Embed linkcell from C

Link the installed CPU library and include linkcell.h. The C ABI is the hourglass waist; every other language wraps lc_*. Python wraps it with DLPack (dlpk); see Embed from Python. Device searches use lc_gpu_* (include/linkcell_gpu.h) from the separate GPU package target.

lc_knearest takes packed double xyz (n triples), size_t n, size_t k, and a caller-owned int buffer of length n * k. Unused slots are -1. lc_knearest_d2 also writes squared distances. lc_knearest_many is the frame-major batch. Returns 0 on success. On failure, read lc_last_error() on the same thread and do not free the pointer.

Meson wrap

subprojects/linkcell.wrap:

[wrap-git]
url = https://github.com/d-SEAMS/linkcell.git
revision = v0.3.3
depth = 1

[provide]
linkcell = linkcell_dep

project('app', 'c', default_options: ['c_std=c11'])
linkcell_dep = dependency('linkcell', fallback: ['linkcell', 'linkcell_dep'])
executable('app', 'app.c', dependencies: linkcell_dep)

linkcell_dep already carries the Rust sysroot (pthread, dl, m on Linux).

For the device API, request linkcell-gpu with fallback ['linkcell', 'linkcell_gpu_dep']. The dependency defines LINKCELL_HAS_GPULITE and links its C++ implementation, so enable C++ in a C-only project that uses lc_gpu_*.

CMake

After cmake --install into $PREFIX:

cmake_minimum_required(VERSION 3.22)
project(app LANGUAGES C)
find_package(linkcell 0.3 REQUIRED)
add_executable(app app.c)
target_link_libraries(app PRIVATE linkcell::linkcell)

For lc_gpu_*, declare project(app LANGUAGES C CXX) and link linkcell::gpu. LINKCELL_WITH_GPULITE controls that target and is on by default.

cmake -S . -B build -DCMAKE_PREFIX_PATH=$PREFIX
cmake --build build

In the linkcell build tree the same imported name is linkcell::linkcell.

Call

#include "linkcell.h"

double xyz[] = {0.0, 0.0, 0.0, 1.0, 0.0, 0.0};
lc_cell box = lc_cell_ortho(10.0, 10.0, 10.0);
int out[2];
if (lc_knearest(xyz, 2, &box, 1, NULL, 0.0, out) != 0) {
  fprintf(stderr, "%s\n", lc_last_error());
}

A sheared box is three lattice vectors plus an origin in lc_cell (ax..cz, ox..oz), the same row layout vesin uses.

Full field list: C ABI. A first program: two points.