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Friday Afternoon Downtime

Midafternoon today, starbeamrainbowlabs.com was down. The reason for this is unclear, but it seems that this site's hosting provider, OVH, was doing some maintenance. The site was down for 29 minutes.

Lessons Learned

Get your server to notify you during the shutdown / startup sequences

Using a service like Uptime Robot is great to monitor your website's uptime, but it is a much better idea to have your server send you an email when your server goes down. That way you will know whether the server got a chance to shut down correctly or not.

Backup often, and before / after major changes

You should take a backup (preferably automated) often - I have a scritp set to do this every week - but you should also backup before and after any major changes that you make.

Sorting: Selection Sort

Since I seem to be doing quite a few sorting algorithsms in my lectures at the moment, it would appear that I will be doing a series of sorting algorithm posts.

Today I did not have all that much time, so I wrote this one in javascript. I present to you: The selection sort.

The selection sort is a sorting algorithm where the smallest number is found and swapped with the number at the beginning, then the next smallest is swaped with the one next to the smallest number, and so on until the whoel sequence has been sorted.

Wikipedia has a rather nice animated GIF that explains the selection sort well here.

My implementation could be made faster be doing it in reverse, but I didn't have time to reverse it at the time of writing this post (check the comments to see if I did it later).

function selectionsort(arr)
{
    var maxid = 0, temp;
    for(var nextid = 0; nextid < arr.length - 1; nextid++)
    {
        //find the next smallest number remaining
        maxid = nextid;
        for(var j = nextid; j < arr.length; j++)
        {
            /*
            Invert to |
            sort desc.V */
            if(arr[j] < arr[maxid])
                maxid = j;
        }
        //swap the next number into place
        arr[nextid] = arr.splice(maxid, 1, arr[nextid])[0];

        console.log("nextid:", nextid, "state:", arr);
    }

    return arr; //for chaining
}

Here is a minified version (146 chars including newlines):

function selectionsort(e){for(var t=0,n=0;n<e.length-1;n++){t=n
for(var l=n;l<e.length;l++)e[l]<e[t]&&(t=l)
e[n]=e.splice(t,1,e[n])[0]}return e}

This was minified with UglifyJS.

Sample Output:

original [ 75, 4, 32, 87, 69, 73, 10, 18, 48, 2, 48, 96, 75, 36, 26 ]
nextid: 0 state: [ 2, 4, 32, 87, 69, 73, 10, 18, 48, 75, 48, 96, 75, 36, 26 ]
nextid: 1 state: [ 2, 4, 32, 87, 69, 73, 10, 18, 48, 75, 48, 96, 75, 36, 26 ]
nextid: 2 state: [ 2, 4, 10, 87, 69, 73, 32, 18, 48, 75, 48, 96, 75, 36, 26 ]
nextid: 3 state: [ 2, 4, 10, 18, 69, 73, 32, 87, 48, 75, 48, 96, 75, 36, 26 ]
nextid: 4 state: [ 2, 4, 10, 18, 26, 73, 32, 87, 48, 75, 48, 96, 75, 36, 69 ]
nextid: 5 state: [ 2, 4, 10, 18, 26, 32, 73, 87, 48, 75, 48, 96, 75, 36, 69 ]
nextid: 6 state: [ 2, 4, 10, 18, 26, 32, 36, 87, 48, 75, 48, 96, 75, 73, 69 ]
nextid: 7 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 87, 75, 48, 96, 75, 73, 69 ]
nextid: 8 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 75, 87, 96, 75, 73, 69 ]
nextid: 9 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 69, 87, 96, 75, 73, 75 ]
nextid: 10 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 69, 73, 96, 75, 87, 75 ]
nextid: 11 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 69, 73, 75, 96, 87, 75 ]
nextid: 12 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 69, 73, 75, 75, 87, 96 ]
nextid: 13 state: [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 69, 73, 75, 75, 87, 96 ]
result [ 2, 4, 10, 18, 26, 32, 36, 48, 48, 69, 73, 75, 75, 87, 96 ]

At some point I may port this to C♯.

(Probably) Coming Soon: (Binary) Insertion sort, Merge Sort, Quick Sort.

Security update to atom.gen.php

Since this website gets a lot of spam (ongoing investigations are currently in force in order to analyse the spambots' patterns, a post will be made here when they have been stopped) and this website also has a comments feed powered by atom.gen.php, I have had a chance to test atom.gen.php out in the wild with real data.

