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) 1992-1996 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"

// Definitions helpful for representing a bitmap as an array of integers
const int BitsInByte =  8;
const int BitsInWord = sizeof(unsigned int) * BitsInByte;

// 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 numItems);       // Initialize a bitmap, with "numItems" 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) const; // Is the "nth" bit set?
    int FindAndSet();         // Return the # of a clear bit, and as a side
                                // effect, set the bit. 
                                // If no bits are clear, return -1.
    int NumClear() const;       // Return the number of clear bits

    void Print() const;         // Print contents of bitmap
    void SelfTest();            // Test whether bitmap is working
    
  protected:
    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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