src/FadingCounter.cc

   1 /*
   2  * Copyright (C) 1996-2020 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #include "squid.h"
  10 #include "base/TextException.h"
  11 #include "Debug.h"
  12 #include "FadingCounter.h"
  13 #include "SquidTime.h"
  14
  15 #include <cmath>
  16
  17 FadingCounter::FadingCounter(): horizon(-1), precision(10), delta(-1),
  18     lastTime(0), total(0)
  19 {
  20     counters.reserve(precision);
  21     while (counters.size() < static_cast<unsigned int>(precision))
  22         counters.push_back(0);
  23 }
  24
  25 void FadingCounter::clear()
  26 {
  27     for (int i = 0; i < precision; ++i)
  28         counters[i] = 0;
  29     lastTime = current_dtime;
  30     total = 0;
  31 }
  32
  33 void FadingCounter::configure(double newHorizon)
  34 {
  35     if (fabs(newHorizon - horizon) >= 1e-3) { // diff exceeds one millisecond
  36         clear(); // for simplicity
  37         horizon = newHorizon;
  38         delta = horizon / precision; // may become negative or zero
  39     }
  40 }
  41
  42 int FadingCounter::count(int howMany)
  43 {
  44     Must(howMany >= 0);
  45
  46     if (delta < 0)
  47         return total += howMany; // forget nothing
  48
  49     if (horizon < 1e-3) // (e.g., zero)
  50         return howMany; // remember nothing
  51
  52     const double deltas = (current_dtime - lastTime) / delta;
  53     if (deltas >= precision || current_dtime < lastTime) {
  54         clear(); // forget all values
  55     } else {
  56         // forget stale values, if any
  57         // fmod() or "current_dtime/delta" will overflow int for small deltas
  58         const int lastSlot = static_cast<int>(fmod(lastTime, horizon) / delta);
  59         const int staleSlots = static_cast<int>(deltas);
  60         for (int i = 0, s = lastSlot + 1; i < staleSlots; ++i, ++s) {
  61             const int idx = s % precision;
  62             total -= counters[idx];
  63             counters[idx] = 0;
  64             Must(total >= 0);
  65         }
  66     }
  67
  68     // apply new information
  69     lastTime = current_dtime;
  70     const int curSlot = static_cast<int>(fmod(lastTime, horizon) / delta);
  71     counters[curSlot % precision] += howMany;
  72     total += howMany;
  73     Must(total >= 0);
  74
  75     return total;
  76 }
  77