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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2011 The Closure Compiler Authors.
 *
 * 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.google.debugging.sourcemap;

import java.util.Arrays;

/**
 * A utility class for working with Base64 values.
 */
public final class Base64 {

  // This is a utility class
  private Base64() {}

  /**
   *  A map used to convert integer values in the range 0-63 to their base64
   *  values.
   */
  private static final String BASE64_MAP =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
      "abcdefghijklmnopqrstuvwxyz" +
      "0123456789+/";

  /**
   * A map used to convert base64 character into integer values.
   */
  private static final int[] BASE64_DECODE_MAP = new int[256];
  static {
      Arrays.fill(BASE64_DECODE_MAP, -1);
      for (int i = 0; i < BASE64_MAP.length(); i++) {
        BASE64_DECODE_MAP[BASE64_MAP.charAt(i)] = i;
      }
  }

  /**
   * @param value A value in the range of 0-63.
   * @return a base64 digit.
   */
  public static char toBase64(int value) {
    assert (value <= 63 && value >= 0) : "value out of range:" + value;
    return BASE64_MAP.charAt(value);
  }

  /**
   * @param c A base64 digit.
   * @return A value in the range of 0-63.
   */
  public static int fromBase64(char c) {
    int result = BASE64_DECODE_MAP[c];
    assert (result != -1) : "invalid char";
    return result;
  }

  /**
   * @param value an integer to base64 encode.
   * @return the six digit long base64 encoded value of the integer.
   */
  public static String base64EncodeInt(int value) {
    char[] c = new char[6];
    for (int i = 0; i < 5; i++) {
      c[i] = Base64.toBase64((value >> (26 - i * 6)) & 0x3f);
    }
    c[5] = Base64.toBase64((value << 4) & 0x3f);
    return new String(c);
  }
}