// translate.h //      Data structures for managing the translation from //      virtual page # -> physical page #, used for managing//      physical memory on behalf of user programs.////      The data structures in this file are "dual-use" - they//      serve both as a page table entry, and as an entry in//      a software-managed translation lookaside buffer (TLB).//      Either way, each entry is of the form://      <virtual page #, physical page #>.//// DO NOT CHANGE -- part of the machine emulation//// Copyright (c) 1992-1993 The Regents of the University of California.// All rights reserved.  See copyright.h for copyright notice and limitation // of liability and disclaimer of warranty provisions.#ifndef TLB_H#define TLB_H#include "copyright.h"#include "utility.h"// The following class defines an entry in a translation table -- either// in a page table or a TLB.  Each entry defines a mapping from one // virtual page to one physical page.// In addition, there are some extra bits for access control (valid and // read-only) and some bits for usage information (use and dirty).class TranslationEntry {  public:    int virtualPage;    // The page number in virtual memory.    int physicalPage;   // The page number in real memory (relative to the                        //  start of "mainMemory"    bool valid;         // If this bit is not set, the translation is ignored.                        // (In other words, the entry hasn't been initialized                        //  or it is not "in-core" or part of the page buffer.    bool legal;         // If not set then a reference to this page is not legal.                        // If referenced then the appropriate process is aborted.    bool readOnly;      // If this bit is set, the user program is not allowed                        // to modify the contents of the page.    bool use;           // This bit is set by the hardware every time the                        // page is referenced or modified.    bool dirty;         // This bit is set by the hardware every time the                        // page is modified.    // Added for MP3    int timeStamp;    // To store the time when last accessed (useful for LRU)};#endif