Trust your compiler: Modern C++ • Hacker News Board

Re: Trust your compiler: Modern C++

#41

Post by anamax » Mon, Jul 06, 2026, 7:59 AM UTC

gmueckl wrote: post #28

Someone wrote: post #18

Earlier quoted context omitted.

> even the best compilers don’t use a third of the opcodes our modern CPUs boast of That’s not necessarily an indication of the weakness of compilers. It also could be an indication that hardware designers could leave out instructions. X86, in particular, will have lots of them for backwards compatibility reasons (extreme example: the old 80-bit x87 FP stack) There also are instructions that are expected to never get…

x87 support may not be the most obscure part of the instruction set. Ther is also hardware support for BCD math in 16 bit amd 32 bit mode. Who uses that anymore?

bcd is a reasonable way to do fixed-point decimal arithmetic.

binary floating point, let alone IEEE, is almost useless for implementing decimal arithmetic.

Re: Trust your compiler: Modern C++

#42

Post by sylware » Mon, Jul 06, 2026, 9:17 AM UTC

galangalalgol wrote: post #17

pjmlp wrote: post #7

Earlier quoted context omitted.

Quite funny comment on the vibe coding age.

Quit poking at the openbsd maintainers. Jokes aside (I mean maybe they are one I don't know), it is at least a coherent opinion that inherently complex but critical software infrastructure would ideally be kept as simple and understandable as possible with all the correctness and verification apparatus staying out of the way so you can see what is there to be backdoored. I use rust primarily and like using it, but th…

If I am not too mistaken, microsoft rust syntax is close to c++ brain damage one, namely it is the issue more than any solution. Not to mention the cost of its runtime.

Re: Trust your compiler: Modern C++

#43

Post by Joker_vD » Mon, Jul 06, 2026, 9:56 AM UTC

ks6g10 wrote: post #33

gmueckl wrote: post #28

Earlier quoted context omitted.

x87 support may not be the most obscure part of the instruction set. Ther is also hardware support for BCD math in 16 bit amd 32 bit mode. Who uses that anymore?

Unfortunately some exchanges (twse) uses packed BCD encoding.

BCD allows for insanely fast conversion to and from decimal string representation. And if doing arithmetic in it is only slightly worse than doing it in binary... it may actually be faster on the whole for some workloads.

Re: Trust your compiler: Modern C++

#44

Post by foxhill » Mon, Jul 06, 2026, 6:24 PM UTC

chrka wrote: post #30

Don't trust your compiler. Your code is only fast if you're lucky. https://tiki.li/blog/lucky_code.html

that's a nice example. on my M4, i measured 3.4s vs. 0.42s. honestly surprised there's ~10x improvement to be found.

as you've pointed out, you've literally micro-optimised this - isn't this what you'd expect? :)

Re: Trust your compiler: Modern C++

#45

Post by gmueckl » Mon, Jul 06, 2026, 7:17 PM UTC

Joker_vD wrote: post #43

ks6g10 wrote: post #33

Earlier quoted context omitted.

Unfortunately some exchanges (twse) uses packed BCD encoding.

BCD allows for insanely fast conversion to and from decimal string representation. And if doing arithmetic in it is only slightly worse than doing it in binary... it may actually be faster on the whole for some workloads.

But those instructions were dropped in 64 bit mode.

Re: Trust your compiler: Modern C++

#46

Post by ks6g10 » Tue, Jul 07, 2026, 6:23 PM UTC

foxhill wrote: post #44

chrka wrote: post #30

Don't trust your compiler. Your code is only fast if you're lucky. https://tiki.li/blog/lucky_code.html

that's a nice example. on my M4, i measured 3.4s vs. 0.42s. honestly surprised there's ~10x improvement to be found. as you've pointed out, you've literally micro-optimised this - isn't this what you'd expect? :)

But what is the resulting assembly? I would assume completely different!

Re: Trust your compiler: Modern C++

#47

Post by deterministic » Thu, Jul 09, 2026, 5:39 AM UTC

I trust the C++ committee to introduce new features in the most convoluted way possible, then spend the next 20 years trying to fix it, while adding even more syntax that makes my eyes hurt.

Case in point: templates. They are essentially a pure functional programming language embedded inside C++, expressed in a verbose syntax that barely resembles the rest of the language, and somehow makes even Java look concise.

It has been a slow-motion train wreck, with one questionable design decision after another. And a perfect example of why design by committee often leads to unnecessary complexity.