Lomuto’s Comeback

The Continental Club in Austin, Texas, USA Sunday, January 5, 1987 “Thank you for your kind invitation, Mr. Lomuto. I will soon return to England so this is quite timely.” “And th…

The D BlogAndrei Alexandrescu

Since a few decades ago people know and use the best implementation of the quicksort.

We never asks if it can be made faster, because we learn this from the textbook, and it is the fastest implementation when we learned it.

Indeed, making a single pass scan from the left to the right fits the computer architect much better than swapping randomly (well, jumping between a forward pass and a backward pass is more random)

We highly recommend reading this article, because the best is always yet to come.

Own your email server for your domain

There are a lot of articles you can find about configuring email server or postfix. With the recent trend of cloud computing there are new services such as Amazon Simple Email Service and Mailgun.

You have your own domain, and you would like to have as many email accounts under your own domain as you need. There are a lot of good reasons to have it all in your control. You have already had a cloud server to run your own email server. That's all you will need. So why not? For example you can create an individual email address for each new website sign up.

The question is, how to setup a full functional email service, and make it as easy as using Gmail? Without the right setup the recipient email server will drop the email, mark it suspicious or deliver it into the spam folder.

Goals

We split the problem into subtasks below:

1. To receive emails addressed to your domain and forward it to another email address;
2. To send email that lands into recipient's inbox;
3. To create as many email accounts as you wish;
4. To connect your favorite email client to the email server to send emails;
5. To use your Gmail account to receive emails to and send emails from your own domain;
6. To block spam emails.

After all, you will have a flexible email system in your full control for 0 additional cost.

Part 2 of the article is available only to paid subscriber.

Non-goals

Other articles teaches you

• To configure your email server to send as your gmail.com account by signing in as SMTP client with password credentials.
• To send email by command line.
• To buy a cloud service to send batch emails.

Details

Receive emails and forward to another email address of your choice

You don't even need to setup your own email server because most domain registrars(e.g. name.com) offer email forwarding for free.

When you have already had your own email service running, the right word to lookup is /etc/aliases or alias_maps.

To send email that lands into recipient's inbox

The recipient's email server needs to know that the email is being sent from a valid email address. Or else a spammer can send emails from any domain and even to pretend to be your contacts!

99% of time people stop here because of the "AI" behind email anti-spamming. Only few understands the trick.

You may have heard about SPF, DKIM, and DMARC and find it too much for you. But the real trick is the PTR record!

You will need to config SPF records for your domain to specify who (domain or ip of the email server) is able to send email. DKIM is intended to use with third-party email server, and DMARC is intended to workaround DKIM on mailing list.

If your email server takes the domain name "email-sender.yourdomain.name", typically you have "a:email-sender" (alternatively "a:email-sender.yourdomain.name" / "a:email-sender aaaa:email-sender") in the SPF records, you need to point the PTR records of your email server's IPs to "email-sender.yourdomain.name".

Become a subscriber if you find this article helpful.

Install postfix

Goals listed above can be achieved with postfix. Installation is straight-forward on all major Linux distros.

Remaining setup

You will be able to figure it out by Google search or reading the manual of postfix.

Head to part 2 to save a few browser tabs. Save javascripts save the earth.

|        let mut map = HashMap::default();

|            -------------------   ^^^^^^^^^^^^^^^^ cannot infer type for `S`

|            |

|            consider giving `map` the explicit type `std::collections::HashMap<.., .., .., S>`, where the type parameter `S` is specified      

patterns aren't allowed in methods without bodies

|    fn commit(mut self, parent: &mut Self) -> Result<()>;

|              ^^^^^^^^

|

= note: #[warn(patterns_in_fns_without_body)] on by default

= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!

= note: for more information, see issue #35203 <https://github.com/rust-lang/rust/issues/35203>

Drop a Lock

let lock = &mut *mutex.lock(); // <== here is wrong

// let lock = &mut mutex.lock() // <= this is also wrong.

