fast_float VS cppfront

> Google put in significant engineering effort into "Ryu", a parsing library for double-precision floating point numbers: https://github.com/ulfjack/ryu

It's not a parsing library, but a printing one, i.e., double -> string. https://github.com/fastfloat/fast_float is a parsing library, i.e., string -> double, not by Google though, but was indeed motivated by parsing JSON fast https://lemire.me/blog/2020/03/10/fast-float-parsing-in-prac...

For those that don't know, gcc 12.x updated its float parsing logic to something similar to fast_float and it's about 1/6 of the cost presented here (sub 100 in the graph presented here). Strongly suggest using that library or upgrading the compiler if you need the performance.

This makes sense for integers but betware floating point from_chars - libc++ still doesn't implement it and libstdc++ implements it by wrapping locale-dependent libc functions which involves temporarily changing the thread locale and possibly memory allocation to make the passed string 0-terminated. IMO libstdc++'s checkbox "solution" is worse than not implementing it at all - user's are better off using Lemire's API-compatible fast_float implementation [0].

[0] https://github.com/fastfloat/fast_float

I'm a bit stuck on how to do the same thing in c++, due to containers only having a single type. The very inefficient way I'm currently doing it is by passing a program as a vector of strings, and then converting the string constants to doubles with the fast_float library.

Just above this comment is a merged PR, which references fast_float library: https://github.com/fastfloat/fast_float

Daniel Lemire @lemire (creator of the algorithm, author of the C++ implementation, and provided constant feedback to help guide the PR).

And out of 6,000 lines in the file, at least 3000 are other people's code: earcut for polygon triangulation and fast_float because .obj files typically contain a lot of floating point numbers so it's important to parse them quickly.

How this compares to https://github.com/fastfloat/fast_float ?

I tried to compare it against Daniel Lemire's excellent fast_float library. Fast float took about 180ms for the same program, and all I did was change "std" namespace prefix to "fast_float". It's a factor of 12 difference, at least my machine. I tried MSVC next, and it is a lot better, but it is still ~4 times slower than fast float. AFAIK, clang currently does not implement the feature at all.

If you don't mind a 3rd party lib until your stdlib updates, https://github.com/fastfloat/fast_float is best-in-class.

In this article, we will explore how CppFront aims to make C++ a better place by introducing a new syntax, improving safety and usability and providing modern features that align with good programming practices - all while maintaining full interoperability with C++.

> And I'm left wondering, is this just how C++ is? Can't the language provide tooling for me to better adhere to its guidelines

Well, first, the language can't provide tooling: C++ is defined formally, not through tools; and tools are not part of the standard. This is unlike, say, Rust, where IIANM - so far, Rust has been what the Rust compiler accepts.

But it's not just that. C++ design principles/goals include:

* multi-paradigmatism;

* good backwards compatibility;

* "don't pay for what you don't use"

and all of these in combination prevent baking in almost anything: It will either break existing code; or force you to program a certain way, while legitimate alternatives exist; or have some overhead, which you may not want to pay necessarily.

And yet - there are attempts to "square the circle". An example is Herb Sutter's initiative, cppfront, whose approach is to take in an arguably nicer/better/easier/safer syntax, and transpile it into C++ :

https://github.com/hsutter/cppfront/

I’m not fond of adding an increasing number of specific compiler options for memory-safety. I love -faddress=sanitizer or -fsanitize. But the historically growing number of warning which need to be turned on is an issue. For example the options -Wconversion, -Wsign-conversion and -Warith-conversion shall be default with C++26. And if your code doesn’t compile use either an older revision or turn it deliberately off (saying: I’m aware, read the handbook, I take the risk).

I want some of not all the ideas of CPP2/cppfront[1] in C++XX. Finally using #unsafe when needed, like Rust. C++ does evolve over decades, more like other languages.

[1] https://github.com/hsutter/cppfront

CPP2/cppfront:

https://github.com/hsutter/cppfront

I hope we see this in C++26 as optional mode i.e. #safe and #unsafe and same for #impdef or so.

C++23 is done. But C++ is not! In this talk, the author shares his personal perspectives on an ongoing and very active evolution of C++, updates on his cppfront experimental compiler, and why compatibility is essential to the further success of the C++ development.

https://github.com/hsutter/cppfront

But his side project at Microsoft didn't gain traction with gcc, clang, etc and everybody else in the industry. So at this point, the C++ committee will be perceived as "so far behind" ... because there's nothing for them to vote on.