diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index c24ee9e..e81a413 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -16,10 +16,8 @@ set(KLOTSKI_CORE_SRC
         raw_code/internal/sundry.cc
         raw_code/internal/mirror.cc
 
-        short_code/convert.cc
-        short_code/serialize.cc
-        short_code/short_code.cc
-        short_code/sundry.cc
+        short_code/internal/convert.cc
+        short_code/internal/serialize.cc
 )
 
 add_library(klotski_core STATIC ${KLOTSKI_CORE_SRC})
diff --git a/src/core/short_code/inline_impl.h b/src/core/short_code/inline_impl.h
deleted file mode 100644
index 8eda2d7..0000000
--- a/src/core/short_code/inline_impl.h
+++ /dev/null
@@ -1,56 +0,0 @@
-#pragma once
-
-namespace klotski {
-namespace codec {
-
-/// Get the original 32-bit code.
-inline uint32_t ShortCode::unwrap() const noexcept {
-    return code_;
-}
-
-/// Implicit conversion to 32-bit code.
-inline ShortCode::operator uint32_t() const noexcept {
-    return code_;
-}
-
-/// Equality comparison between ShortCode and numbers.
-inline bool operator==(ShortCode s1, uint32_t s2) noexcept {
-    return s1.unwrap() == s2;
-}
-
-/// ShortCode equal comparison implement.
-inline bool operator==(ShortCode s1, ShortCode s2) noexcept {
-    return s1.unwrap() == s2.unwrap();
-}
-
-/// ShortCode less than comparison implement.
-inline bool operator<(ShortCode s1, ShortCode s2) noexcept {
-    return s1.unwrap() < s2.unwrap();
-}
-
-/// ShortCode greater than comparison implement.
-inline bool operator>(ShortCode s1, ShortCode s2) noexcept {
-    return s1.unwrap() > s2.unwrap();
-}
-
-/// ShortCode create without any check.
-inline ShortCode ShortCode::unsafe_create(uint32_t short_code) noexcept {
-    return *reinterpret_cast<ShortCode*>(&short_code); // init directly
-}
-
-/// ShortCode create with valid check.
-inline std::optional<ShortCode> ShortCode::create(uint32_t short_code) noexcept {
-    if (!ShortCode::check(short_code)) {
-        return std::nullopt; // invalid short code
-    }
-    return ShortCode::unsafe_create(short_code);
-}
-
-/// Output string encoding of ShortCode.
-inline std::ostream& operator<<(std::ostream &out, ShortCode self) {
-    out << ShortCode::string_encode(self.code_);
-    return out;
-}
-
-} // namespace codec
-} // namespace klotski
diff --git a/src/core/short_code/convert.cc b/src/core/short_code/internal/convert.cc
similarity index 87%
rename from src/core/short_code/convert.cc
rename to src/core/short_code/internal/convert.cc
index b057672..2da6328 100644
--- a/src/core/short_code/convert.cc
+++ b/src/core/short_code/internal/convert.cc
@@ -1,18 +1,17 @@
 #include <algorithm>
-#include "short_code.h"
+
 #include "offset/basic.h"
 #include "offset/range_prefix.h"
+#include "short_code/short_code.h"
 
 using klotski::cases::AllCases;
+using klotski::codec::ShortCode;
 using klotski::cases::BasicRanges;
 
 using klotski::codec::offset::ALL_CASES_OFFSET;
 using klotski::codec::offset::BASIC_RANGES_OFFSET;
 using klotski::codec::offset::RANGE_PREFIX_OFFSET;
 
-namespace klotski {
-namespace codec {
-
 /// FIXME: temporarily used to implement tidy conversion
 static uint32_t check_range(uint32_t head, uint32_t range) noexcept {
     ///   M_1x1   |   M_1x2   |   M_2x1   |   M_2x2
@@ -52,23 +51,20 @@ static uint32_t check_range(uint32_t head, uint32_t range) noexcept {
     return 0; // pass check
 }
 
