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#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>
#define FILE_LENGTH 0x100
int random_range(unsigned const low, unsigned const high)
{
unsigned const range = high - low + 1;
return low + (int) (((double) range) * rand() / (RAND_MAX + 1.0));
}
int main(int argc, char *const argv[])
{
int fd;
void *file_memory;
/* Seed the random number generator */
srand(time(NULL));
/* Prepare a file large enough to hold an unsigned integer */
fd = open(argv[1], O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
lseek(fd, FILE_LENGTH + 1, SEEK_SET);
write(fd, "", 1);
lseek(fd, 0, SEEK_SET);
/* Create the memory mapping */
file_memory = mmap(0, FILE_LENGTH, PROT_WRITE, MAP_SHARED, fd, 0);
close(fd);
/* Write a random integer to memory-mapped area. */
sprintf((char *) file_memory, "%d\n", random_range(-100, 100));
/* Release the memory (unnecessary because the program exits). */
munmap(file_memory, FILE_LENGTH);
return 0;
}
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