BLI_probing_strategies.hh

Go to the documentation of this file.

/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#pragma once
 
#include <numeric>
 
#include <limits>
 
#include "BLI_sys_types.h"
 
namespace blender {
 
class LinearProbingStrategy {
 private:
  uint64_t hash_;
 
 public:
  LinearProbingStrategy(const uint64_t hash) : hash_(hash) {}
 
  void next()
  {
    hash_++;
  }
 
  uint64_t get() const
  {
    return hash_;
  }
 
  int64_t linear_steps() const
  {
    return std::numeric_limits<int64_t>::max();
  }
};
 
class QuadraticProbingStrategy {
 private:
  uint64_t original_hash_;
  uint64_t current_hash_;
  uint64_t iteration_;
 
 public:
  QuadraticProbingStrategy(const uint64_t hash)
      : original_hash_(hash), current_hash_(hash), iteration_(1)
  {
  }
 
  void next()
  {
    current_hash_ = original_hash_ + ((iteration_ * iteration_ + iteration_) >> 1);
    iteration_++;
  }
 
  uint64_t get() const
  {
    return current_hash_;
  }
 
  int64_t linear_steps() const
  {
    return 1;
  }
};
 
template<uint64_t LinearSteps = 1, bool PreShuffle = false> class PythonProbingStrategy {
 private:
  uint64_t hash_;
  uint64_t perturb_;
 
 public:
  PythonProbingStrategy(const uint64_t hash) : hash_(hash), perturb_(hash)
  {
    if (PreShuffle) {
      this->next();
    }
  }
 
  void next()
  {
    perturb_ >>= 5;
    hash_ = 5 * hash_ + 1 + perturb_;
  }
 
  uint64_t get() const
  {
    return hash_;
  }
 
  int64_t linear_steps() const
  {
    return LinearSteps;
  }
};
 
template<uint64_t LinearSteps = 2, bool PreShuffle = false> class ShuffleProbingStrategy {
 private:
  uint64_t hash_;
  uint64_t perturb_;
 
 public:
  ShuffleProbingStrategy(const uint64_t hash) : hash_(hash), perturb_(hash)
  {
    if (PreShuffle) {
      this->next();
    }
  }
 
  void next()
  {
    if (perturb_ != 0) {
      perturb_ >>= 10;
      hash_ = ((hash_ >> 16) ^ hash_) * 0x45d9f3b + perturb_;
    }
    else {
      hash_ = 5 * hash_ + 1;
    }
  }
 
  uint64_t get() const
  {
    return hash_;
  }
 
  int64_t linear_steps() const
  {
    return LinearSteps;
  }
};
 
using DefaultProbingStrategy = PythonProbingStrategy<>;
 
/* Turning off clang format here, because otherwise it will mess up the alignment between the
 * macros. */
// clang-format off
 
#define SLOT_PROBING_BEGIN(PROBING_STRATEGY, HASH, MASK, R_SLOT_INDEX) \
  PROBING_STRATEGY probing_strategy(HASH); \
  do { \
    int64_t linear_offset = 0; \
    uint64_t current_hash = probing_strategy.get(); \
    do { \
      int64_t R_SLOT_INDEX = int64_t((current_hash + uint64_t(linear_offset)) & MASK);
 
#define SLOT_PROBING_END() \
    } while (++linear_offset < probing_strategy.linear_steps()); \
    probing_strategy.next(); \
  } while (true)
 
// clang-format on
 
}  // namespace blender