#define _XOPEN_SOURCE 500

#include <stdio.h>
#include <assert.h>

/* this is an inclusive limit on the number of VCPUs */
#define MAX_CPUS 255

/* @limit is exclusive */
static unsigned
width(unsigned limit)
{
    assert(limit != 0);
    if (limit ==   1) { return 0; }
    if (limit ==   2) { return 1; }
    if (limit <=   4) { return 2; }
    if (limit <=   8) { return 3; }
    if (limit <=  16) { return 4; }
    if (limit <=  32) { return 5; }
    if (limit <=  64) { return 6; }
    if (limit <= 128) { return 7; }
    assert(limit <= 256);
    return 8;
}

int
main(void)
{
    unsigned pkgs, cores, threads;

    for (        pkgs    = 1; pkgs                   <= MAX_CPUS; ++pkgs   ) {
        for (    cores   = 1; pkgs * cores           <= MAX_CPUS; ++cores  ) {
            for (threads = 1; pkgs * cores * threads <= MAX_CPUS; ++threads) {
                /* this is an actual APIC ID, not an exclusive limit */
                unsigned max_apic_id;

                /* we limit the width of APIC IDs in 8 bits */
                if (width(pkgs) + width(cores) + width(threads) > 8) {
                    continue;
                }

                max_apic_id =                                    pkgs    - 1;
                max_apic_id = (max_apic_id << width(cores)  ) | (cores   - 1);
                max_apic_id = (max_apic_id << width(threads)) | (threads - 1);

                assert(max_apic_id < 256);
                if (max_apic_id == 255) {
                    fprintf(stdout, "(%3u, %3u, %3u): "
                            "cpus=%3u max_apic_id=%3u\n",
                            pkgs, cores, threads,
                            pkgs * cores * threads, max_apic_id);
                }
            }
        }
    }
    return 0;
}