diff --git a/src/main.cc b/src/main.cc
index e0f1acb..a989945 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -69,6 +69,17 @@
 //    std::cout << "[" << start << ", " << end << ")" << std::endl;
 //}
 
+void raw_code_check_verify(uint64_t index) {
+    uint64_t start = index * 0x100000000;
+    uint64_t end = start + 0x100000000;
+    for (uint64_t common_code = start; common_code < end; ++common_code) {
+        if (RawCode::check(RawCode::extract(common_code)) != CommonCode::check(common_code)) {
+            printf("Error -> %09lX\n", common_code);
+        }
+    }
+    std::cout << "verify ok: " << std::hex << "[" << start << ", " << end << ")" << std::endl;
+}
+
 int main() {
 
 //    AllCases::build();
@@ -393,19 +404,30 @@ int main() {
 //        if (RawCode::check(RawCode::extract(common_code)) != CommonCode::check(common_code)) {
 //            printf("%09lX\n", common_code);
 //        }
-//        if (common_code % 0x1000 == 0) {
-//            std::cout << std::hex << common_code << std::endl;
+//        if (common_code % 0x1000000 == 0) {
+//            std::cout << (common_code / 0x1000000) << std::endl;
 //        }
 //    }
 
+    std::thread tasks[16];
+    std::cout << "verify start" << std::endl;
+    for (int i = 0; i < 16; ++i) {
+        tasks[i] = std::thread(raw_code_check_verify, i);
+    }
+    for (auto &t : tasks) {
+        t.join();
+    }
+    std::cout << "verify complete" << std::endl;
+
     // TODO: why 0x555a4001 broken extract function?
 //    std::cout << RawCode(RawCode::extract(0x00000FEC4)).dump_case() << std::endl;
 //    std::cout << RawCode(RawCode::extract(0x000055480)).dump_case() << std::endl;
 //    std::cout << RawCode(RawCode::extract(0x0000FF004)).dump_case() << std::endl;
-    std::cout << RawCode::extract(0x555a4001) << std::endl;
+//    std::cout << RawCode::extract(0x555a4001) << std::endl;
 
+    std::cerr << (clock() - start_time) / CLOCKS_PER_SEC << "s" << std::endl;
 //    std::cerr << (clock() - start_time) * 1000 / CLOCKS_PER_SEC << "ms" << std::endl;
-    std::cerr << (clock() - start_time) * 1000000 / CLOCKS_PER_SEC << "us" << std::endl;
+//    std::cerr << (clock() - start_time) * 1000000 / CLOCKS_PER_SEC << "us" << std::endl;
 //    std::cout << "complete benchmark" << std::endl;
 
 //    pause();
diff --git a/src/raw_code/convert.cc b/src/raw_code/convert.cc
index 178fc0e..cae71c0 100644
--- a/src/raw_code/convert.cc
+++ b/src/raw_code/convert.cc
@@ -47,14 +47,14 @@ uint64_t RawCode::compact(uint64_t raw_code) { // raw code --> common code
     return head | (range << (unfilled << 1)); // fill low bits as zero
 }
 
-#include <iostream>
-
 /// NOTE: ensure that input common code is valid !!!
 uint64_t RawCode::extract(uint64_t common_code) { // common code --> raw code
     auto code = C_2x2 << (common_code >> 32) * 3; // flag for 2x2 block
     auto range = Common::range_reverse((uint32_t)common_code); // reversed range
+
     for (int addr = 0; range; range >>= 2) {
-        while (0b111 & code >> addr) { // check low 3-bits -> next empty address
+        /// NOTE: (code >> 65) --> (code >> 1) may cause infinite loop
+        while ((code >> addr) & 0b111 && addr < 60) { // check low 3-bits -> next empty address
             addr += 3; // found available address
         }
 
@@ -62,7 +62,6 @@ uint64_t RawCode::extract(uint64_t common_code) { // common code --> raw code
         if (addr >= 60) {
             return 0;
         }
-//        std::cout << "addr = " << addr << " | block = " << (range & 0b11) << std::endl;
 
         switch (range & 0b11) { // match low 2-bits
             case 0b01: // 1x2 block
diff --git a/src/raw_code/raw_code.cc b/src/raw_code/raw_code.cc
index 1d5c9c7..a633663 100644
--- a/src/raw_code/raw_code.cc
+++ b/src/raw_code/raw_code.cc
@@ -32,19 +32,11 @@ bool RawCode::check(uint64_t raw_code) { // check whether raw code is valid
     constexpr uint64_t MASK_2x1 = MASK_1x1 << 12;
     constexpr uint64_t MASK_2x2 = MASK_1x1 << 3 | MASK_1x1 << 12 | MASK_1x1 << 15;
 
-//    if (MASK_1x2 != 0b100000) {
-//        printf("error\n");
-//    }
-//    if (MASK_2x1 != 0b100000000000000) {
-//        printf("error\n");
-//    }
-//    if (MASK_2x2 != 0b100100000000100000) {
-//        printf("error\n");
-//    }
-
+    /// high 4-bits check
     if (raw_code >> 60) {
         return false; // high 4-bits must be zero
     }
+    /// check each block
     int head_num = 0, space_num = 0; // statistics for space and 2x2 number
     for (int addr = 0; addr < 20; ++addr, raw_code >>= 3) {
         switch (raw_code & 0b111) {