If sth {

drop(lock);

// Do sth, however lock is not released as expected.

}

This is correct: let mut lock = mutex.lock()

Sender Receiver

The Sender can be cloned to send to the same channel multiple times, but only one Receiver is supported.

Sometimes you want to be able to receive from different threads? Especially when you are maintaining the task queue by fetching the receiver with try_recv() then push into an internal task queue from multiple threads.

Lifetime in traits, 2 consecutive trait calls make it unable to compile

See verify_snapshot_db. Compiler error: key_value_iter does not live long enough.

Range for Vec<T> keyed BTreeMap

https://www.reddit.com/r/rust/comments/bxests/borrow_not_implemented_for_vec_i_understand_that/eq61pim/

You ask, why std::Vec has such a strange iterator type signature, and why can't have its iterator type defined as an associate type, when you think a bit more at the programming language level. It's such a common practice to define associate interface for iterator in other programming languages!

Have you ever tried to make your own iterator without unnecessary copy, and supporting all different kind of iterators, return read-only reference, copy of item, or specify the interface that return type should satisfy?

Read this article http://lukaskalbertodt.github.io/2018/08/03/solving-the-generalized-streaming-iterator-problem-without-gats.html, and start your discovery from https://github.com/yangzhe1990/conflux-rust/blob/no_force_create/core/storage/src/utils/wrap.rs.

We will post a series of articles around this topic.

Wet Signatures and the Wonderful World of Schnorr …

Signatures are at the core of our world of trust. For centuries we have used them as a legal way of proving our identity and our…

ASecuritySite: When Bob Met AliceProf Bill Buchanan OBE

There are a few more related articles on his site.

If you have math background, you might find it important to read articles which get to the point.

There is a good read to BLS signature too. Read it in English by Google Translate.

一种跨周期AMM买入卖出方法，帮你跨越比特币牛熊周期、保住本金，在下轮牛市途中收回所有本金，获取数倍于本金的比特币，进入币本位，真有这么好的事？

2021-2-15

引言

在2017年比特币牛市狂热的时候，小王决定加入这股投机热潮。这时，2017年12月1日，比特币价格刚刚达到了$10,870美金，小王决定拿出手上的$120,000美金中的$90,000美金(3/4)买进BTC。

总所周知，比特币上一轮牛市的高点是大约$20,000美金，然而在一年后的2018年12月15日，比特币的价格下跌到了$3,183。任何未经准备的投资者，此时损失了极大的金钱，小王的$90,000美金，已经只剩下$26,355了。在恐惧之中，投资者开始自问，接下来比特币是否还会跌到$300？已经损失了本金70%的小王，恐怕最终会失去所有的投资，即选择了退出。

2年后的2020年10月，牛市重新开始，甚至创下了$48,000美金的新高。新的牛市，加上不断释放的利好消息，让所有人陷入了巨大的焦虑，以前损失过巨款的、提前卖出的，还要不要重新进来？

第一次想要投资比特币，现在买进会大涨，还是会在头部站岗，成为韭菜？伴随最近的巨大震荡，比特币24小时之内可能下跌或者上涨$10,000美金，市场上百亿杠杆资金随时消失，让所有看涨看跌的投资者猝不及防。

消除这些焦虑的唯一方法，是寻找一种与价格波动尽可能不相关的交易方法；并且在跨越至少一个周期的情况下，评估这种交易策略。

交易策略概要

如果Jerome使用了下面的交易策略，在第一轮牛市他和小王一样，花费$90,000在突破$10,000美金后买入，之后在熊市中每月花费$2,000美金定投，在第二轮牛市价格达到$46,517.40时，Jerome总计持有$166,843的现金，10.805枚比特币，总资产$669,460美金，盈利$494,156美金。Jerome手上现金比例是总投资池$175,304的95.17%。也就是通过跨周期的几次操作，几乎免费的得到了将近10.8枚比特币！

