C++ 中文周刊 第69期
从reddit/hackernews/lobsters/meetingcpp摘抄一些c++动态
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2022 07 01
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 2022-06-29 第156期
文章
#include <span>
#include <spanstream>
#include <iostream>
int main() {
char input[] = "1 2 3";
std::ispanstream is{std::span<char>{input}};
int i1, i2, i3;
is >> i1 >> i2 >> i3;
std::cout << i1 << i2 << i3; // prints 123
}
看不懂有啥用
介绍一些优化经验
介绍用range做轮子
代码走读，挺有意思的
科普了一些基本概念
好像没有很新啊，还是带排队的自选锁
了解一点编译器知识
看不懂了
让枚举更紧凑的语义
#include <iostream>
enum class CarOptions : char {
isAutomaticFlag = 0b1,
isElectricFlag = 0b10,
is4x4Flag = 0b100,
hasRooftopFlag = 0b100,
hasGPSFlag = 0b10000,
};
CarOptions operator|(CarOptions lhs, CarOptions rhs) {
using CarOptionsType = std::underlying_type<CarOptions>::type;
return CarOptions(static_cast<CarOptionsType>(lhs) | static_cast<CarOptionsType>(rhs));
}
CarOptions operator&(CarOptions lhs, CarOptions rhs) {
using CarOptionsType = std::underlying_type<CarOptions>::type;
return CarOptions(static_cast<CarOptionsType>(lhs) & static_cast<CarOptionsType>(rhs));
}
int main() {
// flag 32: mutually exclusive with 8, has skibox
CarOptions flags = CarOptions::isElectricFlag | CarOptions::hasRooftopFlag;
std::cout << std::boolalpha;
std::cout << static_cast<bool>(flags & CarOptions::isAutomaticFlag) << '\n';
std::cout << static_cast<bool>(flags & CarOptions::isElectricFlag) << '\n';
std::cout << static_cast<bool>(flags & CarOptions::is4x4Flag) << '\n';
std::cout << static_cast<bool>(flags & CarOptions::hasRooftopFlag) << '\n';
std::cout << static_cast<bool>(flags & CarOptions::hasGPSFlag) << '\n';
}
还是SWAR方法
uint64_t tolower8(uint64_t octets) {
uint64_t all_bytes = 0x0101010101010101;
uint64_t heptets = octets & (0x7F * all_bytes);
uint64_t is_gt_Z = heptets + (0x7F - 'Z') * all_bytes;
uint64_t is_ge_A = heptets + (0x80 - 'A') * all_bytes;
//uint64_t is_ascii = ~octets;
//uint64_t to_lower = (is_upper >> 2) & (0x20 * all_bytes);
//return (octets | to_lower);
uint64_t is_ascii = ~octets & (0x80 * all_bytes);
uint64_t is_upper = is_ascii & (is_ge_A ^ is_gt_Z);
return (octets | is_upper >> 2);
}
比默认实现快一倍。我简单压了一下，效果确实是快了一倍 https://quick-bench.com/q/DTrgQdcp2JIXG2UKP1_jQDjooUA
当然如果不考虑费ascii的话可以用更猥琐的
include(FetchContent) # once in the project to include the module
FetchContent_Declare(googletest
GIT_REPOSITORY https://github.com/google/googletest.git
GIT_TAG 703bd9caab50b139428cea1aaff9974ebee5742e # release-1.10.0)
FetchContent_MakeAvailable(googletest)
# Link against googletest's CMake targets now.
fetchcontent也可以解析zip源码包
lamire常用的gdb
查某段代码的汇编
gdb -q ./benchmark -ex "set pagination off" -ex "set print asm-demangle" -ex "disas 0x000000000001b540" -ex quit > gdbasm.txt
关注生成的指令
gdb -q ./benchmark -ex "set pagination off" -ex "set print asm-demangle" -ex "disas 0x000000000001b540" -ex quit | awk '{print $3}' | sort |uniq -c | sort -r | head
32 and
24 tbl
24 ext
18 cmhi
17 orr
16 ushr
16 eor
14 ldr
13 mov
10 movi
视频
用extern template能快点。
开源项目需要人手
- 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753302367和作者对线
新项目介绍/版本更新
- yap multi-threaded implementation of the pipeline pattern.
- STTL stl-like algorithms for TYPES
- simdutf: Unicode validation and transcoding at billions of characters per second 这大哥真有simd all the things的意思了
- efs 国人写的简单的分布式文件系统。共享文件用的。实现的还挺简单
- tscns 上期提到的快速拿到时间。突然发现有人实现了一个。方法都差不多
工作招聘
有没有需要看大门的我要被开了
