2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (c) 2013 Ronald de Man
4 Copyright (C) 2016-2020 Marco Costalba, Lucas Braesch
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset and std::memcpy
29 #include <type_traits>
32 #include "../bitboard.h"
33 #include "../movegen.h"
34 #include "../position.h"
35 #include "../search.h"
47 #define WIN32_LEAN_AND_MEAN
49 # define NOMINMAX // Disable macros min() and max()
54 using namespace Tablebases;
56 int Tablebases::MaxCardinality;
60 constexpr int TBPIECES = 7; // Max number of supported pieces
62 enum { BigEndian, LittleEndian };
63 enum TBType { WDL, DTZ }; // Used as template parameter
65 // Each table has a set of flags: all of them refer to DTZ tables, the last one to WDL tables
66 enum TBFlag { STM = 1, Mapped = 2, WinPlies = 4, LossPlies = 8, Wide = 16, SingleValue = 128 };
68 inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
69 inline Square operator^(Square s, int i) { return Square(int(s) ^ i); }
71 const std::string PieceToChar = " PNBRQK pnbrqk";
73 int MapPawns[SQUARE_NB];
74 int MapB1H1H7[SQUARE_NB];
75 int MapA1D1D4[SQUARE_NB];
76 int MapKK[10][SQUARE_NB]; // [MapA1D1D4][SQUARE_NB]
78 int Binomial[6][SQUARE_NB]; // [k][n] k elements from a set of n elements
79 int LeadPawnIdx[6][SQUARE_NB]; // [leadPawnsCnt][SQUARE_NB]
80 int LeadPawnsSize[6][4]; // [leadPawnsCnt][FILE_A..FILE_D]
82 // Comparison function to sort leading pawns in ascending MapPawns[] order
83 bool pawns_comp(Square i, Square j) { return MapPawns[i] < MapPawns[j]; }
84 int off_A1H8(Square sq) { return int(rank_of(sq)) - file_of(sq); }
86 constexpr Value WDL_to_value[] = {
87 -VALUE_MATE + MAX_PLY + 1,
91 VALUE_MATE - MAX_PLY - 1
94 template<typename T, int Half = sizeof(T) / 2, int End = sizeof(T) - 1>
95 inline void swap_endian(T& x)
97 static_assert(std::is_unsigned<T>::value, "Argument of swap_endian not unsigned");
99 uint8_t tmp, *c = (uint8_t*)&x;
100 for (int i = 0; i < Half; ++i)
101 tmp = c[i], c[i] = c[End - i], c[End - i] = tmp;
103 template<> inline void swap_endian<uint8_t>(uint8_t&) {}
105 template<typename T, int LE> T number(void* addr)
107 static const union { uint32_t i; char c[4]; } Le = { 0x01020304 };
108 static const bool IsLittleEndian = (Le.c[0] == 4);
112 if ((uintptr_t)addr & (alignof(T) - 1)) // Unaligned pointer (very rare)
113 std::memcpy(&v, addr, sizeof(T));
117 if (LE != IsLittleEndian)
122 // DTZ tables don't store valid scores for moves that reset the rule50 counter
123 // like captures and pawn moves but we can easily recover the correct dtz of the
124 // previous move if we know the position's WDL score.
125 int dtz_before_zeroing(WDLScore wdl) {
126 return wdl == WDLWin ? 1 :
127 wdl == WDLCursedWin ? 101 :
128 wdl == WDLBlessedLoss ? -101 :
129 wdl == WDLLoss ? -1 : 0;
132 // Return the sign of a number (-1, 0, 1)
133 template <typename T> int sign_of(T val) {
134 return (T(0) < val) - (val < T(0));
137 // Numbers in little endian used by sparseIndex[] to point into blockLength[]
139 char block[4]; // Number of block
140 char offset[2]; // Offset within the block
143 static_assert(sizeof(SparseEntry) == 6, "SparseEntry must be 6 bytes");
145 typedef uint16_t Sym; // Huffman symbol
148 enum Side { Left, Right };
150 uint8_t lr[3]; // The first 12 bits is the left-hand symbol, the second 12
151 // bits is the right-hand symbol. If symbol has length 1,
152 // then the left-hand symbol is the stored value.
155 return S == Left ? ((lr[1] & 0xF) << 8) | lr[0] :
156 S == Right ? (lr[2] << 4) | (lr[1] >> 4) : (assert(false), Sym(-1));
160 static_assert(sizeof(LR) == 3, "LR tree entry must be 3 bytes");
162 // Tablebases data layout is structured as following:
164 // TBFile: memory maps/unmaps the physical .rtbw and .rtbz files
165 // TBTable: one object for each file with corresponding indexing information
166 // TBTables: has ownership of TBTable objects, keeping a list and a hash
168 // class TBFile memory maps/unmaps the single .rtbw and .rtbz files. Files are
169 // memory mapped for best performance. Files are mapped at first access: at init
170 // time only existence of the file is checked.
171 class TBFile : public std::ifstream {
176 // Look for and open the file among the Paths directories where the .rtbw
177 // and .rtbz files can be found. Multiple directories are separated by ";"
178 // on Windows and by ":" on Unix-based operating systems.
181 // C:\tb\wdl345;C:\tb\wdl6;D:\tb\dtz345;D:\tb\dtz6
182 static std::string Paths;
184 TBFile(const std::string& f) {
187 constexpr char SepChar = ':';
189 constexpr char SepChar = ';';
191 std::stringstream ss(Paths);
194 while (std::getline(ss, path, SepChar)) {
195 fname = path + "/" + f;
196 std::ifstream::open(fname);
202 // Memory map the file and check it. File should be already open and will be
203 // closed after mapping.
204 uint8_t* map(void** baseAddress, uint64_t* mapping, TBType type) {
208 close(); // Need to re-open to get native file descriptor
212 int fd = ::open(fname.c_str(), O_RDONLY);
215 return *baseAddress = nullptr, nullptr;
219 if (statbuf.st_size % 64 != 16)
221 std::cerr << "Corrupt tablebase file " << fname << std::endl;
225 *mapping = statbuf.st_size;
226 *baseAddress = mmap(nullptr, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
227 madvise(*baseAddress, statbuf.st_size, MADV_RANDOM);
230 if (*baseAddress == MAP_FAILED)
232 std::cerr << "Could not mmap() " << fname << std::endl;
236 // Note FILE_FLAG_RANDOM_ACCESS is only a hint to Windows and as such may get ignored.
237 HANDLE fd = CreateFile(fname.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
238 OPEN_EXISTING, FILE_FLAG_RANDOM_ACCESS, nullptr);
240 if (fd == INVALID_HANDLE_VALUE)
241 return *baseAddress = nullptr, nullptr;
244 DWORD size_low = GetFileSize(fd, &size_high);
246 if (size_low % 64 != 16)
248 std::cerr << "Corrupt tablebase file " << fname << std::endl;
252 HANDLE mmap = CreateFileMapping(fd, nullptr, PAGE_READONLY, size_high, size_low, nullptr);
257 std::cerr << "CreateFileMapping() failed" << std::endl;
261 *mapping = (uint64_t)mmap;
262 *baseAddress = MapViewOfFile(mmap, FILE_MAP_READ, 0, 0, 0);
266 std::cerr << "MapViewOfFile() failed, name = " << fname
267 << ", error = " << GetLastError() << std::endl;
271 uint8_t* data = (uint8_t*)*baseAddress;
273 constexpr uint8_t Magics[][4] = { { 0xD7, 0x66, 0x0C, 0xA5 },
274 { 0x71, 0xE8, 0x23, 0x5D } };
276 if (memcmp(data, Magics[type == WDL], 4))
278 std::cerr << "Corrupted table in file " << fname << std::endl;
279 unmap(*baseAddress, *mapping);
280 return *baseAddress = nullptr, nullptr;
283 return data + 4; // Skip Magics's header
286 static void unmap(void* baseAddress, uint64_t mapping) {
289 munmap(baseAddress, mapping);
291 UnmapViewOfFile(baseAddress);
292 CloseHandle((HANDLE)mapping);
297 std::string TBFile::Paths;
299 // struct PairsData contains low level indexing information to access TB data.
