Move DecayingSample to algorithm

src/ripple/algorithm/api/DecayingSample.h

@@ -0,0 +1,96 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2012, 2013 Ripple Labs Inc.
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef RIPPLE_ALGORITHM_DECAYINGSAMPLE_H_INCLUDED
+#define RIPPLE_ALGORITHM_DECAYINGSAMPLE_H_INCLUDED
+
+namespace ripple {
+
+/** Sampling function using exponential decay to provide a continuous value. */
+template <int Window,
+          typename Value = int,
+          typename Elapsed = int>
+class DecayingSample
+{
+public:
+    typedef Value   value_type;
+    typedef Elapsed elapsed_type;
+
+    /** Create a default constructed sample. */
+    DecayingSample ()
+        : m_value (value_type())
+        , m_when (elapsed_type())
+    {
+    }
+
+    /** Add a new sample.
+        The value is first aged according to the specified time.
+    */
+    Value add (value_type value, elapsed_type now)
+    {
+        decay (now);
+        m_value += value;
+        return m_value / Window;
+    }
+
+    /** Retrieve the current value in normalized units.
+        The samples are first aged according to the specified time.
+    */
+    Value value (elapsed_type now)
+    {
+        decay (now);
+        return m_value / Window;
+    }
+
+private:
+    // Apply exponential decay based on the specified time.
+    void decay (elapsed_type now)
+    {
+        if (now == m_when)
+            return;
+
+        if (m_value != value_type())
+        {
+            elapsed_type n (now - m_when);
+
+            // A span larger than four times the window decays the
+            // value to an insignificant amount so just reset it.
+            //
+            if (n > 4 * Window)
+                m_value = value_type();
+            else
+            {
+                while (n--)
+                    m_value -= (m_value + Window - 1) / Window;
+            }
+        }
+
+        m_when = now;
+    }
+
+    // Current value in exponential units
+    value_type m_value;
+
+    // Last time the aging function was applied
+    elapsed_type m_when;
+};
+
+}
+
+#endif