2 files changed, 42 insertions, 46 deletions

diff --git a/src/Blocks/BlockComparator.h b/src/Blocks/BlockComparator.h
index ffd1bde61..5ba17c691 100644
--- a/src/Blocks/BlockComparator.h
+++ b/src/Blocks/BlockComparator.h
@@ -60,6 +60,11 @@ public:
 		return true;
 	}
 
+	inline static bool IsInSubtractionMode(NIBBLETYPE a_Meta)
+	{
+		return ((a_Meta & 0x4) == 0x4);
+	}
+
 	inline static bool IsOn(NIBBLETYPE a_Meta)
 	{
 		return ((a_Meta & 0x8) == 0x8);
diff --git a/src/Simulator/IncrementalRedstoneSimulator/RedstoneComparatorHandler.h b/src/Simulator/IncrementalRedstoneSimulator/RedstoneComparatorHandler.h
index 9a250a1fe..34c217e67 100644
--- a/src/Simulator/IncrementalRedstoneSimulator/RedstoneComparatorHandler.h
+++ b/src/Simulator/IncrementalRedstoneSimulator/RedstoneComparatorHandler.h
@@ -18,8 +18,33 @@ public:
 	{
 	}
 
-	unsigned char GetFrontPowerLevel(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta, unsigned char a_HighestSidePowerLevel)
+	unsigned char GetFrontPowerLevel(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta, unsigned char a_HighestSidePowerLevel, unsigned char a_HighestRearPowerLevel)
 	{
+		if (cBlockComparatorHandler::IsInSubtractionMode(a_Meta))
+		{
+			// Subtraction mode
+			return static_cast<unsigned char>(std::max(static_cast<char>(a_HighestRearPowerLevel) - a_HighestSidePowerLevel, 0));
+		}
+		else
+		{
+			// Comparison mode
+			return (std::max(a_HighestSidePowerLevel, a_HighestRearPowerLevel) == a_HighestSidePowerLevel) ? 0 : a_HighestRearPowerLevel;
+		}
+	}
+
+	virtual unsigned char GetPowerDeliveredToPosition(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta, const Vector3i & a_QueryPosition, BLOCKTYPE a_QueryBlockType) override
+	{
+		UNUSED(a_QueryPosition);
+		UNUSED(a_QueryBlockType);
+
+		return (cBlockComparatorHandler::GetFrontCoordinate(a_Position, a_Meta & 0x3) == a_QueryPosition) ? static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData()->GetCachedPowerData(a_Position).PowerLevel : 0;
+	}
+
+	virtual unsigned char GetPowerLevel(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta) override
+	{
+		UNUSED(a_Position);
+		UNUSED(a_BlockType);
+
 		class cContainerCallback : public cBlockEntityCallback
 		{
 		public:
@@ -31,12 +56,13 @@ public:
 			{
 				auto & Contents = static_cast<cBlockEntityWithItems *>(a_BlockEntity)->GetContents();
 				float Fullness = 0;  // Is a floating-point type to allow later calculation to produce a non-truncated value
+
 				for (int Slot = 0; Slot != Contents.GetNumSlots(); ++Slot)
 				{
-					Fullness += Contents.GetSlot(Slot).m_ItemCount / Contents.GetSlot(Slot).GetMaxStackSize();
+					Fullness += static_cast<float>(Contents.GetSlot(Slot).m_ItemCount) / Contents.GetSlot(Slot).GetMaxStackSize();
 				}
 
-				m_SignalStrength = static_cast<unsigned char>(1 + (Fullness / Contents.GetNumSlots()) * 14);
+				m_SignalStrength = (Fullness < 0.001 /* container empty? */) ? 0 : static_cast<unsigned char>(1 + (Fullness / Contents.GetNumSlots()) * 14);
 				return false;
 			}
 
