ca-metrics.H File Reference

Free metric helpers for cellular automata frames. More...

#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>

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Namespaces
namespace	Aleph
	Main namespace for Aleph-w library functions.
namespace	Aleph::CA
namespace	Aleph::CA::ca_metrics_detail

Concepts
concept	Aleph::CA::ca_metrics_detail::HasAtNode
	Detect whether L exposes a graph-style at_node(size_t) accessor.

Functions
constexpr std::uint64_t	Aleph::CA::ca_metrics_detail::fnv1a_step (std::uint64_t h, const std::uint8_t b) noexcept
	Mix one byte into an FNV-1a hash.
template<typename T >
std::uint64_t	Aleph::CA::ca_metrics_detail::fnv1a_mix (std::uint64_t h, const T &value) noexcept
	Mix every byte of value (in little-endian order) into an FNV-1a hash.
template<typename Lattice , typename F >
void	Aleph::CA::for_each_cell (const Lattice &lat, F &&f)
	Visit every cell of a lattice in canonical row-major order.
template<typename Lattice >
ca_size_t	Aleph::CA::count_state (const Lattice &lat, const typename Lattice::state_type &s)
template<typename Lattice >
ca_size_t	Aleph::CA::count_alive (const Lattice &lat)
template<typename Lattice >
ca_size_t	Aleph::CA::total_cells (const Lattice &lat) noexcept
template<typename Lattice >
double	Aleph::CA::density (const Lattice &lat, const typename Lattice::state_type &s)
template<typename Lattice >
double	Aleph::CA::alive_density (const Lattice &lat)
template<typename Lattice >
Array< ca_size_t >	Aleph::CA::state_histogram (const Lattice &lat, std::size_t max_state)
	Count occurrences of every integer state in [0, max_state).
template<typename Lattice >
double	Aleph::CA::shannon_entropy (const Lattice &lat, std::size_t max_state)
	Shannon entropy in nats of the [0, max_state) distribution.
template<typename Lattice >
std::uint64_t	Aleph::CA::frame_hash (const Lattice &lat)
	Deterministic 64-bit FNV-1a hash of the lattice cells.
template<typename Lattice >
bool	Aleph::CA::frames_equal (const Lattice &a, const Lattice &b)
template<typename Lattice >
ca_size_t	Aleph::CA::cell_diff_count (const Lattice &a, const Lattice &b)

Variables
constexpr std::uint64_t	Aleph::CA::ca_metrics_detail::fnv_basis = 14695981039346656037ull
	FNV-1a 64-bit basis and prime constants.
constexpr std::uint64_t	Aleph::CA::ca_metrics_detail::fnv_prime = 1099511628211ull

Detailed Description

Free metric helpers for cellular automata frames.

Provides allocation-free utilities to compute simple aggregate statistics over any LatticeLike lattice without coupling them to a particular boundary policy or storage type. Used both by the Phase-7 observers (ca-observer.H) and by user code that needs to evaluate a metric ad-hoc on a frame.

Catalogue:

• for_each_cell(lat, f) — generic cell visitor for ranks 1, 2 and 3, plus the rank-1 graph lattice.
• count_state(lat, s) — number of cells in state s.
• count_alive(lat) — count_state(lat, T{}, true), i.e., number of cells whose value differs from state_type{}.
• density(lat, s) — alive ratio in [0, 1].
• state_histogram(lat, max) — array of counts per integer state in [0, max).
• shannon_entropy(lat, max) — Shannon entropy in nats over the state distribution; 0 for empty or constant lattices.
• frame_hash(lat) — deterministic 64-bit FNV-1a hash of the cell sequence in row-major order. Stable across runs and across builds (no random seed, no implementation- defined hashing).
• frames_equal(a, b) — bit-for-bit comparison.
• cell_diff_count(a, b) — number of cells that differ.

All helpers are header-only inline templates and do not allocate (state_histogram allocates one buffer that the caller may pre-size).

Author

Leandro Rabindranath Leon

Definition in file ca-metrics.H.