SystemsProgrammingAndOperatingSystem/Codes/Group B/Code-B7.cpp

// Assignment-B7 - Page Replacement in C++ (LRU + Optimal)
// BEGINNING OF CODE
#include <cmath>
#include <complex>
#include <iostream>
using namespace std;

int refString[] = {0, 2, 1, 6, 4, 0, 1, 0, 3, 1, 2, 1};
int window = 0, hit = 0, miss = 0, currentPages[4], lastUsed[40];
int len = sizeof(refString) / sizeof(refString[0]);

int findLRU() {
  int min_index = 0;
  for (int i=1; i<window; i++) {
    if (lastUsed[i] < lastUsed[min_index]) {
      min_index = i;
    }
  }
  return min_index;
}

void LRU() {
  for (int i=0; i<window; i++) {
    currentPages[i] = -1;
    lastUsed[i] = -1;
  }

  for (int i=0; i<len; i++) {
    bool hitFlag = false;
    for (int j=0; j<window; j++) {
      if (currentPages[j] == refString[i]) {
        hit++;
        hitFlag = true;
        lastUsed[j] = i;
        break;
      }
    }
    if (hitFlag == false) {
      miss++;
      bool emptyFound = false;
      for (int j=0; j<window; j++) {
        if (currentPages[j] == -1) {
          emptyFound = true;
          currentPages[j] = refString[i];
          lastUsed[j] = i;
          break;
        }
      }
        if (emptyFound == false) {
          int lru_index = findLRU();
          currentPages[lru_index] = refString[i];
          lastUsed[lru_index] = i;
        }
      }
  }
  cout<<endl<<"----- LRU ------";
  cout<<endl<<"Number of hits: "<<hit;
  cout<<endl<<"Number of misses: "<<miss;
}

int findOptimal(int current_index) {
  int max_index = -1, farthest = current_index;
  for (int i=0; i<window; i++) {
    int j;
    for (j=current_index+1; j<len; j++) {
      if (currentPages[i] == refString[j]) {
        if (j > farthest) {
          farthest = j;
          max_index = i;
        }
        break;
      }
    }
    if (j == len) {
      return i;
    }
  }
  return max_index;
}

void Optimal() {
  hit = 0;
  miss = 0;

  for (int i=0; i<window; i++) {
    currentPages[i] = -1;
  }

  for (int i=0; i<len; i++) {
    bool hitFlag = false;
    for (int j=0; j<window; j++) {
      if (currentPages[j] == refString[i]) {
        hit++;
        hitFlag = true;
        break;
      }
    }
    if (hitFlag == false) {
      miss++;
      bool emptyFound = false;
      for (int j=0; j<window; j++) {
        if (currentPages[j] == -1) {
          emptyFound = true;
          currentPages[j] = refString[i];
          break;
        }
      }
      if (emptyFound == false) {
        int optimal_index = findOptimal(i);
        currentPages[optimal_index] = refString[i];
      }
    }
  }
  cout<<endl<<"----- OPTIMAL -----";
  cout<<endl<<"Number of hits: "<<hit;
  cout<<endl<<"Number of misses: "<<miss;
}

void display() {
  cout<<endl<<"Current pages are:\t";
  for (int i=0; i<window; i++) {
    cout<<currentPages[i]<<" ";
  }
  cout<<endl;
}

int main() {
  cout<<endl<<"Enter window size:\t";
  cin>>window;
  LRU();
  display();
  Optimal();
  display();
}
// END OF CODE