enviroment.c

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

#define PAGE_SIZE 4
#define NUM_VIRTUAL_PAGES 8
#define PHYSICAL_MEMORY_SIZE 4

int physical_memory[PHYSICAL_MEMORY_SIZE][PAGE_SIZE];
int disk_storage[NUM_VIRTUAL_PAGES][PAGE_SIZE];
int page_table[NUM_VIRTUAL_PAGES];
int usage_order[PHYSICAL_MEMORY_SIZE];
int current_usage_index = 0;

void initialize_disk_storage() {
    for (int i = 0; i < NUM_VIRTUAL_PAGES; i++) {
        for (int j = 0; j < PAGE_SIZE; j++) {
            disk_storage[i][j] = i;
        }
    }
    for (int i = 0; i < PHYSICAL_MEMORY_SIZE; i++) {
        usage_order[i] = -1;
    }
}

bool is_page_in_memory(int virtual_page_number) {
    return page_table[virtual_page_number] != -1;
}

void update_usage_order(int physical_slot) {
    int i;
    for (i = 0; i < PHYSICAL_MEMORY_SIZE; i++) {
        if (usage_order[i] == physical_slot) {
            break;
        }
    }
    while (i < PHYSICAL_MEMORY_SIZE - 1) {
        usage_order[i] = usage_order[i + 1];
        i++;
    }
    usage_order[PHYSICAL_MEMORY_SIZE - 1] = physical_slot;
}

void load_page_from_disk(int virtual_page_number) {
    int slot_to_load;
    if (current_usage_index < PHYSICAL_MEMORY_SIZE) {
        slot_to_load = current_usage_index++;
    } else {
        int lru_slot = usage_order[0];
        page_table[virtual_page_number] = -1;
        slot_to_load = lru_slot;
        printf("Evicting from slot %d\n", lru_slot);
    }

    for (int j = 0; j < PAGE_SIZE; j++) {
        physical_memory[slot_to_load][j] = disk_storage[virtual_page_number][j];
    }
    page_table[virtual_page_number] = slot_to_load;
    update_usage_order(slot_to_load);
}

void access_page(int virtual_page_number) {
    if (is_page_in_memory(virtual_page_number)) {
        int physical_slot = page_table[virtual_page_number];
        printf("Page %d in memory slot %d\n", virtual_page_number, physical_slot);
        update_usage_order(physical_slot);
    } else {
        printf("Page fault on page %d\n", virtual_page_number);
        load_page_from_disk(virtual_page_number);
    }
}

int main() {
    for (int i = 0; i < NUM_VIRTUAL_PAGES; i++) page_table[i] = -1;
    initialize_disk_storage();

    access_page(2);
    access_page(3);
    access_page(2);
    access_page(4);
    access_page(5);

    return 0;
}