diff --git a/src/Makefile b/src/Makefile
index 88d759d2..aa13603a 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -55,7 +55,7 @@ SRCS = benchmark.cpp bitbase.cpp bitboard.cpp endgame.cpp evaluate.cpp main.cpp
 	nnue/features/castling_right.cpp \
 	nnue/features/enpassant.cpp \
 	nnue/nnue_test_command.cpp \
-	extra/sfen_packer.cpp \
+	learn/sfen_packer.cpp \
 	learn/learn.cpp \
 	learn/gensfen.cpp \
 	learn/convert.cpp \
diff --git a/src/extra/sfen_packer.cpp b/src/extra/sfen_packer.cpp
deleted file mode 100644
index b58ad5dd..00000000
--- a/src/extra/sfen_packer.cpp
+++ /dev/null
@@ -1,407 +0,0 @@
-#if defined (EVAL_LEARN)
-
-#include "sfen_packer.h"
-
-#include "../learn/packed_sfen.h"
-
-#include "../misc.h"
-#include "../position.h"
-
-#include <sstream>
-#include <fstream>
-#include <cstring> // std::memset()
-
-using namespace std;
-
-namespace Learner {
-
-  // Class that handles bitstream
-  // useful when doing aspect encoding
-  struct BitStream
-  {
-    // Set the memory to store the data in advance.
-    // Assume that memory is cleared to 0.
-    void set_data(std::uint8_t* data_) { data = data_; reset(); }
-
-    // Get the pointer passed in set_data().
-    uint8_t* get_data() const { return data; }
-
-    // Get the cursor.
-    int get_cursor() const { return bit_cursor; }
-
-    // reset the cursor
-    void reset() { bit_cursor = 0; }
-
-    // Write 1bit to the stream.
-    // If b is non-zero, write out 1. If 0, write 0.
-    void write_one_bit(int b)
-    {
-      if (b)
-        data[bit_cursor / 8] |= 1 << (bit_cursor & 7);
-
-      ++bit_cursor;
-    }
-
-    // Get 1 bit from the stream.
-    int read_one_bit()
-    {
-      int b = (data[bit_cursor / 8] >> (bit_cursor & 7)) & 1;
-      ++bit_cursor;
-
-      return b;
-    }
-
-    // write n bits of data
-    // Data shall be written out from the lower order of d.
-    void write_n_bit(int d, int n)
-    {
-      for (int i = 0; i <n; ++i)
-        write_one_bit(d & (1 << i));
-    }
-
-    // read n bits of data
-    // Reverse conversion of write_n_bit().
-    int read_n_bit(int n)
-    {
-      int result = 0;
-      for (int i = 0; i < n; ++i)
-        result |= read_one_bit() ? (1 << i) : 0;
-
-      return result;
-    }
-
-  private:
-    // Next bit position to read/write.
-    int bit_cursor;
-
-    // data entity
-    std::uint8_t* data;
-  };
-
-  // Class for compressing/decompressing sfen
-  // sfen can be packed to 256bit (32bytes) by Huffman coding.
-  // This is proven by mini. The above is Huffman coding.
-  //
-  // Internal format = 1-bit turn + 7-bit king position *2 + piece on board (Huffman coding) + hand piece (Huffman coding)
-  // Side to move (White = 0, Black = 1) (1bit)
-  // White King Position (6 bits)
-  // Black King Position (6 bits)
-  // Huffman Encoding of the board
-  // Castling availability (1 bit x 4)
-  // En passant square (1 or 1 + 6 bits)
-  // Rule 50 (6 bits)
-  // Game play (8 bits)
-  //
-  // TODO(someone): Rename SFEN to FEN.
-  //
-  struct SfenPacker
-  {
-    void pack(const Position& pos);
-
-    // sfen packed by pack() (256bit = 32bytes)
-    // Or sfen to decode with unpack()
-    uint8_t *data; // uint8_t[32];
-
-    BitStream stream;
-
-    // Output the board pieces to stream.
-    void write_board_piece_to_stream(Piece pc);
-
-    // Read one board piece from stream
-    Piece read_board_piece_from_stream();
-  };
-
-
-  // Huffman coding
-  // * is simplified from mini encoding to make conversion easier.
