2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (c) 2013 Ronald de Man
4 Copyright (C) 2016-2018 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>
31 #include "../bitboard.h"
32 #include "../movegen.h"
33 #include "../position.h"
34 #include "../search.h"
35 #include "../thread_win32.h"
46 #define WIN32_LEAN_AND_MEAN
51 using namespace Tablebases;
53 int Tablebases::MaxCardinality;
57 constexpr int TBPIECES = 6; // Max number of supported pieces
59 enum TBType { WDL, DTZ }; // Used as template parameter
61 // Each table has a set of flags: all of them refer to DTZ tables, the last one to WDL tables
62 enum TBFlag { STM = 1, Mapped = 2, WinPlies = 4, LossPlies = 8, SingleValue = 128 };
64 inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
65 inline Square operator^=(Square& s, int i) { return s = Square(int(s) ^ i); }
66 inline Square operator^(Square s, int i) { return Square(int(s) ^ i); }
68 // DTZ tables don't store valid scores for moves that reset the rule50 counter
69 // like captures and pawn moves but we can easily recover the correct dtz of the
70 // previous move if we know the position's WDL score.
71 int dtz_before_zeroing(WDLScore wdl) {
72 return wdl == WDLWin ? 1 :
73 wdl == WDLCursedWin ? 101 :
74 wdl == WDLBlessedLoss ? -101 :
75 wdl == WDLLoss ? -1 : 0;
78 // Return the sign of a number (-1, 0, 1)
79 template <typename T> int sign_of(T val) {
80 return (T(0) < val) - (val < T(0));
83 // Numbers in little endian used by sparseIndex[] to point into blockLength[]
85 char block[4]; // Number of block
86 char offset[2]; // Offset within the block
89 static_assert(sizeof(SparseEntry) == 6, "SparseEntry must be 6 bytes");
91 typedef uint16_t Sym; // Huffman symbol
94 enum Side { Left, Right, Value };
96 uint8_t lr[3]; // The first 12 bits is the left-hand symbol, the second 12
97 // bits is the right-hand symbol. If symbol has length 1,
98 // then the first byte is the stored value.
101 return S == Left ? ((lr[1] & 0xF) << 8) | lr[0] :
102 S == Right ? (lr[2] << 4) | (lr[1] >> 4) :
103 S == Value ? lr[0] : (assert(false), Sym(-1));
107 static_assert(sizeof(LR) == 3, "LR tree entry must be 3 bytes");
111 size_t sizeofBlock; // Block size in bytes
112 size_t span; // About every span values there is a SparseIndex[] entry
113 int blocksNum; // Number of blocks in the TB file
114 int maxSymLen; // Maximum length in bits of the Huffman symbols
115 int minSymLen; // Minimum length in bits of the Huffman symbols
116 Sym* lowestSym; // lowestSym[l] is the symbol of length l with the lowest value
117 LR* btree; // btree[sym] stores the left and right symbols that expand sym
118 uint16_t* blockLength; // Number of stored positions (minus one) for each block: 1..65536
119 int blockLengthSize; // Size of blockLength[] table: padded so it's bigger than blocksNum
120 SparseEntry* sparseIndex; // Partial indices into blockLength[]
121 size_t sparseIndexSize; // Size of SparseIndex[] table
122 uint8_t* data; // Start of Huffman compressed data
123 std::vector<uint64_t> base64; // base64[l - min_sym_len] is the 64bit-padded lowest symbol of length l
124 std::vector<uint8_t> symlen; // Number of values (-1) represented by a given Huffman symbol: 1..256
125 Piece pieces[TBPIECES]; // Position pieces: the order of pieces defines the groups
126 uint64_t groupIdx[TBPIECES+1]; // Start index used for the encoding of the group's pieces
127 int groupLen[TBPIECES+1]; // Number of pieces in a given group: KRKN -> (3, 1)
128 uint16_t map_idx[4]; // WDLWin, WDLLoss, WDLCursedWin, WDLBlessedLoss (used in DTZ)
131 template<TBType Type>
133 typedef typename std::conditional<Type == WDL, WDLScore, int>::type Result;
135 static constexpr int Sides = Type == WDL ? 2 : 1;
137 std::atomic_bool ready;
145 bool hasUniquePieces;
146 uint8_t pawnCount[2]; // [Lead color / other color]
147 PairsData items[Sides][4]; // [wtm / btm][FILE_A..FILE_D or 0]
149 PairsData* get(int stm, int f) {
150 return &items[stm % Sides][hasPawns ? f : 0];
153 TBEntry() : ready(false), baseAddress(nullptr) {}
154 explicit TBEntry(const std::string& code);
155 explicit TBEntry(const TBEntry<WDL>& wdl);
160 TBEntry<WDL>::TBEntry(const std::string& code) : TBEntry() {
165 key = pos.set(code, WHITE, &st).material_key();
166 pieceCount = popcount(pos.pieces());
167 hasPawns = pos.pieces(PAWN);
169 hasUniquePieces = false;
170 for (Color c = WHITE; c <= BLACK; ++c)
171 for (PieceType pt = PAWN; pt < KING; ++pt)
172 if (popcount(pos.pieces(c, pt)) == 1)
173 hasUniquePieces = true;
176 // Set the leading color. In case both sides have pawns the leading color
177 // is the side with less pawns because this leads to better compression.
