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/* SPDX-License-Identifier: BSD-2-Clause */
/*
* Copyright (C) 2019, Raspberry Pi Ltd
*
* histogram.cpp - histogram calculations
*/
#include <math.h>
#include <stdio.h>
#include "histogram.h"
using namespace RPiController;
uint64_t Histogram::cumulativeFreq(double bin) const
{
if (bin <= 0)
return 0;
else if (bin >= bins())
return total();
int b = (int)bin;
return cumulative_[b] +
(bin - b) * (cumulative_[b + 1] - cumulative_[b]);
}
double Histogram::quantile(double q, int first, int last) const
{
if (first == -1)
first = 0;
if (last == -1)
last = cumulative_.size() - 2;
assert(first <= last);
uint64_t items = q * total();
while (first < last) /* binary search to find the right bin */
{
int middle = (first + last) / 2;
if (cumulative_[middle + 1] > items)
last = middle; /* between first and middle */
else
first = middle + 1; /* after middle */
}
assert(items >= cumulative_[first] && items <= cumulative_[last + 1]);
double frac = cumulative_[first + 1] == cumulative_[first] ? 0
: (double)(items - cumulative_[first]) /
(cumulative_[first + 1] - cumulative_[first]);
return first + frac;
}
double Histogram::interQuantileMean(double qLo, double qHi) const
{
assert(qHi > qLo);
double pLo = quantile(qLo);
double pHi = quantile(qHi, (int)pLo);
double sumBinFreq = 0, cumulFreq = 0;
for (double pNext = floor(pLo) + 1.0; pNext <= ceil(pHi);
pLo = pNext, pNext += 1.0) {
int bin = floor(pLo);
double freq = (cumulative_[bin + 1] - cumulative_[bin]) *
(std::min(pNext, pHi) - pLo);
sumBinFreq += bin * freq;
cumulFreq += freq;
}
/* add 0.5 to give an average for bin mid-points */
return sumBinFreq / cumulFreq + 0.5;
}
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