@@ -46,43 +72,7 @@ public:
 		auto RearCoordinate = cBlockComparatorHandler::GetRearCoordinate(a_Position, a_Meta & 0x3);
 		m_World.DoWithBlockEntityAt(RearCoordinate.x, RearCoordinate.y, RearCoordinate.z, CCB);
 		auto RearPower = CCB.m_SignalStrength;
-		auto PotentialSourceHandler = cIncrementalRedstoneSimulator::CreateComponent(m_World, m_World.GetBlock(RearCoordinate), static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData());
-		if (PotentialSourceHandler != nullptr)
-		{
-			BLOCKTYPE Type;
-			NIBBLETYPE Meta;
-			if (m_World.GetBlockTypeMeta(RearCoordinate.x, RearCoordinate.y, RearCoordinate.z, Type, Meta))
-			{
-				RearPower = std::max(CCB.m_SignalStrength, PotentialSourceHandler->GetPowerDeliveredToPosition(RearCoordinate, Type, Meta, a_Position, a_BlockType));
-			}
-		}
-
-		if ((a_Meta & 0x4) == 0x4)
-		{
-			// Subtraction mode
-			return static_cast<unsigned char>(std::max(static_cast<char>(RearPower) - a_HighestSidePowerLevel, 0));
-		}
-		else
-		{
-			// Comparison mode
-			return (std::max(a_HighestSidePowerLevel, RearPower) == a_HighestSidePowerLevel) ? 0 : RearPower;
-		}
-	}
-
-	virtual unsigned char GetPowerDeliveredToPosition(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta, const Vector3i & a_QueryPosition, BLOCKTYPE a_QueryBlockType) override
-	{
-		UNUSED(a_QueryPosition);
-		UNUSED(a_QueryBlockType);
-
-		return (cBlockComparatorHandler::GetFrontCoordinate(a_Position, a_Meta & 0x3) == a_QueryPosition) ? static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData()->GetCachedPowerData(a_Position).PowerLevel : 0;
-	}
 
-	virtual unsigned char GetPowerLevel(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta) override
-	{
-		UNUSED(a_Position);
-		UNUSED(a_BlockType);
-
-		auto RearCoordinate = cBlockComparatorHandler::GetRearCoordinate(a_Position, a_Meta & 0x3);
 		auto PotentialSourceHandler = cIncrementalRedstoneSimulator::CreateComponent(m_World, m_World.GetBlock(RearCoordinate), static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData());
 		if (PotentialSourceHandler != nullptr)
 		{
@@ -90,16 +80,16 @@ public:
 			NIBBLETYPE Meta;
 			if (m_World.GetBlockTypeMeta(RearCoordinate.x, RearCoordinate.y, RearCoordinate.z, Type, Meta))
 			{
-				return PotentialSourceHandler->GetPowerDeliveredToPosition(RearCoordinate, Type, Meta, a_Position, a_BlockType);
+				RearPower = std::max(CCB.m_SignalStrength, PotentialSourceHandler->GetPowerDeliveredToPosition(RearCoordinate, Type, Meta, a_Position, a_BlockType));
 			}
 		}
 
-		return 0;
+		return RearPower;
 	}
 
 	virtual cVector3iArray Update(const Vector3i & a_Position, BLOCKTYPE a_BlockType, NIBBLETYPE a_Meta, PoweringData a_PoweringData) override
 	{
-		// Note that a_PoweringData here contains the maximum *side* power level, as specified by GetValidSourcePositions
+		// Note that a_PoweringData here contains the maximum * side * power level, as specified by GetValidSourcePositions
 		// LOGD("Evaluating ALU the comparator (%d %d %d)", a_Position.x, a_Position.y, a_Position.z);
 		auto Data = static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData();
 		auto DelayInfo = Data->GetMechanismDelayInfo(a_Position);
@@ -107,11 +97,12 @@ public:
 		// Delay is used here to prevent an infinite loop (#3168)
 		if (DelayInfo == nullptr)
 		{
-			auto Power = GetFrontPowerLevel(a_Position, a_BlockType, a_Meta, a_PoweringData.PowerLevel);
-			auto PreviousFrontPower = static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData()->ExchangeUpdateOncePowerData(a_Position, PoweringData(a_PoweringData.PoweringBlock, Power));
+			auto RearPower = GetPowerLevel(a_Position, a_BlockType, a_Meta);
+			auto FrontPower = GetFrontPowerLevel(a_Position, a_BlockType, a_Meta, a_PoweringData.PowerLevel, RearPower);
+			auto PreviousFrontPower = static_cast<cIncrementalRedstoneSimulator *>(m_World.GetRedstoneSimulator())->GetChunkData()->ExchangeUpdateOncePowerData(a_Position, PoweringData(a_PoweringData.PoweringBlock, FrontPower));
 
-			bool ShouldBeOn = (GetPowerLevel(a_Position, a_BlockType, a_Meta) > 0);  // Provide visual indication by examining *rear* power level
-			bool ShouldUpdate = (Power != PreviousFrontPower.PowerLevel);  // "Business logic" (:P) - determine by examining *side* power levels
+			bool ShouldBeOn = (RearPower > 0);  // Provide visual indication by examining * rear * power level
+			bool ShouldUpdate = (FrontPower != PreviousFrontPower.PowerLevel);  // "Business logic" (:P) - determine by examining *side* power levels
 
 			if (ShouldUpdate || (ShouldBeOn != cBlockComparatorHandler::IsOn(a_Meta)))
 			{