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Mirror the board instead of rotating when transitioning to black. #118

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Mirror the board instead of rotating when transitioning to black. #118

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29 changes: 21 additions & 8 deletions sunfish.py
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Original file line number Diff line number Diff line change
Expand Up @@ -190,12 +190,25 @@ def gen_moves(self):
if i == H1 and self.board[j + W] == "K" and self.wc[1]:
yield Move(j + W, j + E, "")

@staticmethod
def mirror_square(p):
row = p // 10
col = p % 10
return 110 - row*10 + col

@staticmethod
def mirror_board(board):
# Split the board into 10 rows and reverse their order to mirror the board
rows = [board[i:i+10] for i in range(0, len(board), 10)]
return ''.join(rows[::-1])

def rotate(self, nullmove=False):
"""Rotates the board, preserving enpassant, unless nullmove"""
return Position(
self.board[::-1].swapcase(), -self.score, self.bc, self.wc,
119 - self.ep if self.ep and not nullmove else 0,
119 - self.kp if self.kp and not nullmove else 0,
self.mirror_board(self.board).swapcase(),
-self.score, self.bc, self.wc,
self.mirror_square(self.ep) if self.ep and not nullmove else 0,
self.mirror_square(self.kp) if self.kp and not nullmove else 0,
)

def move(self, move):
Expand Down Expand Up @@ -239,10 +252,10 @@ def value(self, move):
score = pst[p][j] - pst[p][i]
# Capture
if q.islower():
score += pst[q.upper()][119 - j]
score += pst[q.upper()][self.mirror_square(j)]
# Castling check detection
if abs(j - self.kp) < 2:
score += pst["K"][119 - j]
score += pst["K"][self.mirror_square(j)]
# Castling
if p == "K" and abs(i - j) == 2:
score += pst["R"][(i + j) // 2]
Expand All @@ -252,7 +265,7 @@ def value(self, move):
if A8 <= j <= H8:
score += pst[prom][j] - pst["P"][j]
if j == self.ep:
score += pst["P"][119 - (j + S)]
score += pst["P"][self.mirror_square(j + S)]
return score


Expand Down Expand Up @@ -473,7 +486,7 @@ def render(i):
for ply, move in enumerate(args[3:]):
i, j, prom = parse(move[:2]), parse(move[2:4]), move[4:].upper()
if ply % 2 == 1:
i, j = 119 - i, 119 - j
i, j = Position.mirror_square(i), Position.mirror_square(j)
hist.append(hist[-1].move(Move(i, j, prom)))

elif args[0] == "go":
Expand All @@ -490,7 +503,7 @@ def render(i):
if score >= gamma:
i, j = move.i, move.j
if len(hist) % 2 == 0:
i, j = 119 - i, 119 - j
i, j = Position.mirror_square(i), Position.mirror_square(j)
move_str = render(i) + render(j) + move.prom.lower()
print("info depth", depth, "score cp", score, "pv", move_str)
if move_str and time.time() - start > think * 0.8:
Expand Down