1 files changed, 26 insertions, 0 deletions
diff --git a/lib/tar/checksum.c b/lib/tar/checksum.c
new file mode 100644
index 0000000..925f942
--- /dev/null
+++ b/lib/tar/checksum.c
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+#include "internal.h"
+
+void update_checksum(tar_header_t *hdr)
+{
+	unsigned int chksum = 0;
+	size_t i;
+
+	memset(hdr->chksum, ' ', sizeof(hdr->chksum));
+
+	for (i = 0; i < sizeof(*hdr); ++i)
+		chksum += ((unsigned char *)hdr)[i];
+
+	write_octal(hdr->chksum, chksum, 6);
+	hdr->chksum[6] = '\0';
+	hdr->chksum[7] = ' ';
+}
+
+bool is_checksum_valid(const tar_header_t *hdr)
+{
+	tar_header_t copy;
+
+	memcpy(&copy, hdr, sizeof(*hdr));
+	update_checksum(&copy);
+	return memcmp(hdr, &copy, sizeof(*hdr)) == 0;
+}