[TECH] Memory corruption and format specifiers "%s%c" is different from "%s%1s"

I have been fixing several issues last few weeks, and the following issue in someone's code is a clear test for understanding differences between strings and char's.

On the first look "%s%c" and "%s%1s" seem very similar, but unfortunately NO! and they can create some nasty runtime bugs corrupting your variables, suppose the code existing in someone's code like this.

void BuggyScanner(){
    char buf[MAX_SIZE];
    int a;
    char b;
    scanf("%d",&a);
    scanf("%3s%1s",buf,&b);
    printf("a=%d buf=%s b=%c\n",a,buf,b);
}

The format specifier is really a blunder as scanf "%1s" is going to write beyond one byte (the extra '\0' which gets padded for strings)at the address of 'b' , since 'buf','a','b' are on the stack writing one byte beyond the address of 'b' can do really nasty stuff.

• Just as in this corrupted the variables.
• Potentially corrupt the return address of the function, creating a great security bug.

Be Careful guys! Vamsi.

[BOOKS] List of books I want to buy when I'm in india

1. The Practice of Programming (Paperback) by Brian W. Kernighan (Author), Rob Pike (Author) 2. Programming Pearls (2nd Edition) (Paperback) by Jon Bentley (Author). 3. Algorithms on Strings, Trees and Sequences: Computer Science and Computational Biology (Hardcover)

I'll keep adding to this list...
Life has been through a lot of code in Matlab/Octave, Perl and C. Cheers! Vamsi.

[Perl] Don't nest your regular expressions when you use /g switch

I have been busy all these days with quite a few things, well the motive of this blog is to document some of the issues I face in my day to day work.

while($line =~ /input .*? name="(.*?)" .*? value="(.*?)"/g){
  $param_name = $1;
  $param_value = $2;
  if($param_name =~ /blah/){
    # Do some stuff
  }else{
    #Do some stuff
  }
}

The above code can go miserably wrong and hard to debug especially when the outer while loop has hundreds of lines of code in it, as you can see when we use '/g' switch in the matching all the matches within a string, make sure that THERE ARE NO NESTED REGULAR EXPRESSIONS WHEN USING /g switch

I want to become expert in one area

Some times I think what I'm I worth of? what can sell myself?
In fact I did sell myself when I created perl2exe based on my systems knowledge.
few things I think I should concentrate on
1. Parallel Algorithms (they make me to say ahaa!)
2. Systems (Drepper called me Moron! :()
3. EDA (Feels good for me).

[NON-TECH] Puppy

Pic of puppy after a fashion show in hyderabad!
IMG_0495
Originally uploaded by vamsi.

[Tech] Bitonic Sequences and Bitonic Merge

Given a Bitonic Sequence of length 2n (a motonically decreasing (inceasing) and montonically increasing (decreasing).
If we do a Bitonic merge we still of 2 bitonic sequences of length 'n' each.

void BitonicMerge(int *array,size_t size){
 int i;
 assert(!(size%2));
 for(i=0;i lessthan size/2;i++){
   if(a[i+(size/2)] < a[i]){
     swap(a[i+(size/2)],a[i]);
   }
}

What we have is now two Bitonic sequences. Doing a Bitonic sort on a parallel machines with 'p' processors and 'n' elements n >> p. Next post I'll post my code to do the Bitonic merge of the sequences.

[FUN] Top 21 things an Indian does after returning from U.S

(---  Good One!.... Just for fun---)


21. Tries to use credit cards in a road side hotel.


20. Drinks and carries mineral water and always speaks of being health conscious.


19. Sprays deo so that he doesn't need to take bath.


18. Sneezes and says 'Excuse me'.


17. Says "Hey" instead of "Hi".
says "Yogurt" instead of "Curds".
Says "Cab" instead of "Taxi".
Says "Candy" instead of "Chocolate".
Says "Cookie" instead of "Biscuit".
Says "Free Way" instead of "Highway".
Says "got to go" instead of "Have to go".
Says "Oh" instead of "Zero", (for 704, he will say Seven Oh Four Instead of Seven Zero Four)

 

 


16. Doesn't forget to crib about the air pollution. Keeps cribbing every time he steps out.

15. Says all the distances in Miles (Not in Kilo Meters), and counts in Millions. (Not in Lakhs)

14. Tries to figure all the prices in Dollars as far as possible (but deep inside multiplies by 43).


13. Tries to see the % of fat on the cover of a milk pocket.

12. When he needs to say Z (zed), he never says Z (Zed), instead repeats "Zee" several times, and if the other person is unable to get it, then says X, Y Zee(but never says Zed)

11. Writes the date in MM/DD/YYYY. On watching traditional DD/MM/YYYY, says "Oh! British Style!!!!"

10. Makes fun of Indian Standard Time and the Indian Road Conditions.

9. Even after 2 months, complaints about "Jet Lag".

8. Avoids eating spicy food.

7. Tries to drink "Diet Coke", instead of Normal Coke. Eats Pizza instead of Dosa.

6. Tries to complain about any thing in India as if he is experiencing it for the first time. Asks questions etc. about India as though its his first visit to India.

