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