Is about the phone’s calculator. I have a HTC Desire with Android 2.2. My default calculator app that’s called simply “Calc” amazes me. Very rarely happens to need to use it, end even less I’m using it with fractional numbers, but when I’m actually using it I tend to forget that it has an issue.

Let’s say:

12 – 11

In Calc = 1, in JavaScript = 1. Nothing out of the ordinary so far, right?

Let’s take:

1.2 – 1.1

Any elementary school student knows that the result is 0.1.

In Calc it is 0.099999999, weird? In JavaScript is even more interesting, the result is 0.09999999999999987.

It’s about float, and I assume that the difference comes from the digit number displayed on the screen. In both cases IEEE 754 standard is used.

Now… in JavaScript this is a known issue, but who made the Android app, made it transform to a scientific calculator if you rotate the phone and did not see this issue?

Yahoo! Open Hack Europe 2011 will be held in Bucharest! Between 14-15 May we are the lucky Europeans to host this event.

At this event there are two types of tickets: Tech Talk and Hacker. Those who choose Tech Talk will attend seminars and awarding only, while those who choose Hacker will stay overnight to work on the project they’ve chosen.

Important figures from the Yahoo! staff will be present, so in short is an event that you must not miss!

The ssh key based authentication is useful when you don’t want to type the password each time. Also is useful when for instance sshfs is used and mounting takes place without entering a password.

The end result should do login with the following command:

1$ ssh work

Server

In Ubuntu the server installation is done with:

1$ sudo apt-get install ssh

For other distributions the packege is usually called ssh or OpenSSH.

On server-side you must activate the public key authentication in the sshd_config file:

1#/etc/ssh/sshd_config
2
3PubkeyAuthentication yes

Client

On client-side the public/private key pair must be generate:

1$ ssh-keygen -t rsa -b 1024

Where the type of the key is rsa and 1024 is the size. Bigger is safer.

The public key must be copied on the server using the following command:

1$ ssh-copy-id -i ~/.ssh/id_rsa user@192.168.1.1

The -i option and key path are optional, if there was generated a single key on the client in ~/.ssh directory that one will be used as default.

Right now it should work to login using the next command without prompting for password:

1$ ssh user@192.168.1.1

Alias

The last step is creating an alias, in this case it will be called “work”.

You must make a config file in the ~/.ssh directory. The file must have 600 rights, that is reading and writing only for owner.

1$ cd ~/.ssh
2$ touch config
3$ chmod 600 ~/.ssh/config

In this file aliases will be set:

1Host work
2HostName 192.168.1.1
3User user
4IdentityFile ~/.ssh/id_rsa

At this step authentication to the previously defined host can be made with the command:

1$ ssh work

To learn more about ssh aliases checkout the manual:

1$ man ssh_config

Subversionning can be good to you, if you know how to use it!

subversionning

Since I’ve first learned about IPs, I’ve wandered when will the possible number of addresses will run out. Now is official, there are no more IPv4 addresses!

ICANN (Internet Corporation for Assigned Names and Numbers) has officially announced on February 3 that the las IPv4 addresses have been allocated. Off course they haven’t been allocated directly to the users, but they will be used by ISPs.

But what will happen if there are no more IP addresses? Well, as this has become obvious some ware in the evolutionary process of the Internet IPv6 was created. What is the difference? Well, using IPv4 there are about 4 billion addresses, with IPv6 there are 3.4×10³⁸, in fact I don’t even know how to pronounce a number that big, but it will be enough for a very long time.

Fortunately, a lot of operating systems already have support for IPv6, and if they don’t, they will start having very soon.