1/*
2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (c) 2013 Ronald de Man
4 Copyright (C) 2016-2019 Marco Costalba, Lucas Braesch
5
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.
10
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.
15
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/>.
18*/
19
20#include <algorithm>
21#include <atomic>
22#include <cstdint>
23#include <cstring> // For std::memset and std::memcpy
24#include <deque>
25#include <fstream>
26#include <iostream>
27#include <list>
28#include <sstream>
29#include <type_traits>
30
31#include "../bitboard.h"
32#include "../movegen.h"
33#include "../position.h"
34#include "../search.h"
35#include "../thread_win32_osx.h"
36#include "../types.h"
37#include "../uci.h"
38
39#include "tbprobe.h"
40
41#ifndef _WIN32
42#include <fcntl.h>
43#include <unistd.h>
44#include <sys/mman.h>
45#include <sys/stat.h>
46#else
47#define WIN32_LEAN_AND_MEAN
48#define NOMINMAX
49#include <windows.h>
50#endif
51
52using namespace Tablebases;
53
54int Tablebases::MaxCardinality;
55
56namespace {
57
58constexpr int TBPIECES = 7; // Max number of supported pieces
59
60enum { BigEndian, LittleEndian };
61enum TBType { KEY, WDL, DTZ }; // Used as template parameter
62
63// Each table has a set of flags: all of them refer to DTZ tables, the last one to WDL tables
64enum TBFlag { STM = 1, Mapped = 2, WinPlies = 4, LossPlies = 8, Wide = 16, SingleValue = 128 };
65
66inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
67inline Square operator^=(Square& s, int i) { return s = Square(int(s) ^ i); }
68inline Square operator^(Square s, int i) { return Square(int(s) ^ i); }
69
70const std::string PieceToChar = " PNBRQK pnbrqk";
71
72int MapPawns[SQUARE_NB];
73int MapB1H1H7[SQUARE_NB];
74int MapA1D1D4[SQUARE_NB];
75int MapKK[10][SQUARE_NB]; // [MapA1D1D4][SQUARE_NB]
76
77int Binomial[6][SQUARE_NB]; // [k][n] k elements from a set of n elements
78int LeadPawnIdx[6][SQUARE_NB]; // [leadPawnsCnt][SQUARE_NB]
79int LeadPawnsSize[6][4]; // [leadPawnsCnt][FILE_A..FILE_D]
80
81// Comparison function to sort leading pawns in ascending MapPawns[] order
82bool pawns_comp(Square i, Square j) { return MapPawns[i] < MapPawns[j]; }
83int off_A1H8(Square sq) { return int(rank_of(sq)) - file_of(sq); }
84
85constexpr Value WDL_to_value[] = {
86 -VALUE_MATE + MAX_PLY + 1,
87 VALUE_DRAW - 2,
88 VALUE_DRAW,
89 VALUE_DRAW + 2,
90 VALUE_MATE - MAX_PLY - 1
91};
92
93template<typename T, int Half = sizeof(T) / 2, int End = sizeof(T) - 1>
94inline void swap_endian(T& x)
95{
96 static_assert(std::is_unsigned<T>::value, "Argument of swap_endian not unsigned");
97
98 uint8_t tmp, *c = (uint8_t*)&x;
99 for (int i = 0; i < Half; ++i)
100 tmp = c[i], c[i] = c[End - i], c[End - i] = tmp;
101}
102template<> inline void swap_endian<uint8_t>(uint8_t&) {}
103
104template<typename T, int LE> T number(void* addr)
105{
106 static const union { uint32_t i; char c[4]; } Le = { 0x01020304 };
107 static const bool IsLittleEndian = (Le.c[0] == 4);
108
109 T v;
110
111 if ((uintptr_t)addr & (alignof(T) - 1)) // Unaligned pointer (very rare)
112 std::memcpy(&v, addr, sizeof(T));
113 else
114 v = *((T*)addr);
115
116 if (LE != IsLittleEndian)
117 swap_endian(v);
118 return v;
119}
120
121// DTZ tables don't store valid scores for moves that reset the rule50 counter
122// like captures and pawn moves but we can easily recover the correct dtz of the
123// previous move if we know the position's WDL score.
124int dtz_before_zeroing(WDLScore wdl) {
125 return wdl == WDLWin ? 1 :
126 wdl == WDLCursedWin ? 101 :
127 wdl == WDLBlessedLoss ? -101 :
128 wdl == WDLLoss ? -1 : 0;
129}
130
131// Return the sign of a number (-1, 0, 1)
132template <typename T> int sign_of(T val) {
133 return (T(0) < val) - (val < T(0));
134}
135
136// Numbers in little endian used by sparseIndex[] to point into blockLength[]
137struct SparseEntry {
138 char block[4]; // Number of block
139 char offset[2]; // Offset within the block
140};
141
142static_assert(sizeof(SparseEntry) == 6, "SparseEntry must be 6 bytes");
143
144typedef uint16_t Sym; // Huffman symbol
145
146struct LR {
147 enum Side { Left, Right };
148
149 uint8_t lr[3]; // The first 12 bits is the left-hand symbol, the second 12
150 // bits is the right-hand symbol. If symbol has length 1,
151 // then the left-hand symbol is the stored value.
152 template<Side S>
153 Sym get() {
154 return S == Left ? ((lr[1] & 0xF) << 8) | lr[0] :
155 S == Right ? (lr[2] << 4) | (lr[1] >> 4) : (assert(false), Sym(-1));
156 }
157};
158
159static_assert(sizeof(LR) == 3, "LR tree entry must be 3 bytes");
160
161// Tablebases data layout is structured as following:
162//
163// TBFile: memory maps/unmaps the physical .rtbw and .rtbz files
164// TBTable: one object for each file with corresponding indexing information
165// TBTables: has ownership of TBTable objects, keeping a list and a hash
166
167// class TBFile memory maps/unmaps the single .rtbw and .rtbz files. Files are
168// memory mapped for best performance. Files are mapped at first access: at init
169// time only existence of the file is checked.
170class TBFile : public std::ifstream {
171
172 std::string fname;
173
174public:
175 // Look for and open the file among the Paths directories where the .rtbw
176 // and .rtbz files can be found. Multiple directories are separated by ";"
177 // on Windows and by ":" on Unix-based operating systems.
178 //
179 // Example:
180 // C:\tb\wdl345;C:\tb\wdl6;D:\tb\dtz345;D:\tb\dtz6
181 static std::string Paths;
182
183 TBFile(const std::string& f) {
184
185#ifndef _WIN32
186 constexpr char SepChar = ':';
187#else
188 constexpr char SepChar = ';';
189#endif
190 std::stringstream ss(Paths);
191 std::string path;
192
193 while (std::getline(ss, path, SepChar)) {
194 fname = path + "/" + f;
195 std::ifstream::open(fname);
196 if (is_open())
197 return;
198 }
199 }
200
201 // Memory map the file and check it. File should be already open and will be
202 // closed after mapping.
203 uint8_t* map(void** baseAddress, uint64_t* mapping, TBType type) {
204
205 assert(is_open());
206
207 close(); // Need to re-open to get native file descriptor
208
209#ifndef _WIN32
210 struct stat statbuf;
211 int fd = ::open(fname.c_str(), O_RDONLY);
212
213 if (fd == -1)
214 return *baseAddress = nullptr, nullptr;
215
216 fstat(fd, &statbuf);
217
218 if (statbuf.st_size % 64 != 16)
219 {
220 std::cerr << "Corrupt tablebase file " << fname << std::endl;
221 exit(EXIT_FAILURE);
222 }
223
224 *mapping = statbuf.st_size;
225 *baseAddress = mmap(nullptr, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
226 madvise(*baseAddress, statbuf.st_size, MADV_RANDOM);
227 ::close(fd);
228
229 if (*baseAddress == MAP_FAILED)
230 {
231 std::cerr << "Could not mmap() " << fname << std::endl;
232 exit(EXIT_FAILURE);
233 }
234#else
235 // Note FILE_FLAG_RANDOM_ACCESS is only a hint to Windows and as such may get ignored.