I discovered, unfortunately, that the script didn't handle invalid utf-8 and non printable characters very well, and this lead to the feed getting broken because XML doesn't like certain specific characters. This has now been fixed.

If you handle user input and use atom.gen.php to turn it into a feed, you will want to grab an updated copy of the script (quick link here) and overwrite your previous copy in order to fix this.

As well as fixing that, I also added a new option, $usecdata. This controls whether the <content> tag's contents should be wrapped in <![CDATA[...]]>. This should add extra protection again html / javascript injection attacks breaking your feeds. It defaults to false, though, so you need to manually enable it by setting it to true.

The reference has been updated accordingly.

If you find another bug, please comment below. You will recieve full credit at the top of the file (especially if you provide a fix!).

Reverse Bubble Sorting

We had our second algorithms lecture this week - this time is was on bubble sorting. Apparently we will be doing several sorting algorithms over the next few weeks, each with their own strengths and weaknesses.

Today I bring you an optimised bubble sort implementation in C♯! This will be the first C♯ code that I have posted on this blog.

Basically, the bubble sort algorithm iterates over an array of numbers repeatedly and swaps those that are in the wrong order, until there aren't any more numbers left to swap.

Here is the script:

static void DoBubbleSort(int[]arraytosort) {
    int endingpoint = 1,
        temp;
    bool issorted;

    int swaps = 0,
        iterations = 0,
        passes = 0; //debug

    do {
        issorted = true;

        for(int i = arraytosort.Length - 1; i >= endingpoint; i--)
        {
            iterations++; //debug
            //Console.WriteLine("i: " + i + " i-1: " + (i - 1));

            if (arraytosort[i - 1] > arraytosort[i])
            {
                swaps++; //debug
                //swap the numbers around
                temp = arraytosort[i - 1];
                arraytosort[i - 1] = arraytosort[i];
                arraytosort[i] = temp;

                issorted = false;
            }
        }

        Console.Write("pass: " + passes + " ");
        printarray(arraytosort); //debug
        Console.WriteLine();

        passes++; //debug

        endingpoint++;
    } while (!issorted);

    Console.WriteLine("Sorting Complete!");
    Console.WriteLine("Statistics\n----------");
    Console.WriteLine("Passes: " + passes + ", Iterations: " + iterations + " Swaps: " + swaps);
}

...and here is an example of what it outputs:

Original: [66, 51,  0,  5, 42, 92,  8,  8, 28,  8]
pass: 0 [ 0, 66, 51,  5,  8, 42, 92,  8,  8, 28]
pass: 1 [ 0,  5, 66, 51,  8,  8, 42, 92,  8, 28]
pass: 2 [ 0,  5,  8, 66, 51,  8,  8, 42, 92, 28]
pass: 3 [ 0,  5,  8,  8, 66, 51,  8, 28, 42, 92]
pass: 4 [ 0,  5,  8,  8,  8, 66, 51, 28, 42, 92]
pass: 5 [ 0,  5,  8,  8,  8, 28, 66, 51, 42, 92]
pass: 6 [ 0,  5,  8,  8,  8, 28, 42, 66, 51, 92]
pass: 7 [ 0,  5,  8,  8,  8, 28, 42, 51, 66, 92]
pass: 8 [ 0,  5,  8,  8,  8, 28, 42, 51, 66, 92]
Sorting Complete!
Statistics
----------
Passes: 9, Iterations: 45 Swaps: 24

The script keeps track of the furthest point in the array it reached on each pass and goes one less each time - this is because the smallest number will always get pushed into its proper place at the left hand side on each pass.

As for the reason the script iterates backwards, in Javascript it is recommended that you iterate backwards to avoid repeatedly referencing Array.length, since it has to count the contents of an array upon each refernce. This is probably not the case with C♯, but it is a habit of mine :)

It is important to note that even though the function doesn't return anything, it still sorts the array because arrays are passed by reference by default, just like in Javascript (aka Ecmascript).

There are quite a few debug statements in there. Remove then for actual use in your code.

A (64 bit) compiled version of the script is available:

reversebubblesort.exe

Hashes:

Algorithm Hash
CRC32 644f6c6a
MD5 93fba7a072954ee6f34fcf44913eadc7
SHA1 01a54b24c475ec2ff1bf159dc1224e10553f430d
SHA-256 d32d689e2785d738c54e43a9dc70c1d8f2de76383022a87aa4f408519a7941cb
SHA-384 df7c4ac441aabaa1f182ade7532885d8ee5518c26f17d72d7952dcfaa39552dda9ad219a37661591fea169fd6ed514bb
SHA-512 c993509901bb65cd893d1c8455c5ad8dc670632e5476aad899980348b45bc3435cfab3fe6d8fd80606cfea3608770c9900be51e09f6f1a8c9fd5fe28169fd81d

Remember to always verify the integrity of your downloaded files, especially the larger ones. If you would like another type of binary (e.g. 32 bit, ARM, etc.), please post a comment below and I will reply with a download link. The compiler used was csc.exe on a Windows 7 64 bit command line.

