Thursday, April 24, 2008

Making make files

So final class in the CSCI 1730 and Dave has covered make files for the undergraduate students. Alas, during my undergraduate studies we did not work much with Linux at school. Frankly, none of the lab instructors in my school were knowledgeable about Windows itself, leave aside make and stuff. They used to treat the school lab systems as their secret treasure and none of us were allowed to even check our mail. That sucks, I know, that really does. (I completed my Bachelor of Engineering in Information Technology, though I consider myself more of a computer science student than an IT personnel). Anyway, I will write down what I learnt more about make files.

Sample Makefile

Note that make files should have the name "Makefile". Invoking make reads this file for rules to be executed.

Calling just make, invokes the first rule and if you want any other rule to be executed you specify it "make ruleX".

batch: a b c

a: a1 a2

touch a

b: b1 b2

touch b



Here batch is the target for which a,b and c are dependencies. So the batch is only executed when the modification time of batch is different from that of a b or c. Again since a is dependent on a1 and a2, it has to be run only when a1 and a2 has different modification time. A rule with no dependencies always executes it with no considerations.

Make file to compile a C++ program

Suppose we have a which depends on List.h and and we wish to compile to get a main.out

build: clean compile


rm -rf main.out

compile: List.h

g++ List.h -o main.out

So do you always need to write a makefile? Well, the answer is no. For example, if you have a C++ program called "testmyprogram.cpp" and then you just type "make testmyprogram" then based on the extension .cpp it invokes the following command.

g++ testmyprogram.cpp -o testmyprogram

Well, this is kind of nice, especially when you do not want to make a file just for testing a program and best of all, when you are lazy like me. But it does not work for java programs, at least not on my terminal machine.

make -f AnotherMakefile

The above command takes in AnotherMakefile instead of Makefile.

Using "variables" in makefiles

Well, look at the following makefile

TARGETS=foo.o bar.o driver.o

driver: $(TARGETS)
       $(CC) $(TARGETS) -o driver

CFLAGS is an implicit flags variable which you do not need to mention when the rules are defined.

Where things can go wrong in Makefile

look the following code.

class Example
int f1;
int f2;
int f3;

The looks like this

#include "foo.h"

void func(Example &x);

Example obj;
= 7;
"f3 :%d\n",obj.f3);
"f3: %d\n",obj.f3);

The looks like this


void func(Example *e)
= 10;

Your makefile to build this is pretty simple, as shown.

prog: foo.o bar.o
++ -o prog foo.o bar.o

foo.o: foo.h
++ -g -c foo.c

bar.o: foo.h
++ -g -c bar.c

So running make and running the program output is pretty easy and you get to see the output as 7 and 10. Now when you remove the dependency on foo.h from the bar.o rule, comment out the field "int f2" from the foo.h. So when you run the make again, since foo.o depends on foo.h, it runs whereas the rule bar.o does not run and there for the bar.o still knows that Example has three fields(int f1,int f2 and int f3) whereas the foo.o believes Example has two fields only. So when you change f3 to 10 in, it does so in the "third" field whereas f3 is the second field in f2.


So it is always good to remember that weird things happen when your Makefile is not correct. (In the above case, you saw something like a pointer bug).


Working with makedepend


Running the command "makedepend", it generates a Makefile with list of all depenedencies. makedepend is useful but not optimal. It goes through each of the project file specified, identifies the #includes and then further checks these includes to find out further dependencies. It looks like great tool to generate the dependencies. GooD!


I guess that is it for now, I hope to write about Jboost in the next post, hopefully.

Tuesday, April 22, 2008

Making sense out of Adaboost

So, atlast I could make some sense out of the Adaboost algorithm. Atlast I could make something that runs "adaboost". Though, I did not write code for the adaboost(In the past, I have and I did not have that great success). Until yesterday,  I could not understand what Adaboost was all about. Thanks to the lecture at, I now know what Adaboost is and what makes it run. Before I jump into practicals of running an Adaboost application, let me attempt to explain what Adaboost is in my own words.

What is Adaboost?

You have a bunch of "weak" classifiers, and an adaboost classifier is a strong classifier that is made by cascading these weak classifiers. When these classifiers are cascaded, they are multiplied with "weights" which tells how important this feature is.

Wait a second, what is a weak classifier?