178 bool c = !pos.count<PAWN>(BLACK)
179 || ( pos.count<PAWN>(WHITE)
180 && pos.count<PAWN>(BLACK) >= pos.count<PAWN>(WHITE));
182 pawnCount[0] = pos.count<PAWN>(c ? WHITE : BLACK);
183 pawnCount[1] = pos.count<PAWN>(c ? BLACK : WHITE);
186 key2 = pos.set(code, BLACK, &st).material_key();
190 TBEntry<DTZ>::TBEntry(const TBEntry<WDL>& wdl) : TBEntry() {
194 pieceCount = wdl.pieceCount;
195 hasPawns = wdl.hasPawns;
196 hasUniquePieces = wdl.hasUniquePieces;
199 pawnCount[0] = wdl.pawnCount[0];
200 pawnCount[1] = wdl.pawnCount[1];
204 int MapPawns[SQUARE_NB];
205 int MapB1H1H7[SQUARE_NB];
206 int MapA1D1D4[SQUARE_NB];
207 int MapKK[10][SQUARE_NB]; // [MapA1D1D4][SQUARE_NB]
209 // Comparison function to sort leading pawns in ascending MapPawns[] order
210 bool pawns_comp(Square i, Square j) { return MapPawns[i] < MapPawns[j]; }
211 int off_A1H8(Square sq) { return int(rank_of(sq)) - file_of(sq); }
213 constexpr Value WDL_to_value[] = {
214 -VALUE_MATE + MAX_PLY + 1,
218 VALUE_MATE - MAX_PLY - 1
221 const std::string PieceToChar = " PNBRQK pnbrqk";
223 int Binomial[6][SQUARE_NB]; // [k][n] k elements from a set of n elements
224 int LeadPawnIdx[5][SQUARE_NB]; // [leadPawnsCnt][SQUARE_NB]
225 int LeadPawnsSize[5][4]; // [leadPawnsCnt][FILE_A..FILE_D]
227 enum { BigEndian, LittleEndian };
229 template<typename T, int Half = sizeof(T) / 2, int End = sizeof(T) - 1>
230 inline void swap_byte(T& x)
232 char tmp, *c = (char*)&x;
233 for (int i = 0; i < Half; ++i)
234 tmp = c[i], c[i] = c[End - i], c[End - i] = tmp;
236 template<> inline void swap_byte<uint8_t, 0, 0>(uint8_t&) {}
238 template<typename T, int LE> T number(void* addr)
240 const union { uint32_t i; char c[4]; } Le = { 0x01020304 };
241 const bool IsLittleEndian = (Le.c[0] == 4);
245 if ((uintptr_t)addr & (alignof(T) - 1)) // Unaligned pointer (very rare)
246 std::memcpy(&v, addr, sizeof(T));
250 if (LE != IsLittleEndian)
257 typedef std::pair<TBEntry<WDL>*, TBEntry<DTZ>*> EntryPair;
258 typedef std::pair<Key, EntryPair> Entry;
260 static constexpr int TBHASHBITS = 10;
261 static constexpr int HSHMAX = 5;
263 Entry hashTable[1 << TBHASHBITS][HSHMAX];
265 std::deque<TBEntry<WDL>> wdlTable;
266 std::deque<TBEntry<DTZ>> dtzTable;
268 void insert(Key key, TBEntry<WDL>* wdl, TBEntry<DTZ>* dtz) {
269 for (Entry& entry : hashTable[key >> (64 - TBHASHBITS)])
270 if (!entry.second.first || entry.first == key) {
271 entry = std::make_pair(key, std::make_pair(wdl, dtz));
275 std::cerr << "HSHMAX too low!" << std::endl;
280 template<TBType Type>
281 TBEntry<Type>* get(Key key) {
282 for (Entry& entry : hashTable[key >> (64 - TBHASHBITS)])
283 if (entry.first == key)
284 return std::get<Type>(entry.second);
290 memset(hashTable, 0, sizeof(hashTable));
294 size_t size() const { return wdlTable.size(); }
295 void insert(const std::vector<PieceType>& pieces);
298 HashTable EntryTable;
300 class TBFile : public std::ifstream {
305 // Look for and open the file among the Paths directories where the .rtbw
306 // and .rtbz files can be found. Multiple directories are separated by ";"
307 // on Windows and by ":" on Unix-based operating systems.
310 // C:\tb\wdl345;C:\tb\wdl6;D:\tb\dtz345;D:\tb\dtz6
311 static std::string Paths;
313 TBFile(const std::string& f) {
316 constexpr char SepChar = ':';
318 constexpr char SepChar = ';';
320 std::stringstream ss(Paths);
323 while (std::getline(ss, path, SepChar)) {
324 fname = path + "/" + f;
325 std::ifstream::open(fname);
331 // Memory map the file and check it. File should be already open and will be
332 // closed after mapping.
333 uint8_t* map(void** baseAddress, uint64_t* mapping, const uint8_t* TB_MAGIC) {
337 close(); // Need to re-open to get native file descriptor
341 int fd = ::open(fname.c_str(), O_RDONLY);
344 return *baseAddress = nullptr, nullptr;
347 *mapping = statbuf.st_size;
348 *baseAddress = mmap(nullptr, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
351 if (*baseAddress == MAP_FAILED) {
352 std::cerr << "Could not mmap() " << fname << std::endl;
356 HANDLE fd = CreateFile(fname.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
357 OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
359 if (fd == INVALID_HANDLE_VALUE)
360 return *baseAddress = nullptr, nullptr;
363 DWORD size_low = GetFileSize(fd, &size_high);
364 HANDLE mmap = CreateFileMapping(fd, nullptr, PAGE_READONLY, size_high, size_low, nullptr);
368 std::cerr << "CreateFileMapping() failed" << std::endl;
372 *mapping = (uint64_t)mmap;
373 *baseAddress = MapViewOfFile(mmap, FILE_MAP_READ, 0, 0, 0);
376 std::cerr << "MapViewOfFile() failed, name = " << fname
377 << ", error = " << GetLastError() << std::endl;
381 uint8_t* data = (uint8_t*)*baseAddress;
383 if ( *data++ != *TB_MAGIC++
384 || *data++ != *TB_MAGIC++
385 || *data++ != *TB_MAGIC++
386 || *data++ != *TB_MAGIC) {
387 std::cerr << "Corrupted table in file " << fname << std::endl;
388 unmap(*baseAddress, *mapping);
389 return *baseAddress = nullptr, nullptr;
395 static void unmap(void* baseAddress, uint64_t mapping) {
398 munmap(baseAddress, mapping);
400 UnmapViewOfFile(baseAddress);
401 CloseHandle((HANDLE)mapping);
406 std::string TBFile::Paths;
408 template<TBType Type>
409 TBEntry<Type>::~TBEntry() {
411 TBFile::unmap(baseAddress, mapping);
414 void HashTable::insert(const std::vector<PieceType>& pieces) {
418 for (PieceType pt : pieces)
419 code += PieceToChar[pt];
421 TBFile file(code.insert(code.find('K', 1), "v") + ".rtbw"); // KRK -> KRvK
423 if (!file.is_open()) // Only WDL file is checked
428 MaxCardinality = std::max((int)pieces.size(), MaxCardinality);
430 wdlTable.emplace_back(code);
431 dtzTable.emplace_back(wdlTable.back());
433 insert(wdlTable.back().key , &wdlTable.back(), &dtzTable.back());
434 insert(wdlTable.back().key2, &wdlTable.back(), &dtzTable.back());
437 // TB tables are compressed with canonical Huffman code. The compressed data is divided into
438 // blocks of size d->sizeofBlock, and each block stores a variable number of symbols.
439 // Each symbol represents either a WDL or a (remapped) DTZ value, or a pair of other symbols
440 // (recursively). If you keep expanding the symbols in a block, you end up with up to 65536
441 // WDL or DTZ values. Each symbol represents up to 256 values and will correspond after
442 // Huffman coding to at least 1 bit. So a block of 32 bytes corresponds to at most
443 // 32 x 8 x 256 = 65536 values. This maximum is only reached for tables that consist mostly
444 // of draws or mostly of wins, but such tables are actually quite common. In principle, the
445 // blocks in WDL tables are 64 bytes long (and will be aligned on cache lines). But for
446 // mostly-draw or mostly-win tables this can leave many 64-byte blocks only half-filled, so
447 // in such cases blocks are 32 bytes long. The blocks of DTZ tables are up to 1024 bytes long.
448 // The generator picks the size that leads to the smallest table. The "book" of symbols and
449 // Huffman codes is the same for all blocks in the table. A non-symmetric pawnless TB file
450 // will have one table for wtm and one for btm, a TB file with pawns will have tables per
451 // file a,b,c,d also in this case one set for wtm and one for btm.
452 int decompress_pairs(PairsData* d, uint64_t idx) {
454 // Special case where all table positions store the same value
455 if (d->flags & TBFlag::SingleValue)
458 // First we need to locate the right block that stores the value at index "idx".
