With egg prices soaring due to a severe bird flu outbreak, the U.S. Department of Agriculture (USDA) announced a 1 billion plan to contain the disease and help

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As mentioned in the guide, preparation isn't about fear—it's about freedom and peace of mind. The resources collected here complement your reading with practical tools

seasons vary in severity from year to year, and this is a particularly severe season, Sean T. O Leary, M.D., M.P.H., chair of the AAP Committee on Infectious Di

## Boost.Hash2 I’m happy to report that the library I helped Peter Dimov develop, Hash2, was accepted after probably one of the most thorough Boost reviews to have happened in recent history. I can’t claim to have contributed all too much to the design. After all, Hash2 was an implementation of Types Don’t Know #. But I did come along and help implement myriad algorithms and help with the absolutely massive testing burden. Interestingly, I think people who don’t sit and write/maintain Boost libraries all day underestimate just how much testing even something like 10 extra lines of source can require. When you write software with a certain minimum bar of quality, almost all your effort and time go into testing it than anything else. This is because if a Boost library gets it wrong, there’s really no good way to unwind that. Bad versions of `libboost-dev` will have already gone out and then packagers need to re-package and the whole thing is a huge debacle for users and packagers. Working on Hash2 is fun and engaging and more importantly, it finally gives C++ developers something reputable and makes hashing as easy as it should be. The only problem with Hash2 that I can think of as a user of Boost would be that it took until 2024 (and now basically 2025) for Boost to have simple and effective hashing routines. For example, std::string get_digest(std::vector<char> const& buf) { boost::hash2::sha2_256 h; h.update(buf.data(), buf.size()); return to_string(h.result()); } Very simple, very nice and clean and does what it says on the box. The version of the library that was accepted is also far from the final version as well. The library will continue to evolve and quality of implementation will be iterated on and the interfaces will naturally be refined. It’s good for reviewers and authors of Boost libraries to keep in mind that libraries aren’t some static thing that are carved out of stone. The accepted version of a Boost library is very seldom similar to the version 4 releases down the line. Boost.Asio is probably the most emblematic of this, having undergone dramatic refactors over the years. One thing I’m particularly looking forward to is experimenting with sha-256 intrinsics available on certain Intel CPUs but that’ll come later once the base sha2 family has had a nice performance overhaul and maybe a few new algorithms are also added to the collection. ## Boost.Regex I’ve also started working with Boost.Regex author John Maddock to squash CVEs filed against Boost.Regex found by Google’s oss-fuzz project, which is a wonderful contribution to the world of open-source. While as developers we may use regexes in our day-to-day lives, it’s an entirely different world to actually implement a regex engine. Learning what goes into this has been fascinating and I do have to admit, I’m tremendously humbled by John’s prowess and ability to navigate the complexities of the state machine construction. In a similar vein, I’m equally impressed at just how effective fuzzing is at crafting input. I’ve known about fuzzing for a good bit of time now as most modern software developers do but I’ve never stopped to sit down and truly appreciate just how valuable these tools are. One of the first things I essentially had to do for the repo was get it to a place where clangd could handle the generated compiled_commands.json. clangd is one of the better developer tools to come out but has caveats in that it can’t handle non-self-contained header files and old school Boost libraries like to `#include` various implementation headers at the bottom. Fixing this for clangd normally requires recursive `#include`s or just not using implementation headers. In most cases, it’s easiest to deal with the recursion and solve it by simply just adding `#pragma once`. Because this is Boost, the Config module even has all the macros that help detect when `#pragma once` is available so we can support all the compilers and all the toolchains no matter what. I look forward to continuing to work with John on Regex but in the interim, I’m having fun taking a Hash2 break. – Christian

