librope VS SDS

Yep. A few years ago I implemented a skip list based rope library in C[1], and after learning rust I eventually ported it over[2].

The rust implementation was much less code than the C version. It generated a bigger assembly but it ran 20% faster or so. (I don't know why it ran faster than the C version - this was before the noalias analysis was turned on in the compiler).

Its now about 3x faster than C, thanks to some use of clever layered data structures. I could implement those optimizations in C, but I find rust easier to work with.

C has advantages, but performance is a bad reason to choose C over rust. In my experience, the runtime bounds checks it adds are remarkably cheap from a performance perspective. And its more than offset by the extra optimizations the rust compiler can do thanks to the extra knowledge the compiler has about your program. If my experience is anything to go by, naively porting C programs to rust would result in faster code a lot of the time.

And I find it easier to optimize rust code compared to C code, thanks to generics and the (excellent) crates ecosystem. If I was optimizing for runtime speed, I'd pick rust over C every time.

[1] https://github.com/josephg/librope

[2] https://github.com/josephg/jumprope-rs

> it’s not clear if this will be a positive for native dev advocacy

I've rewritten a few things in rust. Seems pretty positive to me, because you can mix some of the best optimizations and data structures you'd write in C, with much better developer ergonomics.

A few years ago I wrote a rope library in C. This is a library for making very fast, arbitrary insert & delete operations in a large string. My C code was about as fast as I could make it at the time. But recently, I took a stab at porting it to Rust to see if I could improve things. Long story short, the rust version is another ~3x faster than the C version.

https://crates.io/crates/jumprope

(Vs in C: https://github.com/josephg/librope )

The competition absolutely isn't fair. In rust, I managed to add another optimization that doesn't exist in the C code. I could add it in C, but it would have been really awkward to weave in. Possible, but awkward in an already very complex bit of C. In rust it was much easier because of the language's ergonomics. In C I'm using lots of complex memory management and I don't want to add complexity in case I add memory corruption bugs. In rust, well, the optimization was entirely safe code.

And as for other languages - I challenge anyone to even approach this level of performance in a non-native language. I'm processing ~30M edit operations per second.

But these sort of performance results probably won't scale for a broader group of programmers. I've seen rust code run slower than equivalent javascript code because the programmers, used to having a GC, just Box<>'ed everything. And all the heap allocations killed performance. If you naively port python line-by-line to rust, you can't expect to magically get 100x the performance.

Its like, if you give a top of the line Porsche to an expert driver, they can absolutely drive faster. But I'm not an expert driver, so I'll probably crash the darn thing. I'd take a simple toyota or something any day. I feel like rust is the porsche, and python is the toyota.

> I have no idea whether that matters or even easy to measure...

It is reasonably easy to measure, and the GP is about right. I've measured a crossover point of around a few hundred items too. (Though I'm sure it'll vary depending on use case and whatnot.)

I made a rope data structure a few years ago in C. Its a fancy string data structure which supports inserts and deletes of characters at arbitrary offsets. (Designed for text editors). The implementation uses a skip list (which performs similarly to a b-tree). At every node we store an array of characters. To insert or delete, we traverse the structure to find the node at the requested offset, then (usually) memmove a bunch of characters at that node.

Q: How large should that per-node array be? A small number would put more burden on the skip list structure and the allocator, and incur more cache misses. A large number will be linearly slower because of all the time spent in memmove.

Benchmarking shows the ideal number is in the ballpark of 100-200, depending on CPU and some specifics of the benchmark itself. Cache misses are extremely expensive. Storing only a single character at each node (like the SGI C++ rope structure does) makes it run several times slower. (!!)

Code: https://github.com/josephg/librope

This is the constant to change if you want to experiment yourself:

https://github.com/josephg/librope/blob/81e1938e45561b0856d4...

In my opinion, hash tables, btrees and the like in the standard library should probably swap to flat lists internally when the number of items in the collection is small. I'm surprised more libraries don't do that.

