Hacker News: teo_zero

New comment by teo_zero in "C++26: Trivial infinite loops are no longer undefined behaviour"

teo_zero — Sun, 20 Sep 2026 13:47:44 +0000

> Why use a for loop with a bound as an example instead of while loops with linked lists?

I'm the author of the example. I wanted to keep it as simple as possible, and this is the most common form of for loop. I was sure that HN readers would be clever enough to "map" it to whatever they have in their mind that satisfy the undecidability of the condition.

But since you're nitpicking, I haven't specified the types of i and n: i is uint8_t and n is uint32_t. Does it terminate? It depends on the value of n!

New comment by teo_zero in "C++26: Trivial infinite loops are no longer undefined behaviour"

teo_zero — Sun, 20 Sep 2026 13:21:31 +0000

Whenever you write a succinct example or a metaphor to try to explain in a few words a complicated concept, someone will nitpick small details of your construction, thus focusing on the form and missing the spirit!

Forget if "iForget if A and B can alias or not: the sense is having two independent actions that can be executed in the same loop or in two consecutive loops.

Let's see... what about the following example, that replaces all a's with @ and all e's with & in a zero-terminated string s?

  for (char *p=s; *p; p++)
    if (*p=='a')
      *p='@';
  for (char *p=s; *p; p++)
    if (*p=='e')
      *p='&';

If a compiler is allowed to assume that the first loop terminates, then it may optimize it to:

  for (char *p=s; *p; p++) {
    if (*p=='a')
      *p='@';
    if (*p=='e')
      *p='&';
  }

Is this explanation less insane?

New comment by teo_zero in "C++26: Trivial infinite loops are no longer undefined behaviour"

teo_zero — Sat, 19 Sep 2026 20:04:14 +0000

> I'm not sure what this has to do with my comment

Because you explicitly mentioned details that belong in the implementation, not in the semantic:

> A halt/abort instruction that trashes [the] state would be undesirable

If you want to attach a debugger, then use a breakpoint, don't try to obtain the same effect within the code.

New comment by teo_zero in "C++26: Trivial infinite loops are no longer undefined behaviour"

teo_zero — Sat, 19 Sep 2026 07:05:20 +0000

Take this example:

  for (i=0;i


It can be conveniently transformed into this:
  for (i=0;i

They are exactly equivalent except if the first loop never terminates.Now, the compiler could try to understand if the first loop does or doesn't terminate, and apply or not the optimization accordingly, but Turing tought us that is indeed a hard task!
Or it could decide to never apply it, for fear of those rare and usually pathological cases where the first loop doesn't terminate.
Or it could decide to apply it by default and accept that in those cases the program does something different than what the source code says. The latter is better known as UB.
The third option won, and that's why infinite loops are UB in the standard.



New comment by teo_zero in "C++26: Trivial infinite loops are no longer undefined behaviour"
teo_zero — Sat, 19 Sep 2026 06:29:02 +0000

Expecting a piece of code to be compiled to a precise sequence of machine instructions is exactly what you should not do with high-level languages like C++. Their task is exactly to abstract the machine away. They give you the guarantee that the final observable result will be what you asked for, not that the means to obtain that result will be what you have in mind.
If you write a loop to zero out some memory, it can be compiled to a loop, or to a call to an optimized predefined function, or even to a sequence of single zeroing instructions, if the size is small enough.
Even a single statement as a=0 may be compiled to a "load immediate" instruction, or an "XOR with itself", or a "sub with itself", or a move from another register known to be 0.



New comment by teo_zero in "Base84 deserves a place in file names"
teo_zero — Mon, 14 Sep 2026 10:57:09 +0000

> How about case-insensitive filesystems? [...] Negligible.
I don't buy this. Finding collisions is pretty easy. In one repository I have these files:
  rank2.cpp
  rank4.cpp
  rankN.cpp

The last two have the same case-insensitive Base84 encoding:
  mz{QkARW;1cB
  mz{QkaRW;1cB




New comment by teo_zero in "Customizing my Compaq MX-11800 keyboard"
teo_zero — Sat, 12 Sep 2026 02:16:24 +0000

> I really like this website design
Reading it on my phone, I beg to differ.



