? My code for 2021:14 runs in 440 microseconds for both parts. 2021:23:2 is the only day I couldn't get under 1 second.

https://github.com/forrestthewoods/aoc2021/blob/master/rust/...

Re: Adventures in Advent of Code

#23

Post by sokoloff »

forrestthewoods wrote: post #22
sokoloff wrote: post #12

Earlier quoted context omitted.

Hat tip if you did 2021:14:2 under this constraint. I didn’t find the trick to allow that type of performance.

Is that the right day? My code for 2021:14 runs in 440 microseconds for both parts. 2021:23:2 is the only day I couldn't get under 1 second. https://github.com/forrestthewoods/aoc2021/blob/master/rust/...

I struggled with that one; thanks for linking your code; I’ll have a look and see the trick I missed.

Re: Adventures in Advent of Code

#24

Post by [deleted] »

js2 wrote: post #16

> The bug is fixed in Swift 5.7, but my computer is running macOS Monterey (12.6) and thus using an earlier version of Swift. I have since confirmed that the code works as expected on macOS Ventura. I guess the bug is apparently in the Swift runtime itself, and since Swift 5.0 and ABT stability, the runtime version is tied to the OS version. https://www.swift.org/blog/abi-stability-and-apple/ But I think that only ap…

[deleted]

Re: Adventures in Advent of Code

#25

Post by js2 »

jamamp wrote: post #15

I'm confused. The post mentioned that this was fixed in Swift 5.7, but I have Swift 5.7.1 on my macOS Monterey and the bug is still present if I modify my AoC solution to exhibit the problem. Is Swift 5.7.1 on Monterey different from the 5.7.1 on Ventura? $ swift -v Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51) Target: arm64-apple-macosx12.0 I love Swift as a language, but the lack of release n…

The bug is apparently in the Swift runtime. You may be compiling with Swift 5.7.1, but you must be picking up the older runtime distributed with macOS 12.6. I think you can still run locally against a more recent Swift runtime though:

https://news.ycombinator.com/item?id=33848354

Re: Adventures in Advent of Code

#26

Post by mtlmtlmtlmtl »

disposedtrolley wrote: post #11
mtlmtlmtlmtl wrote: post #9

I'll be doing AoC in C this year. And I've decided to do that every year as I enjoy doing it in C and trying to get the entire calendar, all 50 parts to run in less than one second on a single core, which it turns out is quite doable, but only with a much deeper understanding of the problems. I end up learning a lot more computer science this way. I also like it since I don't do any work or even side projects in C th…

Nice! I’m writing in C this year too, although I’m very much a beginner in C. What kinds of optimisations have you had to do? Are you hosting your code anywhere?

For doing it in C, by far the most useful thing you could do is implement your own generic hash table. Having a good hash table handy makes things a lot easier. Though since you're a beginner you might want to find a good library for it at first. Writing a hash table is great C exercise though, so I definitely recommend doing it at some point.

I don't necessarily want to share my github as it contains my real name, but I'd be willing to send you a tarball of my 2020 code tomorrow if you send an email to mtlmtlmtlmtl at pm.me

I've just now started on day 1 for this year, so no code there yet worth showing off.

Re: Adventures in Advent of Code

#27

Post by jamamp »

js2 wrote: post #25
jamamp wrote: post #15

I'm confused. The post mentioned that this was fixed in Swift 5.7, but I have Swift 5.7.1 on my macOS Monterey and the bug is still present if I modify my AoC solution to exhibit the problem. Is Swift 5.7.1 on Monterey different from the 5.7.1 on Ventura? $ swift -v Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51) Target: arm64-apple-macosx12.0 I love Swift as a language, but the lack of release n…

The bug is apparently in the Swift runtime. You may be compiling with Swift 5.7.1, but you must be picking up the older runtime distributed with macOS 12.6. I think you can still run locally against a more recent Swift runtime though: https://news.ycombinator.com/item?id=33848354

Ah, I forgot that compiling with an SDK version doesn't necessarily mean you get the runtime with it. Dynamic linking instead of static linking. Sometimes, software development gets too complicated; too many things to keep in mind.

Re: Adventures in Advent of Code

#28

Post by hansvm »

stareatgoats wrote: post #2

When your code fails it's never the fault of the language. It's always ones own fault, a typo, some error in the logic, or something. Debugging always reveals that with a stone face. Always. Except > "It turns out, there was a bug in Set.intersection(_:), but it had only been discovered this past June, and the fix hasn’t made it into a public version of Swift yet. "

Miscompilations (interpretations) are fairly common in my experience; just most of them don't drastically affect the final result.

I used to have a methodical way of investigating most bugs: (1) here's what I know, (2) here's what I don't, (3) here's the thing I would like to know to most restrict the remaining search space. It was fine enough for awhile, but when you don't know things like "I wrote a 0 here, therefore a 0 exists here", or "my code explicitly uses aligned 32-bit reads, so I issued an aligned 32-bit read here", the errors in your assumptions quickly get amplified into nonsense. Nowadays I explicitly includle miscompilation (interpretation), bit-flips, and other such garbage as I write down what I do or don't know about the system, and I throw in ballpark probabilities to figure out where to look next. Most debugging isn't noticably slower that way, but the hairy problems are easily 10x easier when you haven't conditioned yourself to ignore the real solution.

Re: Adventures in Advent of Code

#29

Post by Volundr »

sokoloff wrote: post #12
mtlmtlmtlmtl wrote: post #9

I'll be doing AoC in C this year. And I've decided to do that every year as I enjoy doing it in C and trying to get the entire calendar, all 50 parts to run in less than one second on a single core, which it turns out is quite doable, but only with a much deeper understanding of the problems. I end up learning a lot more computer science this way. I also like it since I don't do any work or even side projects in C th…

Hat tip if you did 2021:14:2 under this constraint. I didn’t find the trick to allow that type of performance.

Day 22 (https://adventofcode.com/2021/day/22) is the one that nearly killed me in 2021. I did get it using a technique of breaking any overlaps into smaller and smaller rectangles, but it took like 30s to run. I looked on the AoC reddit, and honestly I still don't understand what I needed to do to make it better, but visualizing 3d spaces has always been a weakness for me.
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