BitStack.java

/*
 * Copyright (C) 2011 eXo Platform SAS.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */

package org.exoplatform.web.controller.router;

/**
 * A bit stack optimized for speed.
 *
 * @author <a href="mailto:julien.viet@exoplatform.com">Julien Viet</a>
 */
class BitStack {

    private static class Frame {

        /** . */
        private Frame previous;

        /** . */
        private Frame next;

        /** . */
        private long bits;

        /** . */
        private int cardinality;

        private Frame() {
            this(0, 0);
        }

        private Frame(long bits, int cardinality) {
            this.previous = null;
            this.next = null;
            this.bits = bits;
            this.cardinality = cardinality;
        }
    }

    /** . */
    private Frame head;

    /** . */
    private Frame current;

    /** . */
    private int depth;

    /** . */
    private int size;

    BitStack() {
        this.current = null;
        this.depth = 0;
        this.size = 0;
    }

    void init(int size) {
        if (depth > 0) {
            throw new IllegalStateException();
        }
        if (size < 0) {
            throw new IllegalArgumentException();
        }
        this.size = size;
    }

    void reset() {
        if (depth > 0) {
            throw new IllegalStateException();
        }
        this.size = 0;
    }

    void push() {
        if (current == null) {
            if (head == null) {
                head = new Frame();
            }
            current = head;
            depth++;
        } else {
            if (current.next == null) {
                Frame next = new Frame(current.bits, current.cardinality);
                current.next = next;
                next.previous = current;
                current = next;
                depth++;
            } else {
                Frame next = current.next;
                next.bits = current.bits;
                next.cardinality = current.cardinality;
                current = next;
                depth++;
            }
        }
    }

    void pop() {
        if (depth == 0) {
            throw new IllegalStateException();
        }
        current = current.previous;
        depth--;
    }

    int getDepth() {
        return depth;
    }

    void set(int index) {
        if (index > 63) {
            throw new IllegalArgumentException("Index " + index + "  > 63 not allowed");
        }
        if (depth < 1) {
            throw new IllegalStateException();
        }
        if (index > size) {
            throw new IllegalArgumentException();
        }
        long pre = current.bits;
        current.bits |= 1L << index;
        if (current.bits != pre) {
            current.cardinality++;
        }
    }

    boolean get(int index) {
        if (index > 63) {
            throw new IllegalArgumentException("Index " + index + "  > 63 not allowed");
        }
        if (depth < 1) {
            throw new IllegalStateException();
        }
        if (index > size) {
            throw new IllegalArgumentException();
        }
        return (current.bits & (1L << index)) != 0;
    }

    boolean isEmpty() {
        if (depth < 1) {
            throw new IllegalStateException();
        }
        return current.cardinality == size;
    }
}