236 HANDLE fd = CreateFile(fname.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
237 OPEN_EXISTING, FILE_FLAG_RANDOM_ACCESS, nullptr);
238
239 if (fd == INVALID_HANDLE_VALUE)
240 return *baseAddress = nullptr, nullptr;
241
242 DWORD size_high;
243 DWORD size_low = GetFileSize(fd, &size_high);
244
245 if (size_low % 64 != 16)
246 {
247 std::cerr << "Corrupt tablebase file " << fname << std::endl;
248 exit(EXIT_FAILURE);
249 }
250
251 HANDLE mmap = CreateFileMapping(fd, nullptr, PAGE_READONLY, size_high, size_low, nullptr);
252 CloseHandle(fd);
253
254 if (!mmap)
255 {
256 std::cerr << "CreateFileMapping() failed" << std::endl;
257 exit(EXIT_FAILURE);
258 }
259
260 *mapping = (uint64_t)mmap;
261 *baseAddress = MapViewOfFile(mmap, FILE_MAP_READ, 0, 0, 0);
262
263 if (!*baseAddress)
264 {
265 std::cerr << "MapViewOfFile() failed, name = " << fname
266 << ", error = " << GetLastError() << std::endl;
267 exit(EXIT_FAILURE);
268 }
269#endif
270 uint8_t* data = (uint8_t*)*baseAddress;
271
272 constexpr uint8_t Magics[][4] = { { 0xD7, 0x66, 0x0C, 0xA5 },
273 { 0x71, 0xE8, 0x23, 0x5D } };
274
275 if (memcmp(data, Magics[type == WDL], 4))
276 {
277 std::cerr << "Corrupted table in file " << fname << std::endl;
278 unmap(*baseAddress, *mapping);
279 return *baseAddress = nullptr, nullptr;
280 }
281
282 return data + 4; // Skip Magics's header
283 }
284
285 static void unmap(void* baseAddress, uint64_t mapping) {
286
287#ifndef _WIN32
288 munmap(baseAddress, mapping);
289#else
290 UnmapViewOfFile(baseAddress);
291 CloseHandle((HANDLE)mapping);
292#endif
293 }
294};
295
296std::string TBFile::Paths;
297
298// struct PairsData contains low level indexing information to access TB data.
299// There are 8, 4 or 2 PairsData records for each TBTable, according to type of
300// table and if positions have pawns or not. It is populated at first access.
301struct PairsData {
302 uint8_t flags; // Table flags, see enum TBFlag
303 uint8_t maxSymLen; // Maximum length in bits of the Huffman symbols
304 uint8_t minSymLen; // Minimum length in bits of the Huffman symbols
305 uint32_t blocksNum; // Number of blocks in the TB file
306 size_t sizeofBlock; // Block size in bytes
307 size_t span; // About every span values there is a SparseIndex[] entry
308 Sym* lowestSym; // lowestSym[l] is the symbol of length l with the lowest value
309 LR* btree; // btree[sym] stores the left and right symbols that expand sym
310 uint16_t* blockLength; // Number of stored positions (minus one) for each block: 1..65536
311 uint32_t blockLengthSize; // Size of blockLength[] table: padded so it's bigger than blocksNum
312 SparseEntry* sparseIndex; // Partial indices into blockLength[]
313 size_t sparseIndexSize; // Size of SparseIndex[] table
314 uint8_t* data; // Start of Huffman compressed data
315 std::vector<uint64_t> base64; // base64[l - min_sym_len] is the 64bit-padded lowest symbol of length l
316 std::vector<uint8_t> symlen; // Number of values (-1) represented by a given Huffman symbol: 1..256
317 Piece pieces[TBPIECES]; // Position pieces: the order of pieces defines the groups
318 uint64_t groupIdx[TBPIECES+1]; // Start index used for the encoding of the group's pieces
319 int groupLen[TBPIECES+1]; // Number of pieces in a given group: KRKN -> (3, 1)
320 uint16_t map_idx[4]; // WDLWin, WDLLoss, WDLCursedWin, WDLBlessedLoss (used in DTZ)
321};
322
323// struct TBTable contains indexing information to access the corresponding TBFile.
324// There are 2 types of TBTable, corresponding to a WDL or a DTZ file. TBTable
325// is populated at init time but the nested PairsData records are populated at
326// first access, when the corresponding file is memory mapped.
327template<TBType Type>
328struct TBTable {
329 typedef typename std::conditional<Type == WDL, WDLScore, int>::type Ret;
330
331 static constexpr int Sides = Type == WDL ? 2 : 1;
332
333 std::atomic_bool ready;
334 void* baseAddress;
335 uint8_t* map;
336 uint64_t mapping;
337 Key key;
338 Key key2;
339 int pieceCount;
340 bool hasPawns;
341 bool hasUniquePieces;
342 uint8_t pawnCount[2]; // [Lead color / other color]
343 PairsData items[Sides][4]; // [wtm / btm][FILE_A..FILE_D or 0]
344
345 PairsData* get(int stm, int f) {
346 return &items[stm % Sides][hasPawns ? f : 0];
347 }
348
349 TBTable() : ready(false), baseAddress(nullptr) {}
350 explicit TBTable(const std::string& code);
351 explicit TBTable(const TBTable<WDL>& wdl);
352
353 ~TBTable() {
354 if (baseAddress)
355 TBFile::unmap(baseAddress, mapping);
356 }
357};
358
359template<>
360TBTable<WDL>::TBTable(const std::string& code) : TBTable() {
361
362 StateInfo st;
363 Position pos;
364
365 key = pos.set(code, WHITE, &st).material_key();
366 pieceCount = pos.count<ALL_PIECES>();
367 hasPawns = pos.pieces(PAWN);
368
369 hasUniquePieces = false;
370 for (Color c : { WHITE, BLACK })
371 for (PieceType pt = PAWN; pt < KING; ++pt)
372 if (popcount(pos.pieces(c, pt)) == 1)
373 hasUniquePieces = true;
374
375 // Set the leading color. In case both sides have pawns the leading color
376 // is the side with less pawns because this leads to better compression.
377 bool c = !pos.count<PAWN>(BLACK)
378 || ( pos.count<PAWN>(WHITE)
379 && pos.count<PAWN>(BLACK) >= pos.count<PAWN>(WHITE));
380
381 pawnCount[0] = pos.count<PAWN>(c ? WHITE : BLACK);
382 pawnCount[1] = pos.count<PAWN>(c ? BLACK : WHITE);
383
384 key2 = pos.set(code, BLACK, &st).material_key();
385}
386
387template<>
388TBTable<DTZ>::TBTable(const TBTable<WDL>& wdl) : TBTable() {
389
390 // Use the corresponding WDL table to avoid recalculating all from scratch
391 key = wdl.key;
392 key2 = wdl.key2;
393 pieceCount = wdl.pieceCount;
394 hasPawns = wdl.hasPawns;
395 hasUniquePieces = wdl.hasUniquePieces;
396 pawnCount[0] = wdl.pawnCount[0];
397 pawnCount[1] = wdl.pawnCount[1];
398}
399
400// class TBTables creates and keeps ownership of the TBTable objects, one for
401// each TB file found. It supports a fast, hash based, table lookup. Populated
402// at init time, accessed at probe time.
403class TBTables {
404
405 typedef std::tuple<Key, TBTable<WDL>*, TBTable<DTZ>*> Entry;
406
407 static constexpr int Size = 1 << 12; // 4K table, indexed by key's 12 lsb
408 static constexpr int Overflow = 1; // Number of elements allowed to map to the last bucket
409
410 Entry hashTable[Size + Overflow];
411
412 std::deque<TBTable<WDL>> wdlTable;
413 std::deque<TBTable<DTZ>> dtzTable;
414
415 void insert(Key key, TBTable<WDL>* wdl, TBTable<DTZ>* dtz) {
416 uint32_t homeBucket = (uint32_t)key & (Size - 1);
417 Entry entry = std::make_tuple(key, wdl, dtz);
418
419 // Ensure last element is empty to avoid overflow when looking up
420 for (uint32_t bucket = homeBucket; bucket < Size + Overflow - 1; ++bucket) {
421 Key otherKey = std::get<KEY>(hashTable[bucket]);
422 if (otherKey == key || !std::get<WDL>(hashTable[bucket])) {
423 hashTable[bucket] = entry;
424 return;
425 }
426
427 // Robin Hood hashing: If we've probed for longer than this element,
428 // insert here and search for a new spot for the other element instead.