300 // There are 8, 4 or 2 PairsData records for each TBTable, according to type of
301 // table and if positions have pawns or not. It is populated at first access.
303 uint8_t flags; // Table flags, see enum TBFlag
304 uint8_t maxSymLen; // Maximum length in bits of the Huffman symbols
305 uint8_t minSymLen; // Minimum length in bits of the Huffman symbols
306 uint32_t blocksNum; // Number of blocks in the TB file
307 size_t sizeofBlock; // Block size in bytes
308 size_t span; // About every span values there is a SparseIndex[] entry
309 Sym* lowestSym; // lowestSym[l] is the symbol of length l with the lowest value
310 LR* btree; // btree[sym] stores the left and right symbols that expand sym
311 uint16_t* blockLength; // Number of stored positions (minus one) for each block: 1..65536
312 uint32_t blockLengthSize; // Size of blockLength[] table: padded so it's bigger than blocksNum
313 SparseEntry* sparseIndex; // Partial indices into blockLength[]
314 size_t sparseIndexSize; // Size of SparseIndex[] table
315 uint8_t* data; // Start of Huffman compressed data
316 std::vector<uint64_t> base64; // base64[l - min_sym_len] is the 64bit-padded lowest symbol of length l
317 std::vector<uint8_t> symlen; // Number of values (-1) represented by a given Huffman symbol: 1..256
318 Piece pieces[TBPIECES]; // Position pieces: the order of pieces defines the groups
319 uint64_t groupIdx[TBPIECES+1]; // Start index used for the encoding of the group's pieces
320 int groupLen[TBPIECES+1]; // Number of pieces in a given group: KRKN -> (3, 1)
321 uint16_t map_idx[4]; // WDLWin, WDLLoss, WDLCursedWin, WDLBlessedLoss (used in DTZ)
324 // struct TBTable contains indexing information to access the corresponding TBFile.
325 // There are 2 types of TBTable, corresponding to a WDL or a DTZ file. TBTable
326 // is populated at init time but the nested PairsData records are populated at
327 // first access, when the corresponding file is memory mapped.
328 template<TBType Type>
330 typedef typename std::conditional<Type == WDL, WDLScore, int>::type Ret;
332 static constexpr int Sides = Type == WDL ? 2 : 1;
334 std::atomic_bool ready;
342 bool hasUniquePieces;
343 uint8_t pawnCount[2]; // [Lead color / other color]
344 PairsData items[Sides][4]; // [wtm / btm][FILE_A..FILE_D or 0]
346 PairsData* get(int stm, int f) {
347 return &items[stm % Sides][hasPawns ? f : 0];
350 TBTable() : ready(false), baseAddress(nullptr) {}
351 explicit TBTable(const std::string& code);
352 explicit TBTable(const TBTable<WDL>& wdl);
356 TBFile::unmap(baseAddress, mapping);
361 TBTable<WDL>::TBTable(const std::string& code) : TBTable() {
366 key = pos.set(code, WHITE, &st).material_key();
367 pieceCount = pos.count<ALL_PIECES>();
368 hasPawns = pos.pieces(PAWN);
370 hasUniquePieces = false;
371 for (Color c : { WHITE, BLACK })
372 for (PieceType pt = PAWN; pt < KING; ++pt)
373 if (popcount(pos.pieces(c, pt)) == 1)
374 hasUniquePieces = true;
376 // Set the leading color. In case both sides have pawns the leading color
377 // is the side with less pawns because this leads to better compression.
378 bool c = !pos.count<PAWN>(BLACK)
379 || ( pos.count<PAWN>(WHITE)
380 && pos.count<PAWN>(BLACK) >= pos.count<PAWN>(WHITE));
382 pawnCount[0] = pos.count<PAWN>(c ? WHITE : BLACK);
383 pawnCount[1] = pos.count<PAWN>(c ? BLACK : WHITE);
385 key2 = pos.set(code, BLACK, &st).material_key();
389 TBTable<DTZ>::TBTable(const TBTable<WDL>& wdl) : TBTable() {
391 // Use the corresponding WDL table to avoid recalculating all from scratch
394 pieceCount = wdl.pieceCount;
395 hasPawns = wdl.hasPawns;
396 hasUniquePieces = wdl.hasUniquePieces;
397 pawnCount[0] = wdl.pawnCount[0];
398 pawnCount[1] = wdl.pawnCount[1];
401 // class TBTables creates and keeps ownership of the TBTable objects, one for
402 // each TB file found. It supports a fast, hash based, table lookup. Populated
403 // at init time, accessed at probe time.
412 template <TBType Type>
413 TBTable<Type>* get() const {
414 return (TBTable<Type>*)(Type == WDL ? (void*)wdl : (void*)dtz);
418 static constexpr int Size = 1 << 12; // 4K table, indexed by key's 12 lsb
419 static constexpr int Overflow = 1; // Number of elements allowed to map to the last bucket
421 Entry hashTable[Size + Overflow];
423 std::deque<TBTable<WDL>> wdlTable;
424 std::deque<TBTable<DTZ>> dtzTable;
426 void insert(Key key, TBTable<WDL>* wdl, TBTable<DTZ>* dtz) {
427 uint32_t homeBucket = (uint32_t)key & (Size - 1);
428 Entry entry{ key, wdl, dtz };
430 // Ensure last element is empty to avoid overflow when looking up
431 for (uint32_t bucket = homeBucket; bucket < Size + Overflow - 1; ++bucket) {
432 Key otherKey = hashTable[bucket].key;
433 if (otherKey == key || !hashTable[bucket].get<WDL>()) {
434 hashTable[bucket] = entry;
438 // Robin Hood hashing: If we've probed for longer than this element,
439 // insert here and search for a new spot for the other element instead.
440 uint32_t otherHomeBucket = (uint32_t)otherKey & (Size - 1);
441 if (otherHomeBucket > homeBucket) {
442 std::swap(entry, hashTable[bucket]);
444 homeBucket = otherHomeBucket;
447 std::cerr << "TB hash table size too low!" << std::endl;
452 template<TBType Type>
453 TBTable<Type>* get(Key key) {
454 for (const Entry* entry = &hashTable[(uint32_t)key & (Size - 1)]; ; ++entry) {
455 if (entry->key == key || !entry->get<Type>())
456 return entry->get<Type>();
461 memset(hashTable, 0, sizeof(hashTable));
465 size_t size() const { return wdlTable.size(); }
466 void add(const std::vector<PieceType>& pieces);
471 // If the corresponding file exists two new objects TBTable<WDL> and TBTable<DTZ>
472 // are created and added to the lists and hash table. Called at init time.