459 // Because each block n stores blockLength[n] + 1 values, the index i of the block
460 // that contains the value at position idx is:
462 // for (i = -1, sum = 0; sum <= idx; i++)
463 // sum += blockLength[i + 1] + 1;
465 // This can be slow, so we use SparseIndex[] populated with a set of SparseEntry that
466 // point to known indices into blockLength[]. Namely SparseIndex[k] is a SparseEntry
467 // that stores the blockLength[] index and the offset within that block of the value
468 // with index I(k), where:
470 // I(k) = k * d->span + d->span / 2 (1)
472 // First step is to get the 'k' of the I(k) nearest to our idx, using definition (1)
473 uint32_t k = idx / d->span;
475 // Then we read the corresponding SparseIndex[] entry
476 uint32_t block = number<uint32_t, LittleEndian>(&d->sparseIndex[k].block);
477 int offset = number<uint16_t, LittleEndian>(&d->sparseIndex[k].offset);
479 // Now compute the difference idx - I(k). From definition of k we know that
481 // idx = k * d->span + idx % d->span (2)
483 // So from (1) and (2) we can compute idx - I(K):
484 int diff = idx % d->span - d->span / 2;
486 // Sum the above to offset to find the offset corresponding to our idx
489 // Move to previous/next block, until we reach the correct block that contains idx,
490 // that is when 0 <= offset <= d->blockLength[block]
492 offset += d->blockLength[--block] + 1;
494 while (offset > d->blockLength[block])
495 offset -= d->blockLength[block++] + 1;
497 // Finally, we find the start address of our block of canonical Huffman symbols
498 uint32_t* ptr = (uint32_t*)(d->data + block * d->sizeofBlock);
500 // Read the first 64 bits in our block, this is a (truncated) sequence of
501 // unknown number of symbols of unknown length but we know the first one
502 // is at the beginning of this 64 bits sequence.
503 uint64_t buf64 = number<uint64_t, BigEndian>(ptr); ptr += 2;
508 int len = 0; // This is the symbol length - d->min_sym_len
510 // Now get the symbol length. For any symbol s64 of length l right-padded
511 // to 64 bits we know that d->base64[l-1] >= s64 >= d->base64[l] so we
512 // can find the symbol length iterating through base64[].
513 while (buf64 < d->base64[len])
516 // All the symbols of a given length are consecutive integers (numerical
517 // sequence property), so we can compute the offset of our symbol of
518 // length len, stored at the beginning of buf64.
519 sym = (buf64 - d->base64[len]) >> (64 - len - d->minSymLen);
521 // Now add the value of the lowest symbol of length len to get our symbol
522 sym += number<Sym, LittleEndian>(&d->lowestSym[len]);
524 // If our offset is within the number of values represented by symbol sym
526 if (offset < d->symlen[sym] + 1)
529 // ...otherwise update the offset and continue to iterate
530 offset -= d->symlen[sym] + 1;
531 len += d->minSymLen; // Get the real length
532 buf64 <<= len; // Consume the just processed symbol
535 if (buf64Size <= 32) { // Refill the buffer
537 buf64 |= (uint64_t)number<uint32_t, BigEndian>(ptr++) << (64 - buf64Size);
541 // Ok, now we have our symbol that expands into d->symlen[sym] + 1 symbols.
542 // We binary-search for our value recursively expanding into the left and
543 // right child symbols until we reach a leaf node where symlen[sym] + 1 == 1
544 // that will store the value we need.
545 while (d->symlen[sym]) {
547 Sym left = d->btree[sym].get<LR::Left>();
549 // If a symbol contains 36 sub-symbols (d->symlen[sym] + 1 = 36) and
550 // expands in a pair (d->symlen[left] = 23, d->symlen[right] = 11), then
551 // we know that, for instance the ten-th value (offset = 10) will be on
552 // the left side because in Recursive Pairing child symbols are adjacent.
553 if (offset < d->symlen[left] + 1)
556 offset -= d->symlen[left] + 1;
557 sym = d->btree[sym].get<LR::Right>();
561 return d->btree[sym].get<LR::Value>();
564 bool check_dtz_stm(TBEntry<WDL>*, int, File) { return true; }
566 bool check_dtz_stm(TBEntry<DTZ>* entry, int stm, File f) {
568 int flags = entry->get(stm, f)->flags;
569 return (flags & TBFlag::STM) == stm
570 || ((entry->key == entry->key2) && !entry->hasPawns);
573 // DTZ scores are sorted by frequency of occurrence and then assigned the
574 // values 0, 1, 2, ... in order of decreasing frequency. This is done for each
575 // of the four WDLScore values. The mapping information necessary to reconstruct
576 // the original values is stored in the TB file and read during map[] init.
577 WDLScore map_score(TBEntry<WDL>*, File, int value, WDLScore) { return WDLScore(value - 2); }
579 int map_score(TBEntry<DTZ>* entry, File f, int value, WDLScore wdl) {
581 constexpr int WDLMap[] = { 1, 3, 0, 2, 0 };
583 int flags = entry->get(0, f)->flags;
585 uint8_t* map = entry->map;
586 uint16_t* idx = entry->get(0, f)->map_idx;
587 if (flags & TBFlag::Mapped)
588 value = map[idx[WDLMap[wdl + 2]] + value];
590 // DTZ tables store distance to zero in number of moves or plies. We
591 // want to return plies, so we have convert to plies when needed.
592 if ( (wdl == WDLWin && !(flags & TBFlag::WinPlies))
593 || (wdl == WDLLoss && !(flags & TBFlag::LossPlies))
594 || wdl == WDLCursedWin
595 || wdl == WDLBlessedLoss)
601 // Compute a unique index out of a position and use it to probe the TB file. To
602 // encode k pieces of same type and color, first sort the pieces by square in
603 // ascending order s1 <= s2 <= ... <= sk then compute the unique index as:
605 // idx = Binomial[1][s1] + Binomial[2][s2] + ... + Binomial[k][sk]
607 template<TBType Type, typename T = typename TBEntry<Type>::Result>
608 T do_probe_table(const Position& pos, TBEntry<Type>* entry, WDLScore wdl, ProbeState* result) {
610 Square squares[TBPIECES];
611 Piece pieces[TBPIECES];
613 int next = 0, size = 0, leadPawnsCnt = 0;
615 Bitboard b, leadPawns = 0;
616 File tbFile = FILE_A;
618 // A given TB entry like KRK has associated two material keys: KRvk and Kvkr.
619 // If both sides have the same pieces keys are equal. In this case TB tables
620 // only store the 'white to move' case, so if the position to lookup has black
621 // to move, we need to switch the color and flip the squares before to lookup.
622 bool symmetricBlackToMove = (entry->key == entry->key2 && pos.side_to_move());
624 // TB files are calculated for white as stronger side. For instance we have
625 // KRvK, not KvKR. A position where stronger side is white will have its
626 // material key == entry->key, otherwise we have to switch the color and
627 // flip the squares before to lookup.
628 bool blackStronger = (pos.material_key() != entry->key);
630 int flipColor = (symmetricBlackToMove || blackStronger) * 8;
631 int flipSquares = (symmetricBlackToMove || blackStronger) * 070;
632 int stm = (symmetricBlackToMove || blackStronger) ^ pos.side_to_move();
634 // For pawns, TB files store 4 separate tables according if leading pawn is on
635 // file a, b, c or d after reordering. The leading pawn is the one with maximum
636 // MapPawns[] value, that is the one most toward the edges and with lowest rank.
