static byte[] base64decode(String s) {
    byte[] alphaToInt = base64decode_base64toint;
    int sLen = s.length();
    int numGroups = sLen/4;
    if (4*numGroups != sLen)
      throw new IllegalArgumentException(
        "String length must be a multiple of four.");
    int missingBytesInLastGroup = 0;
    int numFullGroups = numGroups;
    if (sLen != 0) {
      if (s.charAt(sLen-1) == '=') {
        missingBytesInLastGroup++;
        numFullGroups--;
      }
      if (s.charAt(sLen-2) == '=')
        missingBytesInLastGroup++;
    }
    byte[] result = new byte[3*numGroups - missingBytesInLastGroup];

    // Translate all full groups from base64 to byte array elements
    int inCursor = 0, outCursor = 0;
    for (int i=0; i<numFullGroups; i++) {
      int ch0 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
      int ch1 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
      int ch2 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
      int ch3 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
      result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
      result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
      result[outCursor++] = (byte) ((ch2 << 6) | ch3);
    }

    // Translate partial group, if present
    if (missingBytesInLastGroup != 0) {
      int ch0 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
      int ch1 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
      result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));

      if (missingBytesInLastGroup == 1) {
        int ch2 = base64decode_base64toint(s.charAt(inCursor++), alphaToInt);
        result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
      }
    }
    // assert inCursor == s.length()-missingBytesInLastGroup;
    // assert outCursor == result.length;
    return result;
  }

  static int base64decode_base64toint(char c, byte[] alphaToInt) {
    int result = alphaToInt[c];
    if (result < 0)
      throw new IllegalArgumentException("Illegal character " + c);
    return result;
  }

  static final byte base64decode_base64toint[] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54,
    55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4,
    5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
    24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34,
    35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
  };