473 void TBTables::add(const std::vector<PieceType>& pieces) {
477 for (PieceType pt : pieces)
478 code += PieceToChar[pt];
480 TBFile file(code.insert(code.find('K', 1), "v") + ".rtbw"); // KRK -> KRvK
482 if (!file.is_open()) // Only WDL file is checked
487 MaxCardinality = std::max((int)pieces.size(), MaxCardinality);
489 wdlTable.emplace_back(code);
490 dtzTable.emplace_back(wdlTable.back());
492 // Insert into the hash keys for both colors: KRvK with KR white and black
493 insert(wdlTable.back().key , &wdlTable.back(), &dtzTable.back());
494 insert(wdlTable.back().key2, &wdlTable.back(), &dtzTable.back());
497 // TB tables are compressed with canonical Huffman code. The compressed data is divided into
498 // blocks of size d->sizeofBlock, and each block stores a variable number of symbols.
499 // Each symbol represents either a WDL or a (remapped) DTZ value, or a pair of other symbols
500 // (recursively). If you keep expanding the symbols in a block, you end up with up to 65536
501 // WDL or DTZ values. Each symbol represents up to 256 values and will correspond after
502 // Huffman coding to at least 1 bit. So a block of 32 bytes corresponds to at most
503 // 32 x 8 x 256 = 65536 values. This maximum is only reached for tables that consist mostly
504 // of draws or mostly of wins, but such tables are actually quite common. In principle, the
505 // blocks in WDL tables are 64 bytes long (and will be aligned on cache lines). But for
506 // mostly-draw or mostly-win tables this can leave many 64-byte blocks only half-filled, so
507 // in such cases blocks are 32 bytes long. The blocks of DTZ tables are up to 1024 bytes long.
508 // The generator picks the size that leads to the smallest table. The "book" of symbols and
509 // Huffman codes is the same for all blocks in the table. A non-symmetric pawnless TB file
510 // will have one table for wtm and one for btm, a TB file with pawns will have tables per
511 // file a,b,c,d also in this case one set for wtm and one for btm.
512 int decompress_pairs(PairsData* d, uint64_t idx) {
514 // Special case where all table positions store the same value
515 if (d->flags & TBFlag::SingleValue)
518 // First we need to locate the right block that stores the value at index "idx".
519 // Because each block n stores blockLength[n] + 1 values, the index i of the block
520 // that contains the value at position idx is:
522 // for (i = -1, sum = 0; sum <= idx; i++)
523 // sum += blockLength[i + 1] + 1;
525 // This can be slow, so we use SparseIndex[] populated with a set of SparseEntry that
526 // point to known indices into blockLength[]. Namely SparseIndex[k] is a SparseEntry
527 // that stores the blockLength[] index and the offset within that block of the value
528 // with index I(k), where:
530 // I(k) = k * d->span + d->span / 2 (1)
532 // First step is to get the 'k' of the I(k) nearest to our idx, using definition (1)
533 uint32_t k = uint32_t(idx / d->span);
535 // Then we read the corresponding SparseIndex[] entry
536 uint32_t block = number<uint32_t, LittleEndian>(&d->sparseIndex[k].block);
537 int offset = number<uint16_t, LittleEndian>(&d->sparseIndex[k].offset);
539 // Now compute the difference idx - I(k). From definition of k we know that
541 // idx = k * d->span + idx % d->span (2)
543 // So from (1) and (2) we can compute idx - I(K):
544 int diff = idx % d->span - d->span / 2;
546 // Sum the above to offset to find the offset corresponding to our idx
549 // Move to previous/next block, until we reach the correct block that contains idx,
550 // that is when 0 <= offset <= d->blockLength[block]
552 offset += d->blockLength[--block] + 1;
554 while (offset > d->blockLength[block])
555 offset -= d->blockLength[block++] + 1;
557 // Finally, we find the start address of our block of canonical Huffman symbols
558 uint32_t* ptr = (uint32_t*)(d->data + ((uint64_t)block * d->sizeofBlock));
560 // Read the first 64 bits in our block, this is a (truncated) sequence of
561 // unknown number of symbols of unknown length but we know the first one
562 // is at the beginning of this 64 bits sequence.
563 uint64_t buf64 = number<uint64_t, BigEndian>(ptr); ptr += 2;
568 int len = 0; // This is the symbol length - d->min_sym_len
570 // Now get the symbol length. For any symbol s64 of length l right-padded
571 // to 64 bits we know that d->base64[l-1] >= s64 >= d->base64[l] so we
572 // can find the symbol length iterating through base64[].
573 while (buf64 < d->base64[len])
576 // All the symbols of a given length are consecutive integers (numerical
577 // sequence property), so we can compute the offset of our symbol of
578 // length len, stored at the beginning of buf64.
579 sym = Sym((buf64 - d->base64[len]) >> (64 - len - d->minSymLen));
581 // Now add the value of the lowest symbol of length len to get our symbol
582 sym += number<Sym, LittleEndian>(&d->lowestSym[len]);
584 // If our offset is within the number of values represented by symbol sym
586 if (offset < d->symlen[sym] + 1)
589 // ...otherwise update the offset and continue to iterate
590 offset -= d->symlen[sym] + 1;
591 len += d->minSymLen; // Get the real length
592 buf64 <<= len; // Consume the just processed symbol
595 if (buf64Size <= 32) { // Refill the buffer
597 buf64 |= (uint64_t)number<uint32_t, BigEndian>(ptr++) << (64 - buf64Size);
601 // Ok, now we have our symbol that expands into d->symlen[sym] + 1 symbols.
602 // We binary-search for our value recursively expanding into the left and
603 // right child symbols until we reach a leaf node where symlen[sym] + 1 == 1
604 // that will store the value we need.
605 while (d->symlen[sym]) {
607 Sym left = d->btree[sym].get<LR::Left>();
609 // If a symbol contains 36 sub-symbols (d->symlen[sym] + 1 = 36) and
610 // expands in a pair (d->symlen[left] = 23, d->symlen[right] = 11), then
611 // we know that, for instance the ten-th value (offset = 10) will be on
612 // the left side because in Recursive Pairing child symbols are adjacent.
613 if (offset < d->symlen[left] + 1)
616 offset -= d->symlen[left] + 1;
617 sym = d->btree[sym].get<LR::Right>();
621 return d->btree[sym].get<LR::Left>();
624 bool check_dtz_stm(TBTable<WDL>*, int, File) { return true; }
626 bool check_dtz_stm(TBTable<DTZ>* entry, int stm, File f) {
628 auto flags = entry->get(stm, f)->flags;
629 return (flags & TBFlag::STM) == stm
630 || ((entry->key == entry->key2) && !entry->hasPawns);
633 // DTZ scores are sorted by frequency of occurrence and then assigned the
634 // values 0, 1, 2, ... in order of decreasing frequency. This is done for each
635 // of the four WDLScore values. The mapping information necessary to reconstruct
636 // the original values is stored in the TB file and read during map[] init.
637 WDLScore map_score(TBTable<WDL>*, File, int value, WDLScore) { return WDLScore(value - 2); }
639 int map_score(TBTable<DTZ>* entry, File f, int value, WDLScore wdl) {
641 constexpr int WDLMap[] = { 1, 3, 0, 2, 0 };
643 auto flags = entry->get(0, f)->flags;
645 uint8_t* map = entry->map;
646 uint16_t* idx = entry->get(0, f)->map_idx;
647 if (flags & TBFlag::Mapped) {
648 if (flags & TBFlag::Wide)
649 value = ((uint16_t *)map)[idx[WDLMap[wdl + 2]] + value];
651 value = map[idx[WDLMap[wdl + 2]] + value];
654 // DTZ tables store distance to zero in number of moves or plies. We
655 // want to return plies, so we have convert to plies when needed.