637 if (entry->hasPawns) {
639 // In all the 4 tables, pawns are at the beginning of the piece sequence and
640 // their color is the reference one. So we just pick the first one.
641 Piece pc = Piece(entry->get(0, 0)->pieces[0] ^ flipColor);
643 assert(type_of(pc) == PAWN);
645 leadPawns = b = pos.pieces(color_of(pc), PAWN);
647 squares[size++] = pop_lsb(&b) ^ flipSquares;
652 std::swap(squares[0], *std::max_element(squares, squares + leadPawnsCnt, pawns_comp));
654 tbFile = file_of(squares[0]);
656 tbFile = file_of(squares[0] ^ 7); // Horizontal flip: SQ_H1 -> SQ_A1
659 // DTZ tables are one-sided, i.e. they store positions only for white to
660 // move or only for black to move, so check for side to move to be stm,
661 // early exit otherwise.
662 if (Type == DTZ && !check_dtz_stm(entry, stm, tbFile))
663 return *result = CHANGE_STM, T();
665 // Now we are ready to get all the position pieces (but the lead pawns) and
666 // directly map them to the correct color and square.
667 b = pos.pieces() ^ leadPawns;
669 Square s = pop_lsb(&b);
670 squares[size] = s ^ flipSquares;
671 pieces[size++] = Piece(pos.piece_on(s) ^ flipColor);
676 d = entry->get(stm, tbFile);
678 // Then we reorder the pieces to have the same sequence as the one stored
679 // in pieces[i]: the sequence that ensures the best compression.
680 for (int i = leadPawnsCnt; i < size; ++i)
681 for (int j = i; j < size; ++j)
682 if (d->pieces[i] == pieces[j])
684 std::swap(pieces[i], pieces[j]);
685 std::swap(squares[i], squares[j]);
689 // Now we map again the squares so that the square of the lead piece is in
690 // the triangle A1-D1-D4.
691 if (file_of(squares[0]) > FILE_D)
692 for (int i = 0; i < size; ++i)
693 squares[i] ^= 7; // Horizontal flip: SQ_H1 -> SQ_A1
695 // Encode leading pawns starting with the one with minimum MapPawns[] and
696 // proceeding in ascending order.
697 if (entry->hasPawns) {
698 idx = LeadPawnIdx[leadPawnsCnt][squares[0]];
700 std::sort(squares + 1, squares + leadPawnsCnt, pawns_comp);
702 for (int i = 1; i < leadPawnsCnt; ++i)
703 idx += Binomial[i][MapPawns[squares[i]]];
705 goto encode_remaining; // With pawns we have finished special treatments
708 // In positions withouth pawns, we further flip the squares to ensure leading
709 // piece is below RANK_5.
710 if (rank_of(squares[0]) > RANK_4)
711 for (int i = 0; i < size; ++i)
712 squares[i] ^= 070; // Vertical flip: SQ_A8 -> SQ_A1
714 // Look for the first piece of the leading group not on the A1-D4 diagonal
715 // and ensure it is mapped below the diagonal.
716 for (int i = 0; i < d->groupLen[0]; ++i) {
717 if (!off_A1H8(squares[i]))
720 if (off_A1H8(squares[i]) > 0) // A1-H8 diagonal flip: SQ_A3 -> SQ_C3
721 for (int j = i; j < size; ++j)
722 squares[j] = Square(((squares[j] >> 3) | (squares[j] << 3)) & 63);
726 // Encode the leading group.
728 // Suppose we have KRvK. Let's say the pieces are on square numbers wK, wR
729 // and bK (each 0...63). The simplest way to map this position to an index
732 // index = wK * 64 * 64 + wR * 64 + bK;
734 // But this way the TB is going to have 64*64*64 = 262144 positions, with
735 // lots of positions being equivalent (because they are mirrors of each
736 // other) and lots of positions being invalid (two pieces on one square,
737 // adjacent kings, etc.).
738 // Usually the first step is to take the wK and bK together. There are just
739 // 462 ways legal and not-mirrored ways to place the wK and bK on the board.
740 // Once we have placed the wK and bK, there are 62 squares left for the wR
741 // Mapping its square from 0..63 to available squares 0..61 can be done like:
743 // wR -= (wR > wK) + (wR > bK);
745 // In words: if wR "comes later" than wK, we deduct 1, and the same if wR
746 // "comes later" than bK. In case of two same pieces like KRRvK we want to
747 // place the two Rs "together". If we have 62 squares left, we can place two
748 // Rs "together" in 62 * 61 / 2 ways (we divide by 2 because rooks can be
749 // swapped and still get the same position.)
751 // In case we have at least 3 unique pieces (inlcuded kings) we encode them
753 if (entry->hasUniquePieces) {
755 int adjust1 = squares[1] > squares[0];
756 int adjust2 = (squares[2] > squares[0]) + (squares[2] > squares[1]);
758 // First piece is below a1-h8 diagonal. MapA1D1D4[] maps the b1-d1-d3
759 // triangle to 0...5. There are 63 squares for second piece and and 62
760 // (mapped to 0...61) for the third.
761 if (off_A1H8(squares[0]))
762 idx = ( MapA1D1D4[squares[0]] * 63
763 + (squares[1] - adjust1)) * 62
764 + squares[2] - adjust2;
766 // First piece is on a1-h8 diagonal, second below: map this occurence to
767 // 6 to differentiate from the above case, rank_of() maps a1-d4 diagonal
768 // to 0...3 and finally MapB1H1H7[] maps the b1-h1-h7 triangle to 0..27.
769 else if (off_A1H8(squares[1]))
770 idx = ( 6 * 63 + rank_of(squares[0]) * 28
771 + MapB1H1H7[squares[1]]) * 62
772 + squares[2] - adjust2;
774 // First two pieces are on a1-h8 diagonal, third below
775 else if (off_A1H8(squares[2]))
776 idx = 6 * 63 * 62 + 4 * 28 * 62
777 + rank_of(squares[0]) * 7 * 28
778 + (rank_of(squares[1]) - adjust1) * 28
779 + MapB1H1H7[squares[2]];
781 // All 3 pieces on the diagonal a1-h8
783 idx = 6 * 63 * 62 + 4 * 28 * 62 + 4 * 7 * 28
784 + rank_of(squares[0]) * 7 * 6
785 + (rank_of(squares[1]) - adjust1) * 6
786 + (rank_of(squares[2]) - adjust2);
788 // We don't have at least 3 unique pieces, like in KRRvKBB, just map
790 idx = MapKK[MapA1D1D4[squares[0]]][squares[1]];
793 idx *= d->groupIdx[0];
794 Square* groupSq = squares + d->groupLen[0];
796 // Encode remainig pawns then pieces according to square, in ascending order
797 bool remainingPawns = entry->hasPawns && entry->pawnCount[1];
799 while (d->groupLen[++next])
801 std::sort(groupSq, groupSq + d->groupLen[next]);
804 // Map down a square if "comes later" than a square in the previous
805 // groups (similar to what done earlier for leading group pieces).
