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diff --git a/engine/audio/private/circularbuffer.h b/engine/audio/private/circularbuffer.h
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+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: Defines an interface for circular buffers. Data can be written to
+//			and read from these buffers as though from a file. When it is 
+//			write-overflowed (you write more data in than the buffer can hold),
+//			the read pointer is advanced to allow the new data to be written.
+//			This means old data will be discarded if you write too much data
+//			into the buffer.
+//
+//	MikeD:	Moved all the functions into a class.
+//			Changed it so when the buffer overflows, the old data
+//			is discarded rather than the new.
+//
+//=====================================================================================//
+
+#ifndef CIRCULARBUFFER_H
+#define CIRCULARBUFFER_H
+
+#pragma once
+
+class CCircularBuffer
+{
+public:
+						CCircularBuffer();
+						CCircularBuffer( int size );
+	void				SetSize( int nSize );
+
+protected:
+	inline void			AssertValid()
+	{
+#ifdef _DEBUG
+		Assert( this );
+		Assert( m_nSize > 0 );
+		Assert( m_nCount >= 0 );
+		Assert( m_nCount <= m_nSize );
+		Assert( m_nWrite < m_nSize );
+
+		// Verify that m_nCount is correct.
+		if( m_nRead == m_nWrite )
+		{
+			Assert( m_nCount == 0 || m_nCount == m_nSize );
+		}
+		else
+		{
+			int testCount=0;
+			if ( m_nRead < m_nWrite )
+				testCount = m_nWrite - m_nRead;
+			else
+				testCount = (m_nSize - m_nRead) + m_nWrite;
+
+			Assert( testCount == m_nCount );
+		}
+#endif
+	}
+
+public:
+
+	void				Flush();
+	int					GetSize();					// Get the size of the buffer (how much can you write without reading
+													// before losing data.
+	
+	int					GetWriteAvailable();		// Get the amount available to write without overflowing.
+													// Note: you can write however much you want, but it may overflow,
+													// in which case the newest data is kept and the oldest is discarded.
+	
+	int					GetReadAvailable();			// Get the amount available to read.
+	
+	int					GetMaxUsed();
+	int					Peek(char *pchDest, int nCount);
+	int					Advance(int nCount);
+	int					Read(void *pchDest, int nCount);
+	int					Write(void *pchData, int nCount);
+
+public:
+	int		m_nCount;			// Space between the read and write pointers (how much data we can read).
+	
+	int		m_nRead;			// Read index into circular buffer
+	int		m_nWrite;			// Write index into circular buffer
+	
+	int		m_nSize;			// Size of circular buffer in bytes (how much data it can hold).
+	char	m_chData[1];		// Circular buffer holding data
+};
+
+
+// Use this to instantiate a CircularBuffer.
+template< int size >
+class CSizedCircularBuffer : public CCircularBuffer
+{
+public:
+	CSizedCircularBuffer() : CCircularBuffer(size) {}
+
+private:
+	char	myData[size-1];
+};
+
+CCircularBuffer *AllocateCircularBuffer( int nSize );
+void FreeCircularBuffer( CCircularBuffer *pCircularBuffer );
+
+#endif // CIRCULARBUFFER_H
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