656 if ( (wdl == WDLWin && !(flags & TBFlag::WinPlies))
657 || (wdl == WDLLoss && !(flags & TBFlag::LossPlies))
658 || wdl == WDLCursedWin
659 || wdl == WDLBlessedLoss)
665 // Compute a unique index out of a position and use it to probe the TB file. To
666 // encode k pieces of same type and color, first sort the pieces by square in
667 // ascending order s1 <= s2 <= ... <= sk then compute the unique index as:
669 // idx = Binomial[1][s1] + Binomial[2][s2] + ... + Binomial[k][sk]
671 template<typename T, typename Ret = typename T::Ret>
672 Ret do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result) {
674 Square squares[TBPIECES];
675 Piece pieces[TBPIECES];
677 int next = 0, size = 0, leadPawnsCnt = 0;
679 Bitboard b, leadPawns = 0;
680 File tbFile = FILE_A;
682 // A given TB entry like KRK has associated two material keys: KRvk and Kvkr.
683 // If both sides have the same pieces keys are equal. In this case TB tables
684 // only store the 'white to move' case, so if the position to lookup has black
685 // to move, we need to switch the color and flip the squares before to lookup.
686 bool symmetricBlackToMove = (entry->key == entry->key2 && pos.side_to_move());
688 // TB files are calculated for white as stronger side. For instance we have
689 // KRvK, not KvKR. A position where stronger side is white will have its
690 // material key == entry->key, otherwise we have to switch the color and
691 // flip the squares before to lookup.
692 bool blackStronger = (pos.material_key() != entry->key);
694 int flipColor = (symmetricBlackToMove || blackStronger) * 8;
695 int flipSquares = (symmetricBlackToMove || blackStronger) * 56;
696 int stm = (symmetricBlackToMove || blackStronger) ^ pos.side_to_move();
698 // For pawns, TB files store 4 separate tables according if leading pawn is on
699 // file a, b, c or d after reordering. The leading pawn is the one with maximum
700 // MapPawns[] value, that is the one most toward the edges and with lowest rank.
701 if (entry->hasPawns) {
703 // In all the 4 tables, pawns are at the beginning of the piece sequence and
704 // their color is the reference one. So we just pick the first one.
705 Piece pc = Piece(entry->get(0, 0)->pieces[0] ^ flipColor);
707 assert(type_of(pc) == PAWN);
709 leadPawns = b = pos.pieces(color_of(pc), PAWN);
711 squares[size++] = pop_lsb(&b) ^ flipSquares;
716 std::swap(squares[0], *std::max_element(squares, squares + leadPawnsCnt, pawns_comp));
718 tbFile = File(edge_distance(file_of(squares[0])));
721 // DTZ tables are one-sided, i.e. they store positions only for white to
722 // move or only for black to move, so check for side to move to be stm,
723 // early exit otherwise.
724 if (!check_dtz_stm(entry, stm, tbFile))
725 return *result = CHANGE_STM, Ret();
727 // Now we are ready to get all the position pieces (but the lead pawns) and
728 // directly map them to the correct color and square.
729 b = pos.pieces() ^ leadPawns;
731 Square s = pop_lsb(&b);
732 squares[size] = s ^ flipSquares;
733 pieces[size++] = Piece(pos.piece_on(s) ^ flipColor);
738 d = entry->get(stm, tbFile);
740 // Then we reorder the pieces to have the same sequence as the one stored
741 // in pieces[i]: the sequence that ensures the best compression.
742 for (int i = leadPawnsCnt; i < size - 1; ++i)
743 for (int j = i + 1; j < size; ++j)
744 if (d->pieces[i] == pieces[j])
746 std::swap(pieces[i], pieces[j]);
747 std::swap(squares[i], squares[j]);
751 // Now we map again the squares so that the square of the lead piece is in
752 // the triangle A1-D1-D4.
753 if (file_of(squares[0]) > FILE_D)
754 for (int i = 0; i < size; ++i)
755 squares[i] = flip_file(squares[i]);
757 // Encode leading pawns starting with the one with minimum MapPawns[] and
758 // proceeding in ascending order.
759 if (entry->hasPawns) {
760 idx = LeadPawnIdx[leadPawnsCnt][squares[0]];
762 std::sort(squares + 1, squares + leadPawnsCnt, pawns_comp);
764 for (int i = 1; i < leadPawnsCnt; ++i)
765 idx += Binomial[i][MapPawns[squares[i]]];
767 goto encode_remaining; // With pawns we have finished special treatments
770 // In positions withouth pawns, we further flip the squares to ensure leading
771 // piece is below RANK_5.
772 if (rank_of(squares[0]) > RANK_4)
773 for (int i = 0; i < size; ++i)
774 squares[i] = flip_rank(squares[i]);
776 // Look for the first piece of the leading group not on the A1-D4 diagonal
777 // and ensure it is mapped below the diagonal.
778 for (int i = 0; i < d->groupLen[0]; ++i) {
779 if (!off_A1H8(squares[i]))
782 if (off_A1H8(squares[i]) > 0) // A1-H8 diagonal flip: SQ_A3 -> SQ_C1
783 for (int j = i; j < size; ++j)
784 squares[j] = Square(((squares[j] >> 3) | (squares[j] << 3)) & 63);
788 // Encode the leading group.
790 // Suppose we have KRvK. Let's say the pieces are on square numbers wK, wR
791 // and bK (each 0...63). The simplest way to map this position to an index
794 // index = wK * 64 * 64 + wR * 64 + bK;
796 // But this way the TB is going to have 64*64*64 = 262144 positions, with
797 // lots of positions being equivalent (because they are mirrors of each
798 // other) and lots of positions being invalid (two pieces on one square,
799 // adjacent kings, etc.).
800 // Usually the first step is to take the wK and bK together. There are just
801 // 462 ways legal and not-mirrored ways to place the wK and bK on the board.
802 // Once we have placed the wK and bK, there are 62 squares left for the wR
803 // Mapping its square from 0..63 to available squares 0..61 can be done like:
805 // wR -= (wR > wK) + (wR > bK);
807 // In words: if wR "comes later" than wK, we deduct 1, and the same if wR
808 // "comes later" than bK. In case of two same pieces like KRRvK we want to
809 // place the two Rs "together". If we have 62 squares left, we can place two
810 // Rs "together" in 62 * 61 / 2 ways (we divide by 2 because rooks can be
811 // swapped and still get the same position.)
813 // In case we have at least 3 unique pieces (inlcuded kings) we encode them
815 if (entry->hasUniquePieces) {
817 int adjust1 = squares[1] > squares[0];
818 int adjust2 = (squares[2] > squares[0]) + (squares[2] > squares[1]);
820 // First piece is below a1-h8 diagonal. MapA1D1D4[] maps the b1-d1-d3
821 // triangle to 0...5. There are 63 squares for second piece and and 62
822 // (mapped to 0...61) for the third.
823 if (off_A1H8(squares[0]))
824 idx = ( MapA1D1D4[squares[0]] * 63
825 + (squares[1] - adjust1)) * 62
826 + squares[2] - adjust2;
828 // First piece is on a1-h8 diagonal, second below: map this occurence to
829 // 6 to differentiate from the above case, rank_of() maps a1-d4 diagonal
830 // to 0...3 and finally MapB1H1H7[] maps the b1-h1-h7 triangle to 0..27.
