Verifies that an array covers every t-way interaction, the certificate check for covering arrays, using compiled C code with optional 'OpenMP' threading. Supports uniform and mixed-level (per-column symbol counts) arrays. Missing values mark flexible ("don't care") entries, which contribute nothing to coverage, so a verified array remains covering however they are filled. Each set of t-1 columns is checked against all later columns at once, one bit per column, which is many times faster than checking every set of t columns on its own on large arrays. Designed to be easy to embed in other packages: a single C file with a registered .Call entry point and one R wrapper.