content: // Portions copyright 2002, Google, Inc.
  //
  // 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.android.vending.licensing.util;
  
  // This code was converted from code at http://iharder.sourceforge.net/base64/
  // Lots of extraneous features were removed.
  /* The original code said:
   * <p>
   * I am placing this code in the Public Domain. Do with it as you will.
   * This software comes with no guarantees or warranties but with
   * plenty of well-wishing instead!
   * Please visit
   * <a href="http://iharder.net/xmlizable">http://iharder.net/xmlizable</a>
   * periodically to check for updates or to contribute improvements.
   * </p>
   *
   * @author Robert Harder
   * @author rharder@usa.net
   * @version 1.3
   */
  
  /**
   * Base64 converter class. This code is not a full-blown MIME encoder;
   * it simply converts binary data to base64 data and back.
   *
   * <p>Note {@link CharBase64} is a GWT-compatible implementation of this
   * class.
   */
  public class Base64 {
    /** Specify encoding (value is {@code true}). */
    public final static boolean ENCODE = true;
  
    /** Specify decoding (value is {@code false}). */
    public final static boolean DECODE = false;
  
    /** The equals sign (=) as a byte. */
    private final static byte EQUALS_SIGN = (byte) '=';
  
    /** The new line character (\n) as a byte. */
    private final static byte NEW_LINE = (byte) '\n';
  
    /**
     * The 64 valid Base64 values.
     */
    private final static byte[] ALPHABET =
        {(byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F',
            (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
            (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P',
            (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
            (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
            (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e',
            (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j',
            (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
            (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
            (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y',
            (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3',
            (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8',
            (byte) '9', (byte) '+', (byte) '/'};
  
    /**
     * The 64 valid web safe Base64 values.
     */
    private final static byte[] WEBSAFE_ALPHABET =
        {(byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F',
            (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
            (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P',
            (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
            (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
            (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e',
            (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j',
            (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
            (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
            (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y',
            (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3',
            (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8',
            (byte) '9', (byte) '-', (byte) '_'};
  
    /**
     * Translates a Base64 value to either its 6-bit reconstruction value
     * or a negative number indicating some other meaning.
     **/
    private final static byte[] DECODABET = {-9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal  0 -  8
        -5, -5, // Whitespace: Tab and Linefeed
        -9, -9, // Decimal 11 - 12
        -5, // Whitespace: Carriage Return
        -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
        -9, -9, -9, -9, -9, // Decimal 27 - 31
        -5, // Whitespace: Space
        -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
        62, // Plus sign at decimal 43
        -9, -9, -9, // Decimal 44 - 46
        63, // Slash at decimal 47
        52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
        -9, -9, -9, // Decimal 58 - 60
        -1, // Equals sign at decimal 61
        -9, -9, -9, // Decimal 62 - 64
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
        14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
        -9, -9, -9, -9, -9, -9, // Decimal 91 - 96
        26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
        39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
        -9, -9, -9, -9, -9 // Decimal 123 - 127
        /*  ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 128 - 139
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 140 - 152
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 153 - 165
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 166 - 178
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 179 - 191
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 192 - 204
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 205 - 217
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 218 - 230
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 231 - 243
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9         // Decimal 244 - 255 */
        };
  
    /** The web safe decodabet */
    private final static byte[] WEBSAFE_DECODABET =
        {-9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal  0 -  8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 44
            62, // Dash '-' sign at decimal 45
            -9, -9, // Decimal 46-47
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
            -9, -9, -9, -9, // Decimal 91-94
            63, // Underscore '_' at decimal 95
            -9, // Decimal 96
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
            -9, -9, -9, -9, -9 // Decimal 123 - 127
        /*  ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 128 - 139
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 140 - 152
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 153 - 165
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 166 - 178
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 179 - 191
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 192 - 204
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 205 - 217
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 218 - 230
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 231 - 243
          -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9         // Decimal 244 - 255 */
        };
  
    // Indicates white space in encoding
    private final static byte WHITE_SPACE_ENC = -5;
    // Indicates equals sign in encoding
    private final static byte EQUALS_SIGN_ENC = -1;
  
