BiQuad.h

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/*
        dsp/BiQuad.h
        
        Copyright 2003-7 Tim Goetze <tim@quitte.de>
        
        http://quitte.de/dsp/
 
        Bi-quad IIR filter.
 
*/
/*
        This program is free software; you can redistribute it and/or
        modify it under the terms of the GNU General Public License
        as published by the Free Software Foundation; either version 2
        of the License, or (at your option) any later version.
 
        This program is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        GNU General Public License for more details.
 
        You should have received a copy of the GNU General Public License
        along with this program; if not, write to the Free Software
        Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
        02111-1307, USA or point your web browser to http://www.gnu.org.
*/
 
#ifndef _DSP_BI_QUAD_H_
#define _DSP_BI_QUAD_H_
 
namespace DSP {
 
class BiQuad
{
        public:
                /* coefficients */
                sample_t a[3], b[3];
 
                /* history */
                int h;
                sample_t x[2], y[2];
 
                BiQuad()
                        {
                                unity();
                                reset();
                        }
                
                void unity()
                        {
                                a[0] = 1;
                                a[1] = a[2] = b[0] = b[1] = b[2] = 0;
                        }
 
                void copy (BiQuad & bq)
                        {
                                for (int i = 0; i < 3; ++i)
                                        a[i] = bq.a[i],
                                        b[i] = bq.b[i];
                        }
 
                void reset()
                        {
                                h = 0;
 
                                x[0] = x[1] = 
                                y[0] = y[1] = 0.;
                        }
 
                /* denormal zapping */
                void flush_0()
                        {
                                for (int i = 0; i < 2; ++i)
                                        if (is_denormal (y[i]))
                                                y[i] = 0;
                        }
 
                inline sample_t process (sample_t s)
                        {
                                int z = h;
 
                                sample_t r = s * a[0];
                                
                                r += a[1] * x[z];
                                r += b[1] * y[z];
 
                                z ^= 1;
                                r += a[2] * x[z];
                                r += b[2] * y[z];
 
                                y[z] = r;
                                x[z] = s;
                                
                                h = z;
 
                                return r;
                        }
 
                /* Following are additional methods for using the biquad to filter an
                 * upsampled signal with 0 padding -- some terms reduce to 0 in this
                 * case */
                inline sample_t process_0_1()
                        {
                                int z = h;
 
                                sample_t r = 0;
                                
                                r += a[1] * x[z];
                                r += b[1] * y[z];
 
                                z ^= 1;
                                r += a[2] * x[z];
                                r += b[2] * y[z];
 
                                y[z] = r;
                                x[z] = 0; 
                                
                                h = z;
 
                                return r;
                        }
 
                inline sample_t process_0_2()
                        {
                                int z = h;
 
                                sample_t r = 0;
                                
                                r += b[1] * y[z];
 
                                z ^= 1;
                                r += a[2] * x[z];
                                r += b[2] * y[z];
 
                                y[z] = r;
                                x[z] = 0;
                                
                                h = z;
 
                                return r;
                        }
 
                inline sample_t process_0_3()
                        {
                                int z = h;
 
                                sample_t r = 0;
                                
                                r += b[1] * y[z];
 
                                z ^= 1;
                                r += b[2] * y[z];
 
                                y[z] = r;
                                x[z] = 0;
                                
                                h = z;
 
                                return r;
                        }
};
 
} /* namespace DSP */
 
#endif /* _DSP_BI_QUAD_H_ */