#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

#define USAGE usage(argv[0])

void usage (char * p)
{
	fprintf (stderr, "usage: %s file count\n", p);
	exit (1);
}

int main (int argc, char ** argv)
{
	int i, k, count, fd, ret, reccount;
	char ch;
	char buf[100];
	struct stat statbuf;
	if (argc != 3)
		USAGE;
	if (sscanf (argv[2], "%d%c", &count, &ch) != 1)
		USAGE;
	if (count < 1 || count > 10)
		USAGE;
	ret = stat (argv[1], &statbuf);
	if (ret < 0) {
		perror ("stat");
		exit (1);
	}
	reccount = 1+statbuf.st_size / (2*sizeof (int)*count);
	for (i=0; i<count-1; ++i) {
		int pid = fork ();
		if (pid <0) {
			perror ("fork");
			/* ATTN: This will not terminate processes
			 * that have been started already. But it will
			 * at least prevent new ones from beeing started.
			 */
			exit (2);
		}
		if (pid ==0) {
			/* Child: break out of for loop an calculate ggt. */
			break;
		}
		/* Parent will continue with the for-loop. */
	}
	/* All processes including the parent will end up here. Once we know
	 * more about wait, the parent should wait for the termination of
	 * all its children.
	 */
	fd = open (argv[1], O_RDONLY);
	if (fd < 0) {
		perror ("open");
		exit (1);
	}
	if (lseek (fd, i*2*sizeof (int)*reccount, SEEK_SET) < 0) {
		perror ("lseek");
		exit (1);
	}
	for (k=0; k<reccount; ++k) {
		int ints[2];
		int ret, a, b;
		ret = read (fd, (char *)ints, 2*sizeof (int));
		if (ret < 0) {
			perror ("read");
			exit (1);
		}
		if (ret == 0) {
			/* End of file. Break out of while loop. */
			break;
		}
		/* Make sure we really got two complete integers. */
		assert (ret == 2*sizeof(int));
		a = ints[0];
		b = ints[1];
		/* Negative numbers are not allowed. */
		assert (a >= 0 && b>= 0);
		while (a && b) {
			if (a > b) {
				a %= b;
			} else {
				b %= a;
			}
		}
		/* GGT is a+b */
		sprintf (buf, "ggt(%d,%d)=%d %ld\n", ints[0], ints[1], a+b, getpid());
		ret = write (1, buf, strlen (buf));
		if (ret < 0) {
			perror ("write");
			exit (1);
		}
		/* Make sure we wrote everything. */
		assert (ret == strlen (buf));
	}
	close (fd);
	return 0;
}