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bitmap.h

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// bitmap.h 
//      Data structures defining a bitmap -- an array of bits each of which
//      can be either on or off.
//
//      Represented as an array of unsigned integers, on which we do
//      modulo arithmetic to find the bit we are interested in.
//
//      The bitmap can be parameterized with with the number of bits being 
//      managed.
//
// 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 BITMAP_H
#define BITMAP_H

#include "copyright.h"
#include "utility.h"
#include "openfile.h"

// Definitions helpful for representing a bitmap as an array of integers
#define BitsInByte      8
#define BitsInWord      32

// The following class defines a "bitmap" -- an array of bits,
// each of which can be independently set, cleared, and tested.
//
// Most useful for managing the allocation of the elements of an array --
// for instance, disk sectors, or main memory pages.
// Each bit represents whether the corresponding sector or page is
// in use or free.

class BitMap {
  public:
    BitMap(int nitems);         // Initialize a bitmap, with "nitems" bits
                                // initially, all bits are cleared.
    ~BitMap();                  // De-allocate bitmap
    
    void Mark(int which);       // Set the "nth" bit
    void Clear(int which);      // Clear the "nth" bit
    bool Test(int which);       // Is the "nth" bit set?
    int Find();                 // Return the # of a clear bit, and as a side
                                // effect, set the bit. 
                                // If no bits are clear, return -1.
    int NumClear();             // Return the number of clear bits

    void Print();               // Print contents of bitmap
    
    // These aren't needed until FILESYS, when we will need to read and 
    // write the bitmap to a file
    void FetchFrom(OpenFile *file);     // fetch contents from disk 
    void WriteBack(OpenFile *file);     // write contents to disk

  private:
    int numBits;                        // number of bits in the bitmap
    int numWords;                       // number of words of bitmap storage
                                        // (rounded up if numBits is not a
                                        //  multiple of the number of bits in
                                        //  a word)
    unsigned int *map;                  // bit storage
};

#endif // BITMAP_H

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