429 uint32_t otherHomeBucket = (uint32_t)otherKey & (Size - 1);
430 if (otherHomeBucket > homeBucket) {
431 swap(entry, hashTable[bucket]);
432 key = otherKey;
433 homeBucket = otherHomeBucket;
434 }
435 }
436 std::cerr << "TB hash table size too low!" << std::endl;
437 exit(EXIT_FAILURE);
438 }
439
440public:
441 template<TBType Type>
442 TBTable<Type>* get(Key key) {
443 for (const Entry* entry = &hashTable[(uint32_t)key & (Size - 1)]; ; ++entry) {
444 if (std::get<KEY>(*entry) == key || !std::get<Type>(*entry))
445 return std::get<Type>(*entry);
446 }
447 }
448
449 void clear() {
450 memset(hashTable, 0, sizeof(hashTable));
451 wdlTable.clear();
452 dtzTable.clear();
453 }
454 size_t size() const { return wdlTable.size(); }
455 void add(const std::vector<PieceType>& pieces);
456};
457
458TBTables TBTables;
459
460// If the corresponding file exists two new objects TBTable<WDL> and TBTable<DTZ>
461// are created and added to the lists and hash table. Called at init time.
462void TBTables::add(const std::vector<PieceType>& pieces) {
463
464 std::string code;
465
466 for (PieceType pt : pieces)
467 code += PieceToChar[pt];
468
469 TBFile file(code.insert(code.find('K', 1), "v") + ".rtbw"); // KRK -> KRvK
470
471 if (!file.is_open()) // Only WDL file is checked
472 return;
473
474 file.close();
475
476 MaxCardinality = std::max((int)pieces.size(), MaxCardinality);
477
478 wdlTable.emplace_back(code);
479 dtzTable.emplace_back(wdlTable.back());
480
481 // Insert into the hash keys for both colors: KRvK with KR white and black
482 insert(wdlTable.back().key , &wdlTable.back(), &dtzTable.back());
483 insert(wdlTable.back().key2, &wdlTable.back(), &dtzTable.back());
484}
485
486// TB tables are compressed with canonical Huffman code. The compressed data is divided into
487// blocks of size d->sizeofBlock, and each block stores a variable number of symbols.
488// Each symbol represents either a WDL or a (remapped) DTZ value, or a pair of other symbols
489// (recursively). If you keep expanding the symbols in a block, you end up with up to 65536
490// WDL or DTZ values. Each symbol represents up to 256 values and will correspond after
491// Huffman coding to at least 1 bit. So a block of 32 bytes corresponds to at most
492// 32 x 8 x 256 = 65536 values. This maximum is only reached for tables that consist mostly
493// of draws or mostly of wins, but such tables are actually quite common. In principle, the
494// blocks in WDL tables are 64 bytes long (and will be aligned on cache lines). But for
495// mostly-draw or mostly-win tables this can leave many 64-byte blocks only half-filled, so
496// in such cases blocks are 32 bytes long. The blocks of DTZ tables are up to 1024 bytes long.
497// The generator picks the size that leads to the smallest table. The "book" of symbols and
498// Huffman codes is the same for all blocks in the table. A non-symmetric pawnless TB file
499// will have one table for wtm and one for btm, a TB file with pawns will have tables per
500// file a,b,c,d also in this case one set for wtm and one for btm.
501int decompress_pairs(PairsData* d, uint64_t idx) {
502
503 // Special case where all table positions store the same value
504 if (d->flags & TBFlag::SingleValue)
505 return d->minSymLen;
506
507 // First we need to locate the right block that stores the value at index "idx".
508 // Because each block n stores blockLength[n] + 1 values, the index i of the block
509 // that contains the value at position idx is:
510 //
511 // for (i = -1, sum = 0; sum <= idx; i++)
512 // sum += blockLength[i + 1] + 1;
513 //
514 // This can be slow, so we use SparseIndex[] populated with a set of SparseEntry that
515 // point to known indices into blockLength[]. Namely SparseIndex[k] is a SparseEntry
516 // that stores the blockLength[] index and the offset within that block of the value
517 // with index I(k), where:
518 //
519 // I(k) = k * d->span + d->span / 2 (1)
520
521 // First step is to get the 'k' of the I(k) nearest to our idx, using definition (1)
522 uint32_t k = idx / d->span;
523
524 // Then we read the corresponding SparseIndex[] entry
525 uint32_t block = number<uint32_t, LittleEndian>(&d->sparseIndex[k].block);
526 int offset = number<uint16_t, LittleEndian>(&d->sparseIndex[k].offset);
527
528 // Now compute the difference idx - I(k). From definition of k we know that
529 //
530 // idx = k * d->span + idx % d->span (2)
531 //
532 // So from (1) and (2) we can compute idx - I(K):
533 int diff = idx % d->span - d->span / 2;
534
535 // Sum the above to offset to find the offset corresponding to our idx
536 offset += diff;
537
538 // Move to previous/next block, until we reach the correct block that contains idx,
539 // that is when 0 <= offset <= d->blockLength[block]
540 while (offset < 0)
541 offset += d->blockLength[--block] + 1;
542
543 while (offset > d->blockLength[block])
544 offset -= d->blockLength[block++] + 1;
545
546 // Finally, we find the start address of our block of canonical Huffman symbols
547 uint32_t* ptr = (uint32_t*)(d->data + ((uint64_t)block * d->sizeofBlock));
548
549 // Read the first 64 bits in our block, this is a (truncated) sequence of
550 // unknown number of symbols of unknown length but we know the first one
551 // is at the beginning of this 64 bits sequence.
552 uint64_t buf64 = number<uint64_t, BigEndian>(ptr); ptr += 2;
553 int buf64Size = 64;
554 Sym sym;
555
556 while (true) {
557 int len = 0; // This is the symbol length - d->min_sym_len
558
559 // Now get the symbol length. For any symbol s64 of length l right-padded
560 // to 64 bits we know that d->base64[l-1] >= s64 >= d->base64[l] so we
561 // can find the symbol length iterating through base64[].
562 while (buf64 < d->base64[len])
563 ++len;
564
565 // All the symbols of a given length are consecutive integers (numerical
566 // sequence property), so we can compute the offset of our symbol of
567 // length len, stored at the beginning of buf64.
568 sym = (buf64 - d->base64[len]) >> (64 - len - d->minSymLen);
569
570 // Now add the value of the lowest symbol of length len to get our symbol
571 sym += number<Sym, LittleEndian>(&d->lowestSym[len]);
572
573 // If our offset is within the number of values represented by symbol sym
574 // we are done...
575 if (offset < d->symlen[sym] + 1)
576 break;
577
578 // ...otherwise update the offset and continue to iterate
579 offset -= d->symlen[sym] + 1;
580 len += d->minSymLen; // Get the real length
581 buf64 <<= len; // Consume the just processed symbol
582 buf64Size -= len;
583
584 if (buf64Size <= 32) { // Refill the buffer
585 buf64Size += 32;
586 buf64 |= (uint64_t)number<uint32_t, BigEndian>(ptr++) << (64 - buf64Size);
587 }
588 }
589
590 // Ok, now we have our symbol that expands into d->symlen[sym] + 1 symbols.
591 // We binary-search for our value recursively expanding into the left and
592 // right child symbols until we reach a leaf node where symlen[sym] + 1 == 1
593 // that will store the value we need.
594 while (d->symlen[sym]) {
595
596 Sym left = d->btree[sym].get<LR::Left>();
597
598 // If a symbol contains 36 sub-symbols (d->symlen[sym] + 1 = 36) and
599 // expands in a pair (d->symlen[left] = 23, d->symlen[right] = 11), then
600 // we know that, for instance the ten-th value (offset = 10) will be on
601 // the left side because in Recursive Pairing child symbols are adjacent.
602 if (offset < d->symlen[left] + 1)
603 sym = left;
604 else {
605 offset -= d->symlen[left] + 1;
606 sym = d->btree[sym].get<LR::Right>();
607 }
608 }
609
610 return d->btree[sym].get<LR::Left>();
611}
612
613bool check_dtz_stm(TBTable<WDL>*, int, File) { return true; }
614
615bool check_dtz_stm(TBTable<DTZ>* entry, int stm, File f) {
616
617 auto flags = entry->get(stm, f)->flags;
618 return (flags & TBFlag::STM) == stm
619 || ((entry->key == entry->key2) && !entry->hasPawns);
620}
621
622// DTZ scores are sorted by frequency of occurrence and then assigned the
623// values 0, 1, 2, ... in order of decreasing frequency. This is done for each
624// of the four WDLScore values. The mapping information necessary to reconstruct
625// the original values is stored in the TB file and read during map[] init.