## Boost.Hash2 I’m happy to report that the library I helped Peter Dimov develop, Hash2, was accepted after probably one of the most thorough Boost reviews to have happened in recent history. I can’t claim to have contributed all too much to the design. After all, Hash2 was an implementation of Types Don’t Know #. But I did come along and help implement myriad algorithms and help with the absolutely massive testing burden. Interestingly, I think people who don’t sit and write/maintain Boost libraries all day underestimate just how much testing even something like 10 extra lines of source can require. When you write software with a certain minimum bar of quality, almost all your effort and time go into testing it than anything else. This is because if a Boost library gets it wrong, there’s really no good way to unwind that. Bad versions of `libboost-dev` will have already gone out and then packagers need to re-package and the whole thing is a huge debacle for users and packagers. Working on Hash2 is fun and engaging and more importantly, it finally gives C++ developers something reputable and makes hashing as easy as it should be. The only problem with Hash2 that I can think of as a user of Boost would be that it took until 2024 (and now basically 2025) for Boost to have simple and effective hashing routines. For example, std::string get_digest(std::vector<char> const& buf) { boost::hash2::sha2_256 h; h.update(buf.data(), buf.size()); return to_string(h.result()); } Very simple, very nice and clean and does what it says on the box. The version of the library that was accepted is also far from the final version as well. The library will continue to evolve and quality of implementation will be iterated on and the interfaces will naturally be refined. It’s good for reviewers and authors of Boost libraries to keep in mind that libraries aren’t some static thing that are carved out of stone. The accepted version of a Boost library is very seldom similar to the version 4 releases down the line. Boost.Asio is probably the most emblematic of this, having undergone dramatic refactors over the years. One thing I’m particularly looking forward to is experimenting with sha-256 intrinsics available on certain Intel CPUs but that’ll come later once the base sha2 family has had a nice performance overhaul and maybe a few new algorithms are also added to the collection. ## Boost.Regex I’ve also started working with Boost.Regex author John Maddock to squash CVEs filed against Boost.Regex found by Google’s oss-fuzz project, which is a wonderful contribution to the world of open-source. While as developers we may use regexes in our day-to-day lives, it’s an entirely different world to actually implement a regex engine. Learning what goes into this has been fascinating and I do have to admit, I’m tremendously humbled by John’s prowess and ability to navigate the complexities of the state machine construction. In a similar vein, I’m equally impressed at just how effective fuzzing is at crafting input. I’ve known about fuzzing for a good bit of time now as most modern software developers do but I’ve never stopped to sit down and truly appreciate just how valuable these tools are. One of the first things I essentially had to do for the repo was get it to a place where clangd could handle the generated compiled_commands.json. clangd is one of the better developer tools to come out but has caveats in that it can’t handle non-self-contained header files and old school Boost libraries like to `#include` various implementation headers at the bottom. Fixing this for clangd normally requires recursive `#include`s or just not using implementation headers. In most cases, it’s easiest to deal with the recursion and solve it by simply just adding `#pragma once`. Because this is Boost, the Config module even has all the macros that help detect when `#pragma once` is available so we can support all the compilers and all the toolchains no matter what. I look forward to continuing to work with John on Regex but in the interim, I’m having fun taking a Hash2 break. – Christian

# 什么是 MR？区块链中的默克尔根详解 **MR（Merkle Root，默克尔根）** 是区块链技术中用于高效验证数据完整性的核心数据结构。它通过将大量交易数据压缩成单一哈希值，为区块链的不可篡改特性提供了数学保障。 作为区块链的"数据指纹"，默克尔根在加密货币交易验证、轻节点同步、智能合约执行等场景中发挥关键作用。理解这一概念是掌握区块链工作原理的重要基础。 ## MR 的详细解释 ### 默克尔树的构建原理 MR 本质上是**默克尔树（Merkle Tree）** 的顶端哈希值，其构建过程遵循分层哈希原则： 1. 将原始数据（如交易记录）分割为多个数据块 2. 对每个数据块进行**哈希运算** 生成叶子节点 3. 相邻两个叶子节点哈希值组合后再次哈希，形成父节点 4. 递归重复组合哈希过程，直至生成唯一的根哈希值 graph TD Root[MR: 根哈希] --> Hash1[层级1哈希] Root --> Hash2[层级1哈希] Hash1 --> Hash3[层级2哈希] Hash1 --> Hash4[层级2哈希] Hash2 --> Hash5[层级2哈希] Hash2 --> Hash6[层级2哈希] ### 核心功能特性 * **高效验证** ：只需对比根哈希即可验证海量数据完整性 * **局部验证** ：通过**默克尔证明** 可验证单个交易而不需下载全部数据 * **防篡改** ：任何数据修改都会导致根哈希值改变 * **空间优化** ：将TB级数据压缩为32字节哈希值 ## MR 的起源与背景 1979年由密码学家 Ralph Merkle 提出原型结构，2010年后被比特币等区块链系统大规模应用。中本聪在比特币白皮书中采用该技术，使SPV（简单支付验证）成为可能，奠定了轻钱包的技术基础。 ## MR 的重要性与应用场景 1. **交易验证** （比特币/以太坊） 2. **状态验证** （以太坊世界状态树） 3. **文件存储** （IPFS分布式存储） 4. **跨链通信** （原子交换验证） 5. **零知识证明** （zk-SNARKs数据完整性证明） ## MR 的优势与局限 **优势** ： * 验证效率提升1000倍以上（相比全节点验证） * 降低存储需求（移动设备可运行轻节点） * 增强系统安全性（哈希嵌套结构抗碰撞） **局限** ： * 量子计算机威胁传统哈希算法 * 构建大型默克尔树需要较高计算资源 * 不支持动态数据的高效更新 ## MR 与相关概念对比 概念 | 功能定位 | 数据结构 | 典型应用 ---|---|---|--- MR | 数据完整性证明 | 树状结构 | 区块链交易验证 普通哈希 | 单一数据指纹 | 线性结构 | 文件校验 布隆过滤器 | 概率性存在证明 | 位数组 | 轻节点交易查询 ## 总结 作为区块链的"数据信任锚"，MR 通过巧妙的哈希嵌套结构，在保证安全性的同时极大提升了验证效率。随着 Layer2 扩容方案和跨链技术的发展，默克尔根衍生出了更高效的变体结构（如 Merkle Patricia Tree），持续推动区块链技术的演进。

When officials in Wisconsin s largest city asked the U.S. Centers for Disease Control and Prevention (CDC) for help dealing with high levels of lead in city sch

Hospitals and imaging centers are now required to track and report radiation exposure from CT scans under new Medicare regulations. The rules, which began rolli

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