diff --git a/conv/CMakeLists.txt b/conv/CMakeLists.txt
index 2476b40..5bbce77 100644
--- a/conv/CMakeLists.txt
+++ b/conv/CMakeLists.txt
@@ -1,3 +1,6 @@
+add_executable(dcode_fcode common.hh dcode_fcode.cc)
+target_link_libraries(dcode_fcode PRIVATE args)
+
 add_executable(fidx_stego common.hh fidx_stego.cc)
 target_link_libraries(fidx_stego PRIVATE args minimp4 openh264)
 
@@ -6,3 +9,6 @@ target_link_libraries(stego_fprob PRIVATE args minimp4 openh264)
 
 add_executable(fcprob_fcode common.hh fcprob_fcode.cc)
 target_link_libraries(fcprob_fcode PRIVATE args)
+
+add_executable(fcode_dcode common.hh fcode_dcode.cc)
+target_link_libraries(fcode_dcode PRIVATE args)
diff --git a/conv/dcode_fcode.cc b/conv/dcode_fcode.cc
new file mode 100644
index 0000000..a522382
--- /dev/null
+++ b/conv/dcode_fcode.cc
@@ -0,0 +1,70 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+
+#include <args.hxx>
+
+#include "common.hh"
+
+
+namespace param {
+using namespace ::args;
+
+ArgumentParser parser {
+  "converter: feature code probability matrix -> feature code"
+};
+HelpFlag help {
+  parser, "help", "display this menu", {'h', "help"},
+};
+
+ValueFlag<std::string> smap {
+  parser, "path", "step map file path", {"smap"},
+};
+
+ValueFlag<size_t> first {
+  parser, "0", "first fcode", {"first"}, 0
+};
+ValueFlag<size_t> fcnum {
+  parser, "50", "number of fcode alphabet", {"fc-num"}, 50
+};
+
+}  // namespace param
+
+
+static void Exec() {
+  const auto fcnum = args::get(param::fcnum);
+  Enforce(fcnum > 0, "fc-num must be greater than 0");
+
+  std::ifstream smap_st {args::get(param::smap)};
+  Enforce(!!smap_st, "smap path is invalid");
+  const auto smap = ReadMatrix<uint32_t>(smap_st);
+  Enforce(smap.size() > 0 && smap[0].size() > 0, "empty smap");
+
+  const auto bn = smap[0].size();
+  for (auto& br : smap) {
+    Enforce(br.size() == bn, "all node should have the same number of branch");
+  }
+
+  size_t fcode = args::get(param::first);
+  std::cout << fcode << '\n';
+
+  for (size_t dcode, t = 0; std::cin >> dcode; ++t) {
+    Enforce(dcode < bn, "dcode must be lower than number of branch");
+    Enforce(fcnum*(t+1) <= smap.size(), "smap row shortage");
+    fcode = smap[t*fcnum + fcode][dcode];
+    std::cout << fcode << '\n';
+  }
+}
+
+int main(int argc, char** argv)
+try {
+  param::parser.ParseCLI(argc, argv);
+  Exec();
+  return EXIT_SUCCESS;
+} catch (const args::Help&) {
+  std::cout << param::parser << std::endl;
+  return EXIT_SUCCESS;
+} catch (const std::exception& e) {
+  std::cerr << e.what() << std::endl;
+  return EXIT_FAILURE;
+}
diff --git a/conv/fcode_dcode.cc b/conv/fcode_dcode.cc
new file mode 100644
index 0000000..fb25bb2
--- /dev/null
+++ b/conv/fcode_dcode.cc
@@ -0,0 +1,71 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+
+#include <args.hxx>
+
+#include "common.hh"
+
+
+namespace param {
+using namespace ::args;
+
+ArgumentParser parser {
+  "converter: feature code probability matrix -> feature code"
+};
+HelpFlag help {
+  parser, "help", "display this menu", {'h', "help"},
+};
+
+ValueFlag<std::string> smap {
+  parser, "path", "step map file path", {"smap"},
+};
+
+ValueFlag<size_t> fcnum {
+  parser, "50", "number of fcode alphabet", {"fc-num"}, 50
+};
+
+}  // namespace param
+
+
+static void Exec() {
+  const auto fcnum = args::get(param::fcnum);
+  Enforce(fcnum > 0, "fc-num must be greater than 0");
+
+  std::ifstream smap_st {args::get(param::smap)};
+  Enforce(!!smap_st, "smap path is invalid");
+  const auto smap = ReadMatrix<uint32_t>(smap_st);
+  Enforce(smap.size() > 0 && smap[0].size() > 0, "empty smap");
+
+  const auto bn = smap[0].size();
+  for (auto& br : smap) {
+    Enforce(br.size() == bn, "all node should have the same number of branch");
+  }
+
+  size_t fcode_p, dcode;
+  std::cin >> fcode_p;
+  for (size_t fcode, t = 0; std::cin >> fcode; ++t) {
+    Enforce(fcode < fcnum, "fcode overflow");
+    Enforce(fcnum*(t+1) <= smap.size(), "smap row shortage");
+
+    const auto& row = smap[t*fcnum + fcode_p];
+    auto itr = std::find(row.begin(), row.end(), fcode);
+    Enforce(itr != row.end(), "invalid step detected");
+    std::cout << std::distance(row.begin(), itr) << '\n';
+    fcode_p = fcode;
+  }
+}
+
+int main(int argc, char** argv)
+try {
+  param::parser.ParseCLI(argc, argv);
+  Exec();
+  return EXIT_SUCCESS;
+} catch (const args::Help&) {
+  std::cout << param::parser << std::endl;
+  return EXIT_SUCCESS;
+} catch (const std::exception& e) {
+  std::cerr << e.what() << std::endl;
+  return EXIT_FAILURE;
+}
+