Finds magic bitboard numbers for rooks and bishops.

./magic-bitboard-finder -a=<ATTEMPTS> -e=<EXTRA> > out.rs

ATTEMPTS is the number of attempts each square gets before failing, in millions. The default is 100 (= 100,000,000).

EXTRA is either true or false, if true, then once a square has reached half the attempts without finding a magic number, an extra bit will be added to the mask for that magic number, effectively doubling the hash space and greatly increasing the likelyhood that a magic number will be found. Some squares are very difficult to find without this (such as rook f8). The default is true.

Info about the running of the program is printed to sterr. If successful, a rust file with static arrays containing the magic numbers, offsets, and masks will be printed to stdout.

out.rs is an example output of the program invoked as:

./magic-bitboard-finder -a=1000 -e=true > out.rs

You can just take this file and use it if you don't want to make your own magic numbers. In the example, only rook f8 required an extra bit to be found.

A suitable function for generating rook moves might be:

// untested, probably works
fn rook_moves(square: usize, friends: u64, enemies: u64) -> u64
{
    ROOK_ATTACKS[square][((((
           (friends | enemies)
        &  ROOK_MASKS [square])
        *  ROOK_MAGICS[square])
        >> ROOK_SHIFTS[square])
        &  ROOK_BITS  [square])
        as usize]
        & !friends
}

The above probably won't work in rust's debug mode, due to the wrapping multiplication. It should work no problem in release mode, though.

Another of a similar form would be made for bishops. Queen moves are simply rook_moves | bishop_moves.