831 else if (off_A1H8(squares[1]))
832 idx = ( 6 * 63 + rank_of(squares[0]) * 28
833 + MapB1H1H7[squares[1]]) * 62
834 + squares[2] - adjust2;
836 // First two pieces are on a1-h8 diagonal, third below
837 else if (off_A1H8(squares[2]))
838 idx = 6 * 63 * 62 + 4 * 28 * 62
839 + rank_of(squares[0]) * 7 * 28
840 + (rank_of(squares[1]) - adjust1) * 28
841 + MapB1H1H7[squares[2]];
843 // All 3 pieces on the diagonal a1-h8
845 idx = 6 * 63 * 62 + 4 * 28 * 62 + 4 * 7 * 28
846 + rank_of(squares[0]) * 7 * 6
847 + (rank_of(squares[1]) - adjust1) * 6
848 + (rank_of(squares[2]) - adjust2);
850 // We don't have at least 3 unique pieces, like in KRRvKBB, just map
852 idx = MapKK[MapA1D1D4[squares[0]]][squares[1]];
855 idx *= d->groupIdx[0];
856 Square* groupSq = squares + d->groupLen[0];
858 // Encode remainig pawns then pieces according to square, in ascending order
859 bool remainingPawns = entry->hasPawns && entry->pawnCount[1];
861 while (d->groupLen[++next])
863 std::sort(groupSq, groupSq + d->groupLen[next]);
866 // Map down a square if "comes later" than a square in the previous
867 // groups (similar to what done earlier for leading group pieces).
868 for (int i = 0; i < d->groupLen[next]; ++i)
870 auto f = [&](Square s) { return groupSq[i] > s; };
871 auto adjust = std::count_if(squares, groupSq, f);
872 n += Binomial[i + 1][groupSq[i] - adjust - 8 * remainingPawns];
875 remainingPawns = false;
876 idx += n * d->groupIdx[next];
877 groupSq += d->groupLen[next];
880 // Now that we have the index, decompress the pair and get the score
881 return map_score(entry, tbFile, decompress_pairs(d, idx), wdl);
884 // Group together pieces that will be encoded together. The general rule is that
885 // a group contains pieces of same type and color. The exception is the leading
886 // group that, in case of positions withouth pawns, can be formed by 3 different
887 // pieces (default) or by the king pair when there is not a unique piece apart
888 // from the kings. When there are pawns, pawns are always first in pieces[].
890 // As example KRKN -> KRK + N, KNNK -> KK + NN, KPPKP -> P + PP + K + K
892 // The actual grouping depends on the TB generator and can be inferred from the
893 // sequence of pieces in piece[] array.
895 void set_groups(T& e, PairsData* d, int order[], File f) {
897 int n = 0, firstLen = e.hasPawns ? 0 : e.hasUniquePieces ? 3 : 2;
900 // Number of pieces per group is stored in groupLen[], for instance in KRKN
901 // the encoder will default on '111', so groupLen[] will be (3, 1).
902 for (int i = 1; i < e.pieceCount; ++i)
903 if (--firstLen > 0 || d->pieces[i] == d->pieces[i - 1])
906 d->groupLen[++n] = 1;
908 d->groupLen[++n] = 0; // Zero-terminated
910 // The sequence in pieces[] defines the groups, but not the order in which
911 // they are encoded. If the pieces in a group g can be combined on the board
912 // in N(g) different ways, then the position encoding will be of the form:
914 // g1 * N(g2) * N(g3) + g2 * N(g3) + g3
916 // This ensures unique encoding for the whole position. The order of the
917 // groups is a per-table parameter and could not follow the canonical leading
918 // pawns/pieces -> remainig pawns -> remaining pieces. In particular the
919 // first group is at order[0] position and the remaining pawns, when present,
920 // are at order[1] position.
921 bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
922 int next = pp ? 2 : 1;
923 int freeSquares = 64 - d->groupLen[0] - (pp ? d->groupLen[1] : 0);
926 for (int k = 0; next < n || k == order[0] || k == order[1]; ++k)
927 if (k == order[0]) // Leading pawns or pieces
929 d->groupIdx[0] = idx;
930 idx *= e.hasPawns ? LeadPawnsSize[d->groupLen[0]][f]
931 : e.hasUniquePieces ? 31332 : 462;
933 else if (k == order[1]) // Remaining pawns
935 d->groupIdx[1] = idx;
936 idx *= Binomial[d->groupLen[1]][48 - d->groupLen[0]];
938 else // Remainig pieces
940 d->groupIdx[next] = idx;
941 idx *= Binomial[d->groupLen[next]][freeSquares];
942 freeSquares -= d->groupLen[next++];
945 d->groupIdx[n] = idx;
948 // In Recursive Pairing each symbol represents a pair of childern symbols. So
949 // read d->btree[] symbols data and expand each one in his left and right child
950 // symbol until reaching the leafs that represent the symbol value.
951 uint8_t set_symlen(PairsData* d, Sym s, std::vector<bool>& visited) {
953 visited[s] = true; // We can set it now because tree is acyclic
954 Sym sr = d->btree[s].get<LR::Right>();
959 Sym sl = d->btree[s].get<LR::Left>();
962 d->symlen[sl] = set_symlen(d, sl, visited);
965 d->symlen[sr] = set_symlen(d, sr, visited);
967 return d->symlen[sl] + d->symlen[sr] + 1;
970 uint8_t* set_sizes(PairsData* d, uint8_t* data) {
974 if (d->flags & TBFlag::SingleValue) {
975 d->blocksNum = d->blockLengthSize = 0;
976 d->span = d->sparseIndexSize = 0; // Broken MSVC zero-init
977 d->minSymLen = *data++; // Here we store the single value
981 // groupLen[] is a zero-terminated list of group lengths, the last groupIdx[]
982 // element stores the biggest index that is the tb size.
983 uint64_t tbSize = d->groupIdx[std::find(d->groupLen, d->groupLen + 7, 0) - d->groupLen];
985 d->sizeofBlock = 1ULL << *data++;
986 d->span = 1ULL << *data++;
987 d->sparseIndexSize = size_t((tbSize + d->span - 1) / d->span); // Round up
988 auto padding = number<uint8_t, LittleEndian>(data++);
989 d->blocksNum = number<uint32_t, LittleEndian>(data); data += sizeof(uint32_t);
990 d->blockLengthSize = d->blocksNum + padding; // Padded to ensure SparseIndex[]
991 // does not point out of range.
992 d->maxSymLen = *data++;
993 d->minSymLen = *data++;
994 d->lowestSym = (Sym*)data;
995 d->base64.resize(d->maxSymLen - d->minSymLen + 1);
997 // The canonical code is ordered such that longer symbols (in terms of
998 // the number of bits of their Huffman code) have lower numeric value,
999 // so that d->lowestSym[i] >= d->lowestSym[i+1] (when read as LittleEndian).
1000 // Starting from this we compute a base64[] table indexed by symbol length
1001 // and containing 64 bit values so that d->base64[i] >= d->base64[i+1].
1002 // See http://www.eecs.harvard.edu/~michaelm/E210/huffman.pdf
1003 for (int i = d->base64.size() - 2; i >= 0; --i) {
1004 d->base64[i] = (d->base64[i + 1] + number<Sym, LittleEndian>(&d->lowestSym[i])
1005 - number<Sym, LittleEndian>(&d->lowestSym[i + 1])) / 2;
1007 assert(d->base64[i] * 2 >= d->base64[i+1]);
1010 // Now left-shift by an amount so that d->base64[i] gets shifted 1 bit more
1011 // than d->base64[i+1] and given the above assert condition, we ensure that
1012 // d->base64[i] >= d->base64[i+1]. Moreover for any symbol s64 of length i
1013 // and right-padded to 64 bits holds d->base64[i-1] >= s64 >= d->base64[i].
