1 files changed, 77 insertions, 0 deletions
diff --git a/difftool/compare_file.c b/difftool/compare_file.c
new file mode 100644
index 0000000..c424220
--- /dev/null
+++ b/difftool/compare_file.c
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * compare_file.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "difftool.h"
+
+int compare_files(file_info_t *a, file_info_t *b, const char *path)
+{
+	uint64_t offset, size, diff;
+	int ret = 0, afd, bfd;
+	void *aptr, *bptr;
+
+	if (a->size != b->size)
+		return 1;
+
+	if (pushd(first_path))
+		return -1;
+	afd = open(path, O_RDONLY);
+	if (afd < 0) {
+		fprintf(stderr, "%s/%s: %s\n", first_path, path,
+			strerror(errno));
+		return -1;
+	}
+	if (popd())
+		goto fail_afd;
+
+	if (pushd(second_path))
+		goto fail_afd;
+	bfd = open(path, O_RDONLY);
+	if (bfd < 0) {
+		fprintf(stderr, "%s/%s: %s\n", second_path, path,
+			strerror(errno));
+		goto fail_afd;
+	}
+	if (popd())
+		goto fail_bfd;
+
+	size = a->size;
+
+	for (offset = 0; offset < size; offset += diff) {
+		diff = size - offset;
+		if (diff > MAX_WINDOW_SIZE)
+			diff = MAX_WINDOW_SIZE;
+
+		aptr = mmap(NULL, diff, PROT_READ, MAP_SHARED, afd, offset);
+		if (aptr == MAP_FAILED) {
+			fprintf(stderr, "mmap %s/%s: %s\n", first_path, path,
+				strerror(errno));
+			goto fail_bfd;
+		}
+
+		bptr = mmap(NULL, diff, PROT_READ, MAP_SHARED, bfd, offset);
+		if (bptr == MAP_FAILED) {
+			fprintf(stderr, "mmap %s/%s: %s\n", second_path, path,
+				strerror(errno));
+			goto fail_bfd;
+		}
+
+		ret = memcmp(aptr, bptr, diff);
+		munmap(aptr, diff);
+		munmap(bptr, diff);
+
+		if (ret != 0)
+			break;
+	}
+
+	close(afd);
+	close(bfd);
+	return ret;
+fail_bfd:
+	close(bfd);
+fail_afd:
+	close(afd);
+	return -1;
+}