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This is a reconstruction of http://www.roman10.net/2011/11/27/how-to-calculate-iptcpudp-checksumpart-2-implementation/ The site is gone so I took it from the archive for the sake of C Programming TCP Checksum's answer Enjoy! All credits go to https://github.com/roman10.

This is a follow up of the previous post, how to calculate IP/TCP/UDP checksum part 1 — theory.

IP Header Checksum Calculation Implementation

To calculate the IP checksum, one can use the code below,

Microsoft.Extensions.Options Deep Dive

最近は .NET Core の仕事をしています。

さて、ASP.NET Core を使っていると、とりあえず構成情報みたいなものは IOptions<TOptions> で受け取っておけみたいな雑な話を目にします。一応公式のドキュメントはあるのですが、正直読んでもよくわからない。柔軟なんだねー、なるほどねーみたいな感じになりました。なので、ここではできる限り（？）網羅的に解説してみようと思います。

IOptions<TOptions> って何？（TOptions を直接注入すればいいじゃん）
IOptionsSnapshot<TOptions> とかたくさんあってよくわかんない
オプションの動的更新に必要なものは？

	import jwt
	import requests
	import datetime
	from simple_salesforce import Salesforce
	from simple_salesforce.exceptions import SalesforceAuthenticationFailed

	def jwt_login(consumer_id, username, private_key, sandbox=False):
	endpoint = 'https://test.salesforce.com' if sandbox is True else 'https://login.salesforce.com'
	jwt_payload = jwt.encode(
	{

	<?xml version="1.0" encoding="UTF-8"?>
	<table xmlns="http://query.yahooapis.com/v1/schema/table.xsd" securityLevel="any">
	<meta>
	<author>Picplz</author>
	<documentationURL>http://picplz.com</documentationURL>
	<sampleQuery>select * from {table} WHERE entity='feed' AND type='interesting'</sampleQuery>
	<sampleQuery>select * from {table} WHERE entity='city' AND id=2 AND include_pics=1</sampleQuery>
	<sampleQuery>select * from {table} WHERE entity='user' AND username='zubillaga' AND include_pics=1;</sampleQuery>
	</meta>
	<bindings>



	long_tweet = 'asdfasdf asd fasd fasdf asdf asdf asdf asdf asdf asdf asdf asdf asdf asdf asdf asdf asdf asdf asdfasdf asdfasdfas dfasd fasd fasdf asdf asdf asdf asdf asdf asdf '
	short_tweet = 'asdfasdf asd fasd fasdf asdf asdf asdf asdf asdf asdf asdf asdf'

	url = "http://sia.tw/4fgs4"


	def join_url(tweet, url):
	max_tweet_length = 139

	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Z-Index Example</title>
	<style>
	@font-face {
	font-family: 'Win95F';
	src: url('data:application/font-woff2;base64,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

	"""
	Extractive is a cool new service that does some on the fly web
	crawling, and machine learning stuff like Entity Extraction, Full
	text extraction, and more things I don't even understand. There
	on demand api was very easy to use, but I built my first crawl
	job the other night, and had some trouble parsing the results.

	I thought I would put this up so people can see how I fixed the
	output.
	"""

	#!ipxe

	set talos_type controlplane
	chain talos-unattended.ipxe

	from collections import namedtuple

	class Money(namedtuple('Money', ['amount', 'currency'])):
	def add(self, amount):
	return Money(self.amount + amount, self.currency)

	m = Money(20, 'USD')
	print(m)
	# Money(amount=20, currency='USD')

	(function(F) {
	var registered_ids = {},
	id_to_module_map = {},
	interim_actions = {},
	cleanup_actions = {},
	clicked_ids = {},
	queueing = true;

	function register_id(id, callbacks, required_module) {
	id = id.replace('', '.');