search_move_ordering.H

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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  SOFTWARE.
*/
 
# ifndef SEARCH_MOVE_ORDERING_H
# define SEARCH_MOVE_ORDERING_H
 
#include <concepts>
#include <cstddef>
#include <optional>
#include <utility>
 
#include <tpl_array.H>
#include <tpl_hash.H>
#include <tpl_sort_utils.H>
 
namespace Aleph {
 
enum class MoveOrderingMode
{
  Domain,           
  Estimated_Score,  
  Estimated_Bound   
};
 
struct MoveOrderingStats
{
  size_t ordered_batches = 0;     
  size_t ordered_moves = 0;       
  size_t priority_estimates = 0;  
  size_t killer_hits = 0;         
  size_t history_hits = 0;        
};
 
template <typename Move, typename Priority>
struct RankedMove
{
  Move move;  
  Priority priority
    = Priority{};            
  size_t ordinal = 0;        
  bool killer = false;       
  size_t history_score = 0;  
};
 
template <typename Move, bool Supported = std::equality_comparable<Move>>
class Killer_Move_Table;
 
template <typename Move>
class Killer_Move_Table<Move, false>
{
public:
  static constexpr bool supported = false;
 
  static void clear() noexcept
  {
    // empty
  }
 
  [[nodiscard]] static bool is_killer(const size_t, const Move &) noexcept
  {
    return false;
  }
 
  static void record(const size_t, const Move &) noexcept
  {
    // empty
  }
};
 
template <typename Move>
class Killer_Move_Table<Move, true>
{
public:
  static constexpr bool supported = true;
 
  void clear() noexcept
  {
    primary_.empty();
    secondary_.empty();
  }
 
  [[nodiscard]] bool is_killer(const size_t depth, const Move &move) const noexcept
  {
    return depth < primary_.size()
       and ((primary_[depth].has_value() and *primary_[depth] == move)
            or (secondary_[depth].has_value() and *secondary_[depth] == move));
  }
 
  void record(const size_t depth, const Move &move)
  {
    ensure_depth(depth + 1);
    if (primary_[depth].has_value() and *primary_[depth] == move)
      return;
 
    secondary_[depth] = primary_[depth];
    primary_[depth] = move;
  }
 
private:
  void ensure_depth(const size_t required)
  {
    while (primary_.size() < required)
      {
        primary_.append(std::optional<Move>{});
        secondary_.append(std::optional<Move>{});
      }
  }
 
  Array<std::optional<Move>> primary_;
  Array<std::optional<Move>> secondary_;
};
 
struct Null_History_Heuristic_Table
{
  static constexpr bool supported = false;
 
  static void clear() noexcept
  {
    // empty
  }
 
  template <typename Key>
  [[nodiscard]] static size_t score(const Key &) noexcept
  {
    return 0;
  }
 
  template <typename Key>
  static void record(const Key &, const size_t = 1) noexcept
  {
    // empty
  }
};
 
template <typename Key,
          template <typename, typename, class> class HashMapTable = MapOLhash,
          class Cmp = Aleph::equal_to<Key>>
class History_Heuristic_Table
{
public:
  static constexpr bool supported = true;
  using Key_Type = Key;
  using Map_Type = DynHashMap<Key, size_t, HashMapTable, Cmp>;
 
  void clear() noexcept
  {
    table_.empty();
  }
 
  [[nodiscard]] size_t score(const Key &key) const noexcept
  {
    if (auto *entry = table_.search(key); entry != nullptr)
      return entry->second;
 
    return 0;
  }
 
  void record(const Key &key, const size_t bonus = 1)
  {
    if (auto *entry = table_.search(key); entry != nullptr)
      {
        entry->second += bonus;
        return;
      }
 
    (void) table_.insert(key, bonus);
  }
 
private:
  Map_Type table_;
};
 
template <typename Move, typename Priority, typename BetterPriority>
void sort_ranked_moves(Array<RankedMove<Move, Priority>> &moves,
                       BetterPriority better_priority,
                       const bool prefer_killer,
                       const bool prefer_history)
{
  if (moves.size() < 2)
    return;
 
  introsort(moves,
            [=](const RankedMove<Move, Priority> &lhs, const RankedMove<Move, Priority> &rhs) noexcept
  {
    if (prefer_killer and lhs.killer != rhs.killer)
      return lhs.killer and not rhs.killer;
 
    if (prefer_history and lhs.history_score != rhs.history_score)
      return lhs.history_score > rhs.history_score;
 
    if (better_priority(lhs.priority, rhs.priority))
      return true;
 
    if (better_priority(rhs.priority, lhs.priority))
      return false;
 
    return lhs.ordinal < rhs.ordinal;
  });
}
 
}  // end namespace Aleph
 
# endif  // SEARCH_MOVE_ORDERING_H