#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <math.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>

int main(int argc, char *argv[])
{
    struct timeval tv;
    gettimeofday(&tv, NULL);
    int start = tv.tv_usec;
    struct stat st;
    stat(argv[1], &st);
    int size = st.st_size;
    printf("File size: %d\n", size);
    int half = round(size/2);
    int half2 = size - half;

    int f = open(argv[1], O_RDONLY);
    int f2 = open(argv[2], O_RDWR | O_CREAT, 0664);
    void *src, *dst;
    lseek(f2, size-1, SEEK_SET);
    write(f2, "", 1);

    src = mmap(NULL, size, PROT_READ, MAP_SHARED, f, 0);
    dst = mmap(NULL, size, PROT_WRITE, MAP_SHARED, f2, 0);
    memcpy(dst, (void*)(src + half), half);
    memcpy((void*)(dst + half), src, half2);

    gettimeofday(&tv, NULL);
    int end = tv.tv_usec;
    double time = end - start;
    printf("Done in %f seconds\n", time/1000000);
    return 0;
}