ca-metrics.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
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
#ifndef CA_METRICS_H
#define CA_METRICS_H
 
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <type_traits>
 
#include <ah-errors.H>
#include <tpl_array.H>
 
#include <ca-traits.H>
#include <tpl_ca_concepts.H>
 
namespace Aleph {
namespace CA {
 
namespace ca_metrics_detail {
 
inline constexpr std::uint64_t fnv_basis = 14695981039346656037ull;
inline constexpr std::uint64_t fnv_prime = 1099511628211ull;
 
inline constexpr std::uint64_t fnv1a_step(std::uint64_t h, const std::uint8_t b) noexcept
{
  h ^= static_cast<std::uint64_t>(b);
  h *= fnv_prime;
  return h;
}
 
template <typename T>
inline std::uint64_t fnv1a_mix(std::uint64_t h, const T &value) noexcept
{
  static_assert(std::is_trivially_copyable_v<T>,
                "frame_hash requires trivially copyable cell states");
  std::uint8_t buf[sizeof(T)];
  // Defensive memcpy avoids strict-aliasing pitfalls.
  __builtin_memcpy(buf, &value, sizeof(T));
  for (std::size_t i = 0; i < sizeof(T); ++i)
    h = fnv1a_step(h, buf[i]);
  return h;
}
 
template <typename L>
concept HasAtNode = requires(const L &l) { l.at_node(std::size_t{}); };
 
}  // namespace ca_metrics_detail
 
template <typename Lattice, typename F>
inline void for_each_cell(const Lattice &lat, F &&f)
{
  using coord_t = typename Lattice::coord_type;
  if constexpr (ca_metrics_detail::HasAtNode<Lattice>)
    {
      const ca_size_t n = lat.size();
      for (ca_size_t i = 0; i < n; ++i)
        f(lat.at_node(i));
    }
  else if constexpr (Lattice::rank == 1)
    {
      const ca_size_t n0 = lat.size(0);
      for (ca_size_t i = 0; i < n0; ++i)
        f(lat.at(coord_t{static_cast<ca_index_t>(i)}));
    }
  else if constexpr (Lattice::rank == 2)
    {
      const ca_size_t n0 = lat.size(0);
      const ca_size_t n1 = lat.size(1);
      for (ca_size_t i = 0; i < n0; ++i)
        for (ca_size_t j = 0; j < n1; ++j)
          f(lat.at(coord_t{static_cast<ca_index_t>(i), static_cast<ca_index_t>(j)}));
    }
  else if constexpr (Lattice::rank == 3)
    {
      const ca_size_t n0 = lat.size(0);
      const ca_size_t n1 = lat.size(1);
      const ca_size_t n2 = lat.size(2);
      for (ca_size_t i = 0; i < n0; ++i)
        for (ca_size_t j = 0; j < n1; ++j)
          for (ca_size_t k = 0; k < n2; ++k)
            f(lat.at(coord_t{static_cast<ca_index_t>(i), static_cast<ca_index_t>(j),
                             static_cast<ca_index_t>(k)}));
    }
  else
    {
      static_assert(Lattice::rank <= 3, "for_each_cell currently supports rank <= 3");
    }
}
 
template <typename Lattice>
[[nodiscard]] inline ca_size_t count_state(const Lattice &lat, const typename Lattice::state_type &s)
{
  ca_size_t cnt = 0;
  for_each_cell(lat, [&](const auto &v)
  {
    if (v == s)
      ++cnt;
  });
  return cnt;
}
 
template <typename Lattice>
[[nodiscard]] inline ca_size_t count_alive(const Lattice &lat)
{
  using state_t = typename Lattice::state_type;
  const state_t dead{};
  ca_size_t cnt = 0;
  for_each_cell(lat, [&](const auto &v)
  {
    if (v != dead)
      ++cnt;
  });
  return cnt;
}
 
template <typename Lattice>
[[nodiscard]] inline ca_size_t total_cells(const Lattice &lat) noexcept
{
  return lat.size();
}
 
template <typename Lattice>
[[nodiscard]] inline double density(const Lattice &lat, const typename Lattice::state_type &s)
{
  const ca_size_t total = total_cells(lat);
  if (total == 0)
    return 0.0;
  return static_cast<double>(count_state(lat, s)) / static_cast<double>(total);
}
 
template <typename Lattice>
[[nodiscard]] inline double alive_density(const Lattice &lat)
{
  const ca_size_t total = total_cells(lat);
  if (total == 0)
    return 0.0;
  return static_cast<double>(count_alive(lat)) / static_cast<double>(total);
}
 
template <typename Lattice>
[[nodiscard]] inline Array<ca_size_t> state_histogram(const Lattice &lat, std::size_t max_state)
{
  Array<ca_size_t> hist(max_state, ca_size_t{0});
  for_each_cell(lat, [&](const auto &v)
  {
    using S = typename Lattice::state_type;
    if constexpr (std::is_integral_v<S> or std::is_enum_v<S>)
      {
        const long long iv = static_cast<long long>(v);
        if (iv >= 0 and iv < static_cast<long long>(max_state))
          ++hist[static_cast<std::size_t>(iv)];
      }
    else
      {
        // Non-integral states are not classifiable into
        // a small histogram; the caller should provide a
        // bespoke metric. Suppress the unused parameter
        // warning while keeping the signature uniform.
        (void) v;
      }
  });
  return hist;
}
 
