diff --git a/lib/Makefile b/lib/Makefile
index e5cf32c..878c2fb 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -63,3 +63,4 @@
 obj-y			+= list_sort.o
 obj-y			+= int_sqrt.o
 obj-y			+= parseopt.o
+obj-y			+= clz_ctz.o
diff --git a/lib/clz_ctz.c b/lib/clz_ctz.c
new file mode 100644
index 0000000..b5ac7f4
--- /dev/null
+++ b/lib/clz_ctz.c
@@ -0,0 +1,59 @@
+/*
+ * lib/clz_ctz.c
+ *
+ * Copyright (C) 2013 Chanho Min <chanho.min@lge.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ * The functions in this file aren't called directly, but are required by
+ * GCC builtins such as __builtin_ctz, and therefore they can't be removed
+ * despite appearing unreferenced in kernel source.
+ *
+ * __c[lt]z[sd]i2 can be overridden by linking arch-specific versions.
+ */
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+
+int __weak __ctzsi2(int val);
+int __weak __ctzsi2(int val)
+{
+	return __ffs(val);
+}
+
+int __weak __clzsi2(int val);
+int __weak __clzsi2(int val)
+{
+	return 32 - fls(val);
+}
+
+int __weak __clzdi2(long val);
+int __weak __ctzdi2(long val);
+#if BITS_PER_LONG == 32
+
+int __weak __clzdi2(long val)
+{
+	return 32 - fls((int)val);
+}
+
+int __weak __ctzdi2(long val)
+{
+	return __ffs((u32)val);
+}
+
+#elif BITS_PER_LONG == 64
+
+int __weak __clzdi2(long val)
+{
+	return 64 - fls64((u64)val);
+}
+
+int __weak __ctzdi2(long val)
+{
+	return __ffs64((u64)val);
+}
+
+#else
+#error BITS_PER_LONG not 32 or 64
+#endif