Magic bitboards, a multiply-right-shift perfect hashing algorithm to index an attack bitboard database – which leaves both line-attacks of bishop or rook in one run. Thanks to the fast 64-bit multiplication and fast and huge caches of recent processors, Magic Bitboards has become a de facto standard…
How are magic bitboards used in chess engines?
“Magic bitboards” are a common technique in computer chess engines for move generation; most modern chess engines use some variant of the technique. While there are plentyof explanations online for how the related techniques of “bitboards” and “rotated bitboards” work, I had a hard time finding an explanation of how and why magic bitboards work.
Are there any magic bitboard move generation functions?
It’s good that we can assume magic bitboard functions are available, but in general bitboard move generation functions can accept any technique that produces a bitboard that gives the possible squares to move to. Say RookMoves is such a function, then you would populate the move list as follows:
What’s the difference between a bitboard and a bitet?
also called bitsets or bitmaps, are among other things used to represent the board inside a chess program in a piece centric manner. Bitboards, are in essence, finite sets of up to 64 elements – all the squares of a chessboard, one bit per square.
How many magic rooks are on a blocker board?
For a certain piece/square, if two blocker boards ever generate the same magical index but these two blocker boards have different move boards, then this is a muggle number, and you should try a new one. Once you get that down, you’ll have 64 magic rook numbers and 64 magic bishop numbers.
How are magic bitboards used in chessprogramming?
Magic bitboards applies perfect hashing. A surjective function, to map the vector of all relevant occupancies to a range of attack-sets per square. The less bits the attack-set – the closer the blockers, the more those attack-sets are shared by occupancies with different, but redundant outer squares.
Why did Gerd Isenberg create the Magic bitboard?
The magic bitboard approach was motivated by Gerd Isenberg’s multi-direction hashing technique kindergarten bitboards and probably by Gerd’s and Tony van Roon-Werten’s early trials to map line-wise occupancies by De Bruijn – or random number multiplication .