-/// Convert CommonCode to ShortCode based on AllCases data.
-uint32_t ShortCode::fast_encode(uint64_t common_code) noexcept {
+uint32_t ShortCode::fast_encode(uint64_t common_code) {
     auto head = common_code >> 32;
     auto &ranges = AllCases::instance().fetch()[head]; // match available ranges
     auto target = std::lower_bound(ranges.begin(), ranges.end(), (uint32_t)common_code);
     return ALL_CASES_OFFSET[head] + (target - ranges.begin());
 }
 
-/// Convert ShortCode to CommonCode based on AllCases data.
-uint64_t ShortCode::fast_decode(uint32_t short_code) noexcept {
+uint64_t ShortCode::fast_decode(uint32_t short_code) {
     auto offset = std::upper_bound(ALL_CASES_OFFSET, ALL_CASES_OFFSET + 16, short_code) - 1;
     uint64_t head = offset - ALL_CASES_OFFSET;
     return (head << 32) | AllCases::instance().fetch()[head][short_code - *offset];
 }
 
-/// Convert CommonCode to ShortCode based on BasicRanges data.
-uint32_t ShortCode::tiny_encode(uint64_t common_code) noexcept {
+uint32_t ShortCode::tiny_encode(uint64_t common_code) {
     uint32_t head = common_code >> 32;
     uint32_t prefix = (common_code >> 20) & 0xFFF;
 
@@ -93,8 +89,7 @@ uint32_t ShortCode::tiny_encode(uint64_t common_code) noexcept {
     return ALL_CASES_OFFSET[head] + RANGE_PREFIX_OFFSET[head][prefix] + offset;
 }
 
-/// NOTE: ensure that input short code is valid!
-uint64_t ShortCode::tiny_decode(uint32_t short_code) noexcept { // short code --> common code
+uint64_t ShortCode::tiny_decode(uint32_t short_code) { // short code --> common code
     auto offset = std::upper_bound(ALL_CASES_OFFSET, ALL_CASES_OFFSET + 16, short_code) - 1;
     auto head = offset - ALL_CASES_OFFSET; // head index
     short_code -= *offset;
@@ -118,6 +113,3 @@ uint64_t ShortCode::tiny_decode(uint32_t short_code) noexcept { // short code --
     }
     return (uint64_t)head << 32 | range_reverse(basic_ranges[index]);
 }
-
-} // namespace codec
-} // namespace klotski
diff --git a/src/core/short_code/offset/basic.h b/src/core/short_code/internal/offset/basic.h
similarity index 99%
rename from src/core/short_code/offset/basic.h
rename to src/core/short_code/internal/offset/basic.h
index 3c9dcce..72ed0de 100644
--- a/src/core/short_code/offset/basic.h
+++ b/src/core/short_code/internal/offset/basic.h
@@ -2,16 +2,14 @@
 
 #include <cstdint>
 
-namespace klotski {
-namespace codec {
-namespace offset {
+namespace klotski::codec::offset {
 
 /// This is the head index, the offset [0, 29334498) in all cases is obtained
 /// according to the `head` (0 ~ 15). In other words, the short code range can
 /// be obtained according to the position of the 2x2 block.
 
 // TODO: using std::array
-const uint32_t ALL_CASES_OFFSET[16] = {
+constexpr uint32_t ALL_CASES_OFFSET[16] {
            0,  2942906,  5203298,  8146204,
      8146204, 10468254, 12345199, 14667249,
     14667249, 16989299, 18866244, 21188294,
@@ -23,7 +21,7 @@ const uint32_t ALL_CASES_OFFSET[16] = {
 /// 32-bit `range`.
 
 // TODO: using std::array
-const uint32_t BASIC_RANGES_OFFSET[4096] = {
+constexpr uint32_t BASIC_RANGES_OFFSET[4096] {
           0,   18272,   24960,   31648,   49920,   56608,   59056,   61504,
       68192,   74880,   77328,   79776,   86464,  104736,  111424,  118112,
      136384,  143072,  145520,  147968,  154656,  157104,  158000,  158896,
@@ -538,6 +536,4 @@ const uint32_t BASIC_RANGES_OFFSET[4096] = {
     7253514, 7259861, 7261646, 7263431, 7268677, 7286266, 7291512, 7296758,
 };
 
