C++ class implementation of RBJ Filters

References : Posted by arguru[AT]smartelectronix[DOT]com
Linked file : CFxRbjFilter.h
(this linked file is included below)
Notes :
[WARNING: This code is not FPU undernormalization safe!]
Linked files
class CFxRbjFilter
{
public:
	
	CFxRbjFilter()
	{
		// reset filter coeffs
		b0a0=b1a0=b2a0=a1a0=a2a0=0.0;
		
		// reset in/out history
		ou1=ou2=in1=in2=0.0f;	
	};

	float filter(float in0)
	{
		// filter
		float const yn = b0a0*in0 + b1a0*in1 + b2a0*in2 - a1a0*ou1 - a2a0*ou2;

		// push in/out buffers
		in2=in1;
		in1=in0;
		ou2=ou1;
		ou1=yn;

		// return output
		return yn;
	};

	void calc_filter_coeffs(int const type,double const frequency,double const sample_rate,double const q,double const db_gain,bool q_is_bandwidth)
	{
		// temp pi
		double const temp_pi=3.1415926535897932384626433832795;
		
		// temp coef vars
		double alpha,a0,a1,a2,b0,b1,b2;

		// peaking, lowshelf and hishelf
		if(type>=6)
		{
			double const A		=	pow(10.0,(db_gain/40.0));
			double const omega	=	2.0*temp_pi*frequency/sample_rate;
			double const tsin	=	sin(omega);
			double const tcos	=	cos(omega);
			
			if(q_is_bandwidth)
			alpha=tsin*sinh(log(2.0)/2.0*q*omega/tsin);
			else
			alpha=tsin/(2.0*q);

			double const beta	=	sqrt(A)/q;
			
			// peaking
			if(type==6)
			{
				b0=float(1.0+alpha*A);
				b1=float(-2.0*tcos);
				b2=float(1.0-alpha*A);
				a0=float(1.0+alpha/A);
				a1=float(-2.0*tcos);
				a2=float(1.0-alpha/A);
			}
			
			// lowshelf
			if(type==7)
			{
				b0=float(A*((A+1.0)-(A-1.0)*tcos+beta*tsin));
				b1=float(2.0*A*((A-1.0)-(A+1.0)*tcos));
				b2=float(A*((A+1.0)-(A-1.0)*tcos-beta*tsin));
				a0=float((A+1.0)+(A-1.0)*tcos+beta*tsin);
				a1=float(-2.0*((A-1.0)+(A+1.0)*tcos));
				a2=float((A+1.0)+(A-1.0)*tcos-beta*tsin);
			}

			// hishelf
			if(type==8)
			{
				b0=float(A*((A+1.0)+(A-1.0)*tcos+beta*tsin));
				b1=float(-2.0*A*((A-1.0)+(A+1.0)*tcos));
				b2=float(A*((A+1.0)+(A-1.0)*tcos-beta*tsin));
				a0=float((A+1.0)-(A-1.0)*tcos+beta*tsin);
				a1=float(2.0*((A-1.0)-(A+1.0)*tcos));
				a2=float((A+1.0)-(A-1.0)*tcos-beta*tsin);
			}
		}
		else
		{
			// other filters
			double const omega	=	2.0*temp_pi*frequency/sample_rate;
			double const tsin	=	sin(omega);
			double const tcos	=	cos(omega);

			if(q_is_bandwidth)
			alpha=tsin*sinh(log(2.0)/2.0*q*omega/tsin);
			else
			alpha=tsin/(2.0*q);

			
			// lowpass
			if(type==0)
			{
				b0=(1.0-tcos)/2.0;
				b1=1.0-tcos;
				b2=(1.0-tcos)/2.0;
				a0=1.0+alpha;
				a1=-2.0*tcos;
				a2=1.0-alpha;
			}

			// hipass
			if(type==1)
			{
				b0=(1.0+tcos)/2.0;
				b1=-(1.0+tcos);
				b2=(1.0+tcos)/2.0;
				a0=1.0+ alpha;
				a1=-2.0*tcos;
				a2=1.0-alpha;
			}

			// bandpass csg
			if(type==2)
			{
				b0=tsin/2.0;
				b1=0.0;
			    b2=-tsin/2;
				a0=1.0+alpha;
				a1=-2.0*tcos;
				a2=1.0-alpha;
			}

			// bandpass czpg
			if(type==3)
			{
				b0=alpha;
				b1=0.0;
				b2=-alpha;
				a0=1.0+alpha;
				a1=-2.0*tcos;
				a2=1.0-alpha;
			}

			// notch
			if(type==4)
			{
				b0=1.0;
				b1=-2.0*tcos;
				b2=1.0;
				a0=1.0+alpha;
				a1=-2.0*tcos;
				a2=1.0-alpha;
			}

			// allpass
			if(type==5)
			{
				b0=1.0-alpha;
				b1=-2.0*tcos;
				b2=1.0+alpha;
				a0=1.0+alpha;
				a1=-2.0*tcos;
				a2=1.0-alpha;
			}
		}

		// set filter coeffs
		b0a0=float(b0/a0);
		b1a0=float(b1/a0);
		b2a0=float(b2/a0);
		a1a0=float(a1/a0);
		a2a0=float(a2/a0);
	};

private:

	// filter coeffs
	float b0a0,b1a0,b2a0,a1a0,a2a0;

	// in/out history
	float ou1,ou2,in1,in2;
};