diff --git a/README.md b/README.md index 58e9340..070d7c8 100644 --- a/README.md +++ b/README.md @@ -20,7 +20,7 @@ RSS使用仓库的release RSS [链接](https://github.com/wanghenshui/cppweeklyn ## 2023 -| [121](./posts/121.md) | [122](./posts/122.md) | [123](./posts/123.md) | [124](./posts/124.md) | [125](./posts/125.md) | [126](./posts/126.md) | [127](./posts/127.md) | | | | +| [121](./posts/121.md) | [122](./posts/122.md) | [123](./posts/123.md) | [124](./posts/124.md) | [125](./posts/125.md) | [126](./posts/126.md) | [127](./posts/127.md) | [128](./posts/128.md) | | | | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | ------------------ | | [111](./posts/111.md) | [112](./posts/112.md) | [113](./posts/113.md) | [114](./posts/114.md) | [115](./posts/115.md) | [116](./posts/116.md) | [117](./posts/117.md) | [118](./posts/118.md) | [119](./posts/119.md) | [120](./posts/120.md) | | [101](./posts/101.md) | [102](./posts/102.md) | [103](./posts/103.md) | [104](./posts/104.md) | [105](./posts/105.md) | [106](./posts/106.md) | [107](./posts/107.md) | [108](./posts/108.md) | [109](./posts/109.md) | [110](./posts/110.md) | @@ -60,7 +60,7 @@ RSS使用仓库的release RSS [链接](https://github.com/wanghenshui/cppweeklyn - 杨杰 - 阿刚 - MSK -- 不语 x16 +- 不语 x17 - ywp - 范天泷 - 罗盛波 @@ -70,4 +70,5 @@ RSS使用仓库的release RSS [链接](https://github.com/wanghenshui/cppweeklyn - GYXL - Concept Matrixtang - chenbh -- 振羽 \ No newline at end of file +- 振羽 +- 汪总 \ No newline at end of file diff --git a/posts/126.md b/posts/126.md index eb02952..508fbea 100644 --- a/posts/126.md +++ b/posts/126.md @@ -376,6 +376,7 @@ consteval auto as_constant(auto value) { return value; } constexpr int Calc(int x) { return 4 * x; } +//consteval int Calc(int x) { return 4 * x; } int main() { auto res = Calc(2); // auto res = as_constant(Calc(2)); @@ -387,6 +388,8 @@ int main() { 如果改成as_constant就能编译过。as_constant看起来傻逼，但是强制编译期计算了 +之前代码抄错 [#68](https://github.com/wanghenshui/cppweeklynews/issues/68) @fanenr 指正，这里表示感谢 + #### [Making your own array](https://muit.xyz/posts/making-your-own-array/) diff --git a/posts/128.md b/posts/128.md new file mode 100644 index 0000000..6c84dba --- /dev/null +++ b/posts/128.md @@ -0,0 +1,371 @@ +--- +layout: post +title: 第128期 +--- +# C++ 中文周刊 第128期 + + +[周刊项目地址](https://github.com/wanghenshui/cppweeklynews) + +公众号 + + + + + +RSS https://github.com/wanghenshui/cppweeklynews/releases.atom + +欢迎投稿，推荐或自荐文章/软件/资源等 + +请[提交 issue](https://github.com/wanghenshui/cppweeklynews/issues) + + +126期代码抄错，这里指正一下 + +```c++ +consteval auto as_constant(auto value) { + return value; +} +constexpr int Calc(int x) { return 4 * x; } +// consteval int Calc(int x) { return 4 * x; } +int main() { + auto res = Calc(2); + // auto res = as_constant(Calc(2)); + ++res; + res = Calc(res); //编译不过 + return res; +} +``` +之前抄成consteval了，这里感谢 @fanenr 指正 + + + +另外感谢 `不语` `汪总` 赞助 + +--- + +## 资讯 + +标准委员会动态/ide/编译器信息放在这里 + +八月提案 https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/#mailing2023-08 + +[编译器信息最新动态推荐关注hellogcc公众号 上周更新 2023-08-16 第215期 ](https://github.com/hellogcc/osdt-weekly/blob/master/weekly-2023/2023-01-04.md) + +本周没更新 + +cppcon 2023开始卖票 + +## 文章 + +#### [Common patterns of typos in programming](https://pvs-studio.com/en/blog/posts/cpp/1064/) + +代码review + +memset用错，看不出问题的罚深蹲五个 + +```cpp +int64_t FileList::VMProcess(int OpCode, + void *vParam, + int64_t iParam) +{ + .... + PluginInfo *PInfo = (PluginInfo *)vParam; + memset(PInfo, 0, sizeof(PInfo)); + .... +} +``` +里面还有各种越界/复制粘贴错误。懒得贴了 + + +#### [The unexpected cost of shared pointers](https://oxla.com/the-unexpected-cost-of-shared-pointers/) + +一段简单的代码 + +```cpp +static constexpr std::size_t kLineSize = (1 << 23); // 8MB + +struct Line { + char _data[kLineSize]; + std::mutex _mtx; + std::atomic _size = 0; +}; + + +auto line = std::make_shared(); + +``` + +查perf图有莫名其妙的memset + +哈哈。