-  //
-  // 1 box on the board (other than NO_PIECE) = 2 to 6 bits (+ 1-bit flag + 1-bit forward and backward)
-  // 1 piece of hand piece = 1-5bit (+ 1-bit flag + 1bit ahead and behind)
-  //
-  // empty xxxxx0 + 0 (none)
-  // step xxxx01 + 2 xxxx0 + 2
-  // incense xx0011 + 2 xx001 + 2
-  // Katsura xx1011 + 2 xx101 + 2
-  // silver xx0111 + 2 xx011 + 2
-  // Gold x01111 + 1 x0111 + 1 // Gold is valid and has no flags.
-  // corner 011111 + 2 01111 + 2
-  // Fly 111111 + 2 11111 + 2
-  //
-  // Assuming all pieces are on the board,
-  // Sky 81-40 pieces = 41 boxes = 41bit
-  // Walk 4bit*18 pieces = 72bit
-  // Incense 6bit*4 pieces = 24bit
-  // Katsura 6bit*4 pieces = 24bit
-  // Silver 6bit*4 pieces = 24bit
-  // Gold 6bit* 4 pieces = 24bit
-  // corner 8bit* 2 pieces = 16bit
-  // Fly 8bit* 2 pieces = 16bit
-  // -------
-  // 241bit + 1bit (turn) + 7bit × 2 (King's position after) = 256bit
-  //
-  // When the piece on the board moves to the hand piece, the piece on the board becomes empty, so the box on the board can be expressed with 1 bit,
-  // Since the hand piece can be expressed by 1 bit less than the piece on the board, the total number of bits does not change in the end.
-  // Therefore, in this expression, any aspect can be expressed by this bit number.
-  // It is a hand piece and no flag is required, but if you include this, the bit number of the piece on the board will be -1
-  // Since the total number of bits can be fixed, we will include this as well.
-
-  // Huffman Encoding
-  //
-  // Empty  xxxxxxx0
-  // Pawn   xxxxx001 + 1 bit (Side to move)
-  // Knight xxxxx011 + 1 bit (Side to move)
-  // Bishop xxxxx101 + 1 bit (Side to move)
-  // Rook   xxxxx111 + 1 bit (Side to move)
-
-  struct HuffmanedPiece
-  {
-    int code; // how it will be coded
-    int bits; // How many bits do you have
-  };
-
-  constexpr HuffmanedPiece huffman_table[] =
-  {
-    {0b0000,1}, // NO_PIECE
-    {0b0001,4}, // PAWN
-    {0b0011,4}, // KNIGHT
-    {0b0101,4}, // BISHOP
-    {0b0111,4}, // ROOK
-    {0b1001,4}, // QUEEN
-  };
-
-  // Pack sfen and store in data[32].
-  void SfenPacker::pack(const Position& pos)
-  {
-  // cout << pos;
-
-    memset(data, 0, 32 /* 256bit */);
-    stream.set_data(data);
-
-    // turn
-    // Side to move.
-    stream.write_one_bit((int)(pos.side_to_move()));
-
-    // 7-bit positions for leading and trailing balls
-    // White king and black king, 6 bits for each.
-    for(auto c: Colors)
-      stream.write_n_bit(pos.king_square(c), 6);
-
-    // Write the pieces on the board other than the kings.
-    for (Rank r = RANK_8; r >= RANK_1; --r)
-    {
-      for (File f = FILE_A; f <= FILE_H; ++f)
-      {
-        Piece pc = pos.piece_on(make_square(f, r));
-        if (type_of(pc) == KING)
-          continue;
-        write_board_piece_to_stream(pc);
-      }
-    }
-
-    // TODO(someone): Support chess960.
-    stream.write_one_bit(pos.can_castle(WHITE_OO));
-    stream.write_one_bit(pos.can_castle(WHITE_OOO));
-    stream.write_one_bit(pos.can_castle(BLACK_OO));
-    stream.write_one_bit(pos.can_castle(BLACK_OOO));
-
-    if (pos.ep_square() == SQ_NONE) {
-      stream.write_one_bit(0);
-    }
-    else {
-      stream.write_one_bit(1);
-      stream.write_n_bit(static_cast<int>(pos.ep_square()), 6);
-    }
-
-    stream.write_n_bit(pos.state()->rule50, 6);
-
-    stream.write_n_bit(1 + (pos.game_ply()-(pos.side_to_move() == BLACK)) / 2, 8);
-
-    assert(stream.get_cursor() <= 256);
-  }
-
-  // Output the board pieces to stream.
