56 fix #5

wanghenshui · Apr 2, 2022 · 558a000 · 558a000
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@@ -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
@@ -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 <iterator>
+#include <forward_list>
+#include <list>
+#include <vector>
+#include <iostream>
+
+template <typename InputIterator, typename Distance>                    
+void advance_impl(InputIterator& i, Distance n, std::input_iterator_tag) {
+    std::cout << "InputIterator used" << '\n'; 
+    while (n--) ++i;
+}
+
+template <typename BidirectionalIterator, typename Distance>              
+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 <typename RandomAccessIterator, typename Distance>             
+void advance_impl(RandomAccessIterator& i, Distance n, std::random_access_iterator_tag) {
+    std::cout << "RandomAccessIterator used" << '\n';
+    i += n;                                                             // (5)
+}
+
+template <typename InputIterator, typename Distance>                    // (4)
+void advance_(InputIterator& i, Distance n) {
+    typename std::iterator_traits<InputIterator>::iterator_category category;    
+    advance_impl(i, n, category);                                               
+}
+  
+int main(){
+    
+    std::cout << '\n';
+    
+    std::vector<int> 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<int> 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<int> 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<double Value> 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\<int>
+
+- [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 <algorithm>
+#include <vector>
+#include <iostream>
+
+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<int> temp;    
+    std::copy_if(begin(numbers), end(numbers), std::back_inserter(temp), even);
+    std::vector<int> temp2(begin(temp)+1, end(temp));
+
+    for (auto iter = rbegin(temp2); iter!=rend(temp2); ++iter)
+        std::cout << *iter << ' ';                                  
+}
+
+```
+
+
+
+range
+
+```c++
+#include <algorithm>
+#include <vector>
+#include <iostream>
+#include <ranges>   // 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)