1014 for (size_t i = 0; i < d->base64.size(); ++i)
1015 d->base64[i] <<= 64 - i - d->minSymLen; // Right-padding to 64 bits
1017 data += d->base64.size() * sizeof(Sym);
1018 d->symlen.resize(number<uint16_t, LittleEndian>(data)); data += sizeof(uint16_t);
1019 d->btree = (LR*)data;
1021 // The compression scheme used is "Recursive Pairing", that replaces the most
1022 // frequent adjacent pair of symbols in the source message by a new symbol,
1023 // reevaluating the frequencies of all of the symbol pairs with respect to
1024 // the extended alphabet, and then repeating the process.
1025 // See http://www.larsson.dogma.net/dcc99.pdf
1026 std::vector<bool> visited(d->symlen.size());
1028 for (Sym sym = 0; sym < d->symlen.size(); ++sym)
1030 d->symlen[sym] = set_symlen(d, sym, visited);
1032 return data + d->symlen.size() * sizeof(LR) + (d->symlen.size() & 1);
1035 uint8_t* set_dtz_map(TBTable<WDL>&, uint8_t* data, File) { return data; }
1037 uint8_t* set_dtz_map(TBTable<DTZ>& e, uint8_t* data, File maxFile) {
1041 for (File f = FILE_A; f <= maxFile; ++f) {
1042 auto flags = e.get(0, f)->flags;
1043 if (flags & TBFlag::Mapped) {
1044 if (flags & TBFlag::Wide) {
1045 data += (uintptr_t)data & 1; // Word alignment, we may have a mixed table
1046 for (int i = 0; i < 4; ++i) { // Sequence like 3,x,x,x,1,x,0,2,x,x
1047 e.get(0, f)->map_idx[i] = (uint16_t)((uint16_t *)data - (uint16_t *)e.map + 1);
1048 data += 2 * number<uint16_t, LittleEndian>(data) + 2;
1052 for (int i = 0; i < 4; ++i) {
1053 e.get(0, f)->map_idx[i] = (uint16_t)(data - e.map + 1);
1060 return data += (uintptr_t)data & 1; // Word alignment
1063 // Populate entry's PairsData records with data from the just memory mapped file.
1064 // Called at first access.
1065 template<typename T>
1066 void set(T& e, uint8_t* data) {
1070 enum { Split = 1, HasPawns = 2 };
1072 assert(e.hasPawns == bool(*data & HasPawns));
1073 assert((e.key != e.key2) == bool(*data & Split));
1075 data++; // First byte stores flags
1077 const int sides = T::Sides == 2 && (e.key != e.key2) ? 2 : 1;
1078 const File maxFile = e.hasPawns ? FILE_D : FILE_A;
1080 bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
1082 assert(!pp || e.pawnCount[0]);
1084 for (File f = FILE_A; f <= maxFile; ++f) {
1086 for (int i = 0; i < sides; i++)
1087 *e.get(i, f) = PairsData();
1089 int order[][2] = { { *data & 0xF, pp ? *(data + 1) & 0xF : 0xF },
1090 { *data >> 4, pp ? *(data + 1) >> 4 : 0xF } };
1093 for (int k = 0; k < e.pieceCount; ++k, ++data)
1094 for (int i = 0; i < sides; i++)
1095 e.get(i, f)->pieces[k] = Piece(i ? *data >> 4 : *data & 0xF);
1097 for (int i = 0; i < sides; ++i)
1098 set_groups(e, e.get(i, f), order[i], f);
1101 data += (uintptr_t)data & 1; // Word alignment
1103 for (File f = FILE_A; f <= maxFile; ++f)
1104 for (int i = 0; i < sides; i++)
1105 data = set_sizes(e.get(i, f), data);
1107 data = set_dtz_map(e, data, maxFile);
1109 for (File f = FILE_A; f <= maxFile; ++f)
1110 for (int i = 0; i < sides; i++) {
1111 (d = e.get(i, f))->sparseIndex = (SparseEntry*)data;
1112 data += d->sparseIndexSize * sizeof(SparseEntry);
1115 for (File f = FILE_A; f <= maxFile; ++f)
1116 for (int i = 0; i < sides; i++) {
1117 (d = e.get(i, f))->blockLength = (uint16_t*)data;
1118 data += d->blockLengthSize * sizeof(uint16_t);
1121 for (File f = FILE_A; f <= maxFile; ++f)
1122 for (int i = 0; i < sides; i++) {
1123 data = (uint8_t*)(((uintptr_t)data + 0x3F) & ~0x3F); // 64 byte alignment
1124 (d = e.get(i, f))->data = data;
1125 data += d->blocksNum * d->sizeofBlock;
1129 // If the TB file corresponding to the given position is already memory mapped
1130 // then return its base address, otherwise try to memory map and init it. Called
1131 // at every probe, memory map and init only at first access. Function is thread
1132 // safe and can be called concurrently.
1133 template<TBType Type>
1134 void* mapped(TBTable<Type>& e, const Position& pos) {
1136 static std::mutex mutex;
1138 // Use 'acquire' to avoid a thread reading 'ready' == true while
1139 // another is still working. (compiler reordering may cause this).
1140 if (e.ready.load(std::memory_order_acquire))
1141 return e.baseAddress; // Could be nullptr if file does not exist
1143 std::unique_lock<std::mutex> lk(mutex);
1145 if (e.ready.load(std::memory_order_relaxed)) // Recheck under lock
1146 return e.baseAddress;
1148 // Pieces strings in decreasing order for each color, like ("KPP","KR")
1149 std::string fname, w, b;
1150 for (PieceType pt = KING; pt >= PAWN; --pt) {
1151 w += std::string(popcount(pos.pieces(WHITE, pt)), PieceToChar[pt]);
1152 b += std::string(popcount(pos.pieces(BLACK, pt)), PieceToChar[pt]);
1155 fname = (e.key == pos.material_key() ? w + 'v' + b : b + 'v' + w)
1156 + (Type == WDL ? ".rtbw" : ".rtbz");
1158 uint8_t* data = TBFile(fname).map(&e.baseAddress, &e.mapping, Type);
1163 e.ready.store(true, std::memory_order_release);
1164 return e.baseAddress;
1167 template<TBType Type, typename Ret = typename TBTable<Type>::Ret>
1168 Ret probe_table(const Position& pos, ProbeState* result, WDLScore wdl = WDLDraw) {
1170 if (pos.count<ALL_PIECES>() == 2) // KvK
1171 return Ret(WDLDraw);
1173 TBTable<Type>* entry = TBTables.get<Type>(pos.material_key());
1175 if (!entry || !mapped(*entry, pos))
1176 return *result = FAIL, Ret();
1178 return do_probe_table(pos, entry, wdl, result);
1181 // For a position where the side to move has a winning capture it is not necessary
1182 // to store a winning value so the generator treats such positions as "don't cares"
1183 // and tries to assign to it a value that improves the compression ratio. Similarly,
1184 // if the side to move has a drawing capture, then the position is at least drawn.
1185 // If the position is won, then the TB needs to store a win value. But if the
1186 // position is drawn, the TB may store a loss value if that is better for compression.
1187 // All of this means that during probing, the engine must look at captures and probe
1188 // their results and must probe the position itself. The "best" result of these
1189 // probes is the correct result for the position.
1190 // DTZ tables do not store values when a following move is a zeroing winning move
1191 // (winning capture or winning pawn move). Also DTZ store wrong values for positions
1192 // where the best move is an ep-move (even if losing). So in all these cases set
1193 // the state to ZEROING_BEST_MOVE.
