#ifndef _GNU_SOURCE
        #define _GNU_SOURCE
#endif

#include <cstdint>
#include <tuple>
#include <iostream>
#include <system_error>

// For `sysconf`.
#include <unistd.h>
// For `CPU_SET`.
#include <sched.h>

void check(int r)
{
        if (r == 0) return;
        throw std::system_error{r, std::system_category()};
}

auto cpuid(uint32_t leaf, uint32_t arg) ->
std::tuple<uint32_t, uint32_t, uint32_t, uint32_t>
{
        uint32_t r1, r2, r3, r4;
        asm("cpuid"
                : "=a" (r1), "=b" (r2), "=c" (r3), "=d" (r4)
                : "a" (leaf), "c" (arg)
        );
        return std::make_tuple(r1, r2, r3, r4);
}

void print_x2apic_id()
{
        uint32_t r1, r2, r3, r4;
        std::tie(r1, r2, r3, r4) = cpuid(11, 0);
        std::cout << r4 << std::endl;
}

int main()
{
        const auto _ = std::ignore;
        auto nprocs = ::sysconf(_SC_NPROCESSORS_ONLN);
        auto set = ::cpu_set_t{};
        std::cout << "Processors online: " << nprocs << std::endl;

        for (auto i = 0; i != nprocs; ++i) {
                CPU_SET(i, &set);
                check(::sched_setaffinity(0, sizeof(::cpu_set_t), &set));
                CPU_CLR(i, &set);
                print_x2apic_id();
                //uint32_t r4;
                //std::tie(_, _, _, r4) = cpuid(11, 0);
                //std::cout << r4 << std::endl;
        }
}