806 for (int i = 0; i < d->groupLen[next]; ++i)
808 auto f = [&](Square s) { return groupSq[i] > s; };
809 auto adjust = std::count_if(squares, groupSq, f);
810 n += Binomial[i + 1][groupSq[i] - adjust - 8 * remainingPawns];
813 remainingPawns = false;
814 idx += n * d->groupIdx[next];
815 groupSq += d->groupLen[next];
818 // Now that we have the index, decompress the pair and get the score
819 return map_score(entry, tbFile, decompress_pairs(d, idx), wdl);
822 // Group together pieces that will be encoded together. The general rule is that
823 // a group contains pieces of same type and color. The exception is the leading
824 // group that, in case of positions withouth pawns, can be formed by 3 different
825 // pieces (default) or by the king pair when there is not a unique piece apart
826 // from the kings. When there are pawns, pawns are always first in pieces[].
828 // As example KRKN -> KRK + N, KNNK -> KK + NN, KPPKP -> P + PP + K + K
830 // The actual grouping depends on the TB generator and can be inferred from the
831 // sequence of pieces in piece[] array.
832 template<TBType Type>
833 void set_groups(TBEntry<Type>& e, PairsData* d, int order[], File f) {
835 int n = 0, firstLen = e.hasPawns ? 0 : e.hasUniquePieces ? 3 : 2;
838 // Number of pieces per group is stored in groupLen[], for instance in KRKN
839 // the encoder will default on '111', so groupLen[] will be (3, 1).
840 for (int i = 1; i < e.pieceCount; ++i)
841 if (--firstLen > 0 || d->pieces[i] == d->pieces[i - 1])
844 d->groupLen[++n] = 1;
846 d->groupLen[++n] = 0; // Zero-terminated
848 // The sequence in pieces[] defines the groups, but not the order in which
849 // they are encoded. If the pieces in a group g can be combined on the board
850 // in N(g) different ways, then the position encoding will be of the form:
852 // g1 * N(g2) * N(g3) + g2 * N(g3) + g3
854 // This ensures unique encoding for the whole position. The order of the
855 // groups is a per-table parameter and could not follow the canonical leading
856 // pawns/pieces -> remainig pawns -> remaining pieces. In particular the
857 // first group is at order[0] position and the remaining pawns, when present,
858 // are at order[1] position.
859 bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
860 int next = pp ? 2 : 1;
861 int freeSquares = 64 - d->groupLen[0] - (pp ? d->groupLen[1] : 0);
864 for (int k = 0; next < n || k == order[0] || k == order[1]; ++k)
865 if (k == order[0]) // Leading pawns or pieces
867 d->groupIdx[0] = idx;
868 idx *= e.hasPawns ? LeadPawnsSize[d->groupLen[0]][f]
869 : e.hasUniquePieces ? 31332 : 462;
871 else if (k == order[1]) // Remaining pawns
873 d->groupIdx[1] = idx;
874 idx *= Binomial[d->groupLen[1]][48 - d->groupLen[0]];
876 else // Remainig pieces
878 d->groupIdx[next] = idx;
879 idx *= Binomial[d->groupLen[next]][freeSquares];
880 freeSquares -= d->groupLen[next++];
883 d->groupIdx[n] = idx;
886 // In Recursive Pairing each symbol represents a pair of childern symbols. So
887 // read d->btree[] symbols data and expand each one in his left and right child
888 // symbol until reaching the leafs that represent the symbol value.
889 uint8_t set_symlen(PairsData* d, Sym s, std::vector<bool>& visited) {
891 visited[s] = true; // We can set it now because tree is acyclic
892 Sym sr = d->btree[s].get<LR::Right>();
897 Sym sl = d->btree[s].get<LR::Left>();
900 d->symlen[sl] = set_symlen(d, sl, visited);
903 d->symlen[sr] = set_symlen(d, sr, visited);
905 return d->symlen[sl] + d->symlen[sr] + 1;
908 uint8_t* set_sizes(PairsData* d, uint8_t* data) {
912 if (d->flags & TBFlag::SingleValue) {
913 d->blocksNum = d->blockLengthSize = 0;
914 d->span = d->sparseIndexSize = 0; // Broken MSVC zero-init
915 d->minSymLen = *data++; // Here we store the single value
919 // groupLen[] is a zero-terminated list of group lengths, the last groupIdx[]
920 // element stores the biggest index that is the tb size.
921 uint64_t tbSize = d->groupIdx[std::find(d->groupLen, d->groupLen + 7, 0) - d->groupLen];
923 d->sizeofBlock = 1ULL << *data++;
924 d->span = 1ULL << *data++;
925 d->sparseIndexSize = (tbSize + d->span - 1) / d->span; // Round up
926 int padding = number<uint8_t, LittleEndian>(data++);
927 d->blocksNum = number<uint32_t, LittleEndian>(data); data += sizeof(uint32_t);
928 d->blockLengthSize = d->blocksNum + padding; // Padded to ensure SparseIndex[]
929 // does not point out of range.
930 d->maxSymLen = *data++;
931 d->minSymLen = *data++;
932 d->lowestSym = (Sym*)data;
933 d->base64.resize(d->maxSymLen - d->minSymLen + 1);
935 // The canonical code is ordered such that longer symbols (in terms of
936 // the number of bits of their Huffman code) have lower numeric value,
937 // so that d->lowestSym[i] >= d->lowestSym[i+1] (when read as LittleEndian).
938 // Starting from this we compute a base64[] table indexed by symbol length
939 // and containing 64 bit values so that d->base64[i] >= d->base64[i+1].
940 // See http://www.eecs.harvard.edu/~michaelm/E210/huffman.pdf
941 for (int i = d->base64.size() - 2; i >= 0; --i) {
942 d->base64[i] = (d->base64[i + 1] + number<Sym, LittleEndian>(&d->lowestSym[i])
943 - number<Sym, LittleEndian>(&d->lowestSym[i + 1])) / 2;
945 assert(d->base64[i] * 2 >= d->base64[i+1]);
948 // Now left-shift by an amount so that d->base64[i] gets shifted 1 bit more
949 // than d->base64[i+1] and given the above assert condition, we ensure that
950 // d->base64[i] >= d->base64[i+1]. Moreover for any symbol s64 of length i
951 // and right-padded to 64 bits holds d->base64[i-1] >= s64 >= d->base64[i].
952 for (size_t i = 0; i < d->base64.size(); ++i)
953 d->base64[i] <<= 64 - i - d->minSymLen; // Right-padding to 64 bits
955 data += d->base64.size() * sizeof(Sym);
956 d->symlen.resize(number<uint16_t, LittleEndian>(data)); data += sizeof(uint16_t);
957 d->btree = (LR*)data;
959 // The comrpession scheme used is "Recursive Pairing", that replaces the most
960 // frequent adjacent pair of symbols in the source message by a new symbol,
961 // reevaluating the frequencies of all of the symbol pairs with respect to
962 // the extended alphabet, and then repeating the process.
