#include "check.h"

#include <cassert>
#include <cstddef>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

const std::size_t N = 50, M = N * N;
const int A = 1, B = 2;

int v1[N][M], v2[M][M], *v3; // pointer to shared memory

void init_v3()
{
    int fd = check(shm_open("/v3", O_CREAT | O_RDWR, S_IRUSR | S_IWUSR));
    check(ftruncate(fd, sizeof(v1)));
    v3 = (int *)check(
        mmap(NULL, sizeof(v1), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
}

struct initializer
{
    initializer(): father(getpid())
    {
        init_v3();
        for (std::size_t i = 0; i < N; ++i)
            for (std::size_t j = 0; j < M; ++j)
            {
                v1[i][j] = A;
                v3[i * M + j] = 0;
            }
        for (std::size_t i = 0; i < M; ++i)
            for (std::size_t j = 0; j < M; ++j)
                v2[i][j] = B;
    }

    ~initializer()
    {
        if (getpid() == father)
        {
            std::size_t sum = 0;
            for (std::size_t i = 0; i < N; ++i)
                for (std::size_t j = 0; j < M; ++j)
                    sum += v3[i * M + j];
            assert(sum == A * B * M * M * N);
        }
    }

    pid_t father;
} _;

void work(std::size_t begin, std::size_t end)
{
    init_v3();
    for (std::size_t i = begin; i < end; ++i)
        for (std::size_t k = 0; k < M; ++k)
            for (std::size_t j = 0; j < M; ++j)
                v3[i * M + j] += v1[i][k] * v2[k][j];
}