    /** Defeats instantiation. */
    private Base64() {
    }
  
    /* ********  E N C O D I N G   M E T H O D S  ******** */
  
    /**
     * Encodes up to three bytes of the array <var>source</var>
     * and writes the resulting four Base64 bytes to <var>destination</var>.
     * The source and destination arrays can be manipulated
     * anywhere along their length by specifying
     * <var>srcOffset</var> and <var>destOffset</var>.
     * This method does not check to make sure your arrays
     * are large enough to accommodate <var>srcOffset</var> + 3 for
     * the <var>source</var> array or <var>destOffset</var> + 4 for
     * the <var>destination</var> array.
     * The actual number of significant bytes in your array is
     * given by <var>numSigBytes</var>.
     *
     * @param source the array to convert
     * @param srcOffset the index where conversion begins
     * @param numSigBytes the number of significant bytes in your array
     * @param destination the array to hold the conversion
     * @param destOffset the index where output will be put
     * @param alphabet is the encoding alphabet
     * @return the <var>destination</var> array
     * @since 1.3
     */
    private static byte[] encode3to4(byte[] source, int srcOffset,
        int numSigBytes, byte[] destination, int destOffset, byte[] alphabet) {
      //           1         2         3
      // 01234567890123456789012345678901 Bit position
      // --------000000001111111122222222 Array position from threeBytes
      // --------|    ||    ||    ||    | Six bit groups to index alphabet
      //          >>18  >>12  >> 6  >> 0  Right shift necessary
      //                0x3f  0x3f  0x3f  Additional AND
  
      // Create buffer with zero-padding if there are only one or two
      // significant bytes passed in the array.
      // We have to shift left 24 in order to flush out the 1's that appear
      // when Java treats a value as negative that is cast from a byte to an int.
      int inBuff =
          (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0)
              | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0)
              | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0);
  
      switch (numSigBytes) {
        case 3:
          destination[destOffset] = alphabet[(inBuff >>> 18)];
          destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
          destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f];
          destination[destOffset + 3] = alphabet[(inBuff) & 0x3f];
          return destination;
        case 2:
          destination[destOffset] = alphabet[(inBuff >>> 18)];
          destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
          destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f];
          destination[destOffset + 3] = EQUALS_SIGN;
          return destination;
        case 1:
          destination[destOffset] = alphabet[(inBuff >>> 18)];
          destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f];
          destination[destOffset + 2] = EQUALS_SIGN;
          destination[destOffset + 3] = EQUALS_SIGN;
          return destination;
        default:
          return destination;
      } // end switch
    } // end encode3to4
  
    /**
     * Encodes a byte array into Base64 notation.
     * Equivalent to calling
     * {@code encodeBytes(source, 0, source.length)}
     *
     * @param source The data to convert
     * @since 1.4
     */
    public static String encode(byte[] source) {
      return encode(source, 0, source.length, ALPHABET, true);
    }
  
    /**
     * Encodes a byte array into web safe Base64 notation.
     *
     * @param source The data to convert
     * @param doPadding is {@code true} to pad result with '=' chars
     *        if it does not fall on 3 byte boundaries
     */
    public static String encodeWebSafe(byte[] source, boolean doPadding) {
      return encode(source, 0, source.length, WEBSAFE_ALPHABET, doPadding);
    }
  
    /**
     * Encodes a byte array into Base64 notation.
     *
     * @param source The data to convert
     * @param off Offset in array where conversion should begin
     * @param len Length of data to convert
     * @param alphabet is the encoding alphabet
     * @param doPadding is {@code true} to pad result with '=' chars
     *        if it does not fall on 3 byte boundaries
     * @since 1.4
     */
    public static String encode(byte[] source, int off, int len, byte[] alphabet,
        boolean doPadding) {
      byte[] outBuff = encode(source, off, len, alphabet, Integer.MAX_VALUE);
      int outLen = outBuff.length;
  
      // If doPadding is false, set length to truncate '='
      // padding characters
      while (doPadding == false && outLen > 0) {
        if (outBuff[outLen - 1] != '=') {
          break;
        }
        outLen -= 1;
      }
  
      return new String(outBuff, 0, outLen);
    }
  
    /**
     * Encodes a byte array into Base64 notation.
     *
     * @param source The data to convert
     * @param off Offset in array where conversion should begin
     * @param len Length of data to convert
     * @param alphabet is the encoding alphabet
     * @param maxLineLength maximum length of one line.
     * @return the BASE64-encoded byte array
     */
    public static byte[] encode(byte[] source, int off, int len, byte[] alphabet,
        int maxLineLength) {
      int lenDiv3 = (len + 2) / 3; // ceil(len / 3)
      int len43 = lenDiv3 * 4;
      byte[] outBuff = new byte[len43 // Main 4:3
          + (len43 / maxLineLength)]; // New lines
  
      int d = 0;
      int e = 0;
      int len2 = len - 2;
      int lineLength = 0;
      for (; d < len2; d += 3, e += 4) {
  
