content: /*
   * Copyright 1999-2017 Alibaba Group Holding Ltd.
   *
   * 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.alibaba.druid.sql.parser;
  
  import java.nio.charset.StandardCharsets;
  
  /**
   * @author wenshao[szujobs@hotmail.com]
   */
  public class SymbolTable {
      private static final boolean JVM_16;
  
      static {
          String version = null;
          try {
              version = System.getProperty("java.specification.version");
          } catch (IllegalArgumentException ex) {
              // skip
          } catch (SecurityException error) {
              // skip
          }
          JVM_16 = "1.6".equals(version);
      }
  
      public static SymbolTable global = new SymbolTable(32768);
  
      private final Entry[] entries;
      private final int indexMask;
  
      public SymbolTable(int tableSize) {
          this.indexMask = tableSize - 1;
          this.entries = new Entry[tableSize];
      }
  
      public String addSymbol(String buffer, int offset, int len, long hash) {
          final int bucket = ((int) hash) & indexMask;
  
          Entry entry = entries[bucket];
          if (entry != null) {
              if (hash == entry.hash) {
                  return entry.value;
              }
  
              String str = JVM_16
                      ? subString(buffer, offset, len)
                      : buffer.substring(offset, offset + len);
  
              return str;
          }
  
          String str = JVM_16
                  ? subString(buffer, offset, len)
                  : buffer.substring(offset, offset + len);
          entry = new Entry(hash, len, str);
          entries[bucket] = entry;
          return str;
      }
  
      public String addSymbol(byte[] buffer, int offset, int len, long hash) {
          final int bucket = ((int) hash) & indexMask;
  
          Entry entry = entries[bucket];
          if (entry != null) {
              if (hash == entry.hash) {
                  return entry.value;
              }
  
              String str = subString(buffer, offset, len);
  
              return str;
          }
  
          String str = subString(buffer, offset, len);
          entry = new Entry(hash, len, str);
          entries[bucket] = entry;
          return str;
      }
  
      public String addSymbol(String symbol, long hash) {
          final int bucket = ((int) hash) & indexMask;
  
          Entry entry = entries[bucket];
          if (entry != null) {
              if (hash == entry.hash) {
                  return entry.value;
              }
  
              return symbol;
          }
  
          entry = new Entry(hash, symbol.length(), symbol);
          entries[bucket] = entry;
          return symbol;
      }
  
      public String findSymbol(long hash) {
          final int bucket = ((int) hash) & indexMask;
          Entry entry = entries[bucket];
          if (entry != null && entry.hash == hash) {
              return entry.value;
          }
          return null;
      }
  
      private static String subString(String src, int offset, int len) {
          char[] chars = new char[len];
          src.getChars(offset, offset + len, chars, 0);
          return new String(chars);
      }
  
      private static String subString(byte[] bytes, int from, int len) {
          byte[] strBytes = new byte[len];
          System.arraycopy(bytes, from, strBytes, 0, len);
          return new String(strBytes, StandardCharsets.UTF_8);
      }
  
      private static class Entry {
          public final long hash;
          public final int len;
          public final String value;
  
          public Entry(long hash, int len, String value) {
              this.hash = hash;
              this.len = len;
              this.value = value;
          }
      }
  }
  