content: /*
   * Copyright (C) 2017 The Android Open Source Project
   *
   * 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 android.util;
  
  /**
   * A utility class for common byte array to hex string operations and vise versa.
   *
   * @hide
   */
  public final class ByteStringUtils {
      private static final char[] HEX_LOWERCASE_ARRAY = "0123456789abcdef".toCharArray();
      private static final char[] HEX_UPPERCASE_ARRAY = "0123456789ABCDEF".toCharArray();
  
      private ByteStringUtils() {
      /* hide constructor */
      }
  
      /**
       * Returns the hex encoded string representation of bytes.
       * @param bytes Byte array to encode.
       * @return Hex encoded string representation of bytes.
       */
      public static String toHexString(byte[] bytes) {
          if (bytes == null || bytes.length == 0 || bytes.length % 2 != 0) {
              return null;
          }
  
          final int byteLength = bytes.length;
          final int charCount = 2 * byteLength;
          final char[] chars = new char[charCount];
  
          for (int i = 0; i < byteLength; i++) {
              final int byteHex = bytes[i] & 0xFF;
              chars[i * 2] = HEX_UPPERCASE_ARRAY[byteHex >>> 4];
              chars[i * 2 + 1] = HEX_UPPERCASE_ARRAY[byteHex & 0x0F];
          }
          return new String(chars);
      }
  
      /**
       * Returns the decoded byte array representation of str.
       * @param str Hex encoded string to decode.
       * @return Decoded byte array representation of str.
       */
      public static byte[] fromHexToByteArray(String str) {
          if (str == null || str.length() == 0 || str.length() % 2 != 0) {
              return null;
          }
  
          final char[] chars = str.toCharArray();
          final int charLength = chars.length;
          final byte[] bytes = new byte[charLength / 2];
  
          for (int i = 0; i < bytes.length; i++) {
              bytes[i] =
                      (byte) (((getIndex(chars[i * 2]) << 4) & 0xF0)
                              | (getIndex(chars[i * 2 + 1]) & 0x0F));
          }
          return bytes;
      }
  
      private static int getIndex(char c) {
          for (int i = 0; i < HEX_UPPERCASE_ARRAY.length; i++) {
              if (HEX_UPPERCASE_ARRAY[i] == c || HEX_LOWERCASE_ARRAY[i] == c) {
                  return i;
              }
          }
          return -1;
      }
  }
  