57 points stmonty 3 hours ago 6 comments

eigenblake 1 hour ago | parent

I'm very simple. I see Richard Feldman post. I like it. I'll leave it to the experts as to whether this is a case of opportunistic mutation.

jandrewrogers 1 hour ago | parent

Much of the difference in optimizability is that C/C++ allows you to do fairly extreme copy elision. This is important because memory bandwidth tends to be a major performance bottleneck.

C/C++ code can trivially reach into some remote bit of state and mutate it directly. The compiler rarely objects, no matter how ugly the access method or pattern. It is up to the programmer to make sure the invariants hold and the compiler can’t always see through it. These elided copies add up, though it usually has a maintainability and safety cost.

It is related to why functional languages tend to be mediocre for supercomputing in practice despite having nice properties for massive parallelism in theory.

whilenot-dev 24 minutes ago | parent

That's a nice explanation, thanks.

Are there any common resources for this kind of access methods and patterns that specifically aim to bridge the soft-/hardware gap? The best one I can come up with is Performance Analysis and Tuning on Modern CPUs[0] by Denis Bakhvalov.

[0]: https://github.com/dendibakh/perf-book

jeffbee 54 minutes ago | parent

This seems to raise the question: is libdeflate fast? My overall impression of libdeflate is that it produces a similar output size to zstd but takes 40 times longer to do it. I realize these are different algorithms of course, but they aren't that different, both being in the Huffman line of the LZ family. So why is libdeflate considered a performance benchmark?

antonvs 28 minutes ago | parent

It’s probably just because a zstd implementation in Lean would be more difficult. The whole project depends on being able to have a correctness proof for the implementation, and implementing that for the DEFLATE algorithm is simpler.

jdw64 53 minutes ago | parent

What are some well known programs made with Roc? And I'm curious about the difficulty level of its syntax