swap Set Of Bits Algorithm
In computing, the sticky bit is a user ownership access right flag that can be assigned to files and directory on UNIX-like systems. typically this is put on the /tmp directory to prevent ordinary users from deleting or move other users' files. No version of Linux has ever backed this traditional behavior; Linux performs caching of executable files in the same manner as all files, so re-execute the plan to flush the cache is not necessary. The sticky bit was introduced in the fifth version of UNIX (in 1974) for purpose with pure executable files. This speeds up subsequent executions by letting the kernel to make a individual operation of move the plan from swap to real memory.
/**
* Problem - Given a number 'num' and two positions (p1 and p2 from right side) in binary representation of num,
* write a function that swaps n bits at given two positions and returns the result.
* It is also given that the two sets of bits do not overlap.
*/
#include <iostream>
int swapBits(unsigned int num, unsigned int p1,
unsigned int p2, unsigned int n )
{
//Step1 lets form a number set1 by moving n bits at position p1 to the rightmost
unsigned int set1 = (num >> p1 ) & ((1U << n) - 1);
// Lets understand what we just did.
// Part1 : (num >> p1), we just right shifted num so that bit at p1 position takes 0th postion.
// Part2 : Remember we needed n bits from position p1(which has become position 0)
// So, (1U << n) moves 1 to nth bit, i.e. it the value formed by this movement is 2^n
// Now, If we substract 1 from the (2^n), it will give us all 1's for n positions.
// For example (1U << 3) = 1000
// and (1U << 3) - 1 = 0111
// Part3 : Thus Part1 & Part2 will give as n bits which were at P1 (now moved to 0)
//similarly for p2
unsigned int set2 = (num >> p2) & ((1U << n) - 1);
// xor two sets ( we are doing similar to xor swap algorithm )
// https://en.wikipedia.org/wiki/XOR_swap_algorithm
unsigned int xorSets = set1 ^ set2;
// now moving back the xor'd sets to p1 and p2
xorSets = (xorSets << p1) | (xorSets << p2);
unsigned int finalVal = xorSets ^ num;
return finalVal;
}
int main()
{
std::cout << "Swaping bits in number 28, such that 2 bits starting from 0th bit and 2 bits "
"starting from 3rd bit are swapped, 28 becomes " << swapBits(28, 0, 3, 2)
<< std::endl;
std::cout << "Swaping bits in number 47, such that 3 bits starting from 1st bit(0 based counting) and 3 bits "
"starting from 5th bit(0 based counting) are swapped, 47 becomes " << swapBits(47, 1, 5, 3)
<< std::endl;
}
