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

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

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

    for (int i = 0; i < log; i++) {
        valid[i] = false;
        timeStamp[i] = 0;
    }

    for (int j = 0; j < phys; j++) {
        freeFrames[j] = phys-j-1;
    }
}

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

void PageTable::SetValid(int index, bool status)
// Assumes: 0 <= index < page table size
// Results: sets the valid bit for that index to status
{
    valid[index] = status;
}

int PageTable::GetFrameNumber(int index)
// Assumes: 0 <= index < page table size
// Returns: the frame number stored at that index of the table
{
    return pageMap[index];
}

void PageTable::SetFrameNumber(int index, int frameNum)
// Assumes: 0 <= index < page table size
// Returns: sets the frame number stored at that index to be frameNum
{
    currentTime++;
    
    pageMap[index] = frameNum;
    timeStamp[index] = currentTime;

    if (FreeRemaining() && freeFrames.back() == frameNum) {
        freeFrames.pop_back();
    }
}
    
bool PageTable::FreeRemaining()
// Returns: true if any free frames are available in physical memory
{
    return freeFrames.size() > 0;
}

int PageTable::GetFree()
// Assumes: freeFrames (list of free frames) is not empty
// Returns: the number of a free frame (which is then removed from freeFrames)
{
    int free = freeFrames.back();
    freeFrames.pop_back();
    return free;;
}

int PageTable::GetOldest()
// 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;
}