simdutf VS uni-algo

The project was mostly inspired by simdutf [0] which has been around for a couple of years already, and I don't think iconv has any of its vectorized implementations for other architectures.

[0] https://github.com/simdutf/simdutf

I'm actually doing something quite similar in my, in progress, unicode conversion routines.

For utf8 validation there is a clever algorithm that uses three 4-bit look-ups to detect utf8 errors: https://github.com/simdutf/simdutf/blob/master/src/icelake/i...

Aside on LMUL, if you haven't encountered it yet: rvv allows you to group vector registers when configuring the vector configuration with vsetvl such that vector instruction operate on multiple vector registers at once. That is, with LMUL=1 you have v0,v1...v31. With LMUL=2 you effectively have v0,v2,...v30, where each vector register is twice as large. with LMUL=4 v0,v4,...v28, with LMUL=8 v0,v8,...v24.

In my code, I happen to read the data with LMUL=2. The trivial implementation would just call vrgather.vv with LMUL=2, but since we only need a lookup table with 128 bits, LMUL=1 would be enough to store the lookup table (V requires a minimum VLEN of 128 bits).

So instead I do six LMUL=1 vrgather.vv's instead of three LMUL=2 vrgather.vv's because there is no lane crossing required and this will run faster in hardware: (see [0] for a relevant mico benchmark)

        # codegen for equivalent of that function

utf8 normalization, stemming, case insensitive comparison. https://github.com/unicode-rs example for rust What are options for C++? 1. translate to utf16 ( https://github.com/simdutf/simdutf ) and use icu -- slow 2. boost text, https://github.com/tzlaine/text , also slow (because the author doesn't care or couldn't care), we made a lot of patches to make our library faster than lucene, but still this part is slower than icu for utf16 (icu for utf16 also very slow...)

You can find the corresponding assembly code in this repository. The main branch only contains implementations based on C++ with intrinsics.

The next big thing is making it LSP-compatible. All language servers must implement UTF-16 based character offsets, which is kinda unfortunate considering that files are much more likely to be stored in UTF-8 (I think?). I don't want to do the UTF-8 -> UTF-16 transcoding, so instead I'll use the excellent simdutf library to count how much code points a UTF-8 string would take if it was transcoded into UTF-16 — which is much faster than actual transcoding. So this is what I'm going to do this week — rewriting parsers to produce UTF-16 offsets + some final benchmarking. After that is done, I'll consider the "research" part of this project completed and will start writing an actual Markdown parser.

You can find the assembly code here: https://github.com/simdutf/simdutf/tree/clausecker The corresponding C++ code is in the main branch.

Or via an ultrafast simdutf.

Safe layer is just bounds checks that work in all cases that I need, before that I was coping with -D_GLIBCXX_DEBUG (doesn't have safe iterators for std::string and std::string_view and that I need the most) and MSVC debug iterators (better but slow as hell in debug). You can read more about the implementation here: https://github.com/uni-algo/uni-algo/blob/main/doc/SAFE_LAYER.md Nothing interesting it's possible to implement all of this even in C++98 but no one cared back then and it's a shame that it's not in C++ standard so we cannot choose to use safe or unsafe std::string for example and must rely on implementations in compilers that are simply incomplete in many cases or implement it from scratch.

Why call your files modules? "Modular programming" or "Modular architecture" is pretty standard term in programming I don't think there are a good synonym for "module" word so I plan to use "Modules" and "C++20 Modules" to avoid ambiguity. You have one cpp file in the project. Any reason for that? Including Unicode data files that may be pretty big into header files hurts compilation speed. C++20 Modules will help with that and I plan to support it. I'd also recommend supporting CMake I will support CMake it just I didn't need it in my development stage. Overall, looks very nice. Thank you. I made a post on GitHub with some of my plans: https://github.com/uni-algo/uni-algo/issues/3