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diff --git a/public/movieobjects/dmeexpressionoperator.h b/public/movieobjects/dmeexpressionoperator.h
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+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// The expression operator class - scalar math calculator
+// for a good list of operators and simple functions, see:
+//   \\fileserver\user\MarcS\boxweb\aliveDistLite\v4.2.0\doc\alive\functions.txt
+// (although we'll want to implement elerp as the standard 3x^2 - 2x^3 with rescale)
+//
+//=============================================================================
+
+#ifndef DMEEXPRESSIONOPERATOR_H
+#define DMEEXPRESSIONOPERATOR_H
+#ifdef _WIN32
+#pragma once
+#endif
+
+#include "movieobjects/dmeoperator.h"
+#include "tier1/utlstack.h" // for calculator
+#include "tier1/utlvector.h" // for calculator
+
+
+//-----------------------------------------------------------------------------
+// Calculator Parsing class
+// precedence order:
+//		unary operators: + - ! func var
+//		* / %
+//		+ -
+//		< > <= >=
+//		== !=
+//		&&
+//		||
+//		?:
+//-----------------------------------------------------------------------------
+class CExpressionCalculator
+{
+public:
+	CExpressionCalculator( const char *expr = NULL ) : m_expr( expr ) {}
+	void SetExpression( const char *expr ) 
+	{
+		m_expr = expr;
+	}
+
+	void SetVariable( const char *var, float value );
+	void SetVariable( int nVariableIndex, float value );
+	int FindVariableIndex( const char *var );
+
+	bool Evaluate( float &value );
+
+	// Builds a list of variable names from the expression
+	bool BuildVariableListFromExpression( );
+
+	// Iterate over variables
+	int VariableCount();
+	const char *VariableName( int nIndex );
+
+private:
+	bool ParseExpr		 ( const char *&expr );
+	bool ParseConditional( const char *&expr );
+	bool ParseOr		 ( const char *&expr );
+	bool ParseAnd		 ( const char *&expr );
+	bool ParseEquality	 ( const char *&expr );
+	bool ParseLessGreater( const char *&expr );
+	bool ParseAddSub	 ( const char *&expr );
+	bool ParseDivMul	 ( const char *&expr );
+	bool ParseUnary		 ( const char *&expr );
+	bool ParsePrimary	 ( const char *&expr );
+	bool Parse1ArgFunc	 ( const char *&expr );
+	bool Parse2ArgFunc	 ( const char *&expr );
+	bool Parse3ArgFunc	 ( const char *&expr );
+	//	bool Parse4ArgFunc	 ( const char *&expr );
+	bool Parse5ArgFunc	 ( const char *&expr );
+
+	CUtlString m_expr;
+	CUtlVector< CUtlString > m_varNames;
+	CUtlVector<float> m_varValues;
+	CUtlStack<float> m_stack;
+	bool m_bIsBuildingArgumentList;
+};
+
+
+//-----------------------------------------------------------------------------
+// An operator which computes the value of expressions 
+//-----------------------------------------------------------------------------
+class CDmeExpressionOperator : public CDmeOperator
+{
+	DEFINE_ELEMENT( CDmeExpressionOperator, CDmeOperator );
+
+public:
+	virtual void Operate();
+
+	virtual void GetInputAttributes ( CUtlVector< CDmAttribute * > &attrs );
+	virtual void GetOutputAttributes( CUtlVector< CDmAttribute * > &attrs );
+
+	void		SetSpewResult( bool state );
+
+protected:
+	bool Parse( const char *expr );
+
+	bool IsInputAttribute( CDmAttribute *pAttribute );
+
+	CDmaVar< float > m_result;
+	CDmaString    m_expr;
+	CDmaVar< bool >  m_bSpewResult;
+};
+
+
+#endif // DMEEXPRESSIONOPERATOR_H