// PagingUnit.cpp        Dave Reed        3/20/06
////////////////////////////////////////////////////////////////////////////////

#include <iostream>
#include <vector>
#include "PagingUnit.h"
using namespace std;

PagingUnit::PagingUnit(int log, int phys)
// constructor
// Assumes: log is the number of pages in the page table
//          phys is the number of frames in physical memory
// Results: creates and initializes the page table & freeFrames list
{
    pageTable.resize(log);
    for (int i = phys-1; i >= 0; i--) {
        freeFrames.push(i);
    }
}

bool PagingUnit::isValid(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Returns: true if valid bit is set for that index, else false
{
    return pageTable[pageNum].valid;
}

void PagingUnit::accessPage(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Returns: the frame number where pageNum is stored
{
    cout << pageNum << ": page found at frame " 
         << pageTable[pageNum].frameNumber << endl;

}

void PagingUnit::loadPage(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Results: loads pageNum in a free frame, updating the table
{
    int frameNum;
    if (freeFrames.empty()) {
        int swapPage = usedPages.front();
        usedPages.pop();
        pageTable[swapPage].valid = false;
        frameNum = pageTable[swapPage].frameNumber;
        cout << pageNum << ": PAGE FAULT -- swapping page " << pageNum 
             << " into frame " << frameNum << endl << "   ";
    }
    else {
        frameNum = freeFrames.top();
        freeFrames.pop();
        cout << pageNum << ": PAGE FAULT -- inserting page " << pageNum 
             << " into frame " << frameNum << endl << "   ";
    }

    pageTable[pageNum].frameNumber = frameNum;
    pageTable[pageNum].valid = true;
    usedPages.push(pageNum);
}