This is going to be a great software!
Showing posts with label C. Show all posts
Showing posts with label C. Show all posts
Thursday, June 20, 2013
Good programming
#include <stdio.h>
#include <stdlib.h>
int main(void) {
printf("Segmentation Fault\n");
exit(EXIT_FAILURE);
}
Sunday, December 18, 2011
Code Obfuscation (Example 1)
Following through the series of posts about code obfuscation and unmaintainable code, I want to show here a C code snippet:
This is indeed a full working program, and the techniques used here to screw the code are simple enough. What's the actual purpose of this program?
Compile & running it (or gcc -E) are good means to see in its internals.
No further explanation is being given here, as I consider this to be easy enough!
#define x(y,z) z , y
#define y(z,x) x z
#define a(b,c) c##b
#define x167 }
#define x879 x167;
#define x798 '\0'x879
#define x98 {
#define _ a(ain,m)
#define __ ()
#define b(c,d) a(c,d)
#define w a(ar,ch)
w ____[] = x98 x(0154, x(0145, 0110)), 108, 111, 30+02, 87, 0x6f, 0162, 0x6c, 0x64, x798
w ___[] = x98 '%', 's', x(x798, '\n')
_ __ x98 y((___, ____),a(ntf,pri)); x167
This is indeed a full working program, and the techniques used here to screw the code are simple enough. What's the actual purpose of this program?
Compile & running it (or gcc -E) are good means to see in its internals.
No further explanation is being given here, as I consider this to be easy enough!
Tuesday, November 8, 2011
Print Bits
I was handling a bitmap some time ago, and I came into the need to see what was the actual bit representation of the numbers I was using. So I wrote this function:
This function accepts an integer, and prints on screen it's actual binary representation. Basically it takes a mask whit only the most significant bit set, bitwise ands it with the number and prints either 0 or 1 depending on that bit's value. Then it shifts the mask one position right and iterates, until all the bits are shown.
The 'b' in the mask is a GNU extension, which tells that the number is represented directly in binary. If you are not using gcc, or don't like that series of 0's, simply replace it with the hex counterpart: 0x80000000.
This works both in 32 and 64 bits on Intel x86, as integers there are both 32 bit wide. If you want to deal with a larger number representation, either change the initial mask, or set it to 0x1 and change the shift from >> to <<.
You can use this code to see how numbers are represented. With some minor changes, you can use it to show any representation, be that a float or a more complex struct, for example by dereferencing a pointer.
void print_bits(int number) {
unsigned long mask = 0b10000000000000000000000000000000 ;
char digit;
while(mask) {
digit = ((mask & number) ? '1' : '0');
putchar(digit);
mask >>= 1;
}
}
This function accepts an integer, and prints on screen it's actual binary representation. Basically it takes a mask whit only the most significant bit set, bitwise ands it with the number and prints either 0 or 1 depending on that bit's value. Then it shifts the mask one position right and iterates, until all the bits are shown.
The 'b' in the mask is a GNU extension, which tells that the number is represented directly in binary. If you are not using gcc, or don't like that series of 0's, simply replace it with the hex counterpart: 0x80000000.
This works both in 32 and 64 bits on Intel x86, as integers there are both 32 bit wide. If you want to deal with a larger number representation, either change the initial mask, or set it to 0x1 and change the shift from >> to <<.
You can use this code to see how numbers are represented. With some minor changes, you can use it to show any representation, be that a float or a more complex struct, for example by dereferencing a pointer.
Monday, October 31, 2011
Multithread Barrier (yes, it's a join!)
This post doesn't want to clearify all aspects of parallel programming. It's just an example to show how you have to thinkg when writing parallel code!
When you deal with concurrent programming, everything is going to be screwed up very easily. Debugging is a pain in the ass, and every one who has ever written a multithreaded software, although very simple as a concurrent server, has experimented with such a pain.
One fundamental operation in multithreaded programs is synchronization. In particular, one operation which I consider very important is a thread barrier, that is a line of code in the program which guarantees that if a thread is executing before it, no one else is executing after it, and if there is some thread after it, then every other thread is, at least, executing that line, but not anything before...
When you deal with concurrent programming, everything is going to be screwed up very easily. Debugging is a pain in the ass, and every one who has ever written a multithreaded software, although very simple as a concurrent server, has experimented with such a pain.
One fundamental operation in multithreaded programs is synchronization. In particular, one operation which I consider very important is a thread barrier, that is a line of code in the program which guarantees that if a thread is executing before it, no one else is executing after it, and if there is some thread after it, then every other thread is, at least, executing that line, but not anything before...
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