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;
    }
  }
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
android/android_framework/base/src/main/java/com/google/android/vending/licensing/util/Base64.java