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diff --git a/lib/crypto/RollingChecksum.h b/lib/crypto/RollingChecksum.h
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+// --------------------------------------------------------------------------
+//
+// File
+//		Name:    RollingChecksum.h
+//		Purpose: A simple rolling checksum over a block of data
+//		Created: 6/12/03
+//
+// --------------------------------------------------------------------------
+
+#ifndef ROLLINGCHECKSUM__H
+#define ROLLINGCHECKSUM__H
+
+// --------------------------------------------------------------------------
+//
+// Class
+//		Name:    RollingChecksum
+//		Purpose: A simple rolling checksum over a block of data -- can move the block
+//				 "forwards" in memory and get the next checksum efficiently.
+//
+//				 Implementation of http://rsync.samba.org/tech_report/node3.html
+//		Created: 6/12/03
+//
+// --------------------------------------------------------------------------
+class RollingChecksum
+{
+public:
+	RollingChecksum(const void *data, unsigned int Length);
+
+	// --------------------------------------------------------------------------
+	//
+	// Function
+	//		Name:    RollingChecksum::RollForward(uint8_t, uint8_t, unsigned int)
+	//		Purpose: Move the checksum forward a block, given the first byte of the current block,
+	//				 last byte of the next block (it's rolling forward to) and the length of the block.
+	//		Created: 6/12/03
+	//
+	// --------------------------------------------------------------------------
+	inline void RollForward(uint8_t StartOfThisBlock, uint8_t LastOfNextBlock, unsigned int Length)
+	{
+		// IMPLEMENTATION NOTE: Everything is implicitly mod 2^16 -- uint16_t's will overflow nicely.
+		a -= StartOfThisBlock;
+		a += LastOfNextBlock;
+		b -= Length * StartOfThisBlock;
+		b += a;
+	}
+
+	// --------------------------------------------------------------------------
+	//
+	// Function
+	//		Name:    RollingChecksum::GetChecksum()
+	//		Purpose: Returns the checksum
+	//		Created: 6/12/03
+	//
+	// --------------------------------------------------------------------------	
+	inline uint32_t GetChecksum()
+	{
+		return ((uint32_t)a) | (((uint32_t)b) << 16);
+	}
+	
+	// Components, just in case they're handy
+	inline uint16_t GetComponent1() {return a;}
+	inline uint16_t GetComponent2() {return b;}
+	
+	// --------------------------------------------------------------------------
+	//
+	// Function
+	//		Name:    RollingChecksum::GetComponentForHashing()
+	//		Purpose: Return the 16 bit component used for hashing and/or quick checks
+	//		Created: 6/12/03
+	//
+	// --------------------------------------------------------------------------
+	inline uint16_t GetComponentForHashing()
+	{
+		return b;
+	}
+	
+	// --------------------------------------------------------------------------
+	//
+	// Function
+	//		Name:    RollingChecksum::ExtractHashingComponent(uint32_t)
+	//		Purpose: Static. Given a full checksum, extract the component used in the hashing table.
+	//		Created: 14/1/04
+	//
+	// --------------------------------------------------------------------------
+	static inline uint16_t ExtractHashingComponent(uint32_t Checksum)
+	{
+		return Checksum >> 16;
+	}
+	
+private:
+	uint16_t a;
+	uint16_t b;
+};
+
+#endif // ROLLINGCHECKSUM__H
+