        // The following block of code is the same as
        // encode3to4( source, d + off, 3, outBuff, e, alphabet );
        // but inlined for faster encoding (~20% improvement)
        int inBuff =
            ((source[d + off] << 24) >>> 8)
                | ((source[d + 1 + off] << 24) >>> 16)
                | ((source[d + 2 + off] << 24) >>> 24);
        outBuff[e] = alphabet[(inBuff >>> 18)];
        outBuff[e + 1] = alphabet[(inBuff >>> 12) & 0x3f];
        outBuff[e + 2] = alphabet[(inBuff >>> 6) & 0x3f];
        outBuff[e + 3] = alphabet[(inBuff) & 0x3f];
  
        lineLength += 4;
        if (lineLength == maxLineLength) {
          outBuff[e + 4] = NEW_LINE;
          e++;
          lineLength = 0;
        } // end if: end of line
      } // end for: each piece of array
  
      if (d < len) {
        encode3to4(source, d + off, len - d, outBuff, e, alphabet);
  
        lineLength += 4;
        if (lineLength == maxLineLength) {
          // Add a last newline
          outBuff[e + 4] = NEW_LINE;
          e++;
        }
        e += 4;
      }
  
      assert (e == outBuff.length);
      return outBuff;
    }
  
  
    /* ********  D E C O D I N G   M E T H O D S  ******** */
  
  
    /**
     * Decodes four bytes from array <var>source</var>
     * and writes the resulting bytes (up to three of them)
     * to <var>destination</var>.
     * The source and destination arrays can be manipulated
     * anywhere along their length by specifying
     * <var>srcOffset</var> and <var>destOffset</var>.
     * This method does not check to make sure your arrays
     * are large enough to accommodate <var>srcOffset</var> + 4 for
     * the <var>source</var> array or <var>destOffset</var> + 3 for
     * the <var>destination</var> array.
     * This method returns the actual number of bytes that
     * were converted from the Base64 encoding.
     *
     *
     * @param source the array to convert
     * @param srcOffset the index where conversion begins
     * @param destination the array to hold the conversion
     * @param destOffset the index where output will be put
     * @param decodabet the decodabet for decoding Base64 content
     * @return the number of decoded bytes converted
     * @since 1.3
     */
    private static int decode4to3(byte[] source, int srcOffset,
        byte[] destination, int destOffset, byte[] decodabet) {
      // Example: Dk==
      if (source[srcOffset + 2] == EQUALS_SIGN) {
        int outBuff =
            ((decodabet[source[srcOffset]] << 24) >>> 6)
                | ((decodabet[source[srcOffset + 1]] << 24) >>> 12);
  
        destination[destOffset] = (byte) (outBuff >>> 16);
        return 1;
      } else if (source[srcOffset + 3] == EQUALS_SIGN) {
        // Example: DkL=
        int outBuff =
            ((decodabet[source[srcOffset]] << 24) >>> 6)
                | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                | ((decodabet[source[srcOffset + 2]] << 24) >>> 18);
  
        destination[destOffset] = (byte) (outBuff >>> 16);
        destination[destOffset + 1] = (byte) (outBuff >>> 8);
        return 2;
      } else {
        // Example: DkLE
        int outBuff =
            ((decodabet[source[srcOffset]] << 24) >>> 6)
                | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                | ((decodabet[source[srcOffset + 2]] << 24) >>> 18)
                | ((decodabet[source[srcOffset + 3]] << 24) >>> 24);
  
        destination[destOffset] = (byte) (outBuff >> 16);
        destination[destOffset + 1] = (byte) (outBuff >> 8);
        destination[destOffset + 2] = (byte) (outBuff);
        return 3;
      }
    } // end decodeToBytes
  
  
    /**
     * Decodes data from Base64 notation.
     *
     * @param s the string to decode (decoded in default encoding)
     * @return the decoded data
     * @since 1.4
     */
    public static byte[] decode(String s) throws Base64DecoderException {
      byte[] bytes = s.getBytes();
      return decode(bytes, 0, bytes.length);
    }
  
    /**
     * Decodes data from web safe Base64 notation.
     * Web safe encoding uses '-' instead of '+', '_' instead of '/'
     *
     * @param s the string to decode (decoded in default encoding)
     * @return the decoded data
     */
    public static byte[] decodeWebSafe(String s) throws Base64DecoderException {
      byte[] bytes = s.getBytes();
      return decodeWebSafe(bytes, 0, bytes.length);
    }
  