626WDLScore map_score(TBTable<WDL>*, File, int value, WDLScore) { return WDLScore(value - 2); }
627
628int map_score(TBTable<DTZ>* entry, File f, int value, WDLScore wdl) {
629
630 constexpr int WDLMap[] = { 1, 3, 0, 2, 0 };
631
632 auto flags = entry->get(0, f)->flags;
633
634 uint8_t* map = entry->map;
635 uint16_t* idx = entry->get(0, f)->map_idx;
636 if (flags & TBFlag::Mapped) {
637 if (flags & TBFlag::Wide)
638 value = ((uint16_t *)map)[idx[WDLMap[wdl + 2]] + value];
639 else
640 value = map[idx[WDLMap[wdl + 2]] + value];
641 }
642
643 // DTZ tables store distance to zero in number of moves or plies. We
644 // want to return plies, so we have convert to plies when needed.
645 if ( (wdl == WDLWin && !(flags & TBFlag::WinPlies))
646 || (wdl == WDLLoss && !(flags & TBFlag::LossPlies))
647 || wdl == WDLCursedWin
648 || wdl == WDLBlessedLoss)
649 value *= 2;
650
651 return value + 1;
652}
653
654// Compute a unique index out of a position and use it to probe the TB file. To
655// encode k pieces of same type and color, first sort the pieces by square in
656// ascending order s1 <= s2 <= ... <= sk then compute the unique index as:
657//
658// idx = Binomial[1][s1] + Binomial[2][s2] + ... + Binomial[k][sk]
659//
660template<typename T, typename Ret = typename T::Ret>
661Ret do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result) {
662
663 Square squares[TBPIECES];
664 Piece pieces[TBPIECES];
665 uint64_t idx;
666 int next = 0, size = 0, leadPawnsCnt = 0;
667 PairsData* d;
668 Bitboard b, leadPawns = 0;
669 File tbFile = FILE_A;
670
671 // A given TB entry like KRK has associated two material keys: KRvk and Kvkr.
672 // If both sides have the same pieces keys are equal. In this case TB tables
673 // only store the 'white to move' case, so if the position to lookup has black
674 // to move, we need to switch the color and flip the squares before to lookup.
675 bool symmetricBlackToMove = (entry->key == entry->key2 && pos.side_to_move());
676
677 // TB files are calculated for white as stronger side. For instance we have
678 // KRvK, not KvKR. A position where stronger side is white will have its
679 // material key == entry->key, otherwise we have to switch the color and
680 // flip the squares before to lookup.
681 bool blackStronger = (pos.material_key() != entry->key);
682
683 int flipColor = (symmetricBlackToMove || blackStronger) * 8;
684 int flipSquares = (symmetricBlackToMove || blackStronger) * 070;
685 int stm = (symmetricBlackToMove || blackStronger) ^ pos.side_to_move();
686
687 // For pawns, TB files store 4 separate tables according if leading pawn is on
688 // file a, b, c or d after reordering. The leading pawn is the one with maximum
689 // MapPawns[] value, that is the one most toward the edges and with lowest rank.
690 if (entry->hasPawns) {
691
692 // In all the 4 tables, pawns are at the beginning of the piece sequence and
693 // their color is the reference one. So we just pick the first one.
694 Piece pc = Piece(entry->get(0, 0)->pieces[0] ^ flipColor);
695
696 assert(type_of(pc) == PAWN);
697
698 leadPawns = b = pos.pieces(color_of(pc), PAWN);
699 do
700 squares[size++] = pop_lsb(&b) ^ flipSquares;
701 while (b);
702
703 leadPawnsCnt = size;
704
705 std::swap(squares[0], *std::max_element(squares, squares + leadPawnsCnt, pawns_comp));
706
707 tbFile = file_of(squares[0]);
708 if (tbFile > FILE_D)
709 tbFile = file_of(squares[0] ^ 7); // Horizontal flip: SQ_H1 -> SQ_A1
710 }
711
712 // DTZ tables are one-sided, i.e. they store positions only for white to
713 // move or only for black to move, so check for side to move to be stm,
714 // early exit otherwise.
715 if (!check_dtz_stm(entry, stm, tbFile))
716 return *result = CHANGE_STM, Ret();
717
718 // Now we are ready to get all the position pieces (but the lead pawns) and
719 // directly map them to the correct color and square.
720 b = pos.pieces() ^ leadPawns;
721 do {
722 Square s = pop_lsb(&b);
723 squares[size] = s ^ flipSquares;
724 pieces[size++] = Piece(pos.piece_on(s) ^ flipColor);
725 } while (b);
726
727 assert(size >= 2);
728
729 d = entry->get(stm, tbFile);
730
731 // Then we reorder the pieces to have the same sequence as the one stored
732 // in pieces[i]: the sequence that ensures the best compression.
733 for (int i = leadPawnsCnt; i < size; ++i)
734 for (int j = i; j < size; ++j)
735 if (d->pieces[i] == pieces[j])
736 {
737 std::swap(pieces[i], pieces[j]);
738 std::swap(squares[i], squares[j]);
739 break;
740 }
741
742 // Now we map again the squares so that the square of the lead piece is in
743 // the triangle A1-D1-D4.
744 if (file_of(squares[0]) > FILE_D)
745 for (int i = 0; i < size; ++i)
746 squares[i] ^= 7; // Horizontal flip: SQ_H1 -> SQ_A1
747
748 // Encode leading pawns starting with the one with minimum MapPawns[] and
749 // proceeding in ascending order.
750 if (entry->hasPawns) {
751 idx = LeadPawnIdx[leadPawnsCnt][squares[0]];
752
753 std::sort(squares + 1, squares + leadPawnsCnt, pawns_comp);
754
755 for (int i = 1; i < leadPawnsCnt; ++i)
756 idx += Binomial[i][MapPawns[squares[i]]];
757
758 goto encode_remaining; // With pawns we have finished special treatments
759 }
760
761 // In positions withouth pawns, we further flip the squares to ensure leading
762 // piece is below RANK_5.
763 if (rank_of(squares[0]) > RANK_4)
764 for (int i = 0; i < size; ++i)
765 squares[i] ^= 070; // Vertical flip: SQ_A8 -> SQ_A1
766
767 // Look for the first piece of the leading group not on the A1-D4 diagonal
768 // and ensure it is mapped below the diagonal.
769 for (int i = 0; i < d->groupLen[0]; ++i) {
770 if (!off_A1H8(squares[i]))
771 continue;
772
773 if (off_A1H8(squares[i]) > 0) // A1-H8 diagonal flip: SQ_A3 -> SQ_C3
774 for (int j = i; j < size; ++j)
775 squares[j] = Square(((squares[j] >> 3) | (squares[j] << 3)) & 63);
776 break;
777 }
778
779 // Encode the leading group.
780 //
781 // Suppose we have KRvK. Let's say the pieces are on square numbers wK, wR
782 // and bK (each 0...63). The simplest way to map this position to an index
783 // is like this:
784 //
785 // index = wK * 64 * 64 + wR * 64 + bK;
786 //
787 // But this way the TB is going to have 64*64*64 = 262144 positions, with
788 // lots of positions being equivalent (because they are mirrors of each
789 // other) and lots of positions being invalid (two pieces on one square,
790 // adjacent kings, etc.).
791 // Usually the first step is to take the wK and bK together. There are just
792 // 462 ways legal and not-mirrored ways to place the wK and bK on the board.
793 // Once we have placed the wK and bK, there are 62 squares left for the wR
794 // Mapping its square from 0..63 to available squares 0..61 can be done like:
795 //
796 // wR -= (wR > wK) + (wR > bK);
797 //
798 // In words: if wR "comes later" than wK, we deduct 1, and the same if wR
799 // "comes later" than bK. In case of two same pieces like KRRvK we want to
800 // place the two Rs "together". If we have 62 squares left, we can place two
801 // Rs "together" in 62 * 61 / 2 ways (we divide by 2 because rooks can be
802 // swapped and still get the same position.)
803 //
804 // In case we have at least 3 unique pieces (inlcuded kings) we encode them
805 // together.
806 if (entry->hasUniquePieces) {
807
808 int adjust1 = squares[1] > squares[0];
809 int adjust2 = (squares[2] > squares[0]) + (squares[2] > squares[1]);
810
811 // First piece is below a1-h8 diagonal. MapA1D1D4[] maps the b1-d1-d3
812 // triangle to 0...5. There are 63 squares for second piece and and 62
813 // (mapped to 0...61) for the third.
814 if (off_A1H8(squares[0]))
815 idx = ( MapA1D1D4[squares[0]] * 63
816 + (squares[1] - adjust1)) * 62
817 + squares[2] - adjust2;
818
819 // First piece is on a1-h8 diagonal, second below: map this occurence to
820 // 6 to differentiate from the above case, rank_of() maps a1-d4 diagonal
821 // to 0...3 and finally MapB1H1H7[] maps the b1-h1-h7 triangle to 0..27.
