diff --git a/program/c_cpp/library/lib.md b/program/c_cpp/library/libs.md
similarity index 99%
rename from program/c_cpp/library/lib.md
rename to program/c_cpp/library/libs.md
index 623dcbe..3a5f1c9 100644
--- a/program/c_cpp/library/lib.md
+++ b/program/c_cpp/library/libs.md
@@ -33,6 +33,7 @@
   - [offsetof](./self/offsetof.h)
   - [string hash](./self/string_hash.c)
   - [thread pool](./self/thread-pool.cpp)
+  - [BIT](./self/bit.h)
 
 ---
 
diff --git a/program/c_cpp/library/self/bit.h b/program/c_cpp/library/self/bit.h
new file mode 100644
index 0000000..f04c973
--- /dev/null
+++ b/program/c_cpp/library/self/bit.h
@@ -0,0 +1,28 @@
+#include <stdint.h>
+#include <assert.h>
+
+// Generate a mask with n bits set to 1
+#define LOW_N_BITS(n) (~((~(uintmax_t)0) << (n)))
+
+#define LOWBIT(x) ((x)&(-(x)))
+
+// Inserts specified data into a bit segment of any type
+#define PACK_BITFIELD(container, value, start_bit, width) \
+    ((container) = (((container) & ~((((uintmax_t)1 << (width)) - 1) << (start_bit))) | \
+    ((((uintmax_t)(value)) & (((uintmax_t)1 << (width)) - 1)) << (start_bit))))
+// Security version
+#define S_PACK_BITFIELD(container, value, start_bit, width) \
+    do { \
+        assert((width) > 0 && (width) < sizeof(uintmax_t)*8); \
+        assert((start_bit) + (width) <= sizeof(container)*8); \
+        PACK_BITFIELD(container, value, start_bit, width); \
+    } while (0)
+
+// Extract data
+#define UNPACK_BITFIELD(container, start_bit, width) \
+    (((container) >> (start_bit)) & (((uintmax_t)1 << (width)) - 1))
+// Security version
+#define S_UNPACK_BITFIELD(container, start_bit, width) \
+    (assert((width) > 0 && (width) < sizeof(uintmax_t)*8), \
+     assert((start_bit) + (width) <= sizeof(container)*8), \
+     (((container) >> (start_bit)) & (((uintmax_t)1 << (width)) - 1)))