Questions and / or comments are welcome below.

Thing list for 3 Thing Game!

The thing list for 3 thing game has just been released!

Find it here.

In case you can't read the list there, the list is as follows:

Tower, Beaver, Brain, Seagull, plane, Polo, Wombat, Harmonica, Pastie, Spam Fritter, Waifu, Shop, Pasta, Apocalypse, Pirate, Haunted, Really large gun, Struggle, Tentacles, Elephant, MLG, Skeleton, Parrot, Mayhem, Heist, Mountain Dew, Rhythm, Wristwatch, Rubber, Cauldron, Jacket, Doritos, Puzzler, stealth, Cat, Kit-Kat, Crimping, Undersea, Grunting, Zeus, Flesh Eating, Spell, Cool Spot, Potato, Clock, Boiler Suit, Pineapple, Space, Ocean Liner, Robot, Boots, Alien, Rainbow, Frantic, Drainpipe, Pig, Puzzle, Mushroom, Dressing Up, Hand grenade, Gong, Ninja, Steroids, Potion, Dilemma, Zombie, Bones, Graveyard, planets, Cube, Wand, Electric, Warlock, Jellyfish , Vampire, German, Paint, Nerds, Circles, Bus, Tunnel, Cupcakes, System, Broomstick, Party, Lazer, Sci-Fi, Panic, Skull, Ethical, Voxel, Plot, Locked, Robotic, Pixies, Unity, Spacecraft, Inventor, kettle, Balloon, Topdown, Ghost, Satan, Nuke, Nose, University , Banjo, Fingers, petril, Panini, Green, Flying Fish, Banana, Gems, Anti-aircraft gun, Android, Falling, Snakes, Combat, Goat, instakill, Chickens, Communism, Tribal, of Doom, Downstairs, Wolf, Umbrella, Maggot, Ship, Time, Weapon, Football, wizard, Cheesebot, Hunting, Grave, Slippery, Endoscope, Meme, Cheese, Yeti, Bat, Beard, Trousers, Attack, Witch, Assassin, Pension, Pea, Web, Triangles, Spider

Binary Searching

We had our first Algorithms lecture on wednesday. We were introduced to two main things: complexity and binary searching. Why it is called binary searching, I do not know (leave a comment below if you do!). The following diagram I created explains it better than I could in words:

Binary Search Algorithm

I have implementated the 'binary search' algorithm in Javascript (should work in Node.JS too), PHP, and Python 3 (not tested in Python 2).

Javascript (editable version here):

/**
 * @summary Binary Search Implementation.
 * @description Takes a sorted array and the target number to find as input.
 * @author Starbeamrainbowlabs
 * 
 * @param arr {array} - The *sorted* array to search.
 * @param target {number} - The number to search array for.
 * 
 * @returns {number} - The index at which the target was found.
 */
function binarysearch(arr, target)
{
    console.log("searching", arr, "to find", target, ".");
    var start = 0,
        end = arr.length,
        midpoint = Math.floor((end + start) / 2);

    do {
        console.log("midpoint:", midpoint, "start:", start, "end:", end);
        if(arr[midpoint] !== target)
        {
            console.log("at", midpoint, "we found", arr[midpoint], ", the target is", target);
            if(arr[midpoint] > target)
            {
                console.log("number found was larger than midpoint - searching bottom half");
                end = midpoint;
            }
            else
            {
                console.log("number found was smaller than midpoint - searching top half");
                start = midpoint;
            }
            midpoint = Math.floor((end + start) / 2);
            console.log("new start/end/midpoint:", start, "/", end, "/", midpoint);
        }
    } while(arr[midpoint] !== target);
    console.log("found", target, "at position", midpoint);
    return midpoint;
}

The javascript can be tested with code like this:

//utility function to make generating random number easier
function rand(min, max)
{
    if(min > max)
        throw new Error("min was greater than max");
    return Math.floor(Math.random()*(max-min))+min;
}

var tosearch = [];
for(var i = 0; i < 10; i++)
{
    tosearch.push(rand(0, 25));
}
tosearch.sort(function(a, b) { return a - b;});
var tofind = tosearch[rand(0, tosearch.length - 1)];
console.log("result:", binarysearch(tosearch, tofind));

