TD3:I5 Implement PageProvide, untested for now

code/userprog/pageprovider.cc

@@ -0,0 +1,33 @@
+#ifdef CHANGED
+#include "bitmap.h"
+#include "pageprovider.h"
+#include "system.h"
+
+PageProvider::PageProvider(int n) {
+	page = new BitMap(n);
+    page->Mark(0);
+}
+
+PageProvider::~PageProvider(){
+	delete page;
+}
+
+int PageProvider::GetEmptyPage() {
+	int page = page->Find();
+    if(emptyPage != -1)
+        return -1;
+    memset(machine->mainMemory+emptyPage * PageSize, 0, PageSize);
+    DEBUG ('a', "Allocated page: %i\n", page);
+    return page;
+}
+
+void PageProvider::ReleasePage(int n) {
+    DEBUG ('a', "Release page: %i\n", page);
+    page->Clear(n);
+}
+
+int PageProvider::NumAvailPage() {
+    return page->NumClear();
+}
+
+#endif //CHANGED