question: private int extract ( final int index , final byte a [ ] , final int offset , final int length ) { final BackingBuffer bb = this . bb ; final int delta = index % ratio ; final int startPos = p [ index / ratio ] ; int pos , prevArrayPos , currLen = 0 , actualCommon ; int arrayLength = bb . readInt ( pos = startPos ) ; if ( delta == 0 ) { pos = p [ index / ratio ] + count ( arrayLength ) ; bb . arraycopy ( pos , a , offset , Math . min ( length , arrayLength ) ) ; return arrayLength ; } int common = 0 ; for ( int i = 0 ; i < delta ; i ++ ) { prevArrayPos = pos + count ( arrayLength ) + ( i != 0 ? count ( common ) : 0 ) ; pos = prevArrayPos + arrayLength ; arrayLength = bb . readInt ( pos ) ; common = bb . readInt ( pos + count ( arrayLength ) ) ; actualCommon = Math . min ( common , length ) ; if ( actualCommon <= currLen ) currLen = actualCommon ; else { bb . arraycopy ( prevArrayPos , a , currLen + offset , actualCommon - currLen ) ; currLen = actualCommon ; } } if ( currLen < length ) bb . arraycopy ( pos + count ( arrayLength ) + count ( common ) , a , currLen + offset , Math . min ( arrayLength , length - currLen ) ) ; return arrayLength + common ; }
target:  Extracts the array at the given index.