Ok, a weak classifier is a classifier that could be understood as classifier that takes one feature and based on a rule, it outputs a class that this feature falls in. For example, I have a weak classifier that takes in "age" as the input feature and based on the rule that "if age is less than 18, he is a minor otherwise he is a major", the classifier returns "major" or "minor". So my classifier in Java could look something like this.

public PeopleClass classify(int age) {
         return (age<18)?PeopleClass.Minor:PeopleClass.Major;

So what is the big deal?

There is nothing great that we get with a weak classifier when it is used on its own. Just an age class would not help you identify if a person is rich or poor. But you have more than one such classifiers (such as salary, property, marital status, etc.). Together when these classifiers are used, they would form a single strong classifier which tells if you if the person whose features are given, is rich or not. But you cannot just add these classifiers (for now, take Minor as -1 and Major as +1) to get a total weighted value. You have to assign some "importance" to the features you input. So how do you decide how important a particular feature is? This is where the "training set" comes into play. Before, I jump in and give training details, you should know that sign(x) is +1 if x>0 and -1 if x<0 and 0 if x=0.

How does training work?

I would like to write a disclaimer that I am not an expert on Adaboost and probably half the stuff I wrote here is wrong. But what I write here is my understanding of Adaboost and hey! it works, at least for me. Now let us look into the training. In a training set, you give different feature-sets and for each feature-set you already know the class the object whose feature-set is the input, falls into. So your training set for a Richness classifier could look something like this.


23,single,12000,100000,smoking drinking,poor

We have such a list of different possible inputs for the Adaboost classifier to train itself and learn what good weights are. So, the magic of the learning works and finally you have good estimate of weights. So later, if you input some feature-set whose class you do not know, then this weights are ideal for the classifier to spit out the class.

Java Implementation of AdaBoost

The theory behind Adaboost is so-far simple and yet it is not so easy to write your own implementation of Adaboost, may be you could write one if you have more in depth understanding of the pseudo-code than what I presented. Anyway, there is a good implementation of Adaboost called the JBoost library, which not only implements Adaboost but also implements few other learning algorithms. Jboost does not have good straight-forward step-by-step example and in my next post, I intend to give a step-by-step guide with application to skin-detection in images. With very simple features like R,G,B values of a pixel, the classifier generated by Jboost does great when it comes to true positives (it identifies all the skin pixels) but it does require improvement in the false positive aspect(it identifies non-skin pixels as skin pixels). Look out for this post and it would be very helpful for a lot of CS guys who works on Computer Vision, Machine Learning and other many fields where classifiers need to be used.

Sunday, April 13, 2008

Why game development?

Well, like I mentioned earlier, I have been thinking a lot about game development as a career. So this is what I think:
  1. Game developer needs to work a lot of overtime. In fact I read that quiet a few companies are exempted from overtime law if they hire developers for game development. I am not sure if it is true. General law says, a person who works 2-4 hours overtime should be paid 1.5 times the actual money, and twice after that. Anyway the point is that you work overtime a lot and the best part is that not even 1% of the community complains about it.
  2. You as a game developer gets to work on exciting projects all the time. As a mobile game developer , you get to learn a lot about writing optimized code, making the code portable otherwise port it somehow. I was informed by one of the devs from Javaground that they tend to port over 100 odd games every year and each game is ported onto at least different devices. That is like generating over 200,00 builds in 300 working days. And if my math is right, it is over 67 builds every day. That is amazing amount of "interesting work", not to forget the semi-annually releasing game-from-the-scratch of their own. Again, the best part is to have the honor of being involved in such an amazing work. As a normal developer, you would hardly be involved in 3-4 products in your lifetime as a developer. Be a mobile developer, you could be involved with so many different products all the time.
  3. After all my ranting about game devs writing optimized code all the time, there is a question - do I enjoy writing Employee e = new Employee(); or do I enjoy manipulating bytecode? Well, I am not sure about others, but I really enjoy working with hardware, I enjoy the fact that software is more closer to a person through a mobile device than through a PC(Of course, PC software is always great). So what is it different? Firstly, I am telling this based on my personal enthusiasm and I am very eager to be termed as Game Dev. Probably, if I miss the opportunity, I would be little disappointed(to say the least). Anyway, as a developer at Javaground, I imagine, I would be learning a lot of internals about JVM, about mobile phones, about ARM Processors and others, a lot about games. I was told that the entire team is amazing and it is for that reason that they come up with super-cool games (I just watched the demos)
Why should we hire you?
This was the question asked by the CTO of Javaground during the interview. I was not expecting such a question after a series of technical questions from different people. Anyway at that moment, I answered that I am a good programmer who plans his work well, who never misses deadlines and who is really good at translating requirements into working code. I guess, when I think over the question, even now I do not have a convincing answer, yet I know I make a good hire and a good team member.

