// PageTable.cpp        Dave Reed        11/20/02

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

PageTable::PageTable(int log, int phys): 
pageMap(log, -1), valid(log, false), timeStamp(log, 0)
// 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 entries in the page table
{
    currentTime = 0;

    for (int j = phys-1; j >= 0; j--) {
        freeFrames.push_back(j);
    }
}

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

int PageTable::LocatePage(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Returns: the frame number where pageNum is stored
{
    return pageMap[pageNum];
}

void PageTable::StorePage(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Results: stores pageNum in a free frame, updating the table
{
    currentTime++;

    int frameNum = freeFrames.back();
    freeFrames.pop_back();

    pageMap[pageNum] = frameNum;
    timeStamp[pageNum] = currentTime;
    valid[pageNum] = true;
}

void PageTable::ReplacePage(int pageNum, int swapPage)
// Assumes: 0 <= pageNum, swapPage < page table size
// Results: replaces swapPage with pageNum in the table
{
    currentTime++;

    int frameNum = LocatePage(swapPage);
    valid[swapPage] = false;

    pageMap[pageNum] = frameNum;
    timeStamp[pageNum] = currentTime;
    valid[pageNum] = true;
}

int PageTable::SelectSwapPage()
// Assumes: at least one page is stored in the table
// Returns: index of the oldest page in the table
{
    int oldFrame, oldTime = currentTime + 1;
    for (int i = 0; i < pageMap.size(); i++) {
        if (valid[i] && timeStamp[i] < oldTime) {
            oldTime = timeStamp[i];
            oldFrame = i;
        }
    }
    return oldFrame;
}

bool PageTable::FreeFramesRemaining()
// Returns: true if any free frames are available in physical memory
{
    return freeFrames.size() > 0;
}