PHP:

<?php
//utility function
function logstr($str) { echo("$str\n"); }

/*
 * @summary Binary Search Implementation.
 * @description Takes a sorted array and the target number to find as input.
 * @author Starbeamrainbowlabs
 * 
 * @param arr {array} - The *sorted* array to search.
 * @param target {number} - The number to search array for.
 * 
 * @returns {number} - The index at which the target was found.
 */
function binarysearch($arr, $target)
{
    logstr("searching [" . implode(", ", $arr) . "] to find " . $target . ".");
    $start = 0;
    $end = count($arr);
    $midpoint = floor(($end + $start) / 2);

    do {
        logstr("midpoint: " . $midpoint . " start: " . $start . " end: " . $end);
        if($arr[$midpoint] != $target)
        {
            logstr("at " . $midpoint . " we found " . $arr[$midpoint] . ", the target is " . $target);
            if($arr[$midpoint] > $target)
            {
                logstr("number found was larger than midpoint - searching bottom half");
                $end = $midpoint;
            }
            else
            {
                logstr("number found was smaller than midpoint - searching top half");
                $start = $midpoint;
            }
            $midpoint = floor(($end + $start) / 2);
            logstr("new start/end/midpoint: " . $start . "/" . $end . "/" . $midpoint);
        }
    } while($arr[$midpoint] != $target);
    logstr("found " . $target . " at position " . $midpoint);
    return $midpoint;
}
?>

The PHP version can be tested with this code:

<?php
$tosearch = [];
for($i = 0; $i < 10; $i++)
{
    $tosearch[] = rand(0, 25);
}
sort($tosearch);

$tofind = $tosearch[array_rand($tosearch)];
logstr("result: " . binarysearch($tosearch, $tofind));
?>

And finally the Python 3 version:

#!/usr/bin/env python
import math;
import random;

"""
" @summary Binary Search Implementation.
" @description Takes a sorted list and the target number to find as input.
" @author Starbeamrainbowlabs
" 
" @param tosearch {list} - The *sorted* list to search.
" @param target {number} - The number to search list for.
" 
" @returns {number} - The index at which the target was found.
"""
def binarysearch(tosearch, target):
    print("searching [" + ", ".join(map(str, tosearch)) + "] to find " + str(target) + ".");
    start = 0;
    end = len(tosearch);
    midpoint = int(math.floor((end + start) / 2));

    while True:
        print("midpoint: " + str(midpoint) + " start: " + str(start) + " end: " + str(end));
        if tosearch[midpoint] != target:
            print("at " + str(midpoint) + " we found " + str(tosearch[midpoint]) + ", the target is " + str(target));
            if tosearch[midpoint] > target:
                print("number found was larger than midpoint - searching bottom half");
                end = midpoint;
            else:
                print("number found was smaller than midpoint - searching top half");
                start = midpoint;

            midpoint = int(math.floor((end + start) / 2));
            print("new start/end/midpoint: " + str(start) + "/" + str(end) + "/" + str(midpoint));

        else:
            break;

    print("found " + str(target) + " at position " + str(midpoint));
    return midpoint;

The python code can be tested with something like this:

tosearch = [];
for i in range(50):
    tosearch.append(random.randrange(0, 75));

tosearch.sort();
tofind = random.choice(tosearch);

print("result: " + str(binarysearch(tosearch, tofind)));

That's a lot of code for one blog post.....

Useful hidden chrome:// pages

Since I have a chromebook, I was browsing the list hidden internal pages over at chrome://about/ the other day to see if they had added any new ones. To my delight I found that they had - this post will be about the interesting ones.

Note: Some of the chrome:// pages mentioned will not be available in the desktop version of chrome.

Keyboard layout

A sample of the chrome://keyboardoverlay/ chrome internal page. May differ depending on device

Can't remember that keyboard shortcut? No problem - just visit chrome://keyboardoverlay/. This is the internal page that gets shown when you hit CTRL+ALT+/ in Chrome OS. It is even interactive, showing you the keyboard shortcuts associated with any combination of the Ctrl, Shift, and Alt keys on your keyboard.

Battery Information

chrome://power/

Chrome OS keeps a log of your battery's percentage charge, and processor frequency data over at chrome://power/ - even when you don't have that tab open. It doesn't remember this data over a restart, though. You can show and hide 3 sections: Battery Charge, Idle State Data, and Frequency State Data.

