Problem:
You are running a configure script on Linux. It exits with a message like this:
./configure: line 3638: LT_INIT: command not found
07
Feb
2013
Uli Köhler
03
Feb
2013
NodeJS: Get IP addresses of local interfaces
Problem:
You want to get the IPv4 and/or IPv6 addresses of the local computer’s network interfaces using NodeJS in an OS-independent manner.
03
Feb
2013
GCC error: declaration of … shadows a parameter
Problem:
You encounter a GCC error message of the form
error: declaration of ... shadows a parameter 03
Feb
2013
How to resolve the GCC error message “default argument for parameter of type … has type …”
Problem:
You encounter a GCC error message of the form
error: default argument for parameter of type <some type> has type <some other type>
25
Jan
2013
Efficiently encoding variable-length integers in C/C++
Using fixed width integers is space-inefficient in many cases, especially if the majority of values are low and only use the less-significant bytes.
This guide describes the basics of varint (varying-length integer) encoding while focusing on C++ as programming language, but the basic concepts apply to any language.
Varint encodings use only the bytes that are needed to represent you integer value appropriately. A varint algorithm can represent the number 10 in only one byte while using 4 bytes to encode 800000000 (800 million). In many application this yields a significant overhead reduction since you would need to use larger integers if there is a slight change that your values grow beyond the boundary of the integer type that is applicable for the majority of your values. Additionally, you usually can only use 8,16,32 or 64 bit integers while 48 bit integers need to be coded manually in most languages. For example, if most of your values are between 0 and 100, but a few might be larger than 16384 (for unsigned integers), you would usually use a full 32-bit integer, even if most values could be represented by a single byte.
11
Jan
2013
Creating a highly compressed SquashFS from a folder
Problem:
You have a large compressible read-only folder that eats up a lot of disk space. You want to compress it using SquashFS.
11
Jan
2013
C++: Check if file exists
Problem:
In C++ you want to check if a given file exists, but you can’t use stat() because your code needs to work cross-plaform.
11
Jan
2013
Enable Menu-Style Autocompletion in ZSH
Problem:
You have installed zsh but you don’t see the menu-style autocompletion (where you can navigate the suggestions using the arrow keys on the keyboard)
11
Jan
2013
Move Minimize, Maximize and Close to the right in Ubuntu Unity
In more recent Ubuntu Versions, the minimize, maximize and close icons have moved to the left upper corner of the window.
If you want them to show up on the right side instead, follow this guide:
- Open a terminal (e.g. click on Ubuntu Dashboard and type Terminal, then click on Terminal)
- Copy and paste this text into the terminal (Ctrl+V doesn’t work here, use right-click -> insert)
gconftool-2 -s /apps/metacity/general/button_layout —type=string “menu:minimize,maximize,close”
- Press Return / Enter
- The icons should shift to the right immediately
02
Jan
2013
A text-to-Brainfuck/RNA converter in ANSI C99
Brainfuck encoder
The following small ANSI C99 program reads a String from stdin and prints out a Brainfuck program that prints the same String on stdout.
Compile using gcc -o bf bf.c
Use it like this:
cat my.txt | ./bf > my.bf
Source code:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv) {
unsigned char c;
unsigned char curval = 0;
//Initialize reg+1 with 8
while(1) {
c = getchar();
if(feof(stdin)) {break;}
while(curval != c) {
if(curval < c) {
putchar('+');
curval++;
} else if(curval > c) {
putchar('-');
curval--;
}
}
putchar('.');
}
}How does it work?
Basically it uses just one of the registers of the Brainfuck Turing machine and incremets or decrements the register to be able to print out the next byte. It doesn’t use any of the more ‘advanced’ features in Brainfuck like loops.
20
Dec
2012
How to resolve ADB Sideload “error: closed”
Problem:
You are using adb sideload to communicate with your Android device (e.g. to flash the Nexus 4 using Clockworkmod recovery), but every time you try to execute `adb sideload` you get this error message:
error: closed
16
Dec
2012
A working Gitlab configuration using Unicorn and Apache Proxy
Problem:
You want to setup gitlab using Apache and unicorn (no passenger!), but it doesn’t work, no matter how hard you try.
14
Dec
2012
Compiling & Installing LevelDB on Linux
Update: Please also take a look at this followup article for an automatic compilation script that builds Ubuntu DEB packages!
Problem:
You want to compile and install LevelDB (including development headers) on your Linux computer. ./configure && make && make install does not work so you don’t know how to do this.
or:
You have successfully compiled LevelDB, but make install doesn’t work (there is no official installation procedure yet) and you don’t know how to install it to your system
09
Dec
2012
Scalar vs packed operations in SSE
If you look at any SSE instruction table, you might notice that there are two basic types of operations:
- Packed instructions (the assembly instruction ends with PS)
- Scalar instructions (the assembly instruction ends with SS)
For most operations, there are two versions, one packed and one scalar.
What’s the difference between them? It’s pretty simple:
- Scalar operations operate on only one element, for example a single integer.
- Packed operations operate on any element in the vector in parallel, e.g. they multiply 4 32-bit integers in a single instruction.
SSE gains it performance from using packed operations implementing the SIMD paradigm (using a single instruction, multiple values are processed). However, it is occasionally useful to avoid expensive copying by using scalar operations operation on the SSE registers.
Also see the Original source
08
Dec
2012
Encoding a Video for HTML5 using ffmpeg
Problem:
You have a video file and want to encode it to support all three HTML5 codecs currently available (WebM, Theora and H.264) on the majority of devices.
08
Dec
2012
Shell: Strip directory from path
Problem:
In the Linux shell, you have a file path and you want to strip everything but the filename, for example you have the path ../images/photo.jpg and want only photo.jpg
07
Dec
2012
Finding the maximum line length of a file in Ruby
23
Nov
2012
Basic Tutorial on Bitfield Arithmetic
This article describes basic operations in manipulating bitfields using boolean operations. Although this article focuses in Java, most programming languages use the same syntax.
What is a Bitfield?
All modern computers use binary arithmetic – that means, the most basic unit of information is a bit – it’s value can either be 0 or 1. On almost all hardware implementations of binary arithmetic, you can’t adress and modify bits directly, but you have to use bytes (= 8 bits). Bitfields are vectors of bits where each bit expresses a specific piece of information that can either be true or false. Depending on the application the bitfield can occupy more or less space.
Possible applications for bitfields include, but are not limited to Bloom Filters and Game artificial intelligences. In the latter case they are called bitboards if they represent a specific state in a game board.
You might also use words (2 bytes = short in most configurations), double words (4 bytes = int in most configurations) or quad words (8 bytes = long in most configurations) instead of single bytes for addressing. On 64-bit platforms, double words or quad words are usually most efficient but anything beyond quad words (i.e. 64 bits) needs more than one instruction in the CPU, which usually makes computation inefficient (there are some tricks involving SIMD, but this is beyond the scope of this article).
23
Nov
2012
Othello in Java: Part 1: Data structures
You’ve got a big problem. Someone forces encourages you to implement a complete Othello UI+AI in Java, but you don’t have any idea how to do that. If you already know how to implement the basics and you are interested in more advanced strategy concepts, you might be interested in the other parts of this series (yet to come).
In this multi-part series I will not provide any complete solution to any of the standard Othello tasks. Instead, I will provide (hopefully) helpful hints how to get your coding going and explain how your code works.
22
Nov
2012
Convert ZIP to TAR using Linux shell
Problem
You have ZIP archive and want to convert it to TAR automatically conserving the original directory structure.