/* Calculates the xor of two files.
 * Copyright (C) 2013 Peter Wu <lekensteyn@gmail.com>
 */

#include <err.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

int open_file(const char *filename) {
	int fd;

	if (!strcmp(filename, "-"))
		return STDIN_FILENO;

	fd = open(filename, O_RDONLY);
	if (fd < 0)
		errx(1, "open(%s)", filename);

	return fd;
}

int main(int argc, char **argv) {
	int fd1, fd2;
	int r1, r2;

	if (argc < 3)
		errx(1, "Usage: xor-files file1 file2");

	fd1 = open_file(argv[1]);
	fd2 = open_file(argv[2]);

	do {
		int errno1, errno2;
		char buf1[1024], buf2[1024];
		int i;

		r1 = read(fd1, buf1, sizeof(buf1));
		errno1 = errno;
		r2 = read(fd2, buf2, sizeof(buf2));
		errno2 = errno;

		if (r1 == -1) {
			errno = errno1;
			warn("read 1 failed");
		}
		if (r2 == -1) {
			errno = errno2;
			warn("read 2 failed");
		}

		if (r1 != r2)
			warnx("read blocks do not match: %i != %i", r1, r2);

		// in case the sizes are not equal, truncate.
		if (r2 < r1)
			r1 = r2;

		if (r1 > 0) {
			for (i = 0; i < r1; i++)
				buf1[i] ^= buf2[i];

			write(STDOUT_FILENO, buf1, r1);
		}
	} while (r1 > 0 && r1 == r2);

	close(fd1);
	close(fd2);

	return 0;
}