-} // namespace offset
-} // namespace codec
-} // namespace klotski
+} // namespace klotski::codec::offset
diff --git a/src/core/short_code/offset/range_prefix.h b/src/core/short_code/internal/offset/range_prefix.h
similarity index 85%
rename from src/core/short_code/offset/range_prefix.h
rename to src/core/short_code/internal/offset/range_prefix.h
index a6730f3..6747994 100644
--- a/src/core/short_code/offset/range_prefix.h
+++ b/src/core/short_code/internal/offset/range_prefix.h
@@ -7,12 +7,10 @@
 
 #include <cstdint>
 
-namespace klotski {
-namespace codec {
-namespace offset {
+namespace klotski::codec::offset {
 
 // TODO: using std::array
-const uint32_t RANGE_PREFIX_OFFSET[16][4096] = {{
+constexpr uint32_t RANGE_PREFIX_OFFSET[16][4096] = {{
 #include "range_prefix/offset_0x0.inc"
 }, {
 #include "range_prefix/offset_0x1.inc"
@@ -46,6 +44,4 @@ const uint32_t RANGE_PREFIX_OFFSET[16][4096] = {{
 /// --------------- 0xF ---------------
 }};
 
-} // namespace offset
-} // namespace codec
-} // namespace klotski
+} // namespace klotski::codec::offset
diff --git a/src/core/short_code/offset/range_prefix/offset_0x0.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x0.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x0.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x0.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x1.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x1.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x1.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x1.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x2.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x2.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x2.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x2.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x4.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x4.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x4.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x4.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x5.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x5.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x5.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x5.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x6.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x6.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x6.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x6.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x8.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x8.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x8.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x8.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0x9.inc b/src/core/short_code/internal/offset/range_prefix/offset_0x9.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0x9.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0x9.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0xA.inc b/src/core/short_code/internal/offset/range_prefix/offset_0xA.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0xA.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0xA.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0xC.inc b/src/core/short_code/internal/offset/range_prefix/offset_0xC.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0xC.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0xC.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0xD.inc b/src/core/short_code/internal/offset/range_prefix/offset_0xD.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0xD.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0xD.inc
diff --git a/src/core/short_code/offset/range_prefix/offset_0xE.inc b/src/core/short_code/internal/offset/range_prefix/offset_0xE.inc
similarity index 100%
rename from src/core/short_code/offset/range_prefix/offset_0xE.inc
rename to src/core/short_code/internal/offset/range_prefix/offset_0xE.inc
diff --git a/src/core/short_code/serialize.cc b/src/core/short_code/internal/serialize.cc
similarity index 54%
rename from src/core/short_code/serialize.cc
rename to src/core/short_code/internal/serialize.cc
index 2e93a9b..2795ca3 100644
--- a/src/core/short_code/serialize.cc
+++ b/src/core/short_code/internal/serialize.cc
@@ -1,26 +1,25 @@
-#include "short_code.h"
 #include "serialize_chars.h"
+#include "short_code/short_code.h"
 
-namespace klotski {
-namespace codec {
+using klotski::codec::ShortCode;
 
-std::string ShortCode::string_encode(uint32_t short_code) noexcept { // encode as 5-bits string
-    char result[6]; // short code length 5
+std::string ShortCode::string_encode(uint32_t short_code) {
+    char result[6];
     result[5] = '\0'; // string ending flag
     for (int n = 0; n < 5; ++n) {
-        result[4 - n] = SHORT_CODE_TABLE[short_code & 0b11111]; // aka _ % 32
-        short_code >>= 5; // aka _ / 32
+        result[4 - n] = SHORT_CODE_TABLE[short_code & 0b11111];
+        short_code >>= 5;
     }
     return result;
 }
 
