block writer: move block comaprison to utility function

Slightly modify the byte-for-byte comparison function to compare an
arbitrary range in a file and move it to libutil. Instead of calling
it for each block in the block writer, simply let it check an entire
range in the block writer and compute the range position/size of the
reference ahead, before looking for potential matches.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

2 files changed, 42 insertions, 0 deletions

diff --git a/lib/util/Makemodule.am b/lib/util/Makemodule.am
index b65ebda..830a338 100644
--- a/lib/util/Makemodule.am
+++ b/lib/util/Makemodule.am
@@ -13,6 +13,7 @@ libutil_a_SOURCES += lib/util/mkdir_p.c
 libutil_a_SOURCES += lib/util/canonicalize_name.c
 libutil_a_SOURCES += lib/util/filename_sane.c
 libutil_a_SOURCES += lib/util/source_date_epoch.c
+libutil_a_SOURCES += lib/util/file_cmp.c
 libutil_a_CFLAGS = $(AM_CFLAGS)
 libutil_a_CPPFLAGS = $(AM_CPPFLAGS)
 
diff --git a/lib/util/file_cmp.c b/lib/util/file_cmp.c
new file mode 100644
index 0000000..2aa0cc2
--- /dev/null
+++ b/lib/util/file_cmp.c
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * file_cmp.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "config.h"
+
+#include "util/util.h"
+#include "sqfs/io.h"
+
+#include <string.h>
+
+int check_file_range_equal(sqfs_file_t *file, void *scratch, size_t scratch_sz,
+			   sqfs_u64 loc_a, sqfs_u64 loc_b, sqfs_u64 size)
+{
+	sqfs_u8 *ptr_a = scratch, *ptr_b = ptr_a + scratch_sz / 2;
+	int ret;
+
+	while (size > 0) {
+		size_t diff = scratch_sz / 2;
+		diff = (sqfs_u64)diff > size ? size : diff;
+
+		ret = file->read_at(file, loc_a, ptr_a, diff);
+		if (ret != 0)
+			return ret;
+
+		ret = file->read_at(file, loc_b, ptr_b, diff);
+		if (ret != 0)
+			return ret;
+
+		if (memcmp(ptr_a, ptr_b, diff) != 0)
+			return 1;
+
+		size -= diff;
+		loc_a += diff;
+		loc_b += diff;
+	}
+
+	return 0;
+}