5. Pronounces "schedule" as "skejule", and "module" as "mojule".

4. Looks suspiciously towards any Hotel/Dhaba food.Few more important ones:

3. From the luggage bag, does not remove the stickers of the Airways by which he traveled back to India, even after 4 months of arrival.

2. Takes the cabin luggage bag to short visits in India and tries to roll the bag on Indian Roads.The Ultimate one


1. Tries to begin any conversation with "In US ...." or "When I was in US..."

[Tech] How to determine the bus bandwidth.

Hi recently I had a need to find out the bus bandwidth. 
The bus had 64 lines and assume that the speed of the bus is xMHz.
This implies the bandwidth = (no.of lines) * (speed of each line).
Bus Bandwidth = ((64/8)*x*10^6)/(2^20) MBytes/sec.

A simple use of this metric is suppose you have 
SMP(Shared memory processors) with a common bus
and the bandwidth of the bus is 1 GBytes/sec
and you have several processors which have an 
(memory) Instruction bandwidth of 250 MBytes/sec
you cannot connect more than 4 processors to 
saturate the bus.  

[Tech] Pathetic non unix standard matlab editor

Well I'm really pissed of this damn editor (matlab editor) , some how I cannot execute my program .m file from the command line so I had to use this matlab's editor to run my program, after using vi for long this is really pathetic, its more worse than windows I just did ctrl+c and ctrl+v it pased some junk instead of the code which I intended to paste.

[SPICE2LAYOUT] 40% Complete

Got back to the SPICE2LAYOUT project updated some Makefiles and added all the skeletal code today. By the mid of the week I should get this up and running, It also needs to have the channel router in that.
Need to get back home and study some stuff for a upcoming Friday jury.

Algorithm for Permuting in place

Problem: Given a set of numbers S = 1...n and a permutation PI(S), how can you rearrange elements in S in O(n) time with no extra space.

I don't like explaining things just code it., here's code below

#include
#include
#include
int a[10];
int b[10];

void ResetArray(){
    unsigned int i;
    for(i=0;i<10;i++){
        a[i] = i; 
    }
}
void swap_elements(unsigned int i,unsigned int j){
    int temp;
    temp = a[i];
    a[i] = a[j];
    a[j] = temp;
}
/*b is the swap list*/
void InplacePermute(int *perm){
    unsigned int i;
    for(i=0;i<10;i++){
        if(perm[i] < i){
            perm[i] = perm[perm[i]];
        }
        if(a[i] < i){
            perm[a[i]] = perm[i];
        }
        swap_elements(i,perm[i]);
    }
}

void PrintPermutation(void){
    unsigned int i;
    for(i=0;i<10;i++){
        printf("%d ",a[i]);
    }
}

int main(){
    int runs=10;
    unsigned int i;
    do{
        ResetArray();
        printf("Please enter the permutation of size 10, 10 unique digits from 0-9\n");
        for(i=0;i<10;i++){
         if(scanf("%d",&b[i])<=0){
            break;
         }
         assert(b[i] >=0 && b[i] <=10);
        }
        if(i<10){
            break;
        }
        InplacePermute(b);
        printf("The permutation is::");
        PrintPermutation();
    }while(1);
}

The following are testcases

7 3 2 1 4 8 9 0 5 6
8 9 1 2 5 6 7 3 4 0
1 2 3 4 5 6 7 8 0 9
1 3 4 8 9 0 7 6 5 2

Well this week has been a little productive, got the space for http://phaedrus.sourceforge.net a library of randomized algorithms
Have Fun.... Vamsi.

Passing multidimensional arrays to functions

Got enlightened by this today. And realized the following.

int a[10][20];

int main(){
 print_array(a); /*results in a crash.*/

}

void print_array(int **a,int i,int j){
 printf("%d",a[i][j]); /*How stupid this can be?*/
}

I love PHP

Have been using PHP with apache to build some stuff really like programming in this I'am in love with PHP.

[Tech] One more reason why MACRO's are Not Preferred over inlines.

...macro.h....
/***Dangerouse Macro1***/
#define print_int_value_twice(c) do{\
 printf("first time %c second time %c\n",c,c);\
}while(0);

/***Stupid Preprocessor***/
#define my_error(c) do{\
 fprintf(stderr,"Error::");
 fprintf(stderr,c);
 fprintf(stderr,"\n");
 exit(1);
}while(0);

.....macro user ....
j=0;
print_int_value_twice(j++);
/*j incremented twice by the preprocessor*/


/*In this case the preprocessor is stupid 
 not treat the string spanned across several lines
 as a incomplete macro argument and fails compilation.*/
my_error(" My error spans three lines
            line1
            line2");

Avoid MACROS start using inlines , if you define macros the users should use them with caution

[Personal] I was not good and never have been.....

