bitmap.java

hsql是很有名的嵌入式数据库

/* Copyright (c) 2001-2005, The HSQL Development Group
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 * software without specific prior written permission.
 *
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package org.hsqldb.store;

/**
 * Implementation of a bit map of any size, together with static methods to
 * manipulate int values as bit maps.
 *
* @author fredt@users
* @version 1.8.0
* @since 1.8.0
*/
public class BitMap {

    int   defaultCapacity;
    int   capacity;
    int[] map;

    public BitMap(int initialCapacity) {

        int words = initialCapacity / 32;

        if (initialCapacity % 32 != 0) {
            words++;
        }

        defaultCapacity = capacity = words * 32;
        map             = new int[words];
    }

    public void reset() {
        map      = new int[defaultCapacity / 32];
        capacity = defaultCapacity;
    }

    /**
     * Sets pos and returns old value
     */
    public int set(int pos) {

        while (pos >= capacity) {
            doubleCapacity();
        }

        int windex = pos >> 5;
        int mask   = 0x80000000 >>> (pos & 0x1F);
        int word   = map[windex];
        int result = (word & mask) == 0 ? 0
                                        : 1;

        map[windex] = (word | mask);

        return result;
    }

    /**
     * Unsets pos and returns old value
     */
    public int unset(int pos) {

        if (pos >= capacity) {
            return 0;
        }

        int windex = pos >> 5;
        int mask   = 0x80000000 >>> (pos & 0x1F);
        int word   = map[windex];
        int result = (word & mask) == 0 ? 0
                                        : 1;

        mask        = ~mask;
        map[windex] = (word & mask);

        return result;
    }

    public int get(int pos) {

        while (pos >= capacity) {
            doubleCapacity();
        }

        int windex = pos >> 5;
        int mask   = 0x80000000 >>> (pos & 0x1F);
        int word   = map[windex];

        return (word & mask) == 0 ? 0
                                  : 1;
    }

    public static int set(int map, int pos) {

        int mask = 0x80000000 >>> pos;

        return (map | mask);
    }

    public static int unset(int map, int pos) {

        int mask = 0x80000000 >>> pos;

        mask = ~mask;

        return (map & mask);
    }

    public static boolean isSet(int map, int pos) {

        int mask = 0x80000000 >>> pos;

        return (map & mask) == 0 ? false
                                 : true;
    }

    private void doubleCapacity() {

        int[] newmap = new int[capacity * 2];

        System.arraycopy(map, 0, newmap, 0, map.length);

        map = newmap;
    }
}