/**
* Alipay.com Inc.
* Copyright (c) 2004-2012 All Rights Reserved.
*/
package com.alipay.zdal.parser.sql.parser;
/**
*
* @author ����
* @version $Id: SymbolTable.java, v 0.1 2012-11-17 ����3:54:52 Exp $
*/
public class SymbolTable {
//
// Constants
//
/** Default table size. */
public static final int DEFAULT_TABLE_SIZE = 128;
/** Buckets. */
private final Entry[] buckets;
private final String[] symbols;
private final char[][] symbols_char;
// actual table size
private final int indexMask;
//
// Constructors
//
/** Constructs a symbol table with a default number of buckets. */
public SymbolTable() {
this(DEFAULT_TABLE_SIZE);
}
/** Constructs a symbol table with a specified number of buckets. */
public SymbolTable(int tableSize) {
this.indexMask = tableSize - 1;
this.buckets = new Entry[tableSize];
this.symbols = new String[tableSize];
this.symbols_char = new char[tableSize][];
}
//
// Public methods
//
/**
* Adds the specified symbol to the symbol table and returns a reference to the unique symbol. If the symbol already
* exists, the previous symbol reference is returned instead, in order guarantee that symbol references remain
* unique.
*
* @param symbol The new symbol.
*/
public String addSymbol(String symbol) {
return addSymbol(symbol.toCharArray(), 0, symbol.length(), symbol.hashCode());
}
public int getIndexMask() {
return indexMask;
}
public String addSymbol(char[] buffer, int offset, int len) {
// search for identical symbol
int hash = hash(buffer, offset, len);
return addSymbol(buffer, offset, len, hash);
}
/**
* Adds the specified symbol to the symbol table and returns a reference to the unique symbol. If the symbol already
* exists, the previous symbol reference is returned instead, in order guarantee that symbol references remain
* unique.
*
* @param buffer The buffer containing the new symbol.
* @param offset The offset into the buffer of the new symbol.
* @param len The length of the new symbol in the buffer.
*/
public String addSymbol(char[] buffer, int offset, int len, int hash) {
// int bucket = indexFor(hash, tableSize);
final int bucket = hash & indexMask;
String sym = symbols[bucket];
boolean match = true;
if (sym != null) {
if (sym.length() == len) {
char[] characters = symbols_char[bucket];
for (int i = 0; i < len; i++) {
if (buffer[offset + i] != characters[i]) {
match = false;
break;
}
}
if (match) {
return sym;
}
} else {
match = false;
}
}
OUTER: for (Entry entry = buckets[bucket]; entry != null; entry = entry.next) {
char[] characters = entry.characters;
if (len == characters.length && hash == entry.hashCode) {
for (int i = 0; i < len; i++) {
if (buffer[offset + i] != characters[i]) {
continue OUTER;
}
}
return entry.symbol;
}
}
// add new entry
Entry entry = new Entry(buffer, offset, len, hash, buckets[bucket]);
buckets[bucket] = entry;
if (match) {
symbols[bucket] = entry.symbol;
symbols_char[bucket] = entry.characters;
}
return entry.symbol;
} // addSymbol(char[],int,int):String
public static final int hash(String symbol) {
return hash(symbol.toCharArray(), 0, symbol.length());
}
// same as String.hashCode
public static final int hash(char[] buffer, int offset, int len) {
int h = 0;
int off = offset;
for (int i = 0; i < len; i++) {
h = 31 * h + buffer[off++];
}
return h;
}
//
// Classes
//
/**
* This class is a symbol table entry. Each entry acts as a node in a linked list.
*/
protected static final class Entry {
public final String symbol;
public final int hashCode;
public final char[] characters;
/** The next entry. */
public Entry next;
//
// Constructors
//
/**
* Constructs a new entry from the specified symbol information and next entry reference.
*/
public Entry(char[] ch, int offset, int length, int hash, Entry next) {
characters = new char[length];
System.arraycopy(ch, offset, characters, 0, length);
symbol = new String(characters).intern();
this.next = next;
this.hashCode = hash;
}
} // class Entry
} // class SymbolTable