ternarytree.java

iText是一个能够快速产生PDF文件的java类库。iText的java类对于那些要产生包含文本

/*
 * Copyright 1999-2004 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.lowagie.text.pdf.hyphenation;

import java.io.Serializable;
import java.util.Enumeration;
import java.util.Stack;

/**
 * <h2>Ternary Search Tree.</h2>
 *
 * <p>A ternary search tree is a hibrid between a binary tree and
 * a digital search tree (trie). Keys are limited to strings.
 * A data value of type char is stored in each leaf node.
 * It can be used as an index (or pointer) to the data.
 * Branches that only contain one key are compressed to one node
 * by storing a pointer to the trailer substring of the key.
 * This class is intended to serve as base class or helper class
 * to implement Dictionary collections or the like. Ternary trees
 * have some nice properties as the following: the tree can be
 * traversed in sorted order, partial matches (wildcard) can be
 * implemented, retrieval of all keys within a given distance
 * from the target, etc. The storage requirements are higher than
 * a binary tree but a lot less than a trie. Performance is
 * comparable with a hash table, sometimes it outperforms a hash
 * function (most of the time can determine a miss faster than a hash).</p>
 *
 * <p>The main purpose of this java port is to serve as a base for
 * implementing TeX's hyphenation algorithm (see The TeXBook,
 * appendix H). Each language requires from 5000 to 15000 hyphenation
 * patterns which will be keys in this tree. The strings patterns
 * are usually small (from 2 to 5 characters), but each char in the
 * tree is stored in a node. Thus memory usage is the main concern.
 * We will sacrify 'elegance' to keep memory requirenments to the
 * minimum. Using java's char type as pointer (yes, I know pointer
 * it is a forbidden word in java) we can keep the size of the node
 * to be just 8 bytes (3 pointers and the data char). This gives
 * room for about 65000 nodes. In my tests the english patterns
 * took 7694 nodes and the german patterns 10055 nodes,
 * so I think we are safe.</p>
 *
 * <p>All said, this is a map with strings as keys and char as value.
 * Pretty limited!. It can be extended to a general map by
 * using the string representation of an object and using the
 * char value as an index to an array that contains the object
 * values.</p>
 *
 * @author [e-mail]
 */

public class TernaryTree implements Cloneable, Serializable {

    /**
     * We use 4 arrays to represent a node. I guess I should have created
     * a proper node class, but somehow Knuth's pascal code made me forget
     * we now have a portable language with virtual memory management and
     * automatic garbage collection! And now is kind of late, furthermore,
     * if it ain't broken, don't fix it.
     */

    private static final long serialVersionUID = 5313366505322983510L;

	/**
     * Pointer to low branch and to rest of the key when it is
     * stored directly in this node, we don't have unions in java!
     */
    protected char[] lo;

    /**
     * Pointer to high branch.
     */
    protected char[] hi;

    /**
     * Pointer to equal branch and to data when this node is a string terminator.
     */
    protected char[] eq;

    /**
     * <P>The character stored in this node: splitchar.
     * Two special values are reserved:</P>
     * <ul><li>0x0000 as string terminator</li>
     * <li>0xFFFF to indicate that the branch starting at
     * this node is compressed</li></ul>
     * <p>This shouldn't be a problem if we give the usual semantics to
     * strings since 0xFFFF is garanteed not to be an Unicode character.</p>
     */
    protected char[] sc;

    /**
     * This vector holds the trailing of the keys when the branch is compressed.
     */
    protected CharVector kv;

    protected char root;
    protected char freenode;
    protected int length;    // number of items in tree

    protected static final int BLOCK_SIZE = 2048;    // allocation size for arrays

    TernaryTree() {
        init();
    }

    protected void init() {
        root = 0;
        freenode = 1;
        length = 0;
        lo = new char[BLOCK_SIZE];
        hi = new char[BLOCK_SIZE];
        eq = new char[BLOCK_SIZE];
        sc = new char[BLOCK_SIZE];
        kv = new CharVector();
    }

    /**
     * Branches are initially compressed, needing
     * one node per key plus the size of the string
     * key. They are decompressed as needed when
     * another key with same prefix
     * is inserted. This saves a lot of space,
     * specially for long keys.
     */
    public void insert(String key, char val) {
        // make sure we have enough room in the arrays
        int len = key.length()
                  + 1;    // maximum number of nodes that may be generated
        if (freenode + len > eq.length) {
            redimNodeArrays(eq.length + BLOCK_SIZE);
        }
        char strkey[] = new char[len--];
        key.getChars(0, len, strkey, 0);
        strkey[len] = 0;
        root = insert(root, strkey, 0, val);
    }

    public void insert(char[] key, int start, char val) {
        int len = strlen(key) + 1;
        if (freenode + len > eq.length) {
            redimNodeArrays(eq.length + BLOCK_SIZE);
        }
        root = insert(root, key, start, val);
    }

