xor-files: xor two files

1 files changed, 63 insertions, 0 deletions

diff --git a/xor-files.c b/xor-files.c
new file mode 100644
index 0000000..762ad63
--- /dev/null
+++ b/xor-files.c
@@ -0,0 +1,63 @@
+/* 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>
+
+int main(int argc, char **argv) {
+	int fd1, fd2;
+	int r1, r2;
+
+	if (argc < 3)
+		errx(1, "Usage: xor-files file1 file2");
+
+	fd1 = open(argv[1], O_RDONLY);
+	if (fd1 < 0)
+		errx(1, "open(%s)", argv[1]);
+
+	fd2 = open(argv[2], O_RDONLY);
+	if (fd2 < 0)
+		errx(1, "open(%s)", 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;
+}