2 files changed, 55 insertions, 0 deletions
diff --git a/lib/util/Makemodule.am b/lib/util/Makemodule.am
index 113855c..c66c786 100644
--- a/lib/util/Makemodule.am
+++ b/lib/util/Makemodule.am
@@ -7,6 +7,7 @@ libutil_a_SOURCES += lib/util/fast_urem_by_const.h
 libutil_a_SOURCES += include/threadpool.h
 libutil_a_SOURCES += include/w32threadwrap.h
 libutil_a_SOURCES += lib/util/threadpool_serial.c
+libutil_a_SOURCES += lib/util/is_memory_zero.c
 libutil_a_CFLAGS = $(AM_CFLAGS)
 libutil_a_CPPFLAGS = $(AM_CPPFLAGS)
 
diff --git a/lib/util/is_memory_zero.c b/lib/util/is_memory_zero.c
new file mode 100644
index 0000000..3974ee2
--- /dev/null
+++ b/lib/util/is_memory_zero.c
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * is_memory_zero.c
+ *
+ * Copyright (C) 2021 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "config.h"
+#include "util.h"
+
+#include <stdint.h>
+
+#define U64THRESHOLD (128)
+
+static bool test_u8(const unsigned char *blob, size_t size)
+{
+	while (size--) {
+		if (*(blob++) != 0)
+			return false;
+	}
+
+	return true;
+}
+
+bool is_memory_zero(const void *blob, size_t size)
+{
+	const sqfs_u64 *u64ptr;
+	size_t diff;
+
+	if (size < U64THRESHOLD)
+		return test_u8(blob, size);
+
+	diff = (uintptr_t)blob % sizeof(sqfs_u64);
+
+	if (diff != 0) {
+		diff = sizeof(sqfs_u64) - diff;
+
+		if (!test_u8(blob, diff))
+			return false;
+
+		blob = (const char *)blob + diff;
+		size -= diff;
+	}
+
+	u64ptr = blob;
+
+	while (size >= sizeof(sqfs_u64)) {
+		if (*(u64ptr++) != 0)
+			return false;
+
+		size -= sizeof(sqfs_u64);
+	}
+
+	return test_u8((const unsigned char *)u64ptr, size);
+}