    /**
     * Decodes Base64 content in byte array format and returns
     * the decoded byte array.
     *
     * @param source The Base64 encoded data
     * @return decoded data
     * @since 1.3
     * @throws Base64DecoderException
     */
    public static byte[] decode(byte[] source) throws Base64DecoderException {
      return decode(source, 0, source.length);
    }
  
    /**
     * Decodes web safe Base64 content in byte array format and returns
     * the decoded data.
     * Web safe encoding uses '-' instead of '+', '_' instead of '/'
     *
     * @param source the string to decode (decoded in default encoding)
     * @return the decoded data
     */
    public static byte[] decodeWebSafe(byte[] source)
        throws Base64DecoderException {
      return decodeWebSafe(source, 0, source.length);
    }
  
    /**
     * Decodes Base64 content in byte array format and returns
     * the decoded byte array.
     *
     * @param source The Base64 encoded data
     * @param off    The offset of where to begin decoding
     * @param len    The length of characters to decode
     * @return decoded data
     * @since 1.3
     * @throws Base64DecoderException
     */
    public static byte[] decode(byte[] source, int off, int len)
        throws Base64DecoderException {
      return decode(source, off, len, DECODABET);
    }
  
    /**
     * Decodes web safe Base64 content in byte array format and returns
     * the decoded byte array.
     * Web safe encoding uses '-' instead of '+', '_' instead of '/'
     *
     * @param source The Base64 encoded data
     * @param off    The offset of where to begin decoding
     * @param len    The length of characters to decode
     * @return decoded data
     */
    public static byte[] decodeWebSafe(byte[] source, int off, int len)
        throws Base64DecoderException {
      return decode(source, off, len, WEBSAFE_DECODABET);
    }
  
    /**
     * Decodes Base64 content using the supplied decodabet and returns
     * the decoded byte array.
     *
     * @param source    The Base64 encoded data
     * @param off       The offset of where to begin decoding
     * @param len       The length of characters to decode
     * @param decodabet the decodabet for decoding Base64 content
     * @return decoded data
     */
    public static byte[] decode(byte[] source, int off, int len, byte[] decodabet)
        throws Base64DecoderException {
      int len34 = len * 3 / 4;
      byte[] outBuff = new byte[2 + len34]; // Upper limit on size of output
      int outBuffPosn = 0;
  
      byte[] b4 = new byte[4];
      int b4Posn = 0;
      int i = 0;
      byte sbiCrop = 0;
      byte sbiDecode = 0;
      for (i = 0; i < len; i++) {
        sbiCrop = (byte) (source[i + off] & 0x7f); // Only the low seven bits
        sbiDecode = decodabet[sbiCrop];
  
        if (sbiDecode >= WHITE_SPACE_ENC) { // White space Equals sign or better
          if (sbiDecode >= EQUALS_SIGN_ENC) {
            // An equals sign (for padding) must not occur at position 0 or 1
            // and must be the last byte[s] in the encoded value
            if (sbiCrop == EQUALS_SIGN) {
              int bytesLeft = len - i;
              byte lastByte = (byte) (source[len - 1 + off] & 0x7f);
              if (b4Posn == 0 || b4Posn == 1) {
                throw new Base64DecoderException(
                    "invalid padding byte '=' at byte offset " + i);
              } else if ((b4Posn == 3 && bytesLeft > 2)
                  || (b4Posn == 4 && bytesLeft > 1)) {
                throw new Base64DecoderException(
                    "padding byte '=' falsely signals end of encoded value "
                        + "at offset " + i);
              } else if (lastByte != EQUALS_SIGN && lastByte != NEW_LINE) {
                throw new Base64DecoderException(
                    "encoded value has invalid trailing byte");
              }
              break;
            }
  
            b4[b4Posn++] = sbiCrop;
            if (b4Posn == 4) {
              outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, decodabet);
              b4Posn = 0;
            }
          }
        } else {
          throw new Base64DecoderException("Bad Base64 input character at " + i
              + ": " + source[i + off] + "(decimal)");
        }
      }
  
      // Because web safe encoding allows non padding base64 encodes, we
      // need to pad the rest of the b4 buffer with equal signs when
      // b4Posn != 0.  There can be at most 2 equal signs at the end of
      // four characters, so the b4 buffer must have two or three
      // characters.  This also catches the case where the input is
      // padded with EQUALS_SIGN
      if (b4Posn != 0) {
        if (b4Posn == 1) {
          throw new Base64DecoderException("single trailing character at offset "
              + (len - 1));
        }
        b4[b4Posn++] = EQUALS_SIGN;
        outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn, decodabet);
      }
  
      byte[] out = new byte[outBuffPosn];
      System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
      return out;
    }
  }
  