diff --git a/README.md b/README.md index 64544f5..b354060 100644 --- a/README.md +++ b/README.md @@ -26,7 +26,7 @@ RSS使用仓库的release RSS [链接](https://github.com/wanghenshui/cppweeklyn | [二十一](./posts/021.md) | [二十二](./posts/022.md) | [二十三](./posts/023.md) | [二十四](./posts/024.md) | [二十五](./posts/025.md) | [二十六](./posts/026.md) | [二十七](./posts/027.md) | [二十八](./posts/028.md) | [二十九](./posts/029.md) | [三十期](./posts/030.md) | | [三十一](./posts/031.md) | [三十二](./posts/032.md) | [三十三](./posts/033.md) | [三十四](./posts/034.md) | [三十五](./posts/035.md) | [三十六](./posts/036.md) | [三十七](./posts/037.md) | [三十八](./posts/038.md) | [三十九](./posts/039.md) | [四十期](./posts/040.md) | | [四十一](./posts/041.md) | [四十二](./posts/042.md) | [四十三](./posts/043.md) | [四十四](./posts/044.md) | [四十五](./posts/045.md) | [四十六](./posts/046.md) | [四十七](./posts/047.md) | [四十八](./posts/048.md) | [四十九](./posts/049.md) | [五十期](./posts/050.md) | -| [五十一](./posts/051.md) | [五十二](./posts/052.md) | [五十三](./posts/053.md) | [五十四](./posts/054.md)| [五十五](./posts/055.md) | | | | | | +| [五十一](./posts/051.md) | [五十二](./posts/052.md) | [五十三](./posts/053.md) | [五十四](./posts/054.md)| [五十五](./posts/055.md) | [五十六](./posts/056.md) | | | | | diff --git a/posts/056.md b/posts/056.md new file mode 100644 index 0000000..aec475a --- /dev/null +++ b/posts/056.md @@ -0,0 +1,346 @@ +--- +layout: post +title: 第56期 +--- + +# C++ 动态新闻推送 第56期 + +从[reddit](https://www.reddit.com/r/cpp/)/[hackernews](https://news.ycombinator.com/)/[lobsters](https://lobste.rs/)/[meetingcpp](https://www.meetingcpp.com/blog/blogroll/items/Meeting-Cpp-Blogroll-323.html/)摘抄一些c++动态 + +[周刊项目地址](https://github.com/wanghenshui/cppweeklynews)｜[在线地址](https://wanghenshui.github.io/cppweeklynews/) ｜[知乎专栏](https://www.zhihu.com/column/jieyaren) |[腾讯云+社区](https://cloud.tencent.com/developer/column/92884) + +弄了个qq频道，[手机qq点击进入](https://qun.qq.com/qqweb/qunpro/share?_wv=3&_wwv=128&inviteCode=xzjHQ&from=246610&biz=ka) + +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) + +最近非常忙，cppcon的视频没怎么看。更新也有拖延，见谅 + +--- + +## 资讯 + +标准委员会动态/ide/编译器信息放在这里 + +[编译器信息最新动态推荐关注hellogcc公众号 本周更新 第143期](https://github.com/hellogcc/osdt-weekly/blob/master/weekly-2022/2022-03-30.md) + +## 文章 + +- [chibicc——可能是可读性最强的 C 编译器](https://zhuanlan.zhihu.com/p/490307409) + +一个读编译器源码的大纲，可以看看 + +- [如何设计一个C++的类](https://zhuanlan.zhihu.com/p/271732707) + +其实是api设计理念的问题。哎。工作踩坑才会明白 + + + +- [Converting integers to decimal strings faster with AVX-512](https://lemire.me/blog/2022/03/28/converting-integers-to-decimal-strings-faster-with-avx-512/) + +[Daniel Lemire](https://lemire.me/blog/)博士老活，还是那个数组转字符串最快的问题，如何用avx实现 + +```c++ +void to_string_avx512ifma(uint64_t n, char *out) { + uint64_t n_15_08 = n / 100000000; + uint64_t n_07_00 = n % 100000000; + __m512i bcstq_h = _mm512_set1_epi64(n_15_08); + __m512i bcstq_l = _mm512_set1_epi64(n_07_00); + __m512i zmmzero = _mm512_castsi128_si512(_mm_cvtsi64_si128(0x1A1A400)); + __m512i zmmTen = _mm512_set1_epi64(10); + __m512i asciiZero = _mm512_set1_epi64('0'); + + __m512i ifma_const = _mm512_setr_epi64(0x00000000002af31dc, 0x0000000001ad7f29b, + 0x0000000010c6f7a0c, 0x00000000a7c5ac472, 0x000000068db8bac72, 0x0000004189374bc6b, + 0x0000028f5c28f5c29, 0x0000199999999999a); + __m512i permb_const = _mm512_castsi128_si512(_mm_set_epi8(0x78, 0x70, 0x68, 0x60, 0x58, + 0x50, 0x48, 0x40, 0x38, 0x30, 0x28, 0x20, 0x18, 0x10, 0x08, 0x00)); + __m512i lowbits_h = _mm512_madd52lo_epu64(zmmzero, bcstq_h, ifma_const); + __m512i lowbits_l = _mm512_madd52lo_epu64(zmmzero, bcstq_l, ifma_const); + __m512i highbits_h = _mm512_madd52hi_epu64(asciiZero, zmmTen, lowbits_h); + __m512i highbits_l = _mm512_madd52hi_epu64(asciiZero, zmmTen, lowbits_l); + __m512i perm = _mm512_permutex2var_epi8(highbits_h, permb_const, highbits_l); + __m128i digits_15_0 = _mm512_castsi512_si128(perm); + _mm_storeu_si128((__m128i *)out, digits_15_0); +} + + +void to_string_tree_table(uint64_t x, char *out) { + static const char table[200] = { + 0x30, 0x30, 0x30, 0x31, 0x30, 0x32, 0x30, 0x33, 0x30, 0x34, 0x30, 0x35, + 0x30, 0x36, 0x30, 0x37, 0x30, 0x38, 0x30, 0x39, 0x31, 0x30, 0x31, 0x31, + 0x31, 0x32, 0x31, 0x33, 0x31, 0x34, 0x31, 0x35, 0x31, 0x36, 0x31, 0x37, + 0x31, 0x38, 0x31, 0x39, 0x32, 0x30, 0x32, 0x31, 0x32, 0x32, 0x32, 0x33, + 0x32, 0x34, 0x32, 0x35, 0x32, 0x36, 0x32, 0x37, 0x32, 0x38, 0x32, 0x39, + 0x33, 0x30, 0x33, 0x31, 0x33, 0x32, 0x33, 0x33, 0x33, 0x34, 0x33, 0x35, + 0x33, 0x36, 0x33, 0x37, 0x33, 0x38, 0x33, 0x39, 0x34, 0x30, 0x34, 0x31, + 0x34, 0x32, 0x34, 0x33, 0x34, 0x34, 0x34, 0x35, 0x34, 0x36, 0x34, 0x37, + 0x34, 0x38, 0x34, 0x39, 0x35, 0x30, 0x35, 0x31, 0x35, 0x32, 0x35, 0x33, + 0x35, 0x34, 0x35, 0x35, 0x35, 0x36, 0x35, 0x37, 0x35, 0x38, 0x35, 0x39, + 0x36, 0x30, 0x36, 0x31, 0x36, 0x32, 0x36, 0x33, 0x36, 0x34, 0x36, 0x35, + 0x36, 0x36, 0x36, 0x37, 0x36, 0x38, 0x36, 0x39, 0x37, 0x30, 0x37, 0x31, + 0x37, 0x32, 0x37, 0x33, 0x37, 0x34, 0x37, 0x35, 0x37, 0x36, 0x37, 0x37, + 0x37, 0x38, 0x37, 0x39, 0x38, 0x30, 0x38, 0x31, 0x38, 0x32, 0x38, 0x33, + 0x38, 0x34, 0x38, 0x35, 0x38, 0x36, 0x38, 0x37, 0x38, 0x38, 0x38, 0x39, + 0x39, 0x30, 0x39, 0x31, 0x39, 0x32, 0x39, 0x33, 0x39, 0x34, 0x39, 0x35, + 0x39, 0x36, 0x39, 0x37, 0x39, 0x38, 0x39, 0x39, + }; + uint64_t top = x / 100000000; + uint64_t bottom = x % 100000000; + uint64_t toptop = top / 10000; + uint64_t topbottom = top % 10000; + uint64_t bottomtop = bottom / 10000; + uint64_t bottombottom = bottom % 10000; + uint64_t toptoptop = toptop / 100; + uint64_t toptopbottom = toptop % 100; + uint64_t topbottomtop = topbottom / 100; + uint64_t topbottombottom = topbottom % 100; + uint64_t bottomtoptop = bottomtop / 100; + uint64_t bottomtopbottom = bottomtop % 100; + uint64_t bottombottomtop = bottombottom / 100; + uint64_t bottombottombottom = bottombottom % 100; + // + memcpy(out, &table[2 * toptoptop], 2); + memcpy(out + 2, &table[2 * toptopbottom], 2); + memcpy(out + 4, &table[2 * topbottomtop], 2); + memcpy(out + 6, &table[2 * topbottombottom], 2); + memcpy(out + 8, &table[2 * bottomtoptop], 2); + memcpy(out + 10, &table[2 * bottomtopbottom], 2); + memcpy(out + 12, &table[2 * bottombottomtop], 2); + memcpy(out + 14, &table[2 * bottombottombottom], 2); +} + +``` + +avx版本要比大表快四倍，我没有编译验证，有空可以贴googlebenchmark跑一下 + +- [Automatic Serialization in C++ for Game Engines](https://indiegamedev.net/2022/03/28/automatic-serialization-in-cpp-for-game-engines/) + +用宏来反射。