So my wellwishers, who-so-ever is reading my blog between today and 25-April-2008, please pray that I get a good offer from Javaground, and if you are reading this after that day, then please pray for my success at whatever firm I am at.

Do I really understand Java? or Computer Science, for that matter?

Like I mentioned in my previous post, I was with Javaground being interviewed for the Developer position. It was an overall amazing and a great learning experience. I am so much thrilled for having interviewed with them that I have been thinking a lot on how I could be like them. The java we write is so lame. I gave a talk on optimizations and now I feel embarassed that I am not eligible to give such a talk. And I did cover a lot of material and left out a lot. But talking with the Javaground team made me realize that I am not as good I felt I was.

I was honored to be in their guest house along with a developer from their Canada team. He was Nigel and I should say that he was amazing and very impressive, very pleasant to talk and very down to earth. He told me simple things that no one would ever find in a book, I bet. So the aspect he told me was "comparisons with a 0(zero) is much faster than with any other numbers". This was just one of the quiet a lot of information he shared with me. Though not always "java" we talked about, he told me various other things - about life as a mobile developer, how mobile game works, stuff like that.

Anyway, I decided I would look into the "comparison with zero" to understand more. So just now I wrote two simple programs - Hello and Hello2. The looks something like this:

public class Hello{
        public static void main(String[] args) {
                 int i = 0;
                 if(i < 1) System.out.println("Test");

The result of running javap is shown. (After compiling with javac)
javap -c -private -verbose Hello

Let me show you the output ....

Compiled from
public class Hello extends java.lang.Object {
    public Hello();
        /* Stack=1, Locals=1, Args_size=1 */
    public static void main(java.lang.String[]);
        /* Stack=2, Locals=2, Args_size=1 */

Method Hello()
   0 aload_0
   1 invokespecial #1 <Method java.lang.Object()>
   4 return

Method void main(java.lang.String[])
   0 iconst_0
   1 istore_1
   2 iload_1
   3 iconst_1
   4 if_icmpge 15
   7 getstatic #2 <Field out>
  10 ldc #3 <String "test">
  12 invokevirtual #4 <Method void println(java.lang.String)>
  15 return

I have made the lines of interest bold. Now my looks like this:

public class Hello2{
        public static void main(String[] args) {
                 int i = 0;
                 if(i < 0) System.out.println("Test");

Now let us look at the javap output shown in the listing.

Compiled from
public class Hello2 extends java.lang.Object {
    public Hello2();
    public static void main(java.lang.String[]);

Method Hello2()
   0 aload_0
   1 invokespecial #1 <Method java.lang.Object()>
   4 return

Method void main(java.lang.String[])
   0 iconst_0
   1 istore_1
   2 iload_1
   3 ifge 14
   6 getstatic #2 <Field out>
   9 ldc #3 <String "test">
  11 invokevirtual #4 <Method void println(java.lang.String)>
  14 return

As you can see the highlighted section again, we would notice an operation missing. So let me put the areas of interest together, side by side.

i < 1

i < 0

   0 iconst_0
   1 istore_1
   2 iload_1
   3 iconst_1
   4 if_icmpge 15
   0 iconst_0
   1 istore_1
   2 iload_1
   3 ifge 14

Frankly, I do not understand the bytecode so well yet, but I do can make out that in comparison with a 1, there is an instruction that creates the constant 1. Where as for comparison with 0, that instruction is missing. I could recall something similar that we learning during Computer Architecture class and the Embedded Systems course that I attended. I wish I invested more time in those classes. How foolish I was back then?

This is not a big deal when you have server class machines or a laptop for that matter. Saving a couple of instructions - no big deal. But in a mobile environment, it makes sense. So out of 200000 odd lines that we write, if we could only save 2 instructions per 100 lines, that would save us 2000 instructions !!! and it is a lot given the limited resources of a mobile device.

