MIT-Curricular/OS/C/Week10/qq1.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

// Function to check if a page exists in frames
bool isPagePresent(int* frames, int num_frames, int page) {
    for (int i = 0; i < num_frames; i++) {
        if (frames[i] == page) {
            return true;
        }
    }
    return false;
}

// FIFO Page Replacement Algorithm
void fifo(int* reference_string, int num_pages, int num_frames) {
    int* frames = (int*)malloc(num_frames * sizeof(int));
    int page_faults = 0;
    int frame_index = 0;

    // Initialize frames with -1 (indicating empty)
    for (int i = 0; i < num_frames; i++) {
        frames[i] = -1;
    }

    printf("\nFIFO Page Replacement Algorithm:\n");
    printf("Reference String: ");
    for (int i = 0; i < num_pages; i++) {
        printf("%d ", reference_string[i]);
    }
    printf("\n\n");

    for (int i = 0; i < num_pages; i++) {
        printf("Page %d: ", reference_string[i]);

        // Check if page already exists in frames
        if (!isPagePresent(frames, num_frames, reference_string[i])) {
            // Replace page at current frame_index
            frames[frame_index] = reference_string[i];
            frame_index = (frame_index + 1) % num_frames;
            page_faults++;

            printf("Page Fault! Frames: ");
        } else {
            printf("No Page Fault. Frames: ");
        }

        // Print current state of frames
        for (int j = 0; j < num_frames; j++) {
            if (frames[j] == -1) {
                printf("[ ] ");
            } else {
                printf("[%d] ", frames[j]);
            }
        }
        printf("\n");
    }

    printf("\nTotal Page Faults (FIFO): %d\n", page_faults);
    free(frames);
}

// Function to find index of page that will be used farthest in future
int findOptimalPage(int* reference_string, int* frames, int num_frames, int num_pages, int current_position) {
    int farthest = -1;
    int index = -1;

    for (int i = 0; i < num_frames; i++) {
        int j;
        for (j = current_position + 1; j < num_pages; j++) {
            if (frames[i] == reference_string[j]) {
                if (j > farthest) {
                    farthest = j;
                    index = i;
                }
                break;
            }
        }

        // If page is never used in future
        if (j == num_pages) {
            return i;
        }
    }

    // If all pages will be used in future, return the one used farthest
    return (index == -1) ? 0 : index;
}

// Optimal Page Replacement Algorithm
void optimal(int* reference_string, int num_pages, int num_frames) {
    int* frames = (int*)malloc(num_frames * sizeof(int));
    int page_faults = 0;

    // Initialize frames with -1 (indicating empty)
    for (int i = 0; i < num_frames; i++) {
        frames[i] = -1;
    }

    printf("\nOptimal Page Replacement Algorithm:\n");
    printf("Reference String: ");
    for (int i = 0; i < num_pages; i++) {
        printf("%d ", reference_string[i]);
    }
    printf("\n\n");

    for (int i = 0; i < num_pages; i++) {
        printf("Page %d: ", reference_string[i]);

        // Check if page already exists in frames
        if (!isPagePresent(frames, num_frames, reference_string[i])) {
            int free_frame = -1;

            // Check if there's an empty frame
            for (int j = 0; j < num_frames; j++) {
                if (frames[j] == -1) {
                    free_frame = j;
                    break;
                }
            }

            if (free_frame != -1) {
                // If empty frame exists, use it
                frames[free_frame] = reference_string[i];
            } else {
                // Find optimal page to replace
                int replace_index = findOptimalPage(reference_string, frames, num_frames, num_pages, i);
                frames[replace_index] = reference_string[i];
            }

            page_faults++;
            printf("Page Fault! Frames: ");
        } else {
            printf("No Page Fault. Frames: ");
        }

        // Print current state of frames
        for (int j = 0; j < num_frames; j++) {
            if (frames[j] == -1) {
                printf("[ ] ");
            } else {
                printf("[%d] ", frames[j]);
            }
        }
        printf("\n");
    }

    printf("\nTotal Page Faults (Optimal): %d\n", page_faults);
    free(frames);
}

int main() {
    int num_pages, num_frames;

    printf("Enter number of frames: ");
    scanf("%d", &num_frames);

    printf("Enter number of pages in reference string: ");
    scanf("%d", &num_pages);

    int* reference_string = (int*)malloc(num_pages * sizeof(int));

    printf("Enter the reference string (page numbers):\n");
    for (int i = 0; i < num_pages; i++) {
        scanf("%d", &reference_string[i]);
    }

    // Run FIFO algorithm
    fifo(reference_string, num_pages, num_frames);

    // Run Optimal algorithm
    optimal(reference_string, num_pages, num_frames);

    free(reference_string);
    return 0;
}