Let me reframe this. What we're saying to do is stop using C string manipulation such as strcat, strcpy, etc. Particularly, I'm saying simply don't use C-style null terminated strings until you actually go to call a C ABI interface where it is necessary.

The argument against this is that you might call something that already does this. Yes, sure, that IS true, but what this betrays is the fact that you have to deal with that regardless of whether or not you add additional error-prone C string manipulation code on top of having to worry about memory ownership, mutation, etc. when passing blobs of memory to "untrusted" APIs.

It's not about passing the buck. Passing a blob of memory to an API that might do horrible things not defined by an API contract is not safe if you do strcat to construct the string or you clone it out of an std::string or you marshal it from Go or Rust. It's about not creating a bigger mess than you already have.

Okay fine, but what if someone hates C++ and Rust and Go and Zig? No problem. There are a slew of options for C that can all handle safer, less error-prone string manipulation, including interoperability with null-terminated C strings. Like this one used in Redis:

https://github.com/antirez/sds

And on top of everything else, it's quite ergonomic, so it seems silly to not consider it.

This entire line of thinking deeply reminds me of Technology Connection's video The LED Traffic Light and the Danger of "But Sometimes!".

https://youtube.com/watch?v=GiYO1TObNz8

I think hypothetically you can construct some scenarios where not using C strings for string manipulation requires more care, but justifying error prone C string manipulation with "well, I might call something that might do something unreasonable" as if that isn't still your problem regardless of how you get there makes zero sense to me.

And besides, these hypothetical incorrect APIs would crash horrifically on the DS9K anyways.

Even better, use a string handling library. Personally I am a big fan of (sds)[https://github.com/antirez/sds] from the Redis creator. It's not even a dependancy you can just copy the .c and .h to your project.

One nice application is length-prefixed string literals to complement dynamic string libraries:

The better answer would be to add data types like SDS[0] to the standard library, and use them as ADTs (Abstract Data Types) [1].

Unfortunely WG14 has proven in 30 years of existence, that it isn't something that they care to fix, and while 3rd party solutions exist, without vocabulary types on the stardard library adoption will never take off.

[0] - https://github.com/antirez/sds

[1] - https://en.wikipedia.org/wiki/Abstract_data_type

With the woes of string.h being known, why not just use an alternative like https://github.com/antirez/sds ?

I’ve also been having a blast with C because writing C feels like being a god! But the biggest thing that I like about C is that the world is sort of written on it!

Just yesterday I needed to parse a JSON… found a bunch of libraries that do that and just picked one that I liked the API.

Please note that the discussion started with requirement for no dynamic allocation in critical code what virtually eliminates std::string. I agree that std::string code tends to be simpler but the main reason is that the standard C library sucks on strings. There are better alternatives like sds but they are ... not standard.

Another day, another post about a writing a bespoke string lib instead of using SDS

d) everything being a macro seems overkill for me (and possibly dangerous, see b)). Maybe implement more as static inline functions, see the sds header: https://github.com/antirez/sds/blob/master/sds.h (which does a similar thing with the header struct).

For example, you can use the C language with sds strings (see https://github.com/antirez/sds) if you want to have an easier time with string formatting and don't want to worry about using the famously unsafe string.h functions correctly. You'll still program in ISO C, but just not in the standard library. The same applies to pretty much all parts of the standard library, the only part unsurpassed is pretty much just printf and the math headers (math.h, fenv.h, tgmath.h, complex.h) imo, and the occasional call to exit. A good place to look for libraries if you want to go that route is the awesome-c collection: https://github.com/oz123/awesome-c

One way around this problem is to declare the container as a pointer to the element type and then store the container’s metadata, alongside its elements, in the heap block to which the pointer points. This approach is already used for dynamic arrays in several container libraries, most notably stb_ds and sds. They place the metadata before the elements and provide the user with a pointer to the elements themselves (this has the nice effect that users can use the [] operator to access elements).