963 // See http://www.larsson.dogma.net/dcc99.pdf
964 std::vector<bool> visited(d->symlen.size());
966 for (Sym sym = 0; sym < d->symlen.size(); ++sym)
968 d->symlen[sym] = set_symlen(d, sym, visited);
970 return data + d->symlen.size() * sizeof(LR) + (d->symlen.size() & 1);
973 uint8_t* set_dtz_map(TBEntry<WDL>&, uint8_t*, File) { return nullptr; }
975 uint8_t* set_dtz_map(TBEntry<DTZ>& e, uint8_t* data, File maxFile) {
979 for (File f = FILE_A; f <= maxFile; ++f) {
980 if (e.get(0, f)->flags & TBFlag::Mapped)
981 for (int i = 0; i < 4; ++i) { // Sequence like 3,x,x,x,1,x,0,2,x,x
982 e.get(0, f)->map_idx[i] = (uint16_t)(data - e.map + 1);
987 return data += (uintptr_t)data & 1; // Word alignment
990 template<TBType Type>
991 void do_init(TBEntry<Type>& e, uint8_t* data) {
995 enum { Split = 1, HasPawns = 2 };
997 assert(e.hasPawns == !!(*data & HasPawns));
998 assert((e.key != e.key2) == !!(*data & Split));
1000 data++; // First byte stores flags
1002 const int sides = Type == WDL && (e.key != e.key2) ? 2 : 1;
1003 const File maxFile = e.hasPawns ? FILE_D : FILE_A;
1005 bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
1007 assert(!pp || e.pawnCount[0]);
1009 for (File f = FILE_A; f <= maxFile; ++f) {
1011 for (int i = 0; i < sides; i++)
1012 *e.get(i, f) = PairsData();
1014 int order[][2] = { { *data & 0xF, pp ? *(data + 1) & 0xF : 0xF },
1015 { *data >> 4, pp ? *(data + 1) >> 4 : 0xF } };
1018 for (int k = 0; k < e.pieceCount; ++k, ++data)
1019 for (int i = 0; i < sides; i++)
1020 e.get(i, f)->pieces[k] = Piece(i ? *data >> 4 : *data & 0xF);
1022 for (int i = 0; i < sides; ++i)
1023 set_groups(e, e.get(i, f), order[i], f);
1026 data += (uintptr_t)data & 1; // Word alignment
1028 for (File f = FILE_A; f <= maxFile; ++f)
1029 for (int i = 0; i < sides; i++)
1030 data = set_sizes(e.get(i, f), data);
1033 data = set_dtz_map(e, data, maxFile);
1035 for (File f = FILE_A; f <= maxFile; ++f)
1036 for (int i = 0; i < sides; i++) {
1037 (d = e.get(i, f))->sparseIndex = (SparseEntry*)data;
1038 data += d->sparseIndexSize * sizeof(SparseEntry);
1041 for (File f = FILE_A; f <= maxFile; ++f)
1042 for (int i = 0; i < sides; i++) {
1043 (d = e.get(i, f))->blockLength = (uint16_t*)data;
1044 data += d->blockLengthSize * sizeof(uint16_t);
1047 for (File f = FILE_A; f <= maxFile; ++f)
1048 for (int i = 0; i < sides; i++) {
1049 data = (uint8_t*)(((uintptr_t)data + 0x3F) & ~0x3F); // 64 byte alignment
1050 (d = e.get(i, f))->data = data;
1051 data += d->blocksNum * d->sizeofBlock;
1055 template<TBType Type>
1056 void* init(TBEntry<Type>& e, const Position& pos) {
1060 // Avoid a thread reads 'ready' == true while another is still in do_init(),
1061 // this could happen due to compiler reordering.
1062 if (e.ready.load(std::memory_order_acquire))
1063 return e.baseAddress;
1065 std::unique_lock<Mutex> lk(mutex);
1067 if (e.ready.load(std::memory_order_relaxed)) // Recheck under lock
1068 return e.baseAddress;
1070 // Pieces strings in decreasing order for each color, like ("KPP","KR")
1071 std::string fname, w, b;
1072 for (PieceType pt = KING; pt >= PAWN; --pt) {
1073 w += std::string(popcount(pos.pieces(WHITE, pt)), PieceToChar[pt]);
1074 b += std::string(popcount(pos.pieces(BLACK, pt)), PieceToChar[pt]);
1077 constexpr uint8_t TB_MAGIC[][4] = { { 0xD7, 0x66, 0x0C, 0xA5 },
1078 { 0x71, 0xE8, 0x23, 0x5D } };
1080 fname = (e.key == pos.material_key() ? w + 'v' + b : b + 'v' + w)
1081 + (Type == WDL ? ".rtbw" : ".rtbz");
1083 uint8_t* data = TBFile(fname).map(&e.baseAddress, &e.mapping,
1084 TB_MAGIC[Type == WDL]);
1088 e.ready.store(true, std::memory_order_release);
1089 return e.baseAddress;
1092 template<TBType Type, typename T = typename TBEntry<Type>::Result>
1093 T probe_table(const Position& pos, ProbeState* result, WDLScore wdl = WDLDraw) {
1095 if (!(pos.pieces() ^ pos.pieces(KING)))
1096 return T(WDLDraw); // KvK
1098 TBEntry<Type>* entry = EntryTable.get<Type>(pos.material_key());
1100 if (!entry || !init(*entry, pos))
1101 return *result = FAIL, T();
1103 return do_probe_table(pos, entry, wdl, result);
1106 // For a position where the side to move has a winning capture it is not necessary
1107 // to store a winning value so the generator treats such positions as "don't cares"
1108 // and tries to assign to it a value that improves the compression ratio. Similarly,
1109 // if the side to move has a drawing capture, then the position is at least drawn.
1110 // If the position is won, then the TB needs to store a win value. But if the
1111 // position is drawn, the TB may store a loss value if that is better for compression.
1112 // All of this means that during probing, the engine must look at captures and probe
1113 // their results and must probe the position itself. The "best" result of these
1114 // probes is the correct result for the position.
1115 // DTZ table don't store values when a following move is a zeroing winning move
1116 // (winning capture or winning pawn move). Also DTZ store wrong values for positions
1117 // where the best move is an ep-move (even if losing). So in all these cases set
1118 // the state to ZEROING_BEST_MOVE.
1119 template<bool CheckZeroingMoves = false>
1120 WDLScore search(Position& pos, ProbeState* result) {
1122 WDLScore value, bestValue = WDLLoss;
1125 auto moveList = MoveList<LEGAL>(pos);
1126 size_t totalCount = moveList.size(), moveCount = 0;
1128 for (const Move& move : moveList)
1130 if ( !pos.capture(move)
1131 && (!CheckZeroingMoves || type_of(pos.moved_piece(move)) != PAWN))
1136 pos.do_move(move, st);
1137 value = -search(pos, result);
1138 pos.undo_move(move);
1140 if (*result == FAIL)
1143 if (value > bestValue)
1147 if (value >= WDLWin)
1149 *result = ZEROING_BEST_MOVE; // Winning DTZ-zeroing move
1155 // In case we have already searched all the legal moves we don't have to probe
1156 // the TB because the stored score could be wrong. For instance TB tables
1157 // do not contain information on position with ep rights, so in this case
1158 // the result of probe_wdl_table is wrong. Also in case of only capture
1159 // moves, for instance here 4K3/4q3/6p1/2k5/6p1/8/8/8 w - - 0 7, we have to
1160 // return with ZEROING_BEST_MOVE set.
