public void FindMagicMultipliers(ColorlessPiece colorlessPiece, Delegates.WriteMessageLine writeMessageLine = null)
{
Direction[] directions;
ulong[] unoccupiedMoveMasks;
ulong[] relevantOccupancyMasks;
ulong[] magicMultipliers;
int[] shifts;
ulong[][] moveMasks;
// ReSharper disable SwitchStatementHandlesSomeKnownEnumValuesWithDefault
switch (colorlessPiece)
{
case ColorlessPiece.Bishop:
directions = new[] { Direction.NorthEast, Direction.SouthEast, Direction.SouthWest, Direction.NorthWest };
unoccupiedMoveMasks = Board.BishopMoveMasks;
relevantOccupancyMasks = _bishopRelevantOccupancyMasks;
magicMultipliers = _bishopMagicMultipliers;
shifts = _bishopShifts;
moveMasks = _bishopMoveMasks;
break;
case ColorlessPiece.Rook:
directions = new[] { Direction.North, Direction.East, Direction.South, Direction.West };
unoccupiedMoveMasks = Board.RookMoveMasks;
relevantOccupancyMasks = _rookRelevantOccupancyMasks;
magicMultipliers = _rookMagicMultipliers;
shifts = _rookShifts;
moveMasks = _rookMoveMasks;
break;
default:
throw new ArgumentException($"{colorlessPiece} piece not supported.");
}
// ReSharper restore SwitchStatementHandlesSomeKnownEnumValuesWithDefault
// Generate moves mask on each square.
var occupancyToMovesMask = new Dictionary <ulong, ulong>();
var uniqueMovesMasks = new HashSet <ulong>();
for (var square = Square.A8; square < Square.Illegal; square++)
{
occupancyToMovesMask.Clear();
uniqueMovesMasks.Clear();
var moveDestinations = unoccupiedMoveMasks[(int)square];
var relevantMoveDestinations = moveDestinations & relevantOccupancyMasks[(int)square];
var uniqueOccupancies = (int)Math.Pow(2, Bitwise.CountSetBits(relevantMoveDestinations));
occupancyToMovesMask.EnsureCapacity(uniqueOccupancies);
// Generate moves mask for every permutation of occupancy of the relevant destination squares.
var occupancyPermutations = Bitwise.GetAllPermutations(relevantMoveDestinations);
for (var occupancyIndex = 0; occupancyIndex < occupancyPermutations.Count; occupancyIndex++)
{
var occupancy = occupancyPermutations[occupancyIndex];
var movesMask = Board.CreateMoveDestinationsMask(square, occupancy, directions);
occupancyToMovesMask.Add(occupancy, movesMask);
if (!uniqueMovesMasks.Contains(movesMask))
{
uniqueMovesMasks.Add(movesMask);
}
}
Debug.Assert(occupancyToMovesMask.Count == uniqueOccupancies);
// Determine bit shift that produces number >= unique occupancies.
// A stricter condition is number >= unique moves but this requires more computing time to find magic multipliers.
var shift = 64 - (int)Math.Ceiling(Math.Log(uniqueOccupancies, 2d));
shifts[(int)square] = shift;
var magicMultiplier = magicMultipliers[(int)square];
var knownMagicMultiplier = magicMultiplier == 0 ? null : (ulong?)magicMultiplier;
(magicMultipliers[(int)square], moveMasks[(int)square]) = FindMagicMultiplier(occupancyToMovesMask, shift, knownMagicMultiplier);
writeMessageLine?.Invoke($"{Board.SquareLocations[(int)square],6} {PieceHelper.GetName(colorlessPiece),6} {shift,5} {occupancyToMovesMask.Count,18} {uniqueMovesMasks.Count,12} {magicMultipliers[(int)square],16:X16}");
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)] public ulong GetPieces(ColorlessPiece piece) => PieceBitboards[(int)piece] | PieceBitboards[(int)piece + (int)Piece.WhiteKing];