The 'Battery Charge' section gives you a graph of how your battery discharged over time, obviously enough. It also shows you a graph of the charge / discharge rate in watts along with appropriate moving averages - useful if you are trying to save power on your chromebook and want to see if turning your wifi off extends your chromebook's life.

The 'Frequency State Data' section is not so useful (to me), but it shows the amount o f time your processor has spent running at different frequencies.

The graphs don't update live from what I can tell though, which would have been a nice feature to have.

Advanced Wifi Information

Chrome OS keeps some interesting information about the wifi networks that are in range and in your preferred list at (chrome://network/)[chrome://network/]. It displays the recent wifi related log entries, along with the MAC address, SSID, signal strength, security type, and more - useful if you want to debug your wifi connection.

Like chrome://power/, this page does not auto refresh either, but it does offer a convenient ?refresh= query string parameter to sutomatically refresh the page every so many seconds.

Other Pages Worthy of Note

THese other pages are also worth checking out, but didn't make it into the top 3:

  • chrome://net-internals/ - Shows everything you every wanted to know abou tthe network interactions that are going under the hood, and probably a whole lot of extra information that you probably don't care about too....
  • chrome://system/ - Holds a ton of informationo about your device, and the version of Chrom(ium) OS running.
  • chrome://gpu/ - Tells you what Chrome (OS) is using your GPU for, and what patches it has applied due to bugs in your GPU.
  • chrome://memory-redirect/ - Displays advanced memory information for each chrome process that is running.
  • chrome://imageburner/ - Houses Chrome OSes revcovery media creator.

Conclusion

I have included the most interesting chrome:// pages in this post. Some of them are only available on Chrome OS. All pages were found using Chrome OS 38 beta. If you find any more that are worthy of note, please leave a comment below.

Three Thing Game!

This is just a quick post to announce that I will be taking part in Hull University's Three Thing Game!

Three Thing Game is a game jam where you get virtual cash to buy 3 'things' at the auction of things, and then you make a game in 24 hours that includes those three things. It is organised by Rob Miles.

In other news I have been rather busy over the last few weeks, so there wasn't a post last Wednesday. It should be up sometime soon.

First Impressions: C♯

I will be learning C♯ over the next year or so, and since I am almost a week into learning it, I thought that I would post my first impressions here on this blog.

C♯ is a compiled language developed by Microsoft that looks a little bit javascript, and a little bit like Rust (If you haven't heard of rust yet, I have written up a first impressions post here). Like rust, it has a type system, so you can't set a variable with the type int to a string. This type system is not a confusing, though, since it only has a single type for strings (rust has two - one that you can change and one that you can't) and you can convert between the different types quite easily (e.g. int.Parse() converts a string to an int).

The brackets syntax is almost identical to that of Javascript, except C♯ has classes and namespacees too (I don't really know what those do yet). Indentation also seems to be fairly important, which is perfectly fine by me since it improves the readability of your code.

Looking around on the internet, it seems that C♯ is tied in with Visual Studio quite closely. This might cause problems in the future, because I don't really want ot install visual studio (express) on my computer because of it's file size (the installer alone is > 600MB!). Hopefully I can continue to use the csc C♯ compiler I found in the .NET 4.0 folder on my computer as my code becomes more complex.

All in all C♯ looks like a good introductory language to the world of compiled programming. The syntax is straight forward and easy to understand so far, and it is kind of similar to Javascript, which eases the learning process considerably.

Imaanvas!

Today marks the release of a larger project that I have been doing, called Imaanvas. It has been in the works for months and is meant to be a web based version of a program called MSW Logo, which is now called FMS Logo. It has a few tweaks, though, to make it slightly easier to use. It was orignally written for a year 5 class in a primary school.

It also does not come with all the commands present in Logo, so if you find that a command is missing please comment below and I will try to add it for you as soon as I have some spare time. (You can also write the command yourself, and I can add it that way, but will probaby need the original source code for that - gulp is used to compact the code - send me an email if you want the code)

Immanvas is a horribly complex piece of code - so if you encounter any bugs (which is likely), please either leave a comment below, or send me an email. Remember to be descriptive about the bug that you have found, otherwise I won't be able to track it down and fix it! Also remember that Imaanavs is meant for modern browsers, so if Imaanvas doesn't work in your browser, try upgrading it to it's latest version.

This post is late since essential maintenance work had to be carried out to try and reduce the amount of spam that is being posted.

Art by Mythdael