private static int decode4to3()

in chill-java/src/main/java/com/twitter/chill/Base64.java [1029:1098]
43 lines of code
7 McCabe index (conditional complexity)

    private static int decode4to3(
    byte[] source, int srcOffset,
    byte[] destination, int destOffset, int options ) {

        // Lots of error checking and exception throwing
        if( source == null ){
            throw new NullPointerException( "Source array was null." );
        }   // end if
        if( destination == null ){
            throw new NullPointerException( "Destination array was null." );
        }   // end if
        if( srcOffset < 0 || srcOffset + 3 >= source.length ){
            throw new IllegalArgumentException( String.format(
            "Source array with length %d cannot have offset of %d and still process four bytes.", source.length, srcOffset ) );
        }   // end if
        if( destOffset < 0 || destOffset +2 >= destination.length ){
            throw new IllegalArgumentException( String.format(
            "Destination array with length %d cannot have offset of %d and still store three bytes.", destination.length, destOffset ) );
        }   // end if


        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 {
            // 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;
        }
    }   // end decodeToBytes