I am very interested in gaining such knowledge and it is only possible, at the moment, when we work at companies like Javaground. I could get a job as a web developer or as a C# developer at any point of time in my life but opportunities like Javaground does not often come. And I have worked very hard for this opportunity. I gave 3 rigorous online tests, attended around 6 interviews and after all I wish if only I could prepare better. "If" i am lucky and "if" I get an offer from Javaground which is good enough for me to make a proper living, then I would see myself learning a lot from the immense talent that Javaground possess and hopefully one day see myself as one of their core people. I know there are a lot of such firms but at the moment, the only such firm that has interviewed me is Javaground. 

The two days made me realize, there is so much I should learn!

Friday, April 11, 2008

What is my favorite programming language?

Well this was one of the tons of questions I was asked during my interview with Javaground. Anyway the environment at the company looked so serious and everyone was kind of busy all the time. I like such a challenging environment and have to see if I was "good enough" to be a part of it. I have an offer with a service company E*Trade but I am not too sure about it. Unless the pay is relatively less at Javaground, I do not want to lose an opportunity to work for them. If I work at Javaground, I would:
1. write optimized code, probably someday write a whole new book on code optimization.
2. work with one of the best minds in the software industry. great developers and everyone talks about compact and great code.
3. better future - game devs make a lot of 1. money 2. fame 3. knowledge about s/w and h/w.

Atleast from what I see, I think they are looking for a good programmer who has strong basics and knows what he writes.
What is my favorite question?
Xavier Kral, the CTO of javaground raised this question. I always felt different about different languages. So let me start one by one.
C - Definitely not my favorite.
C++ - Great language, but then not my favorite - I do not admire or adore pointers
Java - definitely a contender. Write great software in less amount of time. Java is a cool language. Come Java 7 you have closures and it would revamp the style of Java code.
C# - Right now, my best language. The language I am most good at. The C# 3.0 features are amazing.
Groovy - Definitely a great scripting language that is on top of JAva.
So what is my favorite? I feel confused. When I work on Java for a long time, I feel Java is the best thing that has happened to the developer community. But when I work on C# for a long time, I feel C# is much better than Java. So which is my best language? - I prefer C# when working on windows and I prefer Java when I want something on Linux. Both has its pros and cons.
Why game developer job?
The charisma of a game developer is totally different. A game developer is more attractive to girls than a mainframe developer. I am kidding, but I like the challenge to work on real projects which constantly puts your skill to think and code to test. It is great to actually feel as a game developer. So again the reasons I list out are:
1. Game dev make a lot of money, if not now atleast in the near future.
2. Game dev tittle is more attractive than anything else.
3. If there is a possibility that I would own my company or become a major part of a startup, then it is possible only in the Game Development Industry.
4. Even if the economy is not all that great, Game Industry will always survive -> I would always be in demand and it would only increase with time.
5. If I work hard enough, I would end up becoming a very popular developer in the community.
6. The amount of knowledge you gain as a game developer is immense. You create a form of life in the form of games and you should feel close to god!

Wednesday, April 09, 2008

What's with Orkut?

So orkut is owned by Google - nice move by Google to make itself believe that its in all domains on the internet. Agreed Google is great but what I find strange is that Orkut still runs on ASP.NET and I guess, even the newer developments in orkut are using ASP.NET. And we should not forget that google and microsoft are no friends.
So is orkut well designed?
I guess not. I show you two screen shots of my profile taken at the same time...I know what is wrong and I consider it to be a silly thing. so what is the problem? I see different scrap count in the profile page for every two clicks ... and yeah it has nothing to do with the clicks. I guess it is the problem with caching that does(actually the caching that these people has implemented.

how long does it take to fix?
Things are so sweet with that you can design a full fledged portal like orkut in no time. I bet it would take some avg dev like me to write orkut in one week with no bugs. and yeah I did one version of orkut in java servlets and I am confident about what i say. So to fix these problems, it would not take more than 30 minutes.

So my final thoughts are - if you hate something, hate it properly, if you like something then do not act as if you hate it. By the way, I do not hate orkut, I just do not like the way its being taken care of. Google, if it sucks(along with Microsoft) then why would you want to use it. Use GWT and rewrite orkut, your "smart" developers whom you pick after 10 rounds of interviews(out of which 6 tests your english), could rewrite orkut in no less than a week. That way you would not have dummies like me pointing fingers. Rewrite orkut else make it even better. Look at facebook - its done in php and it is an awesome application.