-  void SfenPacker::write_board_piece_to_stream(Piece pc)
-  {
-    // piece type
-    PieceType pr = type_of(pc);
-    auto c = huffman_table[pr];
-    stream.write_n_bit(c.code, c.bits);
-
-    if (pc == NO_PIECE)
-      return;
-
-    // first and second flag
-    stream.write_one_bit(color_of(pc));
-  }
-
-  // Read one board piece from stream
-  Piece SfenPacker::read_board_piece_from_stream()
-  {
-    PieceType pr = NO_PIECE_TYPE;
-    int code = 0, bits = 0;
-    while (true)
-    {
-      code |= stream.read_one_bit() << bits;
-      ++bits;
-
-      assert(bits <= 6);
-
-      for (pr = NO_PIECE_TYPE; pr <KING; ++pr)
-        if (huffman_table[pr].code == code
-          && huffman_table[pr].bits == bits)
-          goto Found;
-    }
-  Found:;
-    if (pr == NO_PIECE_TYPE)
-      return NO_PIECE;
-
-    // first and second flag
-    Color c = (Color)stream.read_one_bit();
-
-    return make_piece(c, pr);
-  }
-
-  int set_from_packed_sfen(Position& pos, const PackedSfen& sfen, StateInfo* si, Thread* th, bool mirror)
-  {
-    SfenPacker packer;
-    auto& stream = packer.stream;
-
-    // TODO: separate streams for writing and reading. Here we actually have to
-    // const_cast which is not safe in the long run.
-    stream.set_data(const_cast<uint8_t*>(reinterpret_cast<const uint8_t*>(&sfen)));
-
-    std::memset(&pos, 0, sizeof(Position));
-    std::memset(si, 0, sizeof(StateInfo));
-    std::fill_n(&pos.pieceList[0][0], sizeof(pos.pieceList) / sizeof(Square), SQ_NONE);
-    pos.st = si;
-
-    // Active color
-    pos.sideToMove = (Color)stream.read_one_bit();
-
-    pos.pieceList[W_KING][0] = SQUARE_NB;
-    pos.pieceList[B_KING][0] = SQUARE_NB;
-
-    // First the position of the ball
-    if (mirror)
-    {
-      for (auto c : Colors)
-        pos.board[flip_file((Square)stream.read_n_bit(6))] = make_piece(c, KING);
-    }
-    else
-    {
-      for (auto c : Colors)
-        pos.board[stream.read_n_bit(6)] = make_piece(c, KING);
-    }
-
-    // Piece placement
-    for (Rank r = RANK_8; r >= RANK_1; --r)
-    {
-      for (File f = FILE_A; f <= FILE_H; ++f)
-      {
-        auto sq = make_square(f, r);
-        if (mirror) {
-          sq = flip_file(sq);
-        }
-
-        // it seems there are already balls
-        Piece pc;
-        if (type_of(pos.board[sq]) != KING)
-        {
-          assert(pos.board[sq] == NO_PIECE);
-          pc = packer.read_board_piece_from_stream();
-        }
-        else
-        {
-          pc = pos.board[sq];
-          // put_piece() will catch ASSERT unless you remove it all.
-          pos.board[sq] = NO_PIECE;
-        }
-
-        // There may be no pieces, so skip in that case.
-        if (pc == NO_PIECE)
-          continue;
-
-        pos.put_piece(Piece(pc), sq);
-
-        if (stream.get_cursor()> 256)
-          return 1;
-
-        //assert(stream.get_cursor() <= 256);
-      }
-    }
-
-    // Castling availability.
-    // TODO(someone): Support chess960.