    /**
     * The actual insertion function, recursive version.
     */
    private char insert(char p, char[] key, int start, char val) {
        int len = strlen(key, start);
        if (p == 0) {
            // this means there is no branch, this node will start a new branch.
            // Instead of doing that, we store the key somewhere else and create
            // only one node with a pointer to the key
            p = freenode++;
            eq[p] = val;           // holds data
            length++;
            hi[p] = 0;
            if (len > 0) {
                sc[p] = 0xFFFF;    // indicates branch is compressed
                lo[p] = (char)kv.alloc(len
                                       + 1);    // use 'lo' to hold pointer to key
                strcpy(kv.getArray(), lo[p], key, start);
            } else {
                sc[p] = 0;
                lo[p] = 0;
            }
            return p;
        }

        if (sc[p] == 0xFFFF) {
            // branch is compressed: need to decompress
            // this will generate garbage in the external key array
            // but we can do some garbage collection later
            char pp = freenode++;
            lo[pp] = lo[p];    // previous pointer to key
            eq[pp] = eq[p];    // previous pointer to data
            lo[p] = 0;
            if (len > 0) {
                sc[p] = kv.get(lo[pp]);
                eq[p] = pp;
                lo[pp]++;
                if (kv.get(lo[pp]) == 0) {
                    // key completly decompressed leaving garbage in key array
                    lo[pp] = 0;
                    sc[pp] = 0;
                    hi[pp] = 0;
                } else {
                    // we only got first char of key, rest is still there
                    sc[pp] = 0xFFFF;
                }
            } else {
                // In this case we can save a node by swapping the new node
                // with the compressed node
                sc[pp] = 0xFFFF;
                hi[p] = pp;
                sc[p] = 0;
                eq[p] = val;
                length++;
                return p;
            }
        }
        char s = key[start];
        if (s < sc[p]) {
            lo[p] = insert(lo[p], key, start, val);
        } else if (s == sc[p]) {
            if (s != 0) {
                eq[p] = insert(eq[p], key, start + 1, val);
            } else {
                // key already in tree, overwrite data
                eq[p] = val;
            }
        } else {
            hi[p] = insert(hi[p], key, start, val);
        }
        return p;
    }

    /**
     * Compares 2 null terminated char arrays
     */
    public static int strcmp(char[] a, int startA, char[] b, int startB) {
        for (; a[startA] == b[startB]; startA++, startB++) {
            if (a[startA] == 0) {
                return 0;
            }
        }
        return a[startA] - b[startB];
    }

    /**
     * Compares a string with null terminated char array
     */
    public static int strcmp(String str, char[] a, int start) {
        int i, d, len = str.length();
        for (i = 0; i < len; i++) {
            d = (int)str.charAt(i) - a[start + i];
            if (d != 0) {
                return d;
            }
            if (a[start + i] == 0) {
                return d;
        }
        }
        if (a[start + i] != 0) {
            return (int)-a[start + i];
        }
        return 0;

    }

    public static void strcpy(char[] dst, int di, char[] src, int si) {
        while (src[si] != 0) {
            dst[di++] = src[si++];
        }
        dst[di] = 0;
    }

    public static int strlen(char[] a, int start) {
        int len = 0;
        for (int i = start; i < a.length && a[i] != 0; i++) {
            len++;
        }
        return len;
    }

    public static int strlen(char[] a) {
        return strlen(a, 0);
    }

    public int find(String key) {
        int len = key.length();
        char strkey[] = new char[len + 1];
        key.getChars(0, len, strkey, 0);
        strkey[len] = 0;

        return find(strkey, 0);
    }

    public int find(char[] key, int start) {
        int d;
        char p = root;
        int i = start;
        char c;

        while (p != 0) {
            if (sc[p] == 0xFFFF) {
                if (strcmp(key, i, kv.getArray(), lo[p]) == 0) {
                    return eq[p];
                } else {
                    return -1;
            }
            }
            c = key[i];
            d = c - sc[p];
            if (d == 0) {
                if (c == 0) {
                    return eq[p];
                }
                i++;
                p = eq[p];
            } else if (d < 0) {
                p = lo[p];
            } else {
                p = hi[p];
        }
        }
        return -1;
    }

    public boolean knows(String key) {
        return (find(key) >= 0);
    }

    // redimension the arrays
    private void redimNodeArrays(int newsize) {
        int len = newsize < lo.length ? newsize : lo.length;
        char[] na = new char[newsize];
        System.arraycopy(lo, 0, na, 0, len);
        lo = na;
        na = new char[newsize];
        System.arraycopy(hi, 0, na, 0, len);