stats.h

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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#ifndef SBITS_STATS_H_INCLUDED
#define SBITS_STATS_H_INCLUDED
 
#include <cstdlib>
 
namespace sbit
{
 
class Stats
{
public:
   void reset() noexcept
   {
      m_count = 0;
   }
 
   void observe(double value) noexcept
   {
      ++m_count;
 
      if (1 == m_count)
      {
         m_mean = value;
      }
      else
      {
         const double oldMean     = m_mean;
         const double oldVariance = m_variance;
 
         m_mean     = oldMean + (value - oldMean) / m_count;
         m_variance = oldVariance + (value - oldMean) * (value - m_mean);
      }
   }
 
   size_t getCount() const noexcept
   {
      return m_count;
   }
 
   double getMean() const noexcept
   {
      return m_mean;
   }
 
   double getVariance() const noexcept
   {
      if (m_count > 1)
      {
         return m_variance / static_cast<double>(m_count - 1);
      }
 
      return 0.0;
   }
 
private:
   size_t m_count = 0;
 
   double m_mean     = 0.0;
   double m_variance = 0.0;
};
 
} // namespace sbit
 
#endif // SBITS_STATS_H_INCLUDED