822 else if (off_A1H8(squares[1]))
823 idx = ( 6 * 63 + rank_of(squares[0]) * 28
824 + MapB1H1H7[squares[1]]) * 62
825 + squares[2] - adjust2;
826
827 // First two pieces are on a1-h8 diagonal, third below
828 else if (off_A1H8(squares[2]))
829 idx = 6 * 63 * 62 + 4 * 28 * 62
830 + rank_of(squares[0]) * 7 * 28
831 + (rank_of(squares[1]) - adjust1) * 28
832 + MapB1H1H7[squares[2]];
833
834 // All 3 pieces on the diagonal a1-h8
835 else
836 idx = 6 * 63 * 62 + 4 * 28 * 62 + 4 * 7 * 28
837 + rank_of(squares[0]) * 7 * 6
838 + (rank_of(squares[1]) - adjust1) * 6
839 + (rank_of(squares[2]) - adjust2);
840 } else
841 // We don't have at least 3 unique pieces, like in KRRvKBB, just map
842 // the kings.
843 idx = MapKK[MapA1D1D4[squares[0]]][squares[1]];
844
845encode_remaining:
846 idx *= d->groupIdx[0];
847 Square* groupSq = squares + d->groupLen[0];
848
849 // Encode remainig pawns then pieces according to square, in ascending order
850 bool remainingPawns = entry->hasPawns && entry->pawnCount[1];
851
852 while (d->groupLen[++next])
853 {
854 std::sort(groupSq, groupSq + d->groupLen[next]);
855 uint64_t n = 0;
856
857 // Map down a square if "comes later" than a square in the previous
858 // groups (similar to what done earlier for leading group pieces).
859 for (int i = 0; i < d->groupLen[next]; ++i)
860 {
861 auto f = [&](Square s) { return groupSq[i] > s; };
862 auto adjust = std::count_if(squares, groupSq, f);
863 n += Binomial[i + 1][groupSq[i] - adjust - 8 * remainingPawns];
864 }
865
866 remainingPawns = false;
867 idx += n * d->groupIdx[next];
868 groupSq += d->groupLen[next];
869 }
870
871 // Now that we have the index, decompress the pair and get the score
872 return map_score(entry, tbFile, decompress_pairs(d, idx), wdl);
873}
874
875// Group together pieces that will be encoded together. The general rule is that
876// a group contains pieces of same type and color. The exception is the leading
877// group that, in case of positions withouth pawns, can be formed by 3 different
878// pieces (default) or by the king pair when there is not a unique piece apart
879// from the kings. When there are pawns, pawns are always first in pieces[].
880//
881// As example KRKN -> KRK + N, KNNK -> KK + NN, KPPKP -> P + PP + K + K
882//
883// The actual grouping depends on the TB generator and can be inferred from the
884// sequence of pieces in piece[] array.
885template<typename T>
886void set_groups(T& e, PairsData* d, int order[], File f) {
887
888 int n = 0, firstLen = e.hasPawns ? 0 : e.hasUniquePieces ? 3 : 2;
889 d->groupLen[n] = 1;
890
891 // Number of pieces per group is stored in groupLen[], for instance in KRKN
892 // the encoder will default on '111', so groupLen[] will be (3, 1).
893 for (int i = 1; i < e.pieceCount; ++i)
894 if (--firstLen > 0 || d->pieces[i] == d->pieces[i - 1])
895 d->groupLen[n]++;
896 else
897 d->groupLen[++n] = 1;
898
899 d->groupLen[++n] = 0; // Zero-terminated
900
901 // The sequence in pieces[] defines the groups, but not the order in which
902 // they are encoded. If the pieces in a group g can be combined on the board
903 // in N(g) different ways, then the position encoding will be of the form:
904 //
905 // g1 * N(g2) * N(g3) + g2 * N(g3) + g3
906 //
907 // This ensures unique encoding for the whole position. The order of the
908 // groups is a per-table parameter and could not follow the canonical leading
909 // pawns/pieces -> remainig pawns -> remaining pieces. In particular the
910 // first group is at order[0] position and the remaining pawns, when present,
911 // are at order[1] position.
912 bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
913 int next = pp ? 2 : 1;
914 int freeSquares = 64 - d->groupLen[0] - (pp ? d->groupLen[1] : 0);
915 uint64_t idx = 1;
916
917 for (int k = 0; next < n || k == order[0] || k == order[1]; ++k)
918 if (k == order[0]) // Leading pawns or pieces
919 {
920 d->groupIdx[0] = idx;
921 idx *= e.hasPawns ? LeadPawnsSize[d->groupLen[0]][f]
922 : e.hasUniquePieces ? 31332 : 462;
923 }
924 else if (k == order[1]) // Remaining pawns
925 {
926 d->groupIdx[1] = idx;
927 idx *= Binomial[d->groupLen[1]][48 - d->groupLen[0]];
928 }
929 else // Remainig pieces
930 {
931 d->groupIdx[next] = idx;
932 idx *= Binomial[d->groupLen[next]][freeSquares];
933 freeSquares -= d->groupLen[next++];
934 }
935
936 d->groupIdx[n] = idx;
937}
938
939// In Recursive Pairing each symbol represents a pair of childern symbols. So
940// read d->btree[] symbols data and expand each one in his left and right child
941// symbol until reaching the leafs that represent the symbol value.
942uint8_t set_symlen(PairsData* d, Sym s, std::vector<bool>& visited) {
943
944 visited[s] = true; // We can set it now because tree is acyclic
945 Sym sr = d->btree[s].get<LR::Right>();
946
947 if (sr == 0xFFF)
948 return 0;
949
950 Sym sl = d->btree[s].get<LR::Left>();
951
952 if (!visited[sl])
953 d->symlen[sl] = set_symlen(d, sl, visited);
954
955 if (!visited[sr])
956 d->symlen[sr] = set_symlen(d, sr, visited);
957
958 return d->symlen[sl] + d->symlen[sr] + 1;
959}
960
961uint8_t* set_sizes(PairsData* d, uint8_t* data) {
962
963 d->flags = *data++;
964
965 if (d->flags & TBFlag::SingleValue) {
966 d->blocksNum = d->blockLengthSize = 0;
967 d->span = d->sparseIndexSize = 0; // Broken MSVC zero-init
968 d->minSymLen = *data++; // Here we store the single value
969 return data;
970 }
971
972 // groupLen[] is a zero-terminated list of group lengths, the last groupIdx[]
973 // element stores the biggest index that is the tb size.
974 uint64_t tbSize = d->groupIdx[std::find(d->groupLen, d->groupLen + 7, 0) - d->groupLen];
975
976 d->sizeofBlock = 1ULL << *data++;
977 d->span = 1ULL << *data++;
978 d->sparseIndexSize = (tbSize + d->span - 1) / d->span; // Round up
979 auto padding = number<uint8_t, LittleEndian>(data++);
980 d->blocksNum = number<uint32_t, LittleEndian>(data); data += sizeof(uint32_t);
981 d->blockLengthSize = d->blocksNum + padding; // Padded to ensure SparseIndex[]
982 // does not point out of range.
983 d->maxSymLen = *data++;
984 d->minSymLen = *data++;
985 d->lowestSym = (Sym*)data;
986 d->base64.resize(d->maxSymLen - d->minSymLen + 1);
987
988 // The canonical code is ordered such that longer symbols (in terms of
989 // the number of bits of their Huffman code) have lower numeric value,
990 // so that d->lowestSym[i] >= d->lowestSym[i+1] (when read as LittleEndian).
991 // Starting from this we compute a base64[] table indexed by symbol length
992 // and containing 64 bit values so that d->base64[i] >= d->base64[i+1].
993 // See http://www.eecs.harvard.edu/~michaelm/E210/huffman.pdf
994 for (int i = d->base64.size() - 2; i >= 0; --i) {
995 d->base64[i] = (d->base64[i + 1] + number<Sym, LittleEndian>(&d->lowestSym[i])
996 - number<Sym, LittleEndian>(&d->lowestSym[i + 1])) / 2;
997
998 assert(d->base64[i] * 2 >= d->base64[i+1]);
999 }
1000
1001 // Now left-shift by an amount so that d->base64[i] gets shifted 1 bit more
1002 // than d->base64[i+1] and given the above assert condition, we ensure that
1003 // d->base64[i] >= d->base64[i+1]. Moreover for any symbol s64 of length i
1004 // and right-padded to 64 bits holds d->base64[i-1] >= s64 >= d->base64[i].