1194 template<bool CheckZeroingMoves>
1195 WDLScore search(Position& pos, ProbeState* result) {
1197 WDLScore value, bestValue = WDLLoss;
1200 auto moveList = MoveList<LEGAL>(pos);
1201 size_t totalCount = moveList.size(), moveCount = 0;
1203 for (const Move& move : moveList)
1205 if ( !pos.capture(move)
1206 && (!CheckZeroingMoves || type_of(pos.moved_piece(move)) != PAWN))
1211 pos.do_move(move, st);
1212 value = -search<false>(pos, result);
1213 pos.undo_move(move);
1215 if (*result == FAIL)
1218 if (value > bestValue)
1222 if (value >= WDLWin)
1224 *result = ZEROING_BEST_MOVE; // Winning DTZ-zeroing move
1230 // In case we have already searched all the legal moves we don't have to probe
1231 // the TB because the stored score could be wrong. For instance TB tables
1232 // do not contain information on position with ep rights, so in this case
1233 // the result of probe_wdl_table is wrong. Also in case of only capture
1234 // moves, for instance here 4K3/4q3/6p1/2k5/6p1/8/8/8 w - - 0 7, we have to
1235 // return with ZEROING_BEST_MOVE set.
1236 bool noMoreMoves = (moveCount && moveCount == totalCount);
1242 value = probe_table<WDL>(pos, result);
1244 if (*result == FAIL)
1248 // DTZ stores a "don't care" value if bestValue is a win
1249 if (bestValue >= value)
1250 return *result = ( bestValue > WDLDraw
1251 || noMoreMoves ? ZEROING_BEST_MOVE : OK), bestValue;
1253 return *result = OK, value;
1259 /// Tablebases::init() is called at startup and after every change to
1260 /// "SyzygyPath" UCI option to (re)create the various tables. It is not thread
1261 /// safe, nor it needs to be.
1262 void Tablebases::init(const std::string& paths) {
1266 TBFile::Paths = paths;
1268 if (paths.empty() || paths == "<empty>")
1271 // MapB1H1H7[] encodes a square below a1-h8 diagonal to 0..27
1273 for (Square s = SQ_A1; s <= SQ_H8; ++s)
1274 if (off_A1H8(s) < 0)
1275 MapB1H1H7[s] = code++;
1277 // MapA1D1D4[] encodes a square in the a1-d1-d4 triangle to 0..9
1278 std::vector<Square> diagonal;
1280 for (Square s = SQ_A1; s <= SQ_D4; ++s)
1281 if (off_A1H8(s) < 0 && file_of(s) <= FILE_D)
1282 MapA1D1D4[s] = code++;
1284 else if (!off_A1H8(s) && file_of(s) <= FILE_D)
1285 diagonal.push_back(s);
1287 // Diagonal squares are encoded as last ones
1288 for (auto s : diagonal)
1289 MapA1D1D4[s] = code++;
1291 // MapKK[] encodes all the 461 possible legal positions of two kings where
1292 // the first is in the a1-d1-d4 triangle. If the first king is on the a1-d4
1293 // diagonal, the other one shall not to be above the a1-h8 diagonal.
1294 std::vector<std::pair<int, Square>> bothOnDiagonal;
1296 for (int idx = 0; idx < 10; idx++)
1297 for (Square s1 = SQ_A1; s1 <= SQ_D4; ++s1)
1298 if (MapA1D1D4[s1] == idx && (idx || s1 == SQ_B1)) // SQ_B1 is mapped to 0
1300 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
1301 if ((PseudoAttacks[KING][s1] | s1) & s2)
1302 continue; // Illegal position
1304 else if (!off_A1H8(s1) && off_A1H8(s2) > 0)
1305 continue; // First on diagonal, second above
1307 else if (!off_A1H8(s1) && !off_A1H8(s2))
1308 bothOnDiagonal.emplace_back(idx, s2);
1311 MapKK[idx][s2] = code++;
1314 // Legal positions with both kings on diagonal are encoded as last ones
1315 for (auto p : bothOnDiagonal)
1316 MapKK[p.first][p.second] = code++;
1318 // Binomial[] stores the Binomial Coefficents using Pascal rule. There
1319 // are Binomial[k][n] ways to choose k elements from a set of n elements.
1322 for (int n = 1; n < 64; n++) // Squares
1323 for (int k = 0; k < 6 && k <= n; ++k) // Pieces
1324 Binomial[k][n] = (k > 0 ? Binomial[k - 1][n - 1] : 0)
1325 + (k < n ? Binomial[k ][n - 1] : 0);
1327 // MapPawns[s] encodes squares a2-h7 to 0..47. This is the number of possible
1328 // available squares when the leading one is in 's'. Moreover the pawn with
1329 // highest MapPawns[] is the leading pawn, the one nearest the edge and,
1330 // among pawns with same file, the one with lowest rank.
1331 int availableSquares = 47; // Available squares when lead pawn is in a2
1333 // Init the tables for the encoding of leading pawns group: with 7-men TB we
1334 // can have up to 5 leading pawns (KPPPPPK).
1335 for (int leadPawnsCnt = 1; leadPawnsCnt <= 5; ++leadPawnsCnt)
1336 for (File f = FILE_A; f <= FILE_D; ++f)
1338 // Restart the index at every file because TB table is splitted
1339 // by file, so we can reuse the same index for different files.
1342 // Sum all possible combinations for a given file, starting with
1343 // the leading pawn on rank 2 and increasing the rank.
1344 for (Rank r = RANK_2; r <= RANK_7; ++r)
1346 Square sq = make_square(f, r);
1348 // Compute MapPawns[] at first pass.
1349 // If sq is the leading pawn square, any other pawn cannot be
1350 // below or more toward the edge of sq. There are 47 available
1351 // squares when sq = a2 and reduced by 2 for any rank increase
1352 // due to mirroring: sq == a3 -> no a2, h2, so MapPawns[a3] = 45
1353 if (leadPawnsCnt == 1)
1355 MapPawns[sq] = availableSquares--;
1356 MapPawns[flip_file(sq)] = availableSquares--;
1358 LeadPawnIdx[leadPawnsCnt][sq] = idx;
1359 idx += Binomial[leadPawnsCnt - 1][MapPawns[sq]];
1361 // After a file is traversed, store the cumulated per-file index
1362 LeadPawnsSize[leadPawnsCnt][f] = idx;
1365 // Add entries in TB tables if the corresponding ".rtbw" file exsists
1366 for (PieceType p1 = PAWN; p1 < KING; ++p1) {
1367 TBTables.add({KING, p1, KING});
1369 for (PieceType p2 = PAWN; p2 <= p1; ++p2) {
1370 TBTables.add({KING, p1, p2, KING});
1371 TBTables.add({KING, p1, KING, p2});
1373 for (PieceType p3 = PAWN; p3 < KING; ++p3)
1374 TBTables.add({KING, p1, p2, KING, p3});
1376 for (PieceType p3 = PAWN; p3 <= p2; ++p3) {
1377 TBTables.add({KING, p1, p2, p3, KING});
1379 for (PieceType p4 = PAWN; p4 <= p3; ++p4) {
1380 TBTables.add({KING, p1, p2, p3, p4, KING});
1382 for (PieceType p5 = PAWN; p5 <= p4; ++p5)
1383 TBTables.add({KING, p1, p2, p3, p4, p5, KING});
1385 for (PieceType p5 = PAWN; p5 < KING; ++p5)
1386 TBTables.add({KING, p1, p2, p3, p4, KING, p5});
1389 for (PieceType p4 = PAWN; p4 < KING; ++p4) {
1390 TBTables.add({KING, p1, p2, p3, KING, p4});
1392 for (PieceType p5 = PAWN; p5 <= p4; ++p5)
1393 TBTables.add({KING, p1, p2, p3, KING, p4, p5});
1397 for (PieceType p3 = PAWN; p3 <= p1; ++p3)
1398 for (PieceType p4 = PAWN; p4 <= (p1 == p3 ? p2 : p3); ++p4)
1399 TBTables.add({KING, p1, p2, KING, p3, p4});
1403 sync_cout << "info string Found " << TBTables.size() << " tablebases" << sync_endl;
1406 // Probe the WDL table for a particular position.
