mirror of
https://github.com/darlinghq/darling-WTF.git
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114 lines
3.1 KiB
C++
114 lines
3.1 KiB
C++
/*
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* Copyright (C) 2012, 2016 Apple Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <wtf/MathExtras.h>
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#include <wtf/StdLibExtras.h>
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namespace WTF {
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// Simple and cheap way of tracking statistics if you're not worried about chopping on
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// the sum of squares (i.e. the sum of squares is unlikely to exceed 2^52).
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class SimpleStats {
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WTF_MAKE_FAST_ALLOCATED;
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public:
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SimpleStats()
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: m_count(0)
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, m_sum(0)
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, m_sumOfSquares(0)
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{
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}
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void add(double value)
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{
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m_count++;
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m_sum += value;
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m_sumOfSquares += value * value;
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}
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explicit operator bool() const
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{
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return !!m_count;
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}
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double count() const
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{
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return m_count;
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}
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double sum() const
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{
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return m_sum;
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}
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double sumOfSquares() const
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{
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return m_sumOfSquares;
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}
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double mean() const
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{
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return m_sum / m_count;
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}
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// NB. This gives a biased variance as it divides by the number of samples rather
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// than the degrees of freedom. This is fine once the count grows large, which in
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// our case will happen rather quickly.
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double variance() const
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{
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if (m_count < 2)
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return 0;
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// Compute <x^2> - <x>^2
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double secondMoment = m_sumOfSquares / m_count;
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double firstMoment = m_sum / m_count;
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double result = secondMoment - firstMoment * firstMoment;
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// It's possible to get -epsilon. Protect against this and turn it into
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// +0.
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if (result <= 0)
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return 0;
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return result;
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}
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// NB. This gives a biased standard deviation. See above.
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double standardDeviation() const
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{
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return sqrt(variance());
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}
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private:
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double m_count;
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double m_sum;
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double m_sumOfSquares;
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};
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} // namespace WTF
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using WTF::SimpleStats;
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