ImplicitNet is a small, allocation-free C17 library for deterministic implicit networks over power-of-two node sets. It computes mappings, dimension-based neighbors, routing steps, and reversible state changes directly from a 64-bit state—without materialising a graph.

It is a compact building block for simulations, constrained systems, and experiments where predictable memory use matters.

• C17, no dependencies, heap allocations, recursion, or mutable global state
• Supported network sizes: N = 2^w, from 4 through 65,536
• State-derived bijective map / unmap operations
• log2(N) implicit neighbor dimensions
• Deterministic next-hop routing and reversible state events
• C invariant tests and a Python reference-oracle cross-check

Requirements: CMake 3.20+ and a C17 compiler. Python 3 is optional for the oracle test.

cmake -S . -B build
cmake --build build --config Release
ctest --test-dir build -C Release --output-on-failure

The shared library and implicit_net_c_test executable are emitted under the selected build directory. On single-configuration generators, omit --config Release and -C Release.

#include "implicit_net.h"
#include <stdint.h>

int main(void) {
    in_state state;
    const uint32_t node_count = 1024;

    if (!in_init(&state, node_count, UINT64_C(0x1234))) return 1;

    uint32_t neighbor = in_neighbor(17, 3, node_count, state);
    uint32_t next_hop = in_next(17, 900, node_count, state);
    return (neighbor == UINT32_MAX || next_hop == UINT32_MAX);
}

All APIs take a valid network size: a power of two in [4, 65536]. Value-returning APIs use UINT32_MAX for invalid input; state-changing APIs return 0 on failure and 1 on success.

For a valid node and direction, in_neighbor is a fixed-point-free involution: calling it again with the same direction returns the original node. in_map and in_unmap are inverses for valid inputs. in_prev reverses in_step when invoked with the same network size and event.

ImplicitNet is an experimental library. It provides a deterministic, compact family of state-configured implicit networks; it does not claim cryptographic security or universal optimal routing. Please validate it for your workload before production use.

Released under the MIT License.