1407 // If *result != FAIL, the probe was successful.
1408 // The return value is from the point of view of the side to move:
1410 // -1 : loss, but draw under 50-move rule
1412 // 1 : win, but draw under 50-move rule
1414 WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) {
1417 return search<false>(pos, result);
1420 // Probe the DTZ table for a particular position.
1421 // If *result != FAIL, the probe was successful.
1422 // The return value is from the point of view of the side to move:
1423 // n < -100 : loss, but draw under 50-move rule
1424 // -100 <= n < -1 : loss in n ply (assuming 50-move counter == 0)
1425 // -1 : loss, the side to move is mated
1427 // 1 < n <= 100 : win in n ply (assuming 50-move counter == 0)
1428 // 100 < n : win, but draw under 50-move rule
1430 // The return value n can be off by 1: a return value -n can mean a loss
1431 // in n+1 ply and a return value +n can mean a win in n+1 ply. This
1432 // cannot happen for tables with positions exactly on the "edge" of
1433 // the 50-move rule.
1435 // This implies that if dtz > 0 is returned, the position is certainly
1436 // a win if dtz + 50-move-counter <= 99. Care must be taken that the engine
1437 // picks moves that preserve dtz + 50-move-counter <= 99.
1439 // If n = 100 immediately after a capture or pawn move, then the position
1440 // is also certainly a win, and during the whole phase until the next
1441 // capture or pawn move, the inequality to be preserved is
1442 // dtz + 50-movecounter <= 100.
1444 // In short, if a move is available resulting in dtz + 50-move-counter <= 99,
1445 // then do not accept moves leading to dtz + 50-move-counter == 100.
1446 int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
1449 WDLScore wdl = search<true>(pos, result);
1451 if (*result == FAIL || wdl == WDLDraw) // DTZ tables don't store draws
1454 // DTZ stores a 'don't care' value in this case, or even a plain wrong
1455 // one as in case the best move is a losing ep, so it cannot be probed.
1456 if (*result == ZEROING_BEST_MOVE)
1457 return dtz_before_zeroing(wdl);
1459 int dtz = probe_table<DTZ>(pos, result, wdl);
1461 if (*result == FAIL)
1464 if (*result != CHANGE_STM)
1465 return (dtz + 100 * (wdl == WDLBlessedLoss || wdl == WDLCursedWin)) * sign_of(wdl);
1467 // DTZ stores results for the other side, so we need to do a 1-ply search and
1468 // find the winning move that minimizes DTZ.
1470 int minDTZ = 0xFFFF;
1472 for (const Move& move : MoveList<LEGAL>(pos))
1474 bool zeroing = pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN;
1476 pos.do_move(move, st);
1478 // For zeroing moves we want the dtz of the move _before_ doing it,
1479 // otherwise we will get the dtz of the next move sequence. Search the
1480 // position after the move to get the score sign (because even in a
1481 // winning position we could make a losing capture or going for a draw).
1482 dtz = zeroing ? -dtz_before_zeroing(search<false>(pos, result))
1483 : -probe_dtz(pos, result);
1485 // If the move mates, force minDTZ to 1
1486 if (dtz == 1 && pos.checkers() && MoveList<LEGAL>(pos).size() == 0)
1489 // Convert result from 1-ply search. Zeroing moves are already accounted
1490 // by dtz_before_zeroing() that returns the DTZ of the previous move.
1492 dtz += sign_of(dtz);
1494 // Skip the draws and if we are winning only pick positive dtz
1495 if (dtz < minDTZ && sign_of(dtz) == sign_of(wdl))
1498 pos.undo_move(move);
1500 if (*result == FAIL)
1504 // When there are no legal moves, the position is mate: we return -1
1505 return minDTZ == 0xFFFF ? -1 : minDTZ;
1509 // Use the DTZ tables to rank root moves.
1511 // A return value false indicates that not all probes were successful.
1512 bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
1517 // Obtain 50-move counter for the root position
1518 int cnt50 = pos.rule50_count();
1520 // Check whether a position was repeated since the last zeroing move.
1521 bool rep = pos.has_repeated();
1523 int dtz, bound = Options["Syzygy50MoveRule"] ? 900 : 1;
1525 // Probe and rank each move
1526 for (auto& m : rootMoves)
1528 pos.do_move(m.pv[0], st);
1530 // Calculate dtz for the current move counting from the root position
1531 if (pos.rule50_count() == 0)
1533 // In case of a zeroing move, dtz is one of -101/-1/0/1/101
1534 WDLScore wdl = -probe_wdl(pos, &result);
1535 dtz = dtz_before_zeroing(wdl);
1539 // Otherwise, take dtz for the new position and correct by 1 ply
1540 dtz = -probe_dtz(pos, &result);
1541 dtz = dtz > 0 ? dtz + 1
1542 : dtz < 0 ? dtz - 1 : dtz;
1545 // Make sure that a mating move is assigned a dtz value of 1
1548 && MoveList<LEGAL>(pos).size() == 0)
1551 pos.undo_move(m.pv[0]);
1556 // Better moves are ranked higher. Certain wins are ranked equally.
1557 // Losing moves are ranked equally unless a 50-move draw is in sight.
1558 int r = dtz > 0 ? (dtz + cnt50 <= 99 && !rep ? 1000 : 1000 - (dtz + cnt50))
1559 : dtz < 0 ? (-dtz * 2 + cnt50 < 100 ? -1000 : -1000 + (-dtz + cnt50))
1563 // Determine the score to be displayed for this move. Assign at least
1564 // 1 cp to cursed wins and let it grow to 49 cp as the positions gets
1565 // closer to a real win.
1566 m.tbScore = r >= bound ? VALUE_MATE - MAX_PLY - 1
1567 : r > 0 ? Value((std::max( 3, r - 800) * int(PawnValueEg)) / 200)
1568 : r == 0 ? VALUE_DRAW
1569 : r > -bound ? Value((std::min(-3, r + 800) * int(PawnValueEg)) / 200)
1570 : -VALUE_MATE + MAX_PLY + 1;
1577 // Use the WDL tables to rank root moves.
1578 // This is a fallback for the case that some or all DTZ tables are missing.
1580 // A return value false indicates that not all probes were successful.
1581 bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves) {
1583 static const int WDL_to_rank[] = { -1000, -899, 0, 899, 1000 };
1588 bool rule50 = Options["Syzygy50MoveRule"];
1590 // Probe and rank each move
1591 for (auto& m : rootMoves)
1593 pos.do_move(m.pv[0], st);
1595 WDLScore wdl = -probe_wdl(pos, &result);
1597 pos.undo_move(m.pv[0]);
1602 m.tbRank = WDL_to_rank[wdl + 2];
1605 wdl = wdl > WDLDraw ? WDLWin
1606 : wdl < WDLDraw ? WDLLoss : WDLDraw;
1607 m.tbScore = WDL_to_value[wdl + 2];