1005 for (size_t i = 0; i < d->base64.size(); ++i)
1006 d->base64[i] <<= 64 - i - d->minSymLen; // Right-padding to 64 bits
1007
1008 data += d->base64.size() * sizeof(Sym);
1009 d->symlen.resize(number<uint16_t, LittleEndian>(data)); data += sizeof(uint16_t);
1010 d->btree = (LR*)data;
1011
1012 // The compression scheme used is "Recursive Pairing", that replaces the most
1013 // frequent adjacent pair of symbols in the source message by a new symbol,
1014 // reevaluating the frequencies of all of the symbol pairs with respect to
1015 // the extended alphabet, and then repeating the process.
1016 // See http://www.larsson.dogma.net/dcc99.pdf
1017 std::vector<bool> visited(d->symlen.size());
1018
1019 for (Sym sym = 0; sym < d->symlen.size(); ++sym)
1020 if (!visited[sym])
1021 d->symlen[sym] = set_symlen(d, sym, visited);
1022
1023 return data + d->symlen.size() * sizeof(LR) + (d->symlen.size() & 1);
1024}
1025
1026uint8_t* set_dtz_map(TBTable<WDL>&, uint8_t* data, File) { return data; }
1027
1028uint8_t* set_dtz_map(TBTable<DTZ>& e, uint8_t* data, File maxFile) {
1029
1030 e.map = data;
1031
1032 for (File f = FILE_A; f <= maxFile; ++f) {
1033 auto flags = e.get(0, f)->flags;
1034 if (flags & TBFlag::Mapped) {
1035 if (flags & TBFlag::Wide) {
1036 data += (uintptr_t)data & 1; // Word alignment, we may have a mixed table
1037 for (int i = 0; i < 4; ++i) { // Sequence like 3,x,x,x,1,x,0,2,x,x
1038 e.get(0, f)->map_idx[i] = (uint16_t)((uint16_t *)data - (uint16_t *)e.map + 1);
1039 data += 2 * number<uint16_t, LittleEndian>(data) + 2;
1040 }
1041 }
1042 else {
1043 for (int i = 0; i < 4; ++i) {
1044 e.get(0, f)->map_idx[i] = (uint16_t)(data - e.map + 1);
1045 data += *data + 1;
1046 }
1047 }
1048 }
1049 }
1050
1051 return data += (uintptr_t)data & 1; // Word alignment
1052}
1053
1054// Populate entry's PairsData records with data from the just memory mapped file.
1055// Called at first access.
1056template<typename T>
1057void set(T& e, uint8_t* data) {
1058
1059 PairsData* d;
1060
1061 enum { Split = 1, HasPawns = 2 };
1062
1063 assert(e.hasPawns == !!(*data & HasPawns));
1064 assert((e.key != e.key2) == !!(*data & Split));
1065
1066 data++; // First byte stores flags
1067
1068 const int sides = T::Sides == 2 && (e.key != e.key2) ? 2 : 1;
1069 const File maxFile = e.hasPawns ? FILE_D : FILE_A;
1070
1071 bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
1072
1073 assert(!pp || e.pawnCount[0]);
1074
1075 for (File f = FILE_A; f <= maxFile; ++f) {
1076
1077 for (int i = 0; i < sides; i++)
1078 *e.get(i, f) = PairsData();
1079
1080 int order[][2] = { { *data & 0xF, pp ? *(data + 1) & 0xF : 0xF },
1081 { *data >> 4, pp ? *(data + 1) >> 4 : 0xF } };
1082 data += 1 + pp;
1083
1084 for (int k = 0; k < e.pieceCount; ++k, ++data)
1085 for (int i = 0; i < sides; i++)
1086 e.get(i, f)->pieces[k] = Piece(i ? *data >> 4 : *data & 0xF);
1087
1088 for (int i = 0; i < sides; ++i)
1089 set_groups(e, e.get(i, f), order[i], f);
1090 }
1091
1092 data += (uintptr_t)data & 1; // Word alignment
1093
1094 for (File f = FILE_A; f <= maxFile; ++f)
1095 for (int i = 0; i < sides; i++)
1096 data = set_sizes(e.get(i, f), data);
1097
1098 data = set_dtz_map(e, data, maxFile);
1099
1100 for (File f = FILE_A; f <= maxFile; ++f)
1101 for (int i = 0; i < sides; i++) {
1102 (d = e.get(i, f))->sparseIndex = (SparseEntry*)data;
1103 data += d->sparseIndexSize * sizeof(SparseEntry);
1104 }
1105
1106 for (File f = FILE_A; f <= maxFile; ++f)
1107 for (int i = 0; i < sides; i++) {
1108 (d = e.get(i, f))->blockLength = (uint16_t*)data;
1109 data += d->blockLengthSize * sizeof(uint16_t);
1110 }
1111
1112 for (File f = FILE_A; f <= maxFile; ++f)
1113 for (int i = 0; i < sides; i++) {
1114 data = (uint8_t*)(((uintptr_t)data + 0x3F) & ~0x3F); // 64 byte alignment
1115 (d = e.get(i, f))->data = data;
1116 data += d->blocksNum * d->sizeofBlock;
1117 }
1118}
1119
1120// If the TB file corresponding to the given position is already memory mapped
1121// then return its base address, otherwise try to memory map and init it. Called
1122// at every probe, memory map and init only at first access. Function is thread
1123// safe and can be called concurrently.
1124template<TBType Type>
1125void* mapped(TBTable<Type>& e, const Position& pos) {
1126
1127 static Mutex mutex;
1128
1129 // Use 'acquire' to avoid a thread reading 'ready' == true while
1130 // another is still working. (compiler reordering may cause this).
1131 if (e.ready.load(std::memory_order_acquire))
1132 return e.baseAddress; // Could be nullptr if file does not exist
1133
1134 std::unique_lock<Mutex> lk(mutex);
1135
1136 if (e.ready.load(std::memory_order_relaxed)) // Recheck under lock
1137 return e.baseAddress;
1138
1139 // Pieces strings in decreasing order for each color, like ("KPP","KR")
1140 std::string fname, w, b;
1141 for (PieceType pt = KING; pt >= PAWN; --pt) {
1142 w += std::string(popcount(pos.pieces(WHITE, pt)), PieceToChar[pt]);
1143 b += std::string(popcount(pos.pieces(BLACK, pt)), PieceToChar[pt]);
1144 }
1145
1146 fname = (e.key == pos.material_key() ? w + 'v' + b : b + 'v' + w)
1147 + (Type == WDL ? ".rtbw" : ".rtbz");
1148
1149 uint8_t* data = TBFile(fname).map(&e.baseAddress, &e.mapping, Type);
1150
1151 if (data)
1152 set(e, data);
1153
1154 e.ready.store(true, std::memory_order_release);
1155 return e.baseAddress;
1156}
1157
1158template<TBType Type, typename Ret = typename TBTable<Type>::Ret>
1159Ret probe_table(const Position& pos, ProbeState* result, WDLScore wdl = WDLDraw) {
1160
1161 if (pos.count<ALL_PIECES>() == 2) // KvK
1162 return Ret(WDLDraw);
1163
1164 TBTable<Type>* entry = TBTables.get<Type>(pos.material_key());
1165
1166 if (!entry || !mapped(*entry, pos))
1167 return *result = FAIL, Ret();
1168
1169 return do_probe_table(pos, entry, wdl, result);
1170}
1171
1172// For a position where the side to move has a winning capture it is not necessary
1173// to store a winning value so the generator treats such positions as "don't cares"
1174// and tries to assign to it a value that improves the compression ratio. Similarly,
1175// if the side to move has a drawing capture, then the position is at least drawn.
1176// If the position is won, then the TB needs to store a win value. But if the
1177// position is drawn, the TB may store a loss value if that is better for compression.
1178// All of this means that during probing, the engine must look at captures and probe
1179// their results and must probe the position itself. The "best" result of these
1180// probes is the correct result for the position.
1181// DTZ tables do not store values when a following move is a zeroing winning move
1182// (winning capture or winning pawn move). Also DTZ store wrong values for positions
1183// where the best move is an ep-move (even if losing). So in all these cases set
1184// the state to ZEROING_BEST_MOVE.