Yes! today I realize my potential, I was never good in fact never have been....I accept my failure. I'm a looser, I cannot win and never have won and in fact I'm obliged to life for letting me live and eat what ever I want and wear what ever I could....in the midst of bitter shame....I gave up...I don't want to live as a looser...I will soon end my life and this blog may be the last. I was never honest to myself I have things which I don't deserve. And I get emotional for small things...what else a looser can say except bending down head in shame.

[TECH-NON-TECH] SPICE2LAYOUT should I use BGL?

A Warm Welcome to a great new year 2007! This is my first blog after 24 days in the new year. Last time I had written my blog was on Dec 31, 2006, well this was the coldest new year eve I had. I just went to bed on Dec 31 night 2006. Its because I was with puppy taking care of puppy...we were really afraid on whats going to happen next....but it was great what happened next day was really a new begining in a new year things went excatly how I wanted (In fact I did'nt know what would be the best solution and just prayed "God! Please do something so that I will be comfortable after that")...a great going new year 2007 from there on, really had great time in Hyd from Jan-1 to Jan-6.....after that I took pathetic AeroSvit flight (Never Ever Take this shoddy airline) back to JFK, travelled all the way from NewYork to Hartford and took a cab to my place....its quite a tiresome journey to travel from India to U.S, next time I will travel by either BA ,Lufthansa or Emirates..... Now I need startoff my coding for the SPICE2LAYOUT project its been a while I took a break and its really a long one....Tomorrow Is a SRM from TopCoder....I was having a dilemma to use Boost Graph library or not...but I guess it will be fine if I write it on my own. Take care...keep Warm :) Cheers! Vamsi

[PERSONAL] Lets solve the problem.....

"Lets solve the problem" , thats what I have been saying to myself for all these days. Well I have decided never to budge and just take the things the way they come..just bought my copies to the Art of Computer Programming. For me right now there are no shortcuts, no quickies I have to take the things the hardway or the toughway more specifically.
I guess I have become a little bit more matured now, because I have to do things more responsibly now. I have a big responsibility now, I don't worry about it but I welcome it into my life, I'am ready to solve it and all the consequences...I will never run-away from the problem. But I need to be a little bit more practical also, well for any problem now there is no way out except to solve it.
So...LETS SOLVE THE PROBLEM RATHER RUNNING AWAY FROM IT....
And when you are solving problem's you need to be very methodological...I know its all spelling mistakes my blog...I may not be a great genius but I'll try my part to solve the problem. And when I solve the problem there will be no shortcuts.
Frankly I have been not getting great results for my Dynamic Programming based Border Length Minimization Problem. What to do I don't know I cannot really fake up any results. It's bad really bad. I leave it
Today puppy came out, she has been not liking the place where she is living but she has to for sometime, she should feel free and I'am a very lucky guy interms of that. I will always care for puppy and will solve the problem and not run away from it.
Happy new year 2007.....LETS SOLVE IT....that's the quote of this year.
Take care guys and keep having fun.....mean while I will lay back and keep thinking....

[NON-TECH] Travelling to india....

I should be indeed thankful to sudha for a ride from Storrs to Stamford. When I reached Stamford it was a little difficult to find out where ravi is and finally found ravi, went to circuit city to buy some stuff, later toured manhattan,brooklyn went to a great Italian restaurant, I really liked the hot bread and that olive oil to eat the bread, I never tried any Italian food apart from the normal pizza. Its really windy today in New York with -7 Centigrade, really had a hard time pulling all my luggage into the airport.....well found a wireless connection at the food court here, IT WORKS...well I'am writing this from that connection only, I need to wait till 4:00 PM to take my flight. Its a long wait.

Good that I got some charge on my laptop so that I can do some work today, I have many things pending, mac,tim,ion and raj. I need to get all the work done in this break good if I could make a proper schedule to fix up all the things.

Lets see how things work......luv....Vamsi

I have not started any packing

Its just 12 hours for my flight I have not packed any thing .....dont know how I will pack....I think in have insomnia I cannot sleep its killing me every day its 4:00 AM in the morning I have been trying to sleep for last 4 hours but failed miserably. God please gimme some sleep please....it would have been great if we could buy sleep :((

[TECH] Algorithm to find euler circuit in a graph in O(|E|)

Important observation I found is that, if we delete a cycle (delete all the edges which form a cycle) from the graph which has a Euler circuit, the property of the graph still remains, i.e the necessary and sufficient condition for the graph to have a Euler cycle is that every vertex should have even degree. And also there has to be a cycle at every vertex.

INPUT: G =(E,V)
v = v
euler_cycle = NULL;
while(|E| > 0){
 /*Find a cycle in G, start
   the search at v, returns c0 around 
  which cycle is formed*/
 c0 = FIND_CYCLE(G,v);
 v = GET_NON_ZERO_DEGREE_VERTEX(c0); 
/*Above can be done in constant time,
 using some space while finding the cycle
 */
 MERGE(c0,euler_cyle);
/*constant time operation,
 put c0 after an edge e1 in
 euler cycle which ends at 
 vertex 'v', we can just remember 
 the position of v n euler_cycle
 every time we merge*/

}