Method load_critpatch_cache_

src/Backends/SVDSBTL/SVDSBTLBackend.cpp:773–812

}

std::optional<std::array<double, 4>> SVDSBTLBackend::load_critpatch_cache_(const std::string& fluid_name, const std::string& source_backend,
                                                                           const std::string& options_canonical) {
    const auto path = critpatch_cache_path_(fluid_name, source_backend, options_canonical);
    std::error_code ec;
    if (!std::filesystem::exists(path, ec) || ec) {
        return std::nullopt;
    }
    // Use FILE* (POSIX/Windows-portable; binary fixed-width 44 bytes is
    // small enough that stdio buffering overhead is irrelevant).
    std::FILE* f = std::fopen(path.string().c_str(), "rb");
    if (!f) {
        return std::nullopt;
    }
    std::array<char, 8> magic{};
    std::uint32_t version = 0;
    std::array<double, 4> mults{};
    const auto rd_n = std::fread(magic.data(), 1, 8, f);
    if (rd_n != 8 || std::string(magic.data(), 8) != "CPCRITPB") {
        (void)std::fclose(f);
        return std::nullopt;
    }
    // v1 → v2: T_hi_cap clamp added in CoolProp-4u9.  Bump to invalidate
    // pre-clamp caches so they get recomputed with the corrected ceiling
    // (no migration — calibrator is cheap, re-runs on cache miss).
    if (std::fread(&version, sizeof(version), 1, f) != 1 || version != 2u) {
        (void)std::fclose(f);
        return std::nullopt;
    }
    if (std::fread(mults.data(), sizeof(double), 4, f) != 4) {
        (void)std::fclose(f);
        return std::nullopt;
    }
    (void)std::fclose(f);
    // Sanity-clamp: refuse obviously-wrong cached values rather than
    // letting a corrupt file silently produce a broken patch.
    if (!(mults[0] > 0.0 && mults[0] < mults[1] && mults[1] < 2.0 && mults[2] > 0.0 && mults[2] < mults[3] && mults[3] < 10.0)) {
        return std::nullopt;
    }
    return mults;
}

void SVDSBTLBackend::save_critpatch_cache_(const std::string& fluid_name, const std::string& source_backend, const std::string& options_canonical,
                                           const std::array<double, 4>& mults) {