Jerome在下面的时间点做出了对比特币周期的判断：

1. 2017年12月1日、$10,869 牛市火爆时入场，态度谨慎，使用AMM卖出方法在买入同时立刻提交一系列卖单维持3/4的持币比例；
2. 价格重新跌至$10,869，Jerome认为牛市可能结束，隐约相信比特币的未来，继续后面的投资步骤，决定只保留净资产1/4的比特币。
3. 2018年6月14日、$6302，此时Jerome只损失$8,699美金，并开始熊市投资策略。
4. 2018年12月15日下跌到$3183，假设B后无任何操作，此时Jerome只损失了$17,620美金
   
   

C-E，使用按日/月定投策略，以平均价格$6,822.04买入总计$57,533的8.43345枚比特币，或者使用更好的按日定投AMM买入策略，以平均价格$6,512.25买入总计$55,304的8.49229枚比特币。

1. 2020年10月24日、$13,128 进入第二轮牛市，调仓至持币3/4。
2. 开始大幅震荡、$33,000。Jerome持谨慎态度，开始使用AMM卖出方法提交了一系列卖单卖出
3. $46,517.40、Jerome总计持有$166,843的现金，10.805枚比特币，总资产$669,460美金，盈利$494,156美金。
   

我们对一类比特币投资者（Jerome）作出这样的假设：

第一次进场投资者Jerome后知后觉。在2017年从$500美金到$20,000美金的牛市中，选择$10,000美金后进场；

之后投资者具有基本的周期判断能力。在之后下跌到10,000美金时，可以判断出牛市很可能会结束；在2018年6月14日下跌到$6,302之后，判断出牛市周期彻底结束，进入长期熊市；在2020年10月价格冲过$13,000美金时，判断出新的牛市已经开始。

按：一切成功的投资至少需要对周期、牛熊做出正确的判断，这只能靠每个人的修炼，或许第一次很难做好，但来日方长。Jerome没有办法对别人作出投资建议和承担责任。

在刚才的操作介绍中我提到了AMM买入卖出方法，这里将具体的操作以表格的形式呈现出来。并用程序计算出具体的交易步骤和总收益。

程序结合周期判断给出的投资行为具体如下：

其中A和F的卖出订单，全部是通过AMM卖出策略生成，Jerome只需要一次性输入几十个卖单，不再需要关注起伏的币价。

在C-E的熊市定投阶段，Jerome可以选择最普通的按月定投，也可以选择更加复杂但是成本更低的AMM买入程序。我们会在第二部分详解AMM买入卖出策略。

使用策略交易的优点

如果投资者还具有一定的寻找买卖时机的能力和特定情况下勇于全仓的信心，理应比Jerome做的更好。

比特币价格下跌过程中时，投资者一般会有两种反应：1）比特币是一场泡沫和骗局 2）相信比特币的未来，愿意继续投入比特币直到下次牛市中退出。

如果Jerome是第一类投资者，他在牛市中不需要关注价格和巨大的波动，可以保持理性。在时刻B，他就会选择获得$4,367收益全部清仓。

如果Jerome隐约相信比特币的未来，他会继续后面的投资步骤，决定只保留净资产1/4的币2.86枚，其余全部持有现金$93,275。

2018年6月14日下跌到$6302，因为之前在牛市中选择了随上涨撤出现金，在跌回入场价格时投资者选择了大幅套现，此时Jerome的净资产一共只损失了$8,698美金。

经历过暴涨暴跌，资金仍然安全，Jerome遭受的短期损失并没有动摇他长期看好比特币的信念，于是他开始了熊市定投的投资策略，为下一轮牛市作准备。

在第二轮牛市，价格达到$46,517.40的时候，时间似乎重新回到了2017年比特币突破$10,000的时刻，经历了差不多正好一个周期，Jerome不仅取回了之前投入的所有现金，还成功让自己进入了币本位！

敬请关注第二篇 什么是AMM，以及详解本文提出的AMM买入、卖出方法