Embed linkcell from C++

include/linkcell.hpp is a C++17 RAII header over linkcell.h. It does not add a second CPU library. Link the same package target a C consumer links.

linkcell::knearest returns an owning packed Neighbours. knearest_into writes a caller-owned int * and takes out_len, which must be n * k. Neither returns std::vector<std::vector<int>>. Unused slots are -1. Failure throws linkcell::Error.

Meson wrap

Same wrap as C. Ask Meson for C++:

project('app', 'cpp', default_options: ['cpp_std=c++17'])
linkcell_dep = dependency('linkcell', fallback: ['linkcell', 'linkcell_dep'])
executable('app', 'app.cpp', dependencies: linkcell_dep)

CMake

cmake_minimum_required(VERSION 3.22)
project(app LANGUAGES CXX)
set(CMAKE_CXX_STANDARD 17)
find_package(linkcell 0.3 REQUIRED)
add_executable(app app.cpp)
target_link_libraries(app PRIVATE linkcell::cpp)

linkcell::cpp links the C ABI and requires C++17. linkcell::linkcell has no C++ language requirement and remains usable by C-only projects. tests/cmake-consumer/ exercises both patterns against an installed prefix.

Call

#include "linkcell.hpp"

const linkcell::Cell box = linkcell::Cell::ortho(10.0, 10.0, 10.0);
const double xyz[] = {0.0, 0.0, 0.0, 1.0, 0.0, 0.0};
const linkcell::Neighbours nn = linkcell::knearest(xyz, 2, box, 1);
int j = nn.neighbour(0, 0);
double r2 = nn.dist2(0, 0);

Device k-nearest (linkcell_gpu.hpp) takes device pointers and writes the same packed buffer. Link linkcell_gpu_dep in Meson, linkcell::gpu in CMake, or linkcell-gpu with pkg-config. A device-packed cell (3 / 9 / 12 doubles) is inverted on device:

#include "linkcell_gpu.hpp"

linkcell::gpu::Workspace ws;
ws.knearest_into(xyz_dev, n, cell, k, out_dev, n * k, nullptr, 5.5);
ws.knearest_into_many_dcell(xyz_dev, n, 1, cell_dev, 9, k, out_dev,
                            n * k);

linkcell::gpu::available() is false when a CUDA driver or NVRTC cannot be loaded. gpulite loads both at runtime; no CUDA SDK is needed to build the target.

A general parallelepiped is linkcell::Cell::from_vectors(a, b, c, origin). Cell::raw() is the lc_cell the ABI consumes.

mask is an optional const int * of length n (nonzero keeps the point). cell_hint <= 0 selects the default bin edge.

Signatures: C ABI. First program: two points.