1185template<bool CheckZeroingMoves>
1186WDLScore search(Position& pos, ProbeState* result) {
1187
1188 WDLScore value, bestValue = WDLLoss;
1189 StateInfo st;
1190
1191 auto moveList = MoveList<LEGAL>(pos);
1192 size_t totalCount = moveList.size(), moveCount = 0;
1193
1194 for (const Move& move : moveList)
1195 {
1196 if ( !pos.capture(move)
1197 && (!CheckZeroingMoves || type_of(pos.moved_piece(move)) != PAWN))
1198 continue;
1199
1200 moveCount++;
1201
1202 pos.do_move(move, st);
1203 value = -search<false>(pos, result);
1204 pos.undo_move(move);
1205
1206 if (*result == FAIL)
1207 return WDLDraw;
1208
1209 if (value > bestValue)
1210 {
1211 bestValue = value;
1212
1213 if (value >= WDLWin)
1214 {
1215 *result = ZEROING_BEST_MOVE; // Winning DTZ-zeroing move
1216 return value;
1217 }
1218 }
1219 }
1220
1221 // In case we have already searched all the legal moves we don't have to probe
1222 // the TB because the stored score could be wrong. For instance TB tables
1223 // do not contain information on position with ep rights, so in this case
1224 // the result of probe_wdl_table is wrong. Also in case of only capture
1225 // moves, for instance here 4K3/4q3/6p1/2k5/6p1/8/8/8 w - - 0 7, we have to
1226 // return with ZEROING_BEST_MOVE set.
1227 bool noMoreMoves = (moveCount && moveCount == totalCount);
1228
1229 if (noMoreMoves)
1230 value = bestValue;
1231 else
1232 {
1233 value = probe_table<WDL>(pos, result);
1234
1235 if (*result == FAIL)
1236 return WDLDraw;
1237 }
1238
1239 // DTZ stores a "don't care" value if bestValue is a win
1240 if (bestValue >= value)
1241 return *result = ( bestValue > WDLDraw
1242 || noMoreMoves ? ZEROING_BEST_MOVE : OK), bestValue;
1243
1244 return *result = OK, value;
1245}
1246
1247} // namespace
1248
1249
1250/// Tablebases::init() is called at startup and after every change to
1251/// "SyzygyPath" UCI option to (re)create the various tables. It is not thread
1252/// safe, nor it needs to be.
1253void Tablebases::init(const std::string& paths) {
1254
1255 TBTables.clear();
1256 MaxCardinality = 0;
1257 TBFile::Paths = paths;
1258
1259 if (paths.empty() || paths == "<empty>")
1260 return;
1261
1262 // MapB1H1H7[] encodes a square below a1-h8 diagonal to 0..27
1263 int code = 0;
1264 for (Square s = SQ_A1; s <= SQ_H8; ++s)
1265 if (off_A1H8(s) < 0)
1266 MapB1H1H7[s] = code++;
1267
1268 // MapA1D1D4[] encodes a square in the a1-d1-d4 triangle to 0..9
1269 std::vector<Square> diagonal;
1270 code = 0;
1271 for (Square s = SQ_A1; s <= SQ_D4; ++s)
1272 if (off_A1H8(s) < 0 && file_of(s) <= FILE_D)
1273 MapA1D1D4[s] = code++;
1274
1275 else if (!off_A1H8(s) && file_of(s) <= FILE_D)
1276 diagonal.push_back(s);
1277
1278 // Diagonal squares are encoded as last ones
1279 for (auto s : diagonal)
1280 MapA1D1D4[s] = code++;
1281
1282 // MapKK[] encodes all the 461 possible legal positions of two kings where
1283 // the first is in the a1-d1-d4 triangle. If the first king is on the a1-d4
1284 // diagonal, the other one shall not to be above the a1-h8 diagonal.
1285 std::vector<std::pair<int, Square>> bothOnDiagonal;
1286 code = 0;
1287 for (int idx = 0; idx < 10; idx++)
1288 for (Square s1 = SQ_A1; s1 <= SQ_D4; ++s1)
1289 if (MapA1D1D4[s1] == idx && (idx || s1 == SQ_B1)) // SQ_B1 is mapped to 0
1290 {
1291 for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
1292 if ((PseudoAttacks[KING][s1] | s1) & s2)
1293 continue; // Illegal position
1294
1295 else if (!off_A1H8(s1) && off_A1H8(s2) > 0)
1296 continue; // First on diagonal, second above
1297
1298 else if (!off_A1H8(s1) && !off_A1H8(s2))
1299 bothOnDiagonal.emplace_back(idx, s2);
1300
1301 else
1302 MapKK[idx][s2] = code++;
1303 }
1304
1305 // Legal positions with both kings on diagonal are encoded as last ones
1306 for (auto p : bothOnDiagonal)
1307 MapKK[p.first][p.second] = code++;
1308
1309 // Binomial[] stores the Binomial Coefficents using Pascal rule. There
1310 // are Binomial[k][n] ways to choose k elements from a set of n elements.
1311 Binomial[0][0] = 1;
1312
1313 for (int n = 1; n < 64; n++) // Squares
1314 for (int k = 0; k < 6 && k <= n; ++k) // Pieces
1315 Binomial[k][n] = (k > 0 ? Binomial[k - 1][n - 1] : 0)
1316 + (k < n ? Binomial[k ][n - 1] : 0);
1317
1318 // MapPawns[s] encodes squares a2-h7 to 0..47. This is the number of possible
1319 // available squares when the leading one is in 's'. Moreover the pawn with
1320 // highest MapPawns[] is the leading pawn, the one nearest the edge and,
1321 // among pawns with same file, the one with lowest rank.
1322 int availableSquares = 47; // Available squares when lead pawn is in a2
1323
1324 // Init the tables for the encoding of leading pawns group: with 7-men TB we
1325 // can have up to 5 leading pawns (KPPPPPK).
1326 for (int leadPawnsCnt = 1; leadPawnsCnt <= 5; ++leadPawnsCnt)
1327 for (File f = FILE_A; f <= FILE_D; ++f)
1328 {
1329 // Restart the index at every file because TB table is splitted
1330 // by file, so we can reuse the same index for different files.
1331 int idx = 0;
1332
1333 // Sum all possible combinations for a given file, starting with
1334 // the leading pawn on rank 2 and increasing the rank.
1335 for (Rank r = RANK_2; r <= RANK_7; ++r)
1336 {
1337 Square sq = make_square(f, r);
1338
1339 // Compute MapPawns[] at first pass.
1340 // If sq is the leading pawn square, any other pawn cannot be
1341 // below or more toward the edge of sq. There are 47 available
1342 // squares when sq = a2 and reduced by 2 for any rank increase
1343 // due to mirroring: sq == a3 -> no a2, h2, so MapPawns[a3] = 45
1344 if (leadPawnsCnt == 1)
1345 {
1346 MapPawns[sq] = availableSquares--;
1347 MapPawns[sq ^ 7] = availableSquares--; // Horizontal flip
1348 }
1349 LeadPawnIdx[leadPawnsCnt][sq] = idx;
1350 idx += Binomial[leadPawnsCnt - 1][MapPawns[sq]];
1351 }
1352 // After a file is traversed, store the cumulated per-file index
1353 LeadPawnsSize[leadPawnsCnt][f] = idx;
1354 }
1355
1356 // Add entries in TB tables if the corresponding ".rtbw" file exsists
1357 for (PieceType p1 = PAWN; p1 < KING; ++p1) {
1358 TBTables.add({KING, p1, KING});
1359
1360 for (PieceType p2 = PAWN; p2 <= p1; ++p2) {
1361 TBTables.add({KING, p1, p2, KING});
1362 TBTables.add({KING, p1, KING, p2});
1363
1364 for (PieceType p3 = PAWN; p3 < KING; ++p3)
1365 TBTables.add({KING, p1, p2, KING, p3});
1366
1367 for (PieceType p3 = PAWN; p3 <= p2; ++p3) {
1368 TBTables.add({KING, p1, p2, p3, KING});
1369
1370 for (PieceType p4 = PAWN; p4 <= p3; ++p4) {
1371 TBTables.add({KING, p1, p2, p3, p4, KING});
1372
1373 for (PieceType p5 = PAWN; p5 <= p4; ++p5)
1374 TBTables.add({KING, p1, p2, p3, p4, p5, KING});
1375
1376 for (PieceType p5 = PAWN; p5 < KING; ++p5)
1377 TBTables.add({KING, p1, p2, p3, p4, KING, p5});
1378 }
1379
1380 for (PieceType p4 = PAWN; p4 < KING; ++p4) {
1381 TBTables.add({KING, p1, p2, p3, KING, p4});
1382
1383 for (PieceType p5 = PAWN; p5 <= p4; ++p5)
1384 TBTables.add({KING, p1, p2, p3, KING, p4, p5});
1385 }
1386 }
1387
1388 for (PieceType p3 = PAWN; p3 <= p1; ++p3)
1389 for (PieceType p4 = PAWN; p4 <= (p1 == p3 ? p2 : p3); ++p4)
1390 TBTables.add({KING, p1, p2, KING, p3, p4});
1391 }
1392 }
1393
1394 sync_cout << "info string Found " << TBTables.size() << " tablebases" << sync_endl;
1395}
1396
1397// Probe the WDL table for a particular position.
