diff --git a/src/benchmark.py b/src/benchmark.py
new file mode 100644
--- /dev/null
+++ b/src/benchmark.py
@@ -0,0 +1,10 @@
+import cProfile
+
+from tests.testEngine import TestTransitions
+
+
+t=TestTransitions()
+
+cProfile.run(r"""
+t.testReal()
+""")
diff --git a/src/go/core.py b/src/go/core.py
--- a/src/go/core.py
+++ b/src/go/core.py
@@ -1,6 +1,6 @@
 import logging as log
 
-from util import EMPTY,BLACK,WHITE, colorNames,hashBoard
+from util import EMPTY,BLACK,WHITE, colorNames,hashBoard,diffHash
 from .helperboard import HelperBoard
 from .gamerecord import GameRecord
 
@@ -12,7 +12,8 @@ class Go:
 		self.board=[[EMPTY]*boardSize for x in range(boardSize)]
 		self.toMove=BLACK
 		self._helper=HelperBoard(self.board)
-		self._hashes=[]
+		self._freshHash=hashBoard(self.board) # always reflecting current state of the board
+		self._hashes=[self._freshHash]
 		self._record=GameRecord()
 
 	## Executes a move.
@@ -21,25 +22,27 @@ class Go:
 	#
 	#  @param color BLACK or WHITE
 	#  @return True on success, False on failure (illegal move)
-	def doMove(self,color,row,col):
+	def doMove(self,color,r,c):
 		if color!=self.toMove: log.warning("move by %s out of order",colorNames[color])
-		if self.board[row][col]!=EMPTY: return False
+		if self.board[r][c]!=EMPTY: return False
 
-		self.board[row][col]=color
+		self.board[r][c]=color
+		self._freshHash^=diffHash(r,c,EMPTY,color)
 
 		# capture neighbors
-		for r,c in ((-1,0),(1,0),(0,-1),(0,1)):
+		for dr,dc in ((-1,0),(1,0),(0,-1),(0,1)):
 			self._helper.clear()
-			if not self._helper.floodFill(-color,row+r,col+c,EMPTY): self._remove()
+			if not self._helper.floodFill(-color,r+dr,c+dc,EMPTY): self._remove()
 
 		# check for suicide and prevent it
 		self._helper.clear()
-		if not self._helper.floodFill(color,row,col,EMPTY):
-			self.board[row][col]=EMPTY
+		if not self._helper.floodFill(color,r,c,EMPTY):
+			self.board[r][c]=EMPTY
+			self._freshHash=self._hashes[-1]
 			return False
-		self._record.move(color,row,col)
+		self._record.move(color,r,c)
 		self.toMove=-1*color
-		self._hashes.append(self.hash())
+		self._hashes.append(self._freshHash)
 		return True
 
 	def undoMove(self,r,c,captures):
@@ -54,6 +57,7 @@ class Go:
 		self.board[r][c]=EMPTY
 		self.toMove*=-1
 		self._hashes.pop()
+		self._freshHash=self._hashes[-1]
 
 	def transitionMove(self,board):
 		res=transitionMove(self.board,board)
@@ -65,9 +69,11 @@ class Go:
 		for (r,row) in enumerate(board):
 			for (c,x) in enumerate(row):
 				self.board[r][c]=x
+		self._freshHash=hashBoard(self.board)
+		self._hashes=[self._freshHash]
 
 	def hash(self):
-		return hashBoard(self.board)
+		return self._hashes[-1]
 
 	## Removes stones at coordinates marked with True in self.helper.
 	def _remove(self):
@@ -75,6 +81,7 @@ class Go:
 
 	def _fill(self,filling):
 		for (r,c) in self._helper.getContinuousArea():
+			self._freshHash^=diffHash(r,c,self.board[r][c],filling)
 			self.board[r][c]=filling
 
 
diff --git a/src/statebag.py b/src/statebag.py
--- a/src/statebag.py
+++ b/src/statebag.py
@@ -39,9 +39,11 @@ class BoardState:
 		self.moves=[]
 		self.weight=0
 		self.diff2Prev=None
+		self._hash=None
 
 	def hash(self):
-		return hashBoard(self._board)
+		if self._hash is None: self._hash=hashBoard(self._board)
+		return self._hash
 
 	def export(self):
 		return exportBoard(self._board)
diff --git a/src/util.py b/src/util.py
--- a/src/util.py
+++ b/src/util.py
@@ -52,6 +52,9 @@ def hashBoard(board):
 			res^=zobristNums[r][c][item+1]
 	return res
 
+def diffHash(r,c,oldItem,newItem):
+	h=zobristNums[r][c]
+	return h[oldItem+1] ^ h[newItem+1]
 
 def exportBoard(board):
 	substitutions={EMPTY:".", BLACK:"X", WHITE:"O"}