1161 bool noMoreMoves = (moveCount && moveCount == totalCount);
1167 value = probe_table<WDL>(pos, result);
1169 if (*result == FAIL)
1173 // DTZ stores a "don't care" value if bestValue is a win
1174 if (bestValue >= value)
1175 return *result = ( bestValue > WDLDraw
1176 || noMoreMoves ? ZEROING_BEST_MOVE : OK), bestValue;
1178 return *result = OK, value;
1183 void Tablebases::init(const std::string& paths) {
1187 TBFile::Paths = paths;
1189 if (paths.empty() || paths == "<empty>")
1192 // MapB1H1H7[] encodes a square below a1-h8 diagonal to 0..27
1194 for (Square s = SQ_A1; s <= SQ_H8; ++s)
1195 if (off_A1H8(s) < 0)
1196 MapB1H1H7[s] = code++;
1198 // MapA1D1D4[] encodes a square in the a1-d1-d4 triangle to 0..9
1199 std::vector<Square> diagonal;
1201 for (Square s = SQ_A1; s <= SQ_D4; ++s)
1202 if (off_A1H8(s) < 0 && file_of(s) <= FILE_D)
1203 MapA1D1D4[s] = code++;
1205 else if (!off_A1H8(s) && file_of(s) <= FILE_D)
1206 diagonal.push_back(s);
1208 // Diagonal squares are encoded as last ones
1209 for (auto s : diagonal)
1210 MapA1D1D4[s] = code++;
1212 // MapKK[] encodes all the 461 possible legal positions of two kings where
1213 // the first is in the a1-d1-d4 triangle. If the first king is on the a1-d4
1214 // diagonal, the other one shall not to be above the a1-h8 diagonal.
1215 std::vector<std::pair<int, Square>> bothOnDiagonal;
1217 for (int idx = 0; idx < 10; idx++)
1218 for (Square s1 = SQ_A1; s1 <= SQ_D4; ++s1)
1219 if (MapA1D1D4[s1] == idx && (idx || s1 == SQ_B1)) // SQ_B1 is mapped to 0
1221 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
1222 if ((PseudoAttacks[KING][s1] | s1) & s2)
1223 continue; // Illegal position
1225 else if (!off_A1H8(s1) && off_A1H8(s2) > 0)
1226 continue; // First on diagonal, second above
1228 else if (!off_A1H8(s1) && !off_A1H8(s2))
1229 bothOnDiagonal.push_back(std::make_pair(idx, s2));
1232 MapKK[idx][s2] = code++;
1235 // Legal positions with both kings on diagonal are encoded as last ones
1236 for (auto p : bothOnDiagonal)
1237 MapKK[p.first][p.second] = code++;
1239 // Binomial[] stores the Binomial Coefficents using Pascal rule. There
1240 // are Binomial[k][n] ways to choose k elements from a set of n elements.
1243 for (int n = 1; n < 64; n++) // Squares
1244 for (int k = 0; k < 6 && k <= n; ++k) // Pieces
1245 Binomial[k][n] = (k > 0 ? Binomial[k - 1][n - 1] : 0)
1246 + (k < n ? Binomial[k ][n - 1] : 0);
1248 // MapPawns[s] encodes squares a2-h7 to 0..47. This is the number of possible
1249 // available squares when the leading one is in 's'. Moreover the pawn with
1250 // highest MapPawns[] is the leading pawn, the one nearest the edge and,
1251 // among pawns with same file, the one with lowest rank.
1252 int availableSquares = 47; // Available squares when lead pawn is in a2
1254 // Init the tables for the encoding of leading pawns group: with 6-men TB we
1255 // can have up to 4 leading pawns (KPPPPK).
1256 for (int leadPawnsCnt = 1; leadPawnsCnt <= 4; ++leadPawnsCnt)
1257 for (File f = FILE_A; f <= FILE_D; ++f)
1259 // Restart the index at every file because TB table is splitted
1260 // by file, so we can reuse the same index for different files.
1263 // Sum all possible combinations for a given file, starting with
1264 // the leading pawn on rank 2 and increasing the rank.
1265 for (Rank r = RANK_2; r <= RANK_7; ++r)
1267 Square sq = make_square(f, r);
1269 // Compute MapPawns[] at first pass.
1270 // If sq is the leading pawn square, any other pawn cannot be
1271 // below or more toward the edge of sq. There are 47 available
1272 // squares when sq = a2 and reduced by 2 for any rank increase
1273 // due to mirroring: sq == a3 -> no a2, h2, so MapPawns[a3] = 45
1274 if (leadPawnsCnt == 1)
1276 MapPawns[sq] = availableSquares--;
1277 MapPawns[sq ^ 7] = availableSquares--; // Horizontal flip
1279 LeadPawnIdx[leadPawnsCnt][sq] = idx;
1280 idx += Binomial[leadPawnsCnt - 1][MapPawns[sq]];
1282 // After a file is traversed, store the cumulated per-file index
1283 LeadPawnsSize[leadPawnsCnt][f] = idx;
1286 for (PieceType p1 = PAWN; p1 < KING; ++p1) {
1287 EntryTable.insert({KING, p1, KING});
1289 for (PieceType p2 = PAWN; p2 <= p1; ++p2) {
1290 EntryTable.insert({KING, p1, p2, KING});
1291 EntryTable.insert({KING, p1, KING, p2});
1293 for (PieceType p3 = PAWN; p3 < KING; ++p3)
1294 EntryTable.insert({KING, p1, p2, KING, p3});
1296 for (PieceType p3 = PAWN; p3 <= p2; ++p3) {
1297 EntryTable.insert({KING, p1, p2, p3, KING});
1299 for (PieceType p4 = PAWN; p4 <= p3; ++p4)
1300 EntryTable.insert({KING, p1, p2, p3, p4, KING});
1302 for (PieceType p4 = PAWN; p4 < KING; ++p4)
1303 EntryTable.insert({KING, p1, p2, p3, KING, p4});
1306 for (PieceType p3 = PAWN; p3 <= p1; ++p3)
1307 for (PieceType p4 = PAWN; p4 <= (p1 == p3 ? p2 : p3); ++p4)
1308 EntryTable.insert({KING, p1, p2, KING, p3, p4});
1312 sync_cout << "info string Found " << EntryTable.size() << " tablebases" << sync_endl;
1315 // Probe the WDL table for a particular position.
1316 // If *result != FAIL, the probe was successful.
1317 // The return value is from the point of view of the side to move:
1319 // -1 : loss, but draw under 50-move rule
1321 // 1 : win, but draw under 50-move rule
1323 WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) {
1326 return search(pos, result);
1329 // Probe the DTZ table for a particular position.
1330 // If *result != FAIL, the probe was successful.
1331 // The return value is from the point of view of the side to move:
1332 // n < -100 : loss, but draw under 50-move rule
1333 // -100 <= n < -1 : loss in n ply (assuming 50-move counter == 0)
1335 // 1 < n <= 100 : win in n ply (assuming 50-move counter == 0)
1336 // 100 < n : win, but draw under 50-move rule
1338 // The return value n can be off by 1: a return value -n can mean a loss
1339 // in n+1 ply and a return value +n can mean a win in n+1 ply. This
1340 // cannot happen for tables with positions exactly on the "edge" of
1341 // the 50-move rule.
1343 // This implies that if dtz > 0 is returned, the position is certainly
1344 // a win if dtz + 50-move-counter <= 99. Care must be taken that the engine
1345 // picks moves that preserve dtz + 50-move-counter <= 99.
1347 // If n = 100 immediately after a capture or pawn move, then the position
1348 // is also certainly a win, and during the whole phase until the next
1349 // capture or pawn move, the inequality to be preserved is
1350 // dtz + 50-movecounter <= 100.
