text: /**
   * Copyright (c) 2018 Inria
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met: redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer;
   * redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution;
   * neither the name of the copyright holders nor the names of its
   * contributors may be used to endorse or promote products derived from
   * this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * Authors: Daniel Carvalho
   */
  
  /**
   * @file
   * Declaration of a Re-Reference Interval Prediction replacement policy.
   *
   * Not-Recently Used (NRU) is an approximation of LRU that uses a single bit
   * to determine if an entry is going to be re-referenced in the near or distant
   * future.
   *
   * Re-Reference Interval Prediction (RRIP) is an extension of NRU that uses a
   * re-reference prediction value to determine if entries are going to be re-
   * used in the near future or not.
   *
   * The higher the value of the RRPV, the more distant the entry is from its
   * next access.
   *
   * Bimodal Re-Reference Interval Prediction (BRRIP) is an extension of RRIP
   * that has a probability of not inserting entries as the LRU. This probability
   * is controlled by the bimodal throtle parameter (btp).
   *
   * From the original paper, this implementation of RRIP is also called
   * Static RRIP (SRRIP), as it always inserts entries with the same RRPV.
   */
  
  #ifndef __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
  #define __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
  
  #include "mem/cache/replacement_policies/base.hh"
  
  struct BRRIPRPParams;
  
  class BRRIPRP : public BaseReplacementPolicy
  {
    protected:
      /** BRRIP-specific implementation of replacement data. */
      struct BRRIPReplData : ReplacementData
      {
          /**
           * Re-Reference Interval Prediction Value.
           * A value equal to max_RRPV + 1 indicates an invalid entry.
           */
          int rrpv;
  
          /**
           * Default constructor. Invalidate data.
           */
          BRRIPReplData(const int max_RRPV) : rrpv(max_RRPV + 1) {}
      };
  
      /**
       * Maximum Re-Reference Prediction Value possible. An entry with this
       * value as the rrpv has the longest possible re-reference interval,
       * that is, it is likely not to be used in the near future, and is
       * among the best eviction candidates.
       * A maxRRPV of 1 implies in a NRU.
       */
      const int maxRRPV;
  
      /**
       * The hit priority (HP) policy replaces entries that do not receive cache
       * hits over any cache entry that receives a hit, while the frequency
       * priority (FP) policy replaces infrequently re-referenced entries.
       */
      const bool hitPriority;
  
      /**
       * Bimodal throtle parameter. Value in the range [0,100] used to decide
       * if a new entry is inserted with long or distant re-reference.
       */
      const unsigned btp;
  
    public:
      /** Convenience typedef. */
      typedef BRRIPRPParams Params;
  
      /**
       * Construct and initiliaze this replacement policy.
       */
      BRRIPRP(const Params *p);
  
      /**
       * Destructor.
       */
      ~BRRIPRP() {}
  
      /**
       * Invalidate replacement data to set it as the next probable victim.
       * Set RRPV as the the most distant re-reference.
       *
       * @param replacement_data Replacement data to be invalidated.
       */
      void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
                                                                const override;
  
      /**
       * Touch an entry to update its replacement data.
       *
       * @param replacement_data Replacement data to be touched.
       */
      void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
                                                                       override;
  
      /**
       * Reset replacement data. Used when an entry is inserted.
       * Set RRPV according to the insertion policy used.
       *
       * @param replacement_data Replacement data to be reset.
       */
      void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
                                                                       override;
  
      /**
       * Find replacement victim using rrpv.
       *
       * @param cands Replacement candidates, selected by indexing policy.
       * @return Replacement entry to be replaced.
       */
      ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
                                                                       override;
  
      /**
       * Instantiate a replacement data entry.
       *
       * @return A shared pointer to the new replacement data.
       */
      std::shared_ptr<ReplacementData> instantiateEntry() override;
  };
  
  #endif // __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
  