1398// If *result != FAIL, the probe was successful.
1399// The return value is from the point of view of the side to move:
1400// -2 : loss
1401// -1 : loss, but draw under 50-move rule
1402// 0 : draw
1403// 1 : win, but draw under 50-move rule
1404// 2 : win
1405WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) {
1406
1407 *result = OK;
1408 return search<false>(pos, result);
1409}
1410
1411// Probe the DTZ table for a particular position.
1412// If *result != FAIL, the probe was successful.
1413// The return value is from the point of view of the side to move:
1414// n < -100 : loss, but draw under 50-move rule
1415// -100 <= n < -1 : loss in n ply (assuming 50-move counter == 0)
1416// -1 : loss, the side to move is mated
1417// 0 : draw
1418// 1 < n <= 100 : win in n ply (assuming 50-move counter == 0)
1419// 100 < n : win, but draw under 50-move rule
1420//
1421// The return value n can be off by 1: a return value -n can mean a loss
1422// in n+1 ply and a return value +n can mean a win in n+1 ply. This
1423// cannot happen for tables with positions exactly on the "edge" of
1424// the 50-move rule.
1425//
1426// This implies that if dtz > 0 is returned, the position is certainly
1427// a win if dtz + 50-move-counter <= 99. Care must be taken that the engine
1428// picks moves that preserve dtz + 50-move-counter <= 99.
1429//
1430// If n = 100 immediately after a capture or pawn move, then the position
1431// is also certainly a win, and during the whole phase until the next
1432// capture or pawn move, the inequality to be preserved is
1433// dtz + 50-movecounter <= 100.
1434//
1435// In short, if a move is available resulting in dtz + 50-move-counter <= 99,
1436// then do not accept moves leading to dtz + 50-move-counter == 100.
1437int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
1438
1439 *result = OK;
1440 WDLScore wdl = search<true>(pos, result);
1441
1442 if (*result == FAIL || wdl == WDLDraw) // DTZ tables don't store draws
1443 return 0;
1444
1445 // DTZ stores a 'don't care' value in this case, or even a plain wrong
1446 // one as in case the best move is a losing ep, so it cannot be probed.
1447 if (*result == ZEROING_BEST_MOVE)
1448 return dtz_before_zeroing(wdl);
1449
1450 int dtz = probe_table<DTZ>(pos, result, wdl);
1451
1452 if (*result == FAIL)
1453 return 0;
1454
1455 if (*result != CHANGE_STM)
1456 return (dtz + 100 * (wdl == WDLBlessedLoss || wdl == WDLCursedWin)) * sign_of(wdl);
1457
1458 // DTZ stores results for the other side, so we need to do a 1-ply search and
1459 // find the winning move that minimizes DTZ.
1460 StateInfo st;
1461 int minDTZ = 0xFFFF;
1462
1463 for (const Move& move : MoveList<LEGAL>(pos))
1464 {
1465 bool zeroing = pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN;
1466
1467 pos.do_move(move, st);
1468
1469 // For zeroing moves we want the dtz of the move _before_ doing it,
1470 // otherwise we will get the dtz of the next move sequence. Search the
1471 // position after the move to get the score sign (because even in a
1472 // winning position we could make a losing capture or going for a draw).
1473 dtz = zeroing ? -dtz_before_zeroing(search<false>(pos, result))
1474 : -probe_dtz(pos, result);
1475
1476 // If the move mates, force minDTZ to 1
1477 if (dtz == 1 && pos.checkers() && MoveList<LEGAL>(pos).size() == 0)
1478 minDTZ = 1;
1479
1480 // Convert result from 1-ply search. Zeroing moves are already accounted
1481 // by dtz_before_zeroing() that returns the DTZ of the previous move.
1482 if (!zeroing)
1483 dtz += sign_of(dtz);
1484
1485 // Skip the draws and if we are winning only pick positive dtz
1486 if (dtz < minDTZ && sign_of(dtz) == sign_of(wdl))
1487 minDTZ = dtz;
1488
1489 pos.undo_move(move);
1490
1491 if (*result == FAIL)
1492 return 0;
1493 }
1494
1495 // When there are no legal moves, the position is mate: we return -1
1496 return minDTZ == 0xFFFF ? -1 : minDTZ;
1497}
1498
1499
1500// Use the DTZ tables to rank root moves.
1501//
1502// A return value false indicates that not all probes were successful.
1503bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
1504
1505 ProbeState result;
1506 StateInfo st;
1507
1508 // Obtain 50-move counter for the root position
1509 int cnt50 = pos.rule50_count();
1510
1511 // Check whether a position was repeated since the last zeroing move.
1512 bool rep = pos.has_repeated();
1513
1514 int dtz, bound = Options["Syzygy50MoveRule"] ? 900 : 1;
1515
1516 // Probe and rank each move
1517 for (auto& m : rootMoves)
1518 {
1519 pos.do_move(m.pv[0], st);
1520
1521 // Calculate dtz for the current move counting from the root position
1522 if (pos.rule50_count() == 0)
1523 {
1524 // In case of a zeroing move, dtz is one of -101/-1/0/1/101
1525 WDLScore wdl = -probe_wdl(pos, &result);
1526 dtz = dtz_before_zeroing(wdl);
1527 }
1528 else
1529 {
1530 // Otherwise, take dtz for the new position and correct by 1 ply
1531 dtz = -probe_dtz(pos, &result);
1532 dtz = dtz > 0 ? dtz + 1
1533 : dtz < 0 ? dtz - 1 : dtz;
1534 }
1535
1536 // Make sure that a mating move is assigned a dtz value of 1
1537 if ( pos.checkers()
1538 && dtz == 2
1539 && MoveList<LEGAL>(pos).size() == 0)
1540 dtz = 1;
1541
1542 pos.undo_move(m.pv[0]);
1543
1544 if (result == FAIL)
1545 return false;
1546
1547 // Better moves are ranked higher. Certain wins are ranked equally.
1548 // Losing moves are ranked equally unless a 50-move draw is in sight.
1549 int r = dtz > 0 ? (dtz + cnt50 <= 99 && !rep ? 1000 : 1000 - (dtz + cnt50))
1550 : dtz < 0 ? (-dtz * 2 + cnt50 < 100 ? -1000 : -1000 + (-dtz + cnt50))
1551 : 0;
1552 m.tbRank = r;
1553
1554 // Determine the score to be displayed for this move. Assign at least
1555 // 1 cp to cursed wins and let it grow to 49 cp as the positions gets
1556 // closer to a real win.
1557 m.tbScore = r >= bound ? VALUE_MATE - MAX_PLY - 1
1558 : r > 0 ? Value((std::max( 3, r - 800) * int(PawnValueEg)) / 200)
1559 : r == 0 ? VALUE_DRAW
1560 : r > -bound ? Value((std::min(-3, r + 800) * int(PawnValueEg)) / 200)
1561 : -VALUE_MATE + MAX_PLY + 1;
1562 }
1563
1564 return true;
1565}
1566
1567
1568// Use the WDL tables to rank root moves.
1569// This is a fallback for the case that some or all DTZ tables are missing.
1570//
1571// A return value false indicates that not all probes were successful.
1572bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves) {
1573
1574 static const int WDL_to_rank[] = { -1000, -899, 0, 899, 1000 };
1575
1576 ProbeState result;
1577 StateInfo st;
1578
1579 bool rule50 = Options["Syzygy50MoveRule"];
1580
1581 // Probe and rank each move
1582 for (auto& m : rootMoves)
1583 {
1584 pos.do_move(m.pv[0], st);
1585
1586 WDLScore wdl = -probe_wdl(pos, &result);
1587
1588 pos.undo_move(m.pv[0]);
1589
1590 if (result == FAIL)
1591 return false;
1592
1593 m.tbRank = WDL_to_rank[wdl + 2];
1594
1595 if (!rule50)
1596 wdl = wdl > WDLDraw ? WDLWin
1597 : wdl < WDLDraw ? WDLLoss : WDLDraw;
1598 m.tbScore = WDL_to_value[wdl + 2];
1599 }
1600
1601 return true;
1602}
1603