mxs-1777: maxutils additions

Adding classes for calculating averages. Update StopWatch to C++11.

maxutils/maxbase/include/maxbase/average.hh

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2018 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+#pragma once
+
+#include <maxbase/ccdefs.hh>
+
+#include <vector>
+
+namespace maxbase
+{
+/** Regular average, but calculated cumulatively. */
+class CumulativeAverage
+{
+public:
+    // add an average made of num_samples
+    void   add(double ave, int num_samples = 1);
+    double average() const;
+    int    num_samples() const;
+    void   reset();
+    CumulativeAverage& operator+=(const CumulativeAverage& rhs);
+    CumulativeAverage operator+(const CumulativeAverage& rhs) const;
+private:
+    double m_ave = 0;
+    int    m_num_samples = 0;
+    int    m_num_last_added = 0;
+};
+
+/** Exponential Moving Average. */
+class EMAverage
+{
+public:
+    EMAverage(double min_alpha, double max_alpha, int sample_max);
+
+    /* add an average made of num_samples
+    *  alpha = m_min_alpha + m_max_alpha * std::min(double(num_samples) / sample_max, 1.0);
+    *  ave = alpha * ave + (1 - alpha) * sample; */
+    void   add(double ave, int num_samples = 1);
+    void   add(const CumulativeAverage& ca);
+    double average() const;
+    int    num_samples() const;
+    void   set_sample_max(int sample_max);
+    int    sample_max() const;
+    void   reset();
+private:
+    const double  m_min_alpha;
+    const double  m_max_alpha;
+    int     m_sample_max;
+    int     m_num_samples = 0;
+    double  m_ave = 0;
+};
+
+} // maxbase