Editing Bitboard (section)

===Incremental update===
Some kinds of bitboards are derived from others by an elaborate process of cross-correlation, such as the attack maps in chess.  Reforming all these maps at each change of game state (such as a move) can be prohibitively expensive, so derived bitmaps are incrementally updated, a process which requires intricate and precise code. This is much faster to execute, because only bitmaps associated with changed spaces, not all bitmaps over the board, need to change.  Without incremental update, bitmapped representation may not be more efficient than the older mailbox representation where update is intrinsically local and incremental.