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The Elements of Programming Style

The following rules of programming style are excerpted from the book "The Elements of Programming Style" by Kernighan and Plauger, published by McGraw Hill. Here is quote from the book: "To paraphrase an observation in The Elements of Style by Strunk and White, the rules of programming style, like those of English, are sometimes broken, even by the best writers. When a rule is broken, however, you will usually find in the program some compensating merit, attained at the cost of the violation. Unless you are certain of doing as well, you will probably do best to follow the rules."

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#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <openssl/rsa.h>
#include <openssl/engine.h>
#include <openssl/pem.h>

// I'm not using BIO for base64 encoding/decoding.  It is difficult to use.
// Using superwills' Nibble And A Half instead 

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1. Separation of immutable and mutable logic

Quite a lot of different people have been on the same trail of thought. Gary Bernhardt's formulation of a "functional core, imperative shell" seems to be the most voiced.

"Boundaries" - Gary Bernhardt

"Imperative shell" that wraps and uses your "functional core".. The result of this is that the shell has fewer paths, but more dependencies. The core contains no dependencies, but encapsulates the different logic paths. So we’re encapsulating dependencies on one side, and business logic on the other side. Or put another way, the way to figure out the separation is by doing as much as you can without mutation, and then encapsulating the mutation separately. Functional core — Many fast unit tests. Imperative shell — Few integration tests

https://www.youtube.com/watch?v=yTkzNHF6rMs

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Table Of Content

Skip to the relevant sections if needed.

• 2-min tutorial to do it the quick-and-dirty-way
• Concepts for resolving Git conflicts
• Setting up different editors / tool for using git mergetool
  • Finding out what mergetool editors are supported
• mergetool simple code example for vimdiff
  • Resolving conflict from a Git pull
• Other great references and tutorials

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## within current branch, squashes all commits that are ahead of master down into one
## useful if you merged with upstream in the middle of your commits (rebase could get very ugly if this is the case)
 
## commit any working changes on branch "mybranchname", then...
git checkout master
git checkout -b mybranchname_temp
git merge --squash mybranchname
git commit -am "Message describing all squashed commits"
git branch -m mybranchname mybranchname_unsquashed
git branch -m mybranchname

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# copied from http://gbayer.com/development/moving-files-from-one-git-repository-to-another-preserving-history/
git clone <git repository A url> # clone source repository
cd <git repository A directory>
git remote rm origin # to make sure it doesn't affect the original repository
git filter-branch --subdirectory-filter <directory 1> -- --all # remove all files other than the ones needed
mkdir <directory 1> # move them into another directory where they will be stored in the destination repository (if needed)
mv * <directory 1>
git add .
git commit

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# source: http://st-on-it.blogspot.com/2010/01/how-to-move-folders-between-git.html
# First of all you need to have a clean clone of the source repository so we didn't screw the things up.

git clone git://server.com/my-repo1.git

# After that you need to do some preparations on the source repository, nuking all the entries except the folder you need to move. Use the following command

git filter-branch --subdirectory-filter your_dir -- -- all

# This will nuke all the other entries and their history, creating a clean git repository that contains only data and history from the directory you need. If you need to move several folders, you have to collect them in a single directory using the git mv command.

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Anti-tests

The requirement

Let's say we've been tasked with returning 400 when GET /users/<userId> is called with a negative userId.

The test

The requirement can be turned into a test that hits the endpoint with a negative userId and checks that a 400 is returned:

    @Test
    public void getUser_InvalidUserId_400() {

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High-Performance Matrix Multiplication

This is a short post that explains how to write a high-performance matrix multiplication program on modern processors. In this tutorial I will use a single core of the Skylake-client CPU with AVX2, but the principles in this post also apply to other processors with different instruction sets (such as AVX512).

Intro

Matrix multiplication is a mathematical operation that defines the product of

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Check that your system supports systemd

pidof systemd
2733

If this return a number then your system supports systemd. Most Linux distributions in 2017 support systemd.

Check out the proceses currently running.

Since systemd starts the process then all processes will be children of systemd