之前咱们也提到过，数组，调用make_xx会帮你初始化，所以有memset + +除了标准库给的make_unique_for_overwrite这种玩意之外，也可以定制构造函数，构造函数为空，啥也不做就行了 + + +这个文章的标题不对了，这个其实和shared_ptr没啥关系，unique_ptr也有，本质是调用构造函数的问题，默认构造函数的问题 + + +#### [ow to Use Monadic Operations for `std::optional` in C++23 ](https://www.cppstories.com/2023/monadic-optional-ops-cpp23/) + +```cpp +std::optional fetchFromCache(int userId); +std::optional fetchFromServer(int userId); +std::optional extractAge(const UserProfile& profile); + +int main() { + const int userId = 12345; + + const auto ageNext = fetchFromCache(userId) + .or_else([&]() { return fetchFromServer(userId); }) + .and_then(extractAge) + .transform([](int age) { return age + 1; }); + + if (ageNext) + cout << format("Next year, the user will be {} years old", *ageNext); + else + cout << "Failed to determine user's age.\n"; +} + +``` + +就是介绍这几个新api的用法 + +其实看一下代码就懂了 + +#### [C/C++ performance pitfall: int8_t, aliasing and the ways out](https://gist.github.com/alexei-zaripov/dcc14c78819c5f1354afe8b70932007c) + +还是老生常谈的 char*歧义，导致不能充分优化，要么就restrict，要么就换成 别的类型来操作 + +别的类型，可以是你自己封装一下char，也可以是char8_t，_BitInt(8) 别用vector std::byte， 没用，背后还是char， + +以下两篇文章来自CppMore，大家也可以关注cppMore公众号 + +#### [Compile time dispatching in C++20](https://www.cppmore.com/2023/08/16/compile-time-dispatching-in-cpp20/) + +用fixed_stding做类型tag，tag有必要这么花哨吗 + +#### [Monads in Modern C++, What, Why, and How](https://www.cppmore.com/2023/08/14/monads-in-modern-c-what-why-and-how/) + +手把手教你熟悉monad，熟悉optional/expect/range，读者反馈讲的特好 + +其实就是状态链式流转，不知道为啥链式调用看起来很叼 + + +#### [现代C++学习——更好的单例模式](https://zhuanlan.zhihu.com/p/651173499) + +直接看代码吧，其实c++11的东西 + +```cpp +template +struct Singleton { + Singleton() = default; + ~Singleton() = default; + + // Delete the copy and move constructors + Singleton(const Singleton &) = delete; + Singleton &operator=(const Singleton &) = delete; + Singleton(Singleton &&) = delete; + Singleton &operator=(Singleton &&) = delete; + + static T &get() { + static T instance{}; + return instance; + } +}; +``` + +#### [Compile time string literal concatenation (or how to make your compiler cry)](https://www.reddit.com/r/cpp/comments/15z14hh/compile_time_string_literal_concatenation_or_how/) + +fixed_string怎么连接？？？？ + + +硬拷呗 + +```cpp +template +constexpr auto concat_fixed_string(basic_fixed_string l, + basic_fixed_string r) noexcept { + basic_fixed_string result; + auto it{ std::copy(l.begin(), l.end(), result.begin()) }; + it = std::copy(r.begin(), r.end(), it); + *it = {}; + return result; +} +``` + +代码来自 https://github.com/arturbac/small_vectors/blob/master/include/coll/basic_fixed_string.h + +或者体验这个 c++20的版本 https://godbolt.org/z/Gdfnsf8Pa 也是硬来 + +#### [C++ 异常与 longjmp](https://blog.hidva.com/2023/05/29/cppexception4/) + +看个乐 + +#### [Phantom and indulgent shared pointers](https://devblogs.microsoft.com/oldnewthing/20230818-00/?p=108619) + +介绍shared_ptr各种转换之后的内存问题，控制块和实际内存块占用关系/判定 + +我的评价是就当不知道这个事儿吧，看了迷糊 + +#### [On writing loops in PPL and continuation-passing style, part 1](https://devblogs.microsoft.com/oldnewthing/20230822-00/?p=108634) +#### [On writing loops in PPL and continuation-passing style, part 2](https://devblogs.microsoft.com/oldnewthing/20230823-00/?p=108640) +#### [On writing loops in PPL and continuation-passing style, part 3](https://devblogs.microsoft.com/oldnewthing/20230824-00/?p=108647) + +看得我眼睛疼 + + +#### [ User-defined class qualifiers in C++23 ](http://bannalia.blogspot.com/2023/08/user-defined-class-qualifiers-in-c23.html) + +利用boost::mp11来做tag + + +```cpp +#include +#include +#include + +template +struct access: T +{ + using qualifier_list=boost::mp11::mp_list; + + using T::T; +}; + +template +concept qualified = + (boost::mp11::mp_contains< + typename std::remove_cvref_t::qualifier_list, + Qualifiers>::value && ...); + +// some qualifiers +struct mut; +struct synchronized; + +template +concept is_mut = qualified; + +template +concept is_synchronized = qualified; + +struct X +{ + void foo() {} + + template + void bar(this Self&&) {} + + template + void baz(this Self&&) {} + + template + void qux(this Self&&) + requires qualified + {} +}; + +int main() +{ + access x; + + x.foo(); + x.bar(); + x.baz(); // error: associated constraints are not satisfied + x.qux(); // error: associated constraints are not satisfied + + X y; + x.foo(); + y.bar(); // error: associated constraints are not satisfied + + access z; + z.bar(); + z.baz(); + z.qux(); +} +``` + +我觉得tag挺简单的，怎么看大家都实现的这么复杂 + + + +#### [Transcoding Latin 1 strings to UTF-8 strings at 18 GB/s using AVX-512](https://lemire.me/blog/2023/08/18/transcoding-latin-1-strings-to-utf-8-strings-at-12-gb-s-using-avx-512/) + + +SIMD时间 + +常规 + +```c + unsigned char byte = data[pos]; +if ((byte & 0x80) == 0) { // if ASCII + // will generate one UTF-8 byte + *utf8_output++ = (char)(byte); + pos++; +} else { + // will generate two UTF-8 bytes + *utf8_output++ = (char)((byte >> 6) | 0b11000000); + *utf8_output++ = (char)((byte & 0b111111) | 0b10000000); + pos++; +} + +``` + +SIMD + +```c +__mmask32 nonascii = _mm256_movepi8_mask(input); +__mmask64 sixth = +_mm512_cmpge_epu8_mask(input, _mm512_set1_epi8(-64)); +const uint64_t alternate_bits = UINT64_C(0x5555555555555555); +uint64_t ascii = ~nonascii; +uint64_t maskA = ~_pdep_u64(ascii, alternate_bits); +uint64_t maskB = ~_pdep_u64(ascii>>32, alternate_bits); +// interleave bytes from top and bottom halves (abcd...ABCD -> aAbBcCdD) +__m512i input_interleaved = _mm512_permutexvar_epi8(_mm512_set_epi32( +0x3f1f3e1e, 0x3d1d3c1c, 0x3b1b3a1a, 0x39193818, +0x37173616, 0x35153414, 0x33133212, 0x31113010, +0x2f0f2e0e, 0x2d0d2c0c, 0x2b0b2a0a, 0x29092808, +0x27072606, 0x25052404, 0x23032202, 0x21012000 +), input); +// double size of each byte, and insert the leading byte +__m512i outputA = _mm512_shldi_epi16(input_interleaved, _mm512_set1_epi8(-62), 8); +outputA = _mm512_mask_add_epi16(outputA, (__mmask32)sixth, outputA, _mm512_set1_epi16(1 - 0x4000)); +__m512i leadingB = _mm512_mask_blend_epi16((__mmask32)(sixth>>32), _mm512_set1_epi16(0x00c2), _mm512_set1_epi16(0x40c3)); +__m512i outputB = _mm512_ternarylogic_epi32(input_interleaved, leadingB, _mm512_set1_epi16((short)0xff00), (240 & 170) ^ 204); // (input_interleaved & 0xff00) ^ leadingB +// prune redundant bytes +outputA = _mm512_maskz_compress_epi8(maskA, outputA); +outputB = _mm512_maskz_compress_epi8(maskB, outputB); +``` + +眼睛花了 + +代码在这里 https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/tree/master/2023/08/18 + + +## 视频 + +- [What is Low Latency C++? (Part 1) - Timur Doumler - CppNow 2023](https://www.youtube.com/watch?v=EzmNeAhWqVs&ab_channel=CppNow) +- [What is Low Latency C++? (Part 2) - Timur Doumler - CppNow 2023](https://www.youtube.com/watch?v=5uIsadq-nyk&ab_channel=CppNow) + +太长了没看完。周末总结一下 + +## 开源项目需要人手 + +- [asteria](https://github.com/lhmouse/asteria) 一个脚本语言，可嵌入，长期找人，希望胖友们帮帮忙，也可以加群384042845和作者对线 +- [Unilang](https://github.com/linuxdeepin/unilang) deepin的一个通用编程语言，点子有点意思，也缺人，感兴趣的可以github讨论区或者deepin论坛看一看。这里也挂着长期推荐了 +- [gcc-mcf](https://gcc-mcf.lhmouse.com/) 懂的都懂 + + +## 新项目介绍/版本更新 + +- https://github.com/fmtlib/fmt/releases/tag/10.1.0 fmt 速度更快了。推荐升级 + + +--- + + + +[本文永久链接](https://wanghenshui.github.io/cppweeklynews/posts/128.html) + +如果有疑问评论最好在上面链接到评论区里评论，这样方便搜索，微信公众号有点封闭/知乎吞评论