-std::optional<uint32_t> ShortCode::string_decode(const std::string &short_code) noexcept { // 5-bits string decode
-    if (short_code.length() != 5) { // check string length
-        return std::nullopt;
+std::optional<uint32_t> ShortCode::string_decode(const std::string &short_code) {
+    if (short_code.length() != 5) {
+        return std::nullopt; // invalid string length
     }
     uint64_t result = 0;
     for (auto bit : short_code) {
-        result <<= 5; // aka _ * 32
+        result <<= 5;
         if (bit >= 'a' && bit <= 'z') {
             bit -= 32; // convert to uppercase
         }
@@ -32,11 +31,8 @@ std::optional<uint32_t> ShortCode::string_decode(const std::string &short_code)
             return std::nullopt;
         }
     }
-    if (!ShortCode::check(result)) { // check converted short code
+    if (!check(result)) { // check converted short code
         return std::nullopt;
     }
     return result; // apply convert result
 }
-
-} // namespace codec
-} // namespace klotski
diff --git a/src/core/short_code/serialize_chars.h b/src/core/short_code/internal/serialize_chars.h
similarity index 88%
rename from src/core/short_code/serialize_chars.h
rename to src/core/short_code/internal/serialize_chars.h
index 2a587da..07b1234 100644
--- a/src/core/short_code/serialize_chars.h
+++ b/src/core/short_code/internal/serialize_chars.h
@@ -17,10 +17,9 @@
 
 #include <cstdint>
 
-namespace klotski {
-namespace codec {
+namespace klotski::codec {
 
-const int8_t SHORT_CODE_TABLE[32] = {
+constexpr int8_t SHORT_CODE_TABLE[32] {
     '1', '2', '3', '4', '5', '6', '7', '8', '9', // skip `0`
     'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // skip `I`
     'J', 'K', // skip `L`
@@ -28,8 +27,7 @@ const int8_t SHORT_CODE_TABLE[32] = {
     'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
 };
 
-/// `1`(49) ~ `Z`(90)
-const int8_t SHORT_CODE_TABLE_REV[42] = {
+constexpr int8_t SHORT_CODE_TABLE_REV[42] {
      0,  1,  2,  3,  4,  5,  6,  7,  8,     // `1`(49) ~ `9`(57)
     -1, -1, -1, -1, -1, -1, -1,             // `:`(58) ~ `@`(64)
      9, 10, 11, 12, 13, 14, 15, 16, -1, 17, // `A`(65) ~ `J`(74)
@@ -37,5 +35,4 @@ const int8_t SHORT_CODE_TABLE_REV[42] = {
     26, 27, 28, 29, 30, 31,                 // `U`(85) ~ `Z`(90)
 };
 