不多说 + +- [[RFC\] Lifetime annotations for C++](https://discourse.llvm.org/t/rfc-lifetime-annotations-for-c/61377) + +llvm考虑引入生命周期标记，这是整体设计文档 + +- [gcc 10, 11 std::span ABI break](https://www.reddit.com/r/cpp/comments/ttpe1p/gcc_10_11_stdspan_abi_break/) + +注意span使用，内存布局不同 + +- [Storing references of pointers in containers in C++](https://www.sandordargo.com/blog/2022/03/30/vector-of-references-of-pointers) + +别用数组存指针，用boost::ptr_vector + +别用数组存指针，局部性非常差 + +- [Software Design with Traits and Tag Dispatching](http://www.modernescpp.com/index.php/softwaredesign-with-traits-and-tag-dispatching) + +古老技术 + +```c++ +#include +#include +#include +#include +#include + +template +void advance_impl(InputIterator& i, Distance n, std::input_iterator_tag) { + std::cout << "InputIterator used" << '\n'; + while (n--) ++i; +} + +template +void advance_impl(BidirectionalIterator& i, Distance n, std::bidirectional_iterator_tag) { + std::cout << "BidirectionalIterator used" << '\n'; + if (n >= 0) + while (n--) ++i; + else + while (n++) --i; +} + +template +void advance_impl(RandomAccessIterator& i, Distance n, std::random_access_iterator_tag) { + std::cout << "RandomAccessIterator used" << '\n'; + i += n; // (5) +} + +template // (4) +void advance_(InputIterator& i, Distance n) { + typename std::iterator_traits::iterator_category category; + advance_impl(i, n, category); +} + +int main(){ + + std::cout << '\n'; + + std::vector myVec{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // (1) + auto myVecIt = myVec.begin(); + std::cout << "*myVecIt: " << *myVecIt << '\n'; + advance_(myVecIt, 5); + std::cout << "*myVecIt: " << *myVecIt << '\n'; + + std::cout << '\n'; + + std::list myList{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // (2) + auto myListIt = myList.begin(); + std::cout << "*myListIt: " << *myListIt << '\n'; + advance_(myListIt, 5); + std::cout << "*myListIt: " << *myListIt << '\n'; + + std::cout << '\n'; + + std::forward_list myForwardList{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // (3) + auto myForwardListIt = myForwardList.begin(); + std::cout << "*myForwardListIt: " << *myForwardListIt << '\n'; + advance_(myForwardListIt, 5); + std::cout << "*myForwardListIt: " << *myForwardListIt << '\n'; + + std::cout << '\n'; + +} +``` + + + +- [C++23 Will Be Really Awesome](https://www.kdab.com/cpp23-will-be-really-awesome/) + +介绍c++23强类型带来的优势 + +- [**Did you know that C++20 added support for floating point values as non-type template parameters?