// Returns true if a path of set bits in 'path' exists that 8-way connect
// any set bit in sq1 to any set bit of sq2
public static bool SquaresAreConnected(ulong sq1, ulong sq2, ulong path)
{
// With bitboard sq1, do an 8-way flood fill, masking off bits not in
// path at every step. Stop when fill reaches any set bit in sq2, or
// fill cannot progress any further
if ((~(sq1 &= path) | ~(sq2 &= path)) != 0)
{
return(false);
}
// Drop bits not in path
// Early exit if sq1 or sq2 not on any path
while ((sq1 & sq2) != 0)
{
ulong temp = sq1;
// Set all 8 neighbours
sq1 |= BitBoardHelper.ShiftEastOne(sq1) | BitBoardHelper.ShiftWestOne(sq1);
sq1 |= BitBoardHelper.ShiftSouthOne(sq1) | BitBoardHelper.ShiftNorthOne(sq1);
// Drop bits not in path
sq1 &= path;
if (sq1 == temp)
{
// Fill has stopped
return(false);
}
}
// Found a good path
return(true);
}
public static ulong[] GenerateAntiDiagonals()
{
ulong[] arr = new ulong[15];
for (int i = 0; i < 8; ++i)
{
ulong board = 0;
ulong minusBoard = 0;
for (int x = 0; x <= i; ++x)
{
int y = i - x;
board |= BitBoardHelper.GetOneBitNumber(x, y);
minusBoard |= BitBoardHelper.GetOneBitNumber(7 - x, 7 - y);
}
arr[14 - i] = minusBoard;
arr[i] = board;
}
return(arr);
}
public static ulong[] GenerateRotatedRanks()
{
return(Enumerable.Range(0, 256)
.Select(b => BitBoardHelper.FlipDiagonalA1H8((ulong)b))
.ToArray());
}
