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ZNet/ZNetBandwidthMeter.cpp

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+/*
+	ZNetBandwidthMeter.cpp
+	Author: Patrick Baggett	<ptbaggett@762studios.com>
+	Created: 7/10/2013
+
+	Purpose:
+
+	** NOT PART OF PUBLIC SDK **
+	This class is not part of the public SDK; its fields and methods are not present
+	in the documentation and cannot be guaranteed in future revisions.
+	** NOT PART OF PUBLIC SDK **
+	
+	Bandwidth metering using a simple token bucket algorithm. A single value is
+	metered, so a incoming / outgoing each need an instance.
+
+	License:
+	
+	Copyright 2013, 762 Studios
+*/
+
+#include <ZNet/ZNetBandwidthMeter.hpp>
+
+/*************************************************************************/
+
+void ZNetBandwidthMeter::SetLimit(uint32_t newLimit)
+{
+	limit = newLimit;
+	
+	//Clamp existing token bucket
+	if(tokens > newLimit)
+		tokens = newLimit;
+
+}
+
+/*************************************************************************/
+	
+void ZNetBandwidthMeter::Reset(uint64_t newStartTime)
+{
+	lastTime = newStartTime;
+	tokens = limit;
+}
+
+/*************************************************************************/
+		
+bool ZNetBandwidthMeter::TryAllocate(uint32_t bytes)
+{
+	if(bytes <= tokens)
+	{
+		tokens -= bytes;
+		return true;
+	}
+	
+	//Not enough
+	return false;
+}
+
+/*************************************************************************/
+
+void ZNetBandwidthMeter::Update(uint64_t newTime)
+{	
+	//Sanity check -- the time _did_ monotonically increase, right?
+	if(newTime > lastTime)
+	{
+		uint32_t delta = (uint32_t)(newTime - lastTime);
+		
+		//If less than a second has passed...
+		if(delta < 1000)
+		{
+			//We could do: delta / 1000.0 * limit, but that involves int -> float conversions
+			//instead we do u32 x u32 = u64 multiply and divide by 1000, keeping it all in fixed
+			//point happiness. Because delta < 1000, dividing by 1000 should put it back in the
+			//range of a u32.
+			uint32_t amount = (uint64_t)delta * (uint64_t)limit / 1000;
+			
+			//Add newly generated tokens, but clamp to the limit.
+			tokens += amount;
+			if(tokens > limit)
+				tokens = limit;
+		}
+		else //More than a second, so restore all tokens
+			tokens = limit;
+			
+		//Save this as the new time
+		lastTime = newTime;
+	}
+}