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diff --git a/src/ceph/src/common/DecayCounter.h b/src/ceph/src/common/DecayCounter.h
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+++ b/src/ceph/src/common/DecayCounter.h
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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software 
+ * Foundation.  See file COPYING.
+ * 
+ */
+
+#ifndef CEPH_DECAYCOUNTER_H
+#define CEPH_DECAYCOUNTER_H
+
+#include "include/utime.h"
+
+/**
+ *
+ * TODO: normalize value based on some fucntion of half_life, 
+ *  so that it can be interpreted as an approximation of a
+ *  moving average of N seconds.  currently, changing half-life
+ *  skews the scale of the value, even at steady state.  
+ *
+ */
+
+class DecayRate {
+  double k;             // k = ln(.5)/half_life
+
+  friend class DecayCounter;
+
+public:
+  DecayRate() : k(0) {}
+  DecayRate(const DecayRate &dr) : k(dr.k) {}
+
+  // cppcheck-suppress noExplicitConstructor
+  DecayRate(double hl) { set_halflife(hl); }
+  void set_halflife(double hl) {
+    k = ::log(.5) / hl;
+  }    
+};
+
+class DecayCounter {
+public:
+  double val;           // value
+  double delta;         // delta since last decay
+  double vel;           // recent velocity
+  utime_t last_decay;   // time of last decay
+  DecayRate rate;
+
+  void encode(bufferlist& bl) const;
+  void decode(const utime_t &t, bufferlist::iterator& p);
+  void dump(Formatter *f) const;
+  static void generate_test_instances(list<DecayCounter*>& ls);
+
+  explicit DecayCounter(const utime_t &now)
+    : val(0), delta(0), vel(0), last_decay(now)
+  {
+  }
+
+  explicit DecayCounter(const utime_t &now, const DecayRate &rate)
+    : val(0), delta(0), vel(0), last_decay(now), rate(rate)
+  {
+  }
+
+  // these two functions are for the use of our dencoder testing infrastructure
+  DecayCounter() : val(0), delta(0), vel(0), last_decay() {}
+
+  void decode(bufferlist::iterator& p) {
+    utime_t fake_time;
+    decode(fake_time, p);
+  }
+
+  /**
+   * reading
+   */
+
+  double get(utime_t now, const DecayRate& rate) {
+    decay(now, rate);
+    return val+delta;
+  }
+  double get(utime_t now) {
+    decay(now, rate);
+    return val+delta;
+  }
+
+  double get_last() {
+    return val;
+  }
+  
+  double get_last_vel() {
+    return vel;
+  }
+
+  utime_t get_last_decay() { 
+    return last_decay; 
+  }
+
+  /**
+   * adjusting
+   */
+
+  double hit(utime_t now, const DecayRate& rate, double v = 1.0) {
+    decay(now, rate);
+    delta += v;
+    return val+delta;
+  }
+  double hit(utime_t now, double v = 1.0) {
+    decay(now, rate);
+    delta += v;
+    return val+delta;
+  }
+
+  void adjust(double a) {
+    val += a;
+  }
+  void adjust(utime_t now, const DecayRate& rate, double a) {
+    decay(now, rate);
+    val += a;
+  }
+  void scale(double f) {
+    val *= f;
+    delta *= f;    
+    vel *= f;
+  }
+
+  /**
+   * decay etc.
+   */
+
+  void reset(utime_t now) {
+    last_decay = now;
+    val = delta = 0;
+  }
+
+  void decay(utime_t now, const DecayRate &rate);
+};
+
+inline void encode(const DecayCounter &c, bufferlist &bl) { c.encode(bl); }
+inline void decode(DecayCounter &c, const utime_t &t, bufferlist::iterator &p) {
+  c.decode(t, p);
+}
+// for dencoder
+inline void decode(DecayCounter &c, bufferlist::iterator &p) {
+  utime_t t;
+  c.decode(t, p);
+}
+
+
+#endif