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riddles >> cs >> Obfuscated code
(Message started by: -D- on Aug 6th, 2002, 11:35am)

Title: Obfuscated code
Post by -D- on Aug 6th, 2002, 11:35am
The code isn't so obfuscated when it's written like PROPER code....

#include <stdio.h>
#define _ F-->00 || F-OO--;
void F_OO();
long F=00,OO=00;
void main()
{
     F_OO();
     printf("%1.3f\n", 4.0*-F/OO/OO);
}
void F_OO()
{
...
}

This is pretty much the first 3 lines expanded.

The #define is a macro that defines the _ character.  But it is only expanded for cases where the _ isn't used in a label (such as it is used in F_OO ).  

F_OO is actually a function that uses long drawn out operation on F and OO to make them become -202 and -16 respectively.  

4 * -202 / -16 / -16 = 3.156 which is what is printed out.  The 4. in the given code is really 4.0.  the - sign is actually a unary minus making the -202 into 202, it doesn't do a subtraction.  It wouldn't have been as obfuscated if it had been written -4.*F/OO/OO see?

So, the code calls the F_00 function to change the values of F and OO, then prints out some math mangling of those values.

The last thing that makes this code more complicated is that they didn't declare their return types for F_OO or main and attempted to assume then as void (which is invalid, proper C would default them to integers).  I'll ignore errors associated with not declaring includes or function prototypes and assume those were just not put in the excerpt.
-D-


Title: Re: Obfuscated code
Post by anton on Dec 25th, 2004, 12:28am
Since 4.*-F/OO/OO results in an approximation of Pi, we get:
Pi = -4F/OO2
Pi*(OO/2)2 = -F

It makes sense to assume that OO is the diameter of a circle, and F is its area (negative). The circle is actually the one "drawn" in the function F_OO(). Later, I will replace F with a and OO with d.

Let's see what happens in the F_OO function. Each line consists of "_" followed by a string of "-_". Each "_" is replaced with "a-->0 || a-d--;" which means following:
  • Subtract one from a. (a--)
  • If, before the subtraction, a was negative then perform "a-d--", since the operator || executes its right part only when the left part is false. The meaningful action here is only "d--"; that is, subtract one from d.

The underscore in each "-_" is replaced with the same thing; the only difference is the initial minus sign. Now -a is compared with zero; since -a is always positive, the second part never gets executed.

And now we get the full picture: each of "_" and "-_" decreases a by one; thus, a contains the negative area of the circle. In addition, each initial "_" decreases d by one - in the end d becomes equal to the negative height of the circle, which is the same as its diameter.

Title: Re: Obfuscated code
Post by Paul on Apr 6th, 2013, 10:07pm
People keep showing fractions of pi.You all need to realise pi is a whole number and the rest of the numbers are the fractions.Point then nonpoint.The nonpoint should be a whole number?Ok,seems right doesn't it?



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