-} // namespace codec
-} // namespace klotski
+} // namespace klotski::codec
diff --git a/src/core/short_code/internal/short_code.inl b/src/core/short_code/internal/short_code.inl
new file mode 100644
index 0000000..7807161
--- /dev/null
+++ b/src/core/short_code/internal/short_code.inl
@@ -0,0 +1,120 @@
+#pragma once
+
+#include <bit>
+
+#include "common_code/common_code.h"
+
+namespace klotski::codec {
+
+// ------------------------------------------------------------------------------------- //
+
+inline ShortCode::ShortCode(const CommonCode common_code) {
+    // TODO: test the affect of CPU branch prediction.
+    if (cases::AllCases::instance().is_available()) {
+        code_ = fast_encode(common_code.unwrap());
+    } else {
+        code_ = tiny_encode(common_code.unwrap());
+    }
+}
+
+inline ShortCode ShortCode::unsafe_create(const uint32_t short_code) {
+    return std::bit_cast<ShortCode>(short_code); // init directly
+}
+
+inline std::optional<ShortCode> ShortCode::create(const uint32_t short_code) {
+    if (!check(short_code)) {
+        return std::nullopt; // invalid short code
+    }
+    return unsafe_create(short_code);
+}
+
+// ------------------------------------------------------------------------------------- //
+
+inline ShortCode::operator uint32_t() const {
+    return code_;
+}
+
+inline bool ShortCode::check(const uint32_t short_code) {
+    return short_code < SHORT_CODE_LIMIT; // [0, SHORT_CODE_LIMIT)
+}
+
+inline void ShortCode::speed_up(const bool fast_mode) {
+    if (fast_mode) {
+        cases::AllCases::instance().build();
+    } else {
+        cases::BasicRanges::instance().build();
+    }
+}
+
+#ifndef KLSK_NDEBUG
+inline std::ostream& operator<<(std::ostream &out, const ShortCode self) {
+    out << ShortCode::string_encode(self.code_);
+    return out;
+}
+#endif
+
+// ----------------------------------------------------------------------------------------- //
+
+inline uint32_t ShortCode::unwrap() const {
+    return code_;
+}
+
+inline std::string ShortCode::to_string() const {
+    return string_encode(code_);
+}
+
+inline CommonCode ShortCode::to_common_code() const {
+    // TODO: test the affect of CPU branch prediction.
+    if (cases::AllCases::instance().is_available()) {
+        return CommonCode::unsafe_create(fast_decode(code_));
+    }
+    return CommonCode::unsafe_create(tiny_decode(code_));
+}
+
+// ----------------------------------------------------------------------------------------- //
+
+inline std::optional<ShortCode> ShortCode::from_string(const std::string &short_code) {
+    return string_decode(short_code).transform(unsafe_create);
+}
+
+// ----------------------------------------------------------------------------------------- //
+
+inline ShortCode ShortCode::from_common_code(const CommonCode common_code) {
+    return common_code.to_short_code();
+}
+
+inline std::optional<ShortCode> ShortCode::from_common_code(const uint64_t common_code) {
+    const auto convert = [](const CommonCode code) {
+        return code.to_short_code();
+    };
+    return CommonCode::create(common_code).transform(convert);
+}
+
+inline std::optional<ShortCode> ShortCode::from_common_code(const std::string &common_code) {
+    const auto convert = [](const CommonCode code) {
+        return code.to_short_code();
+    };
+    return CommonCode::from_string(common_code).transform(convert);
+}
+
+// ------------------------------------------------------------------------------------- //
+
+constexpr auto operator==(const ShortCode &lhs, const uint32_t rhs) {
+    return lhs.code_ == rhs;
+}
+
+constexpr auto operator<=>(const ShortCode &lhs, const uint32_t rhs) {
+    return lhs.code_ <=> rhs;
+}
+
+constexpr auto operator==(const ShortCode &lhs, const ShortCode &rhs) {
+    return lhs.code_ == rhs.code_;
+}
+
+constexpr auto operator<=>(const ShortCode &lhs, const ShortCode &rhs) {
+    return lhs.code_ <=> rhs.code_;
+}
+
+// ----------------------------------------------------------------------------------------- //
+
+} // namespace klotski::codec
diff --git a/src/core/short_code/short_code.cc b/src/core/short_code/short_code.cc
deleted file mode 100644
index b2a8d7b..0000000
--- a/src/core/short_code/short_code.cc
+++ /dev/null
@@ -1,24 +0,0 @@
-#include "all_cases.h"
-#include "short_code.h"
-
-using klotski::cases::AllCases;
-using klotski::cases::BasicRanges;
-
-namespace klotski {
-namespace codec {
-
-/// Check the validity of the original ShortCode.
-bool ShortCode::check(uint32_t short_code) noexcept {
-    return short_code < SHORT_CODE_LIMIT; // 0 ~ (SHORT_CODE_LIMIT - 1)
-}
-
-void ShortCode::speed_up(bool fast_mode) noexcept {
-    if (fast_mode) {
-        AllCases::instance().build();
-    } else {
-        BasicRanges::instance().build();
-    }
-}
-
-} // namespace codec
-} // namespace klotski
diff --git a/src/core/short_code/short_code.h b/src/core/short_code/short_code.h
index 85d4fef..9a6d5d8 100644
--- a/src/core/short_code/short_code.h
+++ b/src/core/short_code/short_code.h
@@ -1,4 +1,4 @@
-#pragma once
+/// Klotski Engine by Dnomd343 @2024
 
 /// ShortCode is a high-compression encoding scheme based on CommonCode. Since
 /// there are a total of 29334498 valid klotski cases, arrange then from small
@@ -66,58 +66,119 @@
 ///            => "AXCZN"                                                                        ///
 /// -------------------------------------------------------------------------------------------- ///
 
+#pragma once
+
 #include <string>
 #include <cstdint>
 #include <ostream>
 #include <optional>
-#include "all_cases.h"
 
