src/main/java/org/jivesoftware/smack/util/Base64.java
private static int decode4to3(byte[] source, int srcOffset,
            byte[] destination, int destOffset, int options) {
        byte[] DECODABET = getDecodabet(options);

        // Example: Dk==
        if (source[srcOffset + 2] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1] ] << 24 ) >>> 12 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                    | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12);

            destination[destOffset] = (byte) (outBuff >>> 16);
            return 1;
        }

        // Example: DkL=
        else if (source[srcOffset + 3] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 )
            // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                    | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
                    | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6);

            destination[destOffset] = (byte) (outBuff >>> 16);
            destination[destOffset + 1] = (byte) (outBuff >>> 8);
            return 2;
        }

        // Example: DkLE
        else {
            try {
                // Two ways to do the same thing. Don't know which way I like
                // best.
                // 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 );
                int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                        | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
                        | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6)
                        | ((DECODABET[source[srcOffset + 3]] & 0xFF));

                destination[destOffset] = (byte) (outBuff >> 16);
                destination[destOffset + 1] = (byte) (outBuff >> 8);
                destination[destOffset + 2] = (byte) (outBuff);

                return 3;
            } catch (Exception e) {
                log.log(Level.ERROR, e.getMessage(), e);
                log.error("" + source[srcOffset] + ": "
                        + (DECODABET[source[srcOffset]]));
                log.error("" + source[srcOffset + 1] + ": "
                        + (DECODABET[source[srcOffset + 1]]));
                log.error("" + source[srcOffset + 2] + ": "
                        + (DECODABET[source[srcOffset + 2]]));
                log.error("" + source[srcOffset + 3] + ": "
                        + (DECODABET[source[srcOffset + 3]]));
                return -1;
            } // end catch
        }
    }
private static int decode4to3(byte[] source, int srcOffset,
            byte[] destination, int destOffset, int options) {
        byte[] DECODABET = getDecodabet(options);

        // Example: Dk==
        if (source[srcOffset + 2] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1] ] << 24 ) >>> 12 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                    | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12);

            destination[destOffset] = (byte) (outBuff >>> 16);
            return 1;
        }

        // Example: DkL=
        else if (source[srcOffset + 3] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 )
            // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                    | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
                    | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6);

            destination[destOffset] = (byte) (outBuff >>> 16);
            destination[destOffset + 1] = (byte) (outBuff >>> 8);
            return 2;
        }

        // Example: DkLE
        else {
            try {
                // Two ways to do the same thing. Don't know which way I like
                // best.
                // 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 );
                int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                        | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
                        | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6)
                        | ((DECODABET[source[srcOffset + 3]] & 0xFF));

                destination[destOffset] = (byte) (outBuff >> 16);
                destination[destOffset + 1] = (byte) (outBuff >> 8);
                destination[destOffset + 2] = (byte) (outBuff);

                return 3;
            } catch (Exception e) {
                log.log(Level.ERROR, e.getMessage(), e);
                log.error("" + source[srcOffset] + ": "
                        + (DECODABET[source[srcOffset]]));
                log.error("" + source[srcOffset + 1] + ": "
                        + (DECODABET[source[srcOffset + 1]]));
                log.error("" + source[srcOffset + 2] + ": "
                        + (DECODABET[source[srcOffset + 2]]));
                log.error("" + source[srcOffset + 3] + ": "
                        + (DECODABET[source[srcOffset + 3]]));
                return -1;
            } // end catch
        }
    }
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 accomodate
<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.
<p>
This is the lowest level of the decoding methods with all possible
parameters.
</p>


@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 options
alphabet type is pulled from this (standard, url-safe,
ordered)
@return the number of decoded bytes converted
@since 1.3