annotate PeakInterpolator.cpp @ 39:822cf7b8e070

Start separating out PeakInterpolator & writing test for it

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
/*
    This file is Copyright (c) 2012 Chris Cannam
  
    Permission is hereby granted, free of charge, to any person
    obtaining a copy of this software and associated documentation
    files (the "Software"), to deal in the Software without
    restriction, including without limitation the rights to use, copy,
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    of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
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    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#include "PeakInterpolator.h"

static double cubicInterpolate(const double y[4], double x)
{
    double a0 = y[3] - y[2] - y[0] + y[1];
    double a1 = y[0] - y[1] - a0;
    double a2 = y[2] - y[0];
    double a3 = y[1];
    return
        a0 * x * x * x +
        a1 * x * x +
        a2 * x +
        a3;
}

double
PeakInterpolator::findPeakLocation(const double *data, int size, int peakIndex)
{
    if (peakIndex < 2 || peakIndex > size - 3) {
        return peakIndex;
    }

    double maxval = 0.0;
    double location = peakIndex;

    const int divisions = 10;
    double y[4];

    y[0] = data[peakIndex-1];
    y[1] = data[peakIndex];
    y[2] = data[peakIndex+1];
    y[3] = data[peakIndex+2];
    for (int i = 0; i < divisions; ++i) {
        double probe = double(i) / double(divisions);
        double value = cubicInterpolate(y, probe);
        if (value > maxval) {
            maxval = value; 
            location = peakIndex + probe;
        }
    }

    y[3] = y[2];
    y[2] = y[1];
    y[1] = y[0];
    y[0] = data[peakIndex-2];
    for (int i = 0; i < divisions; ++i) {
        double probe = double(i) / double(divisions);
        double value = cubicInterpolate(y, probe);
        if (value > maxval) {
            maxval = value; 
            location = peakIndex - 1 + probe;
        }
    }

    return location;
}