-namespace klotski {
-namespace codec {
+#include "all_cases/all_cases.h"
+
+namespace klotski::codec {
 
 constexpr uint32_t SHORT_CODE_LIMIT = cases::ALL_CASES_NUM_;
 
 class CommonCode;
+
 class ShortCode {
 public:
-    explicit operator uint32_t() const noexcept;
-    static bool check(uint32_t short_code) noexcept;
-    static void speed_up(bool fast_mode = false) noexcept;
+    // ------------------------------------------------------------------------------------- //
+
+    ShortCode() = delete;
+
+    /// Construct ShortCode from CommonCode.
+    explicit ShortCode(CommonCode common_code);
+
+    /// Create ShortCode without any check.
+    static ShortCode unsafe_create(uint32_t short_code);
+
+    /// Create ShortCode with validity check.
+    static std::optional<ShortCode> create(uint32_t short_code);
+
+    // ------------------------------------------------------------------------------------- //
+
+    /// Explicit conversion to u32 code.
+    explicit operator uint32_t() const;
+
+    /// Check the validity of the original ShortCode.
+    static bool check(uint32_t short_code);
+
+    /// Build the conversion index for ShortCode.
+    static void speed_up(bool fast_mode = false);
+
+#ifndef KLSK_NDEBUG
+    /// Output string encoding of ShortCode only for debug.
     friend std::ostream& operator<<(std::ostream &out, ShortCode self);
+#endif
 
-    [[nodiscard]] uint32_t unwrap() const noexcept;
-    [[nodiscard]] std::string to_string() const noexcept;
-    [[nodiscard]] CommonCode to_common_code() const noexcept;
+    // ------------------------------------------------------------------------------------- //
 
-public:
-    ShortCode() = delete;
-    explicit ShortCode(CommonCode common_code) noexcept;
+    /// Get the original u32 code.
+    [[nodiscard]] uint32_t unwrap() const;
+
+    /// Convert ShortCode to string form.
+    [[nodiscard]] std::string to_string() const;
+
+    /// Convert ShortCode to CommonCode.
+    [[nodiscard]] CommonCode to_common_code() const;
+
+    // ------------------------------------------------------------------------------------- //
+
+    /// Create ShortCode from string form.
+    static std::optional<ShortCode> from_string(const std::string &short_code);
+
+    // ------------------------------------------------------------------------------------- //
+
+    /// Create ShortCode from CommonCode.
+    static ShortCode from_common_code(CommonCode common_code);
+
+    /// Create ShortCode from CommonCode in u64.
+    static std::optional<ShortCode> from_common_code(uint64_t common_code);
 
-    static ShortCode unsafe_create(uint32_t short_code) noexcept;
-    static std::optional<ShortCode> create(uint32_t short_code) noexcept;
+    /// Create ShortCode from CommonCode in string form.
+    static std::optional<ShortCode> from_common_code(const std::string &common_code);
 
-    static std::optional<ShortCode> from_string(std::string &&short_code) noexcept;
-    static std::optional<ShortCode> from_string(const std::string &short_code) noexcept;
+    // ------------------------------------------------------------------------------------- //
 
-    static ShortCode from_common_code(CommonCode common_code) noexcept;
-    static std::optional<ShortCode> from_common_code(uint64_t common_code) noexcept;
-    static std::optional<ShortCode> from_common_code(std::string &&common_code) noexcept;
-    static std::optional<ShortCode> from_common_code(const std::string &common_code) noexcept;
+    /// Compare ShortCode with u32 value.
+    friend constexpr auto operator==(const ShortCode &lhs, uint32_t rhs);
+    friend constexpr auto operator<=>(const ShortCode &lhs, uint32_t rhs);
+
+    /// Compare the original values of two ShortCodes.
+    friend constexpr auto operator==(const ShortCode &lhs, const ShortCode &rhs);
+    friend constexpr auto operator<=>(const ShortCode &lhs, const ShortCode &rhs);
+
+    // ------------------------------------------------------------------------------------- //
 
 private:
     uint32_t code_;
 