template <typename Lattice>
[[nodiscard]] inline double shannon_entropy(const Lattice &lat, std::size_t max_state)
{
  const auto hist = state_histogram(lat, max_state);
  ca_size_t total = 0;
  for (auto c : hist)
    total += c;
  if (total == 0)
    return 0.0;
  double h = 0.0;
  const double inv = 1.0 / static_cast<double>(total);
  for (auto c : hist)
    if (c != 0)
      {
        const double p = static_cast<double>(c) * inv;
        h -= p * std::log(p);
      }
  return h;
}
 
template <typename Lattice>
[[nodiscard]] inline std::uint64_t frame_hash(const Lattice &lat)
{
  std::uint64_t h = ca_metrics_detail::fnv_basis;
  for_each_cell(lat, [&](const auto &v)
  {
    h = ca_metrics_detail::fnv1a_mix(h, v);
  });
  return h;
}
 
template <typename Lattice>
[[nodiscard]] inline bool frames_equal(const Lattice &a, const Lattice &b)
{
  if (a.extents() != b.extents())
    return false;
  using coord_t = typename Lattice::coord_type;
  if constexpr (ca_metrics_detail::HasAtNode<Lattice>)
    {
      const ca_size_t n = a.size();
      for (ca_size_t i = 0; i < n; ++i)
        if (a.at_node(i) != b.at_node(i))
          return false;
      return true;
    }
  else if constexpr (Lattice::rank == 1)
    {
      const ca_size_t n0 = a.size(0);
      for (ca_size_t i = 0; i < n0; ++i)
        {
          const coord_t c{static_cast<ca_index_t>(i)};
          if (a.at(c) != b.at(c))
            return false;
        }
      return true;
    }
  else if constexpr (Lattice::rank == 2)
    {
      const ca_size_t n0 = a.size(0);
      const ca_size_t n1 = a.size(1);
      for (ca_size_t i = 0; i < n0; ++i)
        for (ca_size_t j = 0; j < n1; ++j)
          {
            const coord_t c{static_cast<ca_index_t>(i), static_cast<ca_index_t>(j)};
            if (a.at(c) != b.at(c))
              return false;
          }
      return true;
    }
  else if constexpr (Lattice::rank == 3)
    {
      const ca_size_t n0 = a.size(0);
      const ca_size_t n1 = a.size(1);
      const ca_size_t n2 = a.size(2);
      for (ca_size_t i = 0; i < n0; ++i)
        for (ca_size_t j = 0; j < n1; ++j)
          for (ca_size_t k = 0; k < n2; ++k)
            {
              const coord_t c{static_cast<ca_index_t>(i), static_cast<ca_index_t>(j),
                              static_cast<ca_index_t>(k)};
              if (a.at(c) != b.at(c))
                return false;
            }
      return true;
    }
  else
    {
      static_assert(Lattice::rank <= 3, "frames_equal currently supports rank <= 3");
      return false;
    }
}
 
template <typename Lattice>
[[nodiscard]] inline ca_size_t cell_diff_count(const Lattice &a, const Lattice &b)
{
  ah_length_error_if(a.extents() != b.extents())
    << "cell_diff_count: lattices have different extents";
 
  using coord_t = typename Lattice::coord_type;
  ca_size_t diff = 0;
  if constexpr (ca_metrics_detail::HasAtNode<Lattice>)
    {
      const ca_size_t n = a.size();
      for (ca_size_t i = 0; i < n; ++i)
        if (a.at_node(i) != b.at_node(i))
          ++diff;
    }
  else if constexpr (Lattice::rank == 1)
    {
      const ca_size_t n0 = a.size(0);
      for (ca_size_t i = 0; i < n0; ++i)
        {
          const coord_t c{static_cast<ca_index_t>(i)};
          if (a.at(c) != b.at(c))
            ++diff;
        }
    }
  else if constexpr (Lattice::rank == 2)
    {
      const ca_size_t n0 = a.size(0);
      const ca_size_t n1 = a.size(1);
      for (ca_size_t i = 0; i < n0; ++i)
        for (ca_size_t j = 0; j < n1; ++j)
          {
            const coord_t c{static_cast<ca_index_t>(i), static_cast<ca_index_t>(j)};
            if (a.at(c) != b.at(c))
              ++diff;
          }
    }
  else if constexpr (Lattice::rank == 3)
    {
      const ca_size_t n0 = a.size(0);
      const ca_size_t n1 = a.size(1);
      const ca_size_t n2 = a.size(2);
      for (ca_size_t i = 0; i < n0; ++i)
        for (ca_size_t j = 0; j < n1; ++j)
          for (ca_size_t k = 0; k < n2; ++k)
            {
              const coord_t c{static_cast<ca_index_t>(i), static_cast<ca_index_t>(j),
                              static_cast<ca_index_t>(k)};
              if (a.at(c) != b.at(c))
                ++diff;
            }
    }
  else
    {
      static_assert(Lattice::rank <= 3, "cell_diff_count currently supports rank <= 3");
    }
  return diff;
}
 
}  // namespace CA
}  // namespace Aleph
 
#endif  // CA_METRICS_H