sdrangel/sdrbase/util/interpolation.h

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3.2 KiB
C++

///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2021 Jon Beniston, M7RCE //
// //
// 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 as 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 V3 for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program. If not, see <http://www.gnu.org/licenses/>. //
///////////////////////////////////////////////////////////////////////////////////
#ifndef INCLUDE_INTERPOLATION_H
#define INCLUDE_INTERPOLATION_H
#include "export.h"
#include <iterator>
class SDRBASE_API Interpolation {
public:
// Linear interpolation/extrapolation
// Assumes x is sorted in increasing order
template<class Iter, class T>
static T linear(Iter xBegin, Iter xEnd, Iter yBegin, T x)
{
// Find first point in x that target is bigger than
int i = 0;
while (xBegin != xEnd)
{
if (x < *xBegin) {
break;
}
++xBegin;
i++;
}
T x0, x1, y0, y1;
if (i == 0) {
// Extrapolate left
x0 = *xBegin;
++xBegin;
x1 = *xBegin;
y0 = *yBegin;
++yBegin;
y1 = *yBegin;
return extrapolate(x0, y0, x1, y1, x);
} else if (xBegin > xEnd) {
// Extrapolate right
Iter xCur = xBegin;
std::advance(xCur, i - 2);
x0 = *xCur;
++xCur;
x1 = *xCur;
Iter yCur = yBegin;
std::advance(yCur, i - 2);
y0 = *yCur;
++yCur;
y1 = *yCur;
return extrapolate(x0, y0, x1, y1, x);
} else {
// Interpolate
x1 = *xBegin;
--xBegin;
x0 = *xBegin;
Iter yCur = yBegin;
std::advance(yCur, i - 1);
y0 = *yCur;
++yCur;
y1 = *yCur;
return interpolate(x0, y0, x1, y1, x);
}
}
// Linear extrapolation
template<class T>
static T extrapolate(T x0, T y0, T x1, T y1, T x)
{
return y0 + ((x-x0)/(x1-x0)) * (y1-y0);
}
// Linear interpolation
template<class T>
static T interpolate(T x0, T y0, T x1, T y1, T x)
{
return (y0*(x1-x) + y1*(x-x0)) / (x1-x0);
}
};
#endif // INCLUDE_INTERPOLATION_H