1352 // In short, if a move is available resulting in dtz + 50-move-counter <= 99,
1353 // then do not accept moves leading to dtz + 50-move-counter == 100.
1354 int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
1357 WDLScore wdl = search<true>(pos, result);
1359 if (*result == FAIL || wdl == WDLDraw) // DTZ tables don't store draws
1362 // DTZ stores a 'don't care' value in this case, or even a plain wrong
1363 // one as in case the best move is a losing ep, so it cannot be probed.
1364 if (*result == ZEROING_BEST_MOVE)
1365 return dtz_before_zeroing(wdl);
1367 int dtz = probe_table<DTZ>(pos, result, wdl);
1369 if (*result == FAIL)
1372 if (*result != CHANGE_STM)
1373 return (dtz + 100 * (wdl == WDLBlessedLoss || wdl == WDLCursedWin)) * sign_of(wdl);
1375 // DTZ stores results for the other side, so we need to do a 1-ply search and
1376 // find the winning move that minimizes DTZ.
1378 int minDTZ = 0xFFFF;
1380 for (const Move& move : MoveList<LEGAL>(pos))
1382 bool zeroing = pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN;
1384 pos.do_move(move, st);
1386 // For zeroing moves we want the dtz of the move _before_ doing it,
1387 // otherwise we will get the dtz of the next move sequence. Search the
1388 // position after the move to get the score sign (because even in a
1389 // winning position we could make a losing capture or going for a draw).
1390 dtz = zeroing ? -dtz_before_zeroing(search(pos, result))
1391 : -probe_dtz(pos, result);
1393 pos.undo_move(move);
1395 if (*result == FAIL)
1398 // Convert result from 1-ply search. Zeroing moves are already accounted
1399 // by dtz_before_zeroing() that returns the DTZ of the previous move.
1401 dtz += sign_of(dtz);
1403 // Skip the draws and if we are winning only pick positive dtz
1404 if (dtz < minDTZ && sign_of(dtz) == sign_of(wdl))
1408 // Special handle a mate position, when there are no legal moves, in this
1409 // case return value is somewhat arbitrary, so stick to the original TB code
1410 // that returns -1 in this case.
1411 return minDTZ == 0xFFFF ? -1 : minDTZ;
1414 // Check whether there has been at least one repetition of positions
1415 // since the last capture or pawn move.
1416 static int has_repeated(StateInfo *st)
1419 int i = 4, e = std::min(st->rule50, st->pliesFromNull);
1424 StateInfo *stp = st->previous->previous;
1427 stp = stp->previous->previous;
1429 if (stp->key == st->key)
1439 // Use the DTZ tables to filter out moves that don't preserve the win or draw.
1440 // If the position is lost, but DTZ is fairly high, only keep moves that
1443 // A return value false indicates that not all probes were successful and that
1444 // no moves were filtered out.
1445 bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, Value& score)
1447 assert(rootMoves.size());
1450 int dtz = probe_dtz(pos, &result);
1458 for (size_t i = 0; i < rootMoves.size(); ++i) {
1459 Move move = rootMoves[i].pv[0];
1460 pos.do_move(move, st);
1463 if (pos.checkers() && dtz > 0) {
1464 ExtMove s[MAX_MOVES];
1466 if (generate<LEGAL>(pos, s) == s)
1471 if (st.rule50 != 0) {
1472 v = -probe_dtz(pos, &result);
1479 v = -probe_wdl(pos, &result);
1480 v = dtz_before_zeroing(WDLScore(v));
1484 pos.undo_move(move);
1489 rootMoves[i].score = (Value)v;
1492 // Obtain 50-move counter for the root position.
1493 // In Stockfish there seems to be no clean way, so we do it like this:
1494 int cnt50 = st.previous ? st.previous->rule50 : 0;
1496 // Use 50-move counter to determine whether the root position is
1497 // won, lost or drawn.
1498 WDLScore wdl = WDLDraw;
1501 wdl = (dtz + cnt50 <= 100) ? WDLWin : WDLCursedWin;
1503 wdl = (-dtz + cnt50 <= 100) ? WDLLoss : WDLBlessedLoss;
1505 // Determine the score to report to the user.
1506 score = WDL_to_value[wdl + 2];
1508 // If the position is winning or losing, but too few moves left, adjust the
1509 // score to show how close it is to winning or losing.
1510 // NOTE: int(PawnValueEg) is used as scaling factor in score_to_uci().
1511 if (wdl == WDLCursedWin && dtz <= 100)
1512 score = (Value)(((200 - dtz - cnt50) * int(PawnValueEg)) / 200);
1513 else if (wdl == WDLBlessedLoss && dtz >= -100)
1514 score = -(Value)(((200 + dtz - cnt50) * int(PawnValueEg)) / 200);
1516 // Now be a bit smart about filtering out moves.
1519 if (dtz > 0) { // winning (or 50-move rule draw)
1522 for (size_t i = 0; i < rootMoves.size(); ++i) {
1523 int v = rootMoves[i].score;
1525 if (v > 0 && v < best)
1531 // If the current phase has not seen repetitions, then try all moves
1532 // that stay safely within the 50-move budget, if there are any.
1533 if (!has_repeated(st.previous) && best + cnt50 <= 99)
1536 for (size_t i = 0; i < rootMoves.size(); ++i) {
1537 int v = rootMoves[i].score;
1539 if (v > 0 && v <= max)
1540 rootMoves[j++] = rootMoves[i];
1542 } else if (dtz < 0) { // losing (or 50-move rule draw)
1545 for (size_t i = 0; i < rootMoves.size(); ++i) {
1546 int v = rootMoves[i].score;
1552 // Try all moves, unless we approach or have a 50-move rule draw.
1553 if (-best * 2 + cnt50 < 100)
1556 for (size_t i = 0; i < rootMoves.size(); ++i) {
1557 if (rootMoves[i].score == best)
1558 rootMoves[j++] = rootMoves[i];
1561 // Try all moves that preserve the draw.
1562 for (size_t i = 0; i < rootMoves.size(); ++i) {
1563 if (rootMoves[i].score == 0)
1564 rootMoves[j++] = rootMoves[i];
1568 rootMoves.resize(j, Search::RootMove(MOVE_NONE));
1573 // Use the WDL tables to filter out moves that don't preserve the win or draw.
1574 // This is a fallback for the case that some or all DTZ tables are missing.
1576 // A return value false indicates that not all probes were successful and that
1577 // no moves were filtered out.
1578 bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves, Value& score)
1582 WDLScore wdl = Tablebases::probe_wdl(pos, &result);
1587 score = WDL_to_value[wdl + 2];
1594 for (size_t i = 0; i < rootMoves.size(); ++i) {
1595 Move move = rootMoves[i].pv[0];
1596 pos.do_move(move, st);
1597 WDLScore v = -Tablebases::probe_wdl(pos, &result);
1598 pos.undo_move(move);
1603 rootMoves[i].score = (Value)v;
1611 for (size_t i = 0; i < rootMoves.size(); ++i) {
1612 if (rootMoves[i].score == best)
1613 rootMoves[j++] = rootMoves[i];
1616 rootMoves.resize(j, Search::RootMove(MOVE_NONE));