content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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.sohu.idcenter;
  
  /**
   * A Base62 method
   * @author adyliu (imxylz@gmail.com)
   * @since 1.0
   */
  public class Base62 {
  
      private static final String baseDigits = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
      private static final int BASE = baseDigits.length();
      private static final char[] digitsChar = baseDigits.toCharArray();
      private static final int FAST_SIZE = 'z';
      private static final int[] digitsIndex = new int[FAST_SIZE + 1];
  
  
      static {
          for (int i = 0; i < FAST_SIZE; i++) {
              digitsIndex[i] = -1;
          }
          //
          for (int i = 0; i < BASE; i++) {
              digitsIndex[digitsChar[i]] = i;
          }
      }
  
      public static long decode(String s) {
          long result = 0L;
          long multiplier = 1;
          for (int pos = s.length() - 1; pos >= 0; pos--) {
              int index = getIndex(s, pos);
              result += index * multiplier;
              multiplier *= BASE;
          }
          return result;
      }
  
      public static String encode(long number) {
          if (number < 0) throw new IllegalArgumentException("Number(Base62) must be positive: " + number);
          if (number == 0) return "0";
          StringBuilder buf = new StringBuilder();
          while (number != 0) {
              buf.append(digitsChar[(int) (number % BASE)]);
              number /= BASE;
          }
          return buf.reverse().toString();
      }
  
      private static int getIndex(String s, int pos) {
          char c = s.charAt(pos);
          if (c > FAST_SIZE) {
              throw new IllegalArgumentException("Unknow character for Base62: " + s);
          }
          int index = digitsIndex[c];
          if (index == -1) {
              throw new IllegalArgumentException("Unknow character for Base62: " + s);
          }
          return index;
      }
  }
  