//compilation: g++ -O3 -Wall mmap_test.cpp

//run:
//      time ./a.out large_file 0 #mmap test
//      time ./a.out large_file 1 #fread test

//3Gb file generation:
//    python -c "s = 'x'*(2**27); f = open('large_file', 'wb'); [f.write(s) for i in xrange(3*8)]; f.close()"
//
//

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>


void fatal(const char *msg) {
    fprintf(stderr, "%s\n", msg);
    exit(1);
}

off_t file_length(FILE *f) {
    struct stat stat_buf;
    if (fstat(fileno(f), &stat_buf) == -1)
        fatal("file_length failed");
    return (stat_buf.st_size);
}

const unsigned char *mmapfile1(const char *filename, off_t *n) {
    FILE *f = fopen(filename, "rb");
    if (!f) fatal("can't open file");
    *n = file_length(f);
    void *p = mmap(NULL, *n, PROT_READ, MAP_PRIVATE, fileno(f), 0);
    if (p == MAP_FAILED)
        fatal("mmap failed");
    return (const unsigned char*)p;
}

const unsigned char *mmapfile2(const char *filename, off_t *n) {
    FILE *f = fopen(filename, "rb");
    if (!f) fatal("can't open file");
    *n = file_length(f);
    unsigned char *buf = new unsigned char[*n];
    if (*n != (off_t)fread(buf, 1, *n, f))
        fatal("fread failed");
    return buf;
}

int main(int argc, char **argv) {
    if(argc != 3)
        fatal("invalid cmd line, expected filename and mmmap-type (0/1)");

    long long int s = 0;
    {
        off_t n;
        bool which_mmap = (argv[2][0] == '0');
        const char *filename = argv[1];
        const unsigned char *data = (which_mmap ? mmapfile1 : mmapfile2)(filename, &n);

        printf("%lld\n", (long long int)n);
        printf("%p\n", data);

        for(off_t i = 0; i<n; i += 1024) {
            s += (unsigned char)data[i];
        }
    }
    printf("s: %lld\n", s); //verify, that all data is really loaded (no lazy optimizations)
}