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29 #include <wtf/MathExtras.h>
30 #include <wtf/StdLibExtras.h>
34 // Simple and cheap way of tracking statistics if you're not worried about chopping on
35 // the sum of squares (i.e. the sum of squares is unlikely to exceed 2^52).
45 void add(double value)
49 m_sumOfSquares += value * value;
52 bool operator!() const
67 double sumOfSquares() const
69 return m_sumOfSquares;
74 return m_sum / m_count;
77 // NB. This gives a biased variance as it divides by the number of samples rather
78 // than the degrees of freedom. This is fine once the count grows large, which in
79 // our case will happen rather quickly.
80 double variance() const
85 // Compute <x^2> - <x>^2
86 double secondMoment = m_sumOfSquares / m_count;
87 double firstMoment = m_sum / m_count;
89 double result = secondMoment - firstMoment * firstMoment;
91 // It's possible to get -epsilon. Protect against this and turn it into
99 // NB. This gives a biased standard deviation. See above.
100 double standardDeviation() const
102 return sqrt(variance());
108 double m_sumOfSquares;
113 #endif // SimpleStats_h