-    static uint64_t fast_decode(uint32_t short_code) noexcept;
-    static uint32_t fast_encode(uint64_t common_code) noexcept;
+    // ------------------------------------------------------------------------------------- //
+
+    /// Convert ShortCode to CommonCode based on AllCases data.
+    static uint64_t fast_decode(uint32_t short_code);
+
+    /// Convert CommonCode to ShortCode based on AllCases data.
+    static uint32_t fast_encode(uint64_t common_code);
+
+    /// Convert ShortCode to CommonCode based on BasicRanges data.
+    static uint64_t tiny_decode(uint32_t short_code);
+
+    /// Convert CommonCode to ShortCode based on BasicRanges data.
+    static uint32_t tiny_encode(uint64_t common_code);
+
+    // ------------------------------------------------------------------------------------- //
+
+    /// Serialize ShortCode into 5-bit length string.
+    static std::string string_encode(uint32_t short_code);
 
-    static uint64_t tiny_decode(uint32_t short_code) noexcept;
-    static uint32_t tiny_encode(uint64_t common_code) noexcept;
+    /// Deserialize ShortCode from string and return nullopt on error.
+    static std::optional<uint32_t> string_decode(const std::string &short_code);
 
-    static std::string string_encode(uint32_t short_code) noexcept;
-    static std::optional<uint32_t> string_decode(const std::string &short_code) noexcept;
+    // ------------------------------------------------------------------------------------- //
 };
 
-} // namespace codec
-} // namespace klotski
+} // namespace klotski::codec
 
-#include "inline_impl.h"
+#include "internal/short_code.inl"
diff --git a/src/core/short_code/sundry.cc b/src/core/short_code/sundry.cc
deleted file mode 100644
index ccf7c5d..0000000
--- a/src/core/short_code/sundry.cc
+++ /dev/null
@@ -1,71 +0,0 @@
-#include "short_code.h"
-#include "common_code.h"
-
-using klotski::cases::AllCases;
-
-namespace klotski {
-namespace codec {
-
-// ----------------------------------------------------------------------------------------- //
-
-ShortCode::ShortCode(CommonCode common_code) noexcept {
-    if (AllCases::instance().is_available()) {
-        code_ = fast_encode(common_code.unwrap());
-    } else {
-        code_ = tiny_encode(common_code.unwrap());
-    }
-}
-
-// ----------------------------------------------------------------------------------------- //
-
-std::string ShortCode::to_string() const noexcept {
-    return string_encode(code_);
-}
-
-CommonCode ShortCode::to_common_code() const noexcept {
-    if (AllCases::instance().is_available()) {
-        return CommonCode::unsafe_create(fast_decode(code_));
-    }
-    return CommonCode::unsafe_create(tiny_decode(code_));
-}
-
-// ----------------------------------------------------------------------------------------- //
-
-std::optional<ShortCode> ShortCode::from_string(std::string &&short_code) noexcept {
-    return ShortCode::from_string(short_code);
-}
-
-std::optional<ShortCode> ShortCode::from_string(const std::string &short_code) noexcept {
-    return ShortCode::string_decode(short_code).transform([](auto code) {
-        return ShortCode::unsafe_create(code);
-    });
-}
-
-// ----------------------------------------------------------------------------------------- //
-
-ShortCode ShortCode::from_common_code(CommonCode common_code) noexcept {
-    return common_code.to_short_code();
-}
-
-std::optional<ShortCode> ShortCode::from_common_code(uint64_t common_code) noexcept {
-    return CommonCode::create(common_code).transform([](auto common_code) {
-        return common_code.to_short_code();
-    });
-}
-
-std::optional<ShortCode> ShortCode::from_common_code(std::string &&common_code) noexcept {
-    return CommonCode::from_string(std::move(common_code)).transform([](auto common_code) {
-        return common_code.to_short_code();
-    });
-}
-
-std::optional<ShortCode> ShortCode::from_common_code(const std::string &common_code) noexcept {
-    return CommonCode::from_string(common_code).transform([](auto common_code) {
-        return common_code.to_short_code();
-    });
-}
-
-// ----------------------------------------------------------------------------------------- //
-
-} // namespace codec
-} // namespace klotski