PAREngine: fixed annealing so that probability always depends on iteration count rather than saturating at 100% p(accept) when we have >100 iterations allowed

azonenberg · azonenberg · commit d1a7d8f6b97e · 2017-05-21T14:42:09.000-07:00
diff --git a/src/xbpar/PAREngine.cpp b/src/xbpar/PAREngine.cpp
@@ -29,6 +29,7 @@ PAREngine::PAREngine(PARGraph* netlist, PARGraph* device)
 	: m_netlist(netlist)
 	, m_device(device)
 	, m_temperature(0)
+	, m_maxTemperature(500)	//max number of iterations allowed
 {
 
 }
@@ -48,7 +49,7 @@ PAREngine::~PAREngine()
 bool PAREngine::PlaceAndRoute(map<uint32_t, string> label_names, uint32_t seed)
 {
 	LogVerbose("\nXBPAR initializing...\n");
-	m_temperature = 250;
+	m_temperature = m_maxTemperature;
 
 	//TODO: glibc rand sucks, replace with something a bit more random
 	//(this may not make a difference for a device this tiny though)
@@ -346,11 +347,11 @@ bool PAREngine::OptimizePlacement(
 
 	//LogVerbose("Original cost %u, new cost %u\n", original_cost, new_cost);
 
-	//If new cost is less, or greater with probability temperature, accept it
+	//If new cost is less, or greater with temperature-dependent probability, accept it
 	//TODO: make probability depend on dCost?
 	if(new_cost < original_cost)
 		return true;
-	if( (rand() % 100) < (int)m_temperature )
+	if( (rand() % m_maxTemperature) < m_temperature )
 		return true;
 
 	//If we don't like the change, revert
diff --git a/src/xbpar/PAREngine.h b/src/xbpar/PAREngine.h
@@ -73,6 +73,7 @@ class PAREngine
 	void RestorePreviousBestPlacement();
 
 	uint32_t m_temperature;
+	uint32_t m_maxTemperature;
 };
 
 #endif
