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/*
dsp/ChebyshevPoly.h
Copyright 2001-2012 Tim Goetze <tim@quitte.de>
http://quitte.de/dsp/
Chebyshev polynomial calculation.
*/
/*
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 3
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_CHEBYSHEV_POLY_H
#define DSP_CHEBYSHEV_POLY_H
namespace DSP {
template <int N> /* number of harmonics */
class ChebPoly
{
public:
float c[N];
double process (sample_t x)
{
int n = N-1;
double y = c[n];
while (n > 0)
y *= x,
y += c[--n];
return y;
}
/* Showing results for cheap pc
* Search instead for chebpc
*
* right on, googlebots!
*/
void calculate (float * amplitudes)
{
float sv, dd[N], a[N];
for (int i=0; i < N; ++i)
{
/* adjust amplitudes -- not quite sure about this.
if (amplitudes[i])
a[i] = amplitudes[i] * sqrt (1./fabs(amplitudes[i]));
else
a[i] = amplitudes[i];
*/
a[i] = amplitudes[i];
c[i] = dd[i] = 0;
}
c[0] = a[N-1];
for (int j = N-2; j >= 1; --j)
{
for (int k = N-j; k >= 1; --k)
{
sv = c[k];
c[k] = 2*c[k-1] - dd[k];
dd[k] = sv;
}
sv = c[0];
c[0] = -dd[0] + a[j];
dd[0] = sv;
}
for (int j = N-1; j >= 1; --j)
c[j] = c[j-1] - dd[j];
c[0] = -dd[0] + .5*a[0];
}
};
}; /* namespace DSP */
#endif /* DSP_CHEBYSHEV_POLY_H */
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