-    pos.st->castlingRights = 0;
-    if (stream.read_one_bit()) {
-      Square rsq;
-      for (rsq = relative_square(WHITE, SQ_H1); pos.piece_on(rsq) != W_ROOK; --rsq) {}
-      pos.set_castling_right(WHITE, rsq);
-    }
-    if (stream.read_one_bit()) {
-      Square rsq;
-      for (rsq = relative_square(WHITE, SQ_A1); pos.piece_on(rsq) != W_ROOK; ++rsq) {}
-      pos.set_castling_right(WHITE, rsq);
-    }
-    if (stream.read_one_bit()) {
-      Square rsq;
-      for (rsq = relative_square(BLACK, SQ_H1); pos.piece_on(rsq) != B_ROOK; --rsq) {}
-      pos.set_castling_right(BLACK, rsq);
-    }
-    if (stream.read_one_bit()) {
-      Square rsq;
-      for (rsq = relative_square(BLACK, SQ_A1); pos.piece_on(rsq) != B_ROOK; ++rsq) {}
-      pos.set_castling_right(BLACK, rsq);
-    }
-
-    // En passant square. Ignore if no pawn capture is possible
-    if (stream.read_one_bit()) {
-      Square ep_square = static_cast<Square>(stream.read_n_bit(6));
-      if (mirror) {
-        ep_square = flip_file(ep_square);
-      }
-      pos.st->epSquare = ep_square;
-
-      if (!(pos.attackers_to(pos.st->epSquare) & pos.pieces(pos.sideToMove, PAWN))
-        || !(pos.pieces(~pos.sideToMove, PAWN) & (pos.st->epSquare + pawn_push(~pos.sideToMove))))
-        pos.st->epSquare = SQ_NONE;
-    }
-    else {
-      pos.st->epSquare = SQ_NONE;
-    }
-
-    // Halfmove clock
-    pos.st->rule50 = static_cast<Square>(stream.read_n_bit(6));
-
-    // Fullmove number
-    pos.gamePly = static_cast<Square>(stream.read_n_bit(8));
-
-    // Convert from fullmove starting from 1 to gamePly starting from 0,
-    // handle also common incorrect FEN with fullmove = 0.
-    pos.gamePly = std::max(2 * (pos.gamePly - 1), 0) + (pos.sideToMove == BLACK);
-
-    assert(stream.get_cursor() <= 256);
-
-    pos.chess960 = false;
-    pos.thisThread = th;
-    pos.set_state(pos.st);
-
-    assert(pos_is_ok());
-
-    return 0;
-  }
-
-  PackedSfen sfen_pack(Position& pos)
-  {
-    PackedSfen sfen;
-
-    SfenPacker sp;
-    sp.data = (uint8_t*)&sfen;
-    sp.pack(pos);
-
-    return sfen;
-  }
-}
-
-
-#endif // USE_SFEN_PACKER
diff --git a/src/extra/sfen_packer.h b/src/extra/sfen_packer.h
deleted file mode 100644
index c3832db2..00000000
--- a/src/extra/sfen_packer.h
+++ /dev/null
@@ -1,23 +0,0 @@
-#ifndef _SFEN_PACKER_H_
-#define _SFEN_PACKER_H_
-
-#if defined(EVAL_LEARN)
-
-#include <cstdint>
-
-#include "../types.h"
-
-#include "../learn/packed_sfen.h"
-class Position;
-struct StateInfo;
-class Thread;
-
-namespace Learner {
-
-    int set_from_packed_sfen(Position& pos, const PackedSfen& sfen, StateInfo* si, Thread* th, bool mirror);
-    PackedSfen sfen_pack(Position& pos);
-}
-
-#endif
-
-#endif
\ No newline at end of file
diff --git a/src/position.cpp b/src/position.cpp
index a9fc8272..9465afbc 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -34,7 +34,7 @@
 
 #if defined(EVAL_LEARN)
 #include "learn/packed_sfen.h"
-#include "extra/sfen_packer.h"
+#include "learn/sfen_packer.h"
 #endif
 
 using std::string;
diff --git a/src/position.h b/src/position.h
index 382748af..10cf45ba 100644
--- a/src/position.h
+++ b/src/position.h
@@ -32,7 +32,7 @@
 
 #if defined(EVAL_LEARN)
 #include "learn/packed_sfen.h"
-#include "extra/sfen_packer.h"
+#include "learn/sfen_packer.h"
 #endif