Hi,

This small document explaining how working the generator of the wining Board.

To be able to provide information that the player could still win the game, the generate-board-files executable will compute all the possible position to win a game and store it in two separate files.

By default the program will compute only winning board for game that finish the a pawn in central position, but you can adapt it to compute for other end.

Technically, the programme will start from the final positions and play in reverse to fill the board.

Everytime the program find a unknow board, it will be add to two lists that store all winning boards.

The first containing the boards with a pawn at central position and the other one without.

The design coming from the encoding of the board and to safe memory by using only 32 bits to store the other pawn.

You could consider that the board is encoded with a very uncommon way.

Sorry for that, it make program very complex to understand but this encoding method also permit to compute very fast rotation and axial symetry of the board.

That is permit to optimize number of computation by cutting the branch of the resolution tree when a symetric or equivalent by rotation board is found.

The boards are store on 32 bits variable (sorry 64 bits computer was not available at the time I started this program).

Every pawn presence in the board are significated by a bit.

**********************

****** 02 03 08 ******

****** 01 04 07 ******

*16 15 14 05 06 25 26*

*11 12 13 XX 29 28 27*

*10 09 22 21 30 31 32*

****** 23 20 17 ******

****** 24 19 18 ******

**********************

They are 76 differents possible moves on the board.

This move are precoded in some tabs initialized by inittab function in libsolitaire librairie.

-cache is the mask of three bit to store position of the pawn involved in the move.

-result is the position of the pawn after the move

-coup is the position of the pawn before the move

-pawn indicate the position of the pawn that will move (this one is only used in the interface program)

The first 12 move envolved the pawn in the middle of the board (cache will have only two bits flags).

The others one are fully coded with in the 32 bits structure (cache will have 3 bits flags)

After this done find an avaible move of apply it to the board become just a bit operation.