Do not modify alpha in split()

[stockfish] / src / thread.cpp

diff --git a/src/thread.cpp b/src/thread.cpp
index 5d2b39f57c8c4791dd6b28975448a55d89fa2622..e1330396d0007f30815c3ba95d2142c9ad8bb1d7 100644 (file)
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -238,13 +238,13 @@ bool ThreadsManager::available_slave_exists(int master) const {
 // call search().When all threads have returned from search() then split() returns.
 
 template <bool Fake>
 // call search().When all threads have returned from search() then split() returns.
 
 template <bool Fake>

-void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const Value beta,
-                           Value* bestValue, Depth depth, Move threatMove,
-                           int moveCount, MovePicker* mp, int nodeType) {
+Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value beta,
+                            Value bestValue, Depth depth, Move threatMove,
+                            int moveCount, MovePicker* mp, int nodeType) {

   assert(pos.is_ok());
   assert(pos.is_ok());

-  assert(*bestValue >= -VALUE_INFINITE);
-  assert(*bestValue <= *alpha);
-  assert(*alpha < beta);
+  assert(bestValue >= -VALUE_INFINITE);
+  assert(bestValue <= alpha);
+  assert(alpha < beta);

   assert(beta <= VALUE_INFINITE);
   assert(depth > DEPTH_ZERO);
   assert(pos.thread() >= 0 && pos.thread() < activeThreads);
   assert(beta <= VALUE_INFINITE);
   assert(depth > DEPTH_ZERO);
   assert(pos.thread() >= 0 && pos.thread() < activeThreads);


@@ -255,7 +255,7 @@ void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const V
 
   // If we already have too many active split points, don't split
   if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
 
   // If we already have too many active split points, don't split
   if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)

-      return;
+      return bestValue;

 
   // Pick the next available split point object from the split point stack
   SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints];
 
   // Pick the next available split point object from the split point stack
   SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints];


@@ -266,10 +266,10 @@ void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const V
   splitPoint.is_betaCutoff = false;
   splitPoint.depth = depth;
   splitPoint.threatMove = threatMove;
   splitPoint.is_betaCutoff = false;
   splitPoint.depth = depth;
   splitPoint.threatMove = threatMove;

-  splitPoint.alpha = *alpha;
+  splitPoint.alpha = alpha;

   splitPoint.beta = beta;
   splitPoint.nodeType = nodeType;
   splitPoint.beta = beta;
   splitPoint.nodeType = nodeType;

-  splitPoint.bestValue = *bestValue;
+  splitPoint.bestValue = bestValue;

   splitPoint.mp = mp;
   splitPoint.moveCount = moveCount;
   splitPoint.pos = &pos;
   splitPoint.mp = mp;
   splitPoint.moveCount = moveCount;
   splitPoint.pos = &pos;


@@ -301,12 +301,12 @@ void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const V
 
   // We failed to allocate even one slave, return
   if (!Fake && !booked)
 
   // We failed to allocate even one slave, return
   if (!Fake && !booked)

-      return;
+      return bestValue;

 
   masterThread.activeSplitPoints++;
   masterThread.splitPoint = &splitPoint;
 
 
   masterThread.activeSplitPoints++;
   masterThread.splitPoint = &splitPoint;
 

-  // Tell the threads that they have work to do. This will make them leave
+  // Tell the threads that they have some work to do. This will make them leave

   // their idle loop.
   for (i = 0; i < activeThreads; i++)
       if (i == master || splitPoint.is_slave[i])
   // their idle loop.
   for (i = 0; i < activeThreads; i++)
       if (i == master || splitPoint.is_slave[i])


@@ -328,9 +328,8 @@ void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const V
   idle_loop(master, &splitPoint);
 
   // We have returned from the idle loop, which means that all threads are
   idle_loop(master, &splitPoint);
 
   // We have returned from the idle loop, which means that all threads are

-  // finished. Update alpha and bestValue, and return. Note that changing
-  // state and decreasing activeSplitPoints is done under lock protection
-  // to avoid a race with Thread::is_available_to().
+  // finished. Note that changing state and decreasing activeSplitPoints is done
+  // under lock protection to avoid a race with Thread::is_available_to().

   lock_grab(&threadsLock);
 
   masterThread.state = Thread::SEARCHING;
   lock_grab(&threadsLock);
 
   masterThread.state = Thread::SEARCHING;


@@ -339,11 +338,10 @@ void ThreadsManager::split(Position& pos, SearchStack* ss, Value* alpha, const V
 
   lock_release(&threadsLock);
 
 
   lock_release(&threadsLock);
 

-  *alpha = splitPoint.alpha;
-  *bestValue = splitPoint.bestValue;

   pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
   pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);

+  return splitPoint.bestValue;

 }
 
 // Explicit template instantiations
 }
 
 // Explicit template instantiations

-template void ThreadsManager::split<false>(Position&, SearchStack*, Value*, const Value, Value*, Depth, Move, int, MovePicker*, int);
-template void ThreadsManager::split<true>(Position&, SearchStack*, Value*, const Value, Value*, Depth, Move, int, MovePicker*, int);
+template Value ThreadsManager::split<false>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
+template Value ThreadsManager::split<true>(Position&, SearchStack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);