New comment by teo_zero in "Show HN: GET Together – A social network where you don't need POST to Post"
teo_zero — Mon, 07 Sep 2026 05:19:23 +0000

Doesn't pressing "back" in the browser repost the same message?



New comment by teo_zero in "New type of dice guarantees no tie when deciding who goes first"
teo_zero — Fri, 04 Sep 2026 05:26:33 +0000

How do you decide who is going to pull the tokens?



New comment by teo_zero in "New type of dice guarantees no tie when deciding who goes first"
teo_zero — Fri, 04 Sep 2026 05:20:22 +0000

And how do you decide who is going to throw that one die?



New comment by teo_zero in "Why OOP Exists"
teo_zero — Mon, 31 Aug 2026 08:28:18 +0000

> this is just structs.
Yes. And structs are just bytes. Levels of abstractions don't do anything the underlying levels don't already do, they just give you means to express your intent in a clearer form.



New comment by teo_zero in "Creepy Crawlies"
teo_zero — Sun, 30 Aug 2026 14:43:39 +0000

But there are "cubic bazillions" of possible URLs that are being requested. Even if they boil down to "only" some millions actual commits, their rendered HTMLs are all different.



New comment by teo_zero in "Benchmarking Pocket-Scale Inference"
teo_zero — Sun, 30 Aug 2026 14:29:01 +0000

Tangent question: what about NPU performance? I always read about CPU vs GPU, but nobody talks about NPUs; I don't even know if llama supports them.
Why do phones and laptops get equipped with NPUs if there's no use for them?



New comment by teo_zero in "Tether: iMessage, SMS, etc. on Linux"
teo_zero — Sat, 29 Aug 2026 17:55:59 +0000

This is for iPhones only. Do I assume correctly that the issue is solved for Android, instead?



New comment by teo_zero in "Don't Wordle"
teo_zero — Wed, 26 Aug 2026 06:14:06 +0000

> count undo as a partial game over
Not at all. Contrary to other games where undos are cheating, here they are part of the game. Without them it would be 80% luck and only 20% strategy.
> which is heavily implied
I can't find anything that implies this. It explicitly says:
> This uses undos deliberately rather than only as an emergency
while avoiding undos is mentioned at the end as "The Purist approach", which I read as slightly mocking.
I see it like a chess problem where you have to find the best sequence of moves, so you start off with an intial move, then backtrack, explore another idea, etc. Not like a chess match where of course you cannot undo any move.



New comment by teo_zero in "Don't Wordle"
teo_zero — Tue, 25 Aug 2026 20:06:14 +0000

If your first word is four greens it's actually pretty good: you get to know four letters to avoid with just one undo!



New comment by teo_zero in "Turns are Better than Radians (2022)"
teo_zero — Thu, 20 Aug 2026 08:33:36 +0000

You might have misunderstood TFA. No push for trig reform, just a consideration on what internal representation is optimal in code.
Imagine it like someone suggesting (understandably) that you express memory sizes in hex: no push to make everybody stop using decimal numbers!



New comment by teo_zero in "Turns are Better than Radians (2022)"
teo_zero — Thu, 20 Aug 2026 08:24:46 +0000

The C standard defines the functions sinpi(), cospi(), etc. that act on half-turns. If you have a modern compiler, all you have to do is to include math.h



New comment by teo_zero in "AI;DR (AI; Didn't Read)"
teo_zero — Tue, 18 Aug 2026 12:27:41 +0000

Sure, it's your choice where to put your precious time. Exactly like Sheldon, you prefer not to dedicate any energy to question a judgment you have decided a priori. And like him, you might be missing out on some good stuff.



New comment by teo_zero in "AI;DR (AI; Didn't Read)"
teo_zero — Tue, 18 Aug 2026 12:12:51 +0000

While you went this road of the medical metaphor, taking antibiotics at the first suspect of sickness without checking what's really going on, is a sure way to help develop antibiotic-resistant viruses.
Please note the key item is without checking. I'm not denying that many AI-generated documents are likely to be garbage. But refusing to read them just because of it will result in a lot of throwing the baby out with the bathwater.