** ](https://github.com/QuantlabFinancial/cpp_tip_of_the_week/blob/master/271.md/) + +```c++ +emplate constexpr auto value = Value; + +int main() { + std::cout << value<4.2>; // prints 4.2 +} +``` + +以前只支持整数，现在浮点数也可以了（有啥用？？？？？？？？ ） + +- [`saturating_add` vs. `saturating_int` – new function vs. new type?](https://www.foonathan.net/2022/03/behavior-function-type/) + +实现一个能处理溢出的整型，实现一个函数好还是实现一个新类型好？想象int和std::atomic\ + +- [Working with Strings in Embedded C++](https://blog.feabhas.com/2022/02/working-with-strings-in-embedded-c/) + +嵌入式IoT环境 string选型，std::string想用用不了，std::pmr::string想用用不了 string_view可以用 + +- [C++20 Ranges: The Key Advantage - Algorithm Composition ](https://www.cppstories.com/2022/ranges-composition/) + +range的算法要比以前的stl算法优雅，建议多用 + +比如 + +```c++ +#include +#include +#include + +int main() { + const std::vector numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; + + auto even = [](int i) { return 0 == i % 2; }; + + std::vector temp; + std::copy_if(begin(numbers), end(numbers), std::back_inserter(temp), even); + std::vector temp2(begin(temp)+1, end(temp)); + + for (auto iter = rbegin(temp2); iter!=rend(temp2); ++iter) + std::cout << *iter << ' '; +} + +``` + + + +range + +```c++ +#include +#include +#include +#include // new header! + +int main() { + const std::vector numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; + + auto even = [](int i) { return 0 == i % 2; }; + + std::ranges::reverse_view rv{ + std::ranges::drop_view { + std::ranges::filter_view{ numbers, even }, 1 + } + }; + for (auto& i : rv) + std::cout << i << ' ';; +} + +``` + +明显range更好看 + + + +- [C and C++ coding style for best performance ](https://www.ibm.com/docs/en/aix/7.1?topic=implementation-c-c-coding-style-best-performance) + +Int char short，尽可能用int + +用char尽可能unsigned，（笔者注：不过最好标记出你到底用哪个。不同平台默认行为不同 arm默认unsigned x86默认signed） + +尽可能用局部变量不用全局变量，如果用，拷贝一份拿过来用 + +业务场景能用二进制判定就不要用字符串判定，字符串很浪费 + +Good + +```c +#define situation_1 1 +#define situation_2 2 +#define situation_3 3 +int situation_val; + +situation_val = situation_2; +. . . +if (situation_val == situation_1) +``` + +bad + +```c +char situation_val[20]; + +strcpy(situation_val,"situation_2"); +. . . +if ((strcmp(situation_val,"situation_1"))==0) +``` + +如果非要用string，尽量用fixed size封装结合mem\*算法使用，不要用str\*算法 会检查\0 + +## 视频 + +- [C++ Weekly - Ep 317 - Do You Really Understand Member Functions? ](https://www.youtube.com/watch?v=4etjb2_KAaE) + +成员函数是怎么工作的，this指针能不能复制一份？ + + + +## 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 +- [pika](https://github.com/OpenAtomFoundation/pika) 一个nosql 存储， redis over rocksdb，非常需要人贡献代码胖友们， 感兴趣的欢迎加群294254078前来对线 + +## 新项目介绍/版本更新 + +- [一个代码检测小工具，检查头文件](https://github.com/wqking/cpp-header-checker) +- [有哪些值得推荐的小型 C 语言开源项目？](https://www.zhihu.com/question/20792016/answer/2408343848) + +## 工作招聘 + +- [腾讯)编译器高级研发工程师 （北京/上海/杭州/深圳）](https://mp.weixin.qq.com/s/DF-2qmHmpKZtJ1djHXM1Ug) + +--- + +看到这里或许你有建议或者疑问或者指出错误，请留言评论! 多谢! 你的评论非常重要！也可以帮忙点赞收藏转发！多谢支持！ + +[本文永久链接](https://wanghenshui.github.io/cppweeklynews/posts/056.html)