fast_float
draft
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fast_float
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Parquet: More than just “Turbo CSV”
> 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...
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What do number conversions (from string) cost?
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.
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Can sanitizers find the two bugs I wrote in C++?
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
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Passing Programs To A Stack Machine
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.
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Parsing can become accidentally quadratic because of sscanf
Just above this comment is a merged PR, which references fast_float library: https://github.com/fastfloat/fast_float
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Making Rust Float Parsing Fast: libcore Edition
Daniel Lemire @lemire (creator of the algorithm, author of the C++ implementation, and provided constant feedback to help guide the PR).
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RapidObj v0.1 - A fast, header-only, C++17 library for parsing Wavefront .obj files.
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.
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First release of dragonbox, a fast float-to-string conversion algorithm, is available
How this compares to https://github.com/fastfloat/fast_float ?
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Why is std::from_chars<float> slow?
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.
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Iterator invalidation of std::string_view
If you don't mind a 3rd party lib until your stdlib updates, https://github.com/fastfloat/fast_float is best-in-class.
draft
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C++23: The Next C++ Standard
I should have said the "latest standard", not "spec", if we're being technical. But EVERY bit of official material is very clear about asserting that C++23 is still a preview/in-progress, not a standard. Saying otherwise is, strictly speaking, incorrect.
https://isocpp.org/std/the-standard
https://www.iso.org/standard/79358.html
https://github.com/cplusplus/draft/blob/main/papers/n4951.md
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Never trust a programmer who says they know C++
[3] https://github.com/cplusplus/draft/releases/tag/n4917
*This is a joke, but only barely so.
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How to become a C++ Chad ?
pdf
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Why is the token "designator brace-or-equal-initializer" not defined in the C++ 20 standard document?
I'm currently going through Annex A of C++20, but I can't find the definition of "designator brace-or-equal-initializer", and couldn't find much formal information on it in an obvious way. The newest source on [decl] (https://github.com/cplusplus/draft/blob/main/source/declarations.tex) also doesn't seem to have it. Am I missing anything, or is this a missing definition in the standard grammar?
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Can sanitizers find the two bugs I wrote in C++?
> I don't have a copy of the standard at hand, can anyone quote the relevant section?
The C++ (draft) standard is on GitHub! [0] Compiling it needs Perl and some LaTeX packages, but is reasonably straightforwards otherwise. In addition, links to specific draft standards can be found on cppreference [1].
But anyways, in the first C++20 post-publication draft (N4868), the wording you're interested in is in multiple sections. Section 22.2.3 Sequence Containers [sequence.reqmts] has Table 78: Optional sequence container operations [tab:container.seq.opt] (starting on page 815), which states that a precondition of pop_back() is that empty() returns false. Section 16.3.2.4 Detailed Specifications [structure.specifications] (page 481) states:
> Preconditions: the conditions that the function assumes to hold whenever it is called; violation of any preconditions results in undefined behavior.
Therefore, calling pop_back() on an empty vector results in undefined behavior.
> Is this something that in practice is implemented in different (exception-throwing) ways?
Based on a quick glance at the major implementations (libc++ 15.0.7 at [2], MSVC at [3], libstdc++ at [4]), it looks like asserts are used. Whether those result in exceptions probably depends on whether the asserts are compiled in in the first place and how they are implemented, but it's definitely not a guaranteed exception.
[0]: https://github.com/cplusplus/draft
[1]: https://en.cppreference.com/w/cpp/links
[2]: https://github.com/llvm/llvm-project/blob/llvmorg-15.0.7/lib...
[3]: https://github.com/llvm/llvm-project/blob/8dfdcc7b7bf66834a7...
[4]: https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=libstdc%2B%2B-v3...
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How does Rust handle bounds checks that are incorrect in C/C++ due to signed integer conversion?
Which standard specifically are you quoting there? I checked an old and a new C++ draft in https://github.com/cplusplus/draft/tree/main/papers, and in neither one did 6.3 have anything like that.
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Rust and C++
https://github.com/cplusplus/draft/releases/download/n4917/n4917.pdf (page 1, chapter 1 scope):
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WG21, aka C++ Standard Committee, October 2022 Mailing
PRs for C++ are at https://github.com/cplusplus/draft But the discussion for a PR is via https://isocpp.org/std/submit-a-proposal
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My programming language history
C/C++
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How to overload function parameter to accept either raw pointer or c-array
By the way, https://github.com/cplusplus/draft/releases/tag/n4910 , says
What are some alternatives?
dragonbox - Reference implementation of Dragonbox in C++
team - Rust teams structure
rapidobj - A fast, header-only, C++17 library for parsing Wavefront .obj files.
LLVMSharp - LLVM bindings for .NET Standard written in C# using ClangSharp
C++ Format - A modern formatting library
papers
fast-float-rust - Super-fast float parser in Rust (now part of Rust core)
Asciidoctor - :gem: A fast, open source text processor and publishing toolchain, written in Ruby, for converting AsciiDoc content to HTML 5, DocBook 5, and other formats.
RapidJSON - A fast JSON parser/generator for C++ with both SAX/DOM style API
cppwp - HTML version of the current C++ working paper
simdutf8 - SIMD-accelerated UTF-8 validation for Rust.
libhal - A collection of interfaces and abstractions for embedded peripherals and devices using modern C++