diff --git a/klotski/common_code.cc b/klotski/common_code.cc
index 75b9fbd..83374ae 100644
--- a/klotski/common_code.cc
+++ b/klotski/common_code.cc
@@ -1,6 +1,27 @@
+#include <stdexcept>
 #include "common.h"
 #include "common_code.h"
 
+inline uint8_t last_zero_num(uint32_t bin) { // get last zero number
+    bin ^= (bin - 1);
+    return __builtin_popcount(bin >> 1);
+}
+
+std::string CommonCode::code_to_string(uint64_t common_code, bool shorten) {
+    if (!CommonCode::check(common_code)) {
+        throw std::invalid_argument("invalid common code");
+    }
+    char result[10];
+    sprintf(result, "%09lX", common_code);
+    if (shorten) { // remove `0` after common code
+        if (common_code == 0x000000000) {
+            return "0"; // special case
+        }
+        result[9 - last_zero_num(common_code) / 4] = '\0'; // truncate string
+    }
+    return result;
+}
+
 bool CommonCode::check(uint64_t common_code) {
     uint32_t head = common_code >> 32;
     if (head >= 16 || (head & 0b11) == 0b11) { // check 2x2 block address
diff --git a/klotski/common_code.h b/klotski/common_code.h
index 9a2005c..833adc8 100644
--- a/klotski/common_code.h
+++ b/klotski/common_code.h
@@ -1,8 +1,11 @@
 #pragma once
 
+#include <string>
 #include <cstdint>
 
 class CommonCode {
 public:
     static bool check(uint64_t common_code);
+//    static uint64_t code_from_string(const std::string &common_code);
+    static std::string code_to_string(uint64_t common_code, bool shorten = false);
 };
diff --git a/klotski/main.cc b/klotski/main.cc
index 6af547e..b73f139 100644
--- a/klotski/main.cc
+++ b/klotski/main.cc
@@ -1,35 +1,39 @@
 #include <iostream>
 #include "all_cases.h"
 #include "short_code.h"
-//#include "common_code.h"
+#include "common_code.h"
 
 int main() {
 
 //    auto a = AllCases();
 //    auto a = AllCases(AllCases::Build::BASIC_RANGES);
 //    auto a = AllCases(AllCases::Build::ALL_CASES);
-//
+
 //    std::cout << "start getting basic ranges" << std::endl;
 //    std::cout << "basic range: " << a.get_basic_ranges()->size() << std::endl;
-//
+
 //    std::cout << "start getting all cases" << std::endl;
 //    for (const auto &temp : *a.get_all_cases()) {
 //        std::cout << "  " << temp.size() << std::endl;
 //    }
 
 
-    auto s = ShortCode();
+//    auto s = ShortCode();
 //    auto s = ShortCode(ShortCode::Mode::NORMAL);
 //    auto s = ShortCode(ShortCode::Mode::FAST);
 
 //    s.speed_up(ShortCode::Mode::NORMAL);
 //    s.speed_up(ShortCode::Mode::FAST);
 
-    printf("%d\n", s.zip_short_code(0x6EC0F8800));
-    printf("%09lX\n", s.unzip_short_code(14323231));
+//    printf("%d\n", s.zip_short_code(0x6EC0F8800));
+//    printf("%09lX\n", s.unzip_short_code(14323231));
+
+//    std::cout << ShortCode::code_to_string(14323231) << std::endl;
+//    std::cout << ShortCode::code_from_string("EP4HZ") << std::endl;
+
 
-    std::cout << ShortCode::code_to_string(14323231) << std::endl;
-    std::cout << ShortCode::code_from_string("EP4HZ") << std::endl;
+    std::cout << CommonCode::code_to_string(0x4FEA13400, true) << std::endl;
+    std::cout << CommonCode::code_to_string(0x4FEA13400) << std::endl;
 
     return 0;
 }