diff --git a/src/klotski_core/raw_code/raw_code.h b/src/klotski_core/raw_code/raw_code.h
index f6b7822..0bb5d54 100644
--- a/src/klotski_core/raw_code/raw_code.h
+++ b/src/klotski_core/raw_code/raw_code.h
@@ -1,13 +1,14 @@
 #pragma once
 
-/// RawCode is an uncompressed coding scheme, which is used for program calculation.
-/// It encodes a `5x4` chessboard as `0 ~ 19`, and uses 3-bits to represent each position,
-/// occupying a total of 60-bits, and stored in a `uint64_t` variable.
+/// RawCode is an uncompressed coding scheme, which is used for program calculation. It
+/// encodes a `5x4` chessboard as `0 ~ 19`, and uses 3-bits to represent each position,
+/// occupying a total of 60-bits, and stored in a `uint64_t` variable. Among them, the
+/// upper 4-bits are reserved and filled with `0`.
 ///
 ///   00 01 02 03
-///   04 05 06 07    fill  20-slots
-///   08 09 10 11    0000  (19) (18) (17) (16) ... (03) (02) (01) (00)
-///   12 13 14 15    (4b)  (60b)
+///   04 05 06 07    fill   20-slots
+///   08 09 10 11    0000   (19) (18) (17) (16) ... (03) (02) (01) (00)
+///   12 13 14 15    (4b) + (3b) * 20 => 64-bits
 ///   16 17 18 19
 ///
 ///   Eg1:
@@ -17,10 +18,11 @@
 ///     @ & * @    ... 1x1 1x1 ...    111 011 011 111
 ///     *     &    1x1 0x0 0x0 1x1    011 000 000 011
 ///
-///            19  18  17  16  15  14  13  12  11  10  09  08  07  06  05  04  03  02  01  00
-///      0000 011 000 000 011 111 011 011 111 010 111 001 010 111 111 111 111 010 111 100 010
-///      0000  0110 0000 0011  1110 1101 1111  0101 1100 1010  1111 1111 1111  0101 1110 0010
-///         0     6    0    3     E    D    F     5    C    A     F    F    F     5    E    2
+///          |  19  18  17  16 |  15  14  13  12 |  11  10  09  08 |  07  06  05  04 |  03  02  01  00
+///     0000 | 011 000 000 011 | 111 011 011 111 | 010 111 001 010 | 111 111 111 111 | 010 111 100 010
+///     0000 |  0110 0000 0011 |  1110 1101 1111 |  0101 1100 1010 |  1111 1111 1111 |  0101 1110 0010
+///        0       6    0    3       E    D    F       5    C    A       F    F    F       5    E    2
+///     => 0x0603'EDF5'CAFF'F5E2
 ///
 ///   Eg2:
 ///     * @ & %    1x1 1x1 1x1 2x1    011 011 011 010
@@ -29,10 +31,11 @@
 ///       ~ ~ ^    0x0 1x2 ... ...    000 001 111 111
 ///       @ % %    0x0 1x1 1x2 ...    000 011 001 111
 ///
-///            19  18  17  16  15  14  13  12  11  10  09  08  07  06  05  04  03  02  01  00
-///      0000 111 001 011 000 111 111 001 000 010 111 111 111 111 010 111 100 010 011 011 011
-///      0000  1110 0101 1000  1111 1100 1000  0101 1111 1111  1110 1011 1100  0100 1101 1011
-///         0     E    5    8     F    C    8     5    F    F     E    B    C     4    D    B
+///          |  19  18  17  16 |  15  14  13  12 |  11  10  09  08 |  07  06  05  04 |  03  02  01  00
+///     0000 | 111 001 011 000 | 111 111 001 000 | 010 111 111 111 | 111 010 111 100 | 010 011 011 011
+///     0000 |  1110 0101 1000 |  1111 1100 1000 |  0101 1111 1111 |  1110 1011 1100 |  0100 1101 1011
+///        0       E    5    8       F    C    8       5    F    F       E    B    C       4    D    B
+///     => 0x0E58'FC85'FFEB'C4DB
 
 #include <string>
 #include <cstdint>