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stockfish/src/syzygy/tbprobe.cpp

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <algorithm>
#include <atomic>
#include <cstdint>
#include <cstring> // For std::memset and std::memcpy
#include <deque>
#include <fstream>
#include <iostream>
#include <list>
#include <sstream>
#include <type_traits>
#include <mutex>
#include "../bitboard.h"
#include "../movegen.h"
#include "../position.h"
#include "../search.h"
#include "../types.h"
#include "../uci.h"
#include "tbprobe.h"
#ifndef _WIN32
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#else
#define WIN32_LEAN_AND_MEAN
#ifndef NOMINMAX
# define NOMINMAX // Disable macros min() and max()
#endif
#include <windows.h>
#endif
using namespace Stockfish::Tablebases;
int Stockfish::Tablebases::MaxCardinality;
namespace Stockfish {
namespace {
constexpr int TBPIECES = 7; // Max number of supported pieces
enum { BigEndian, LittleEndian };
enum TBType { WDL, DTZ }; // Used as template parameter
// Each table has a set of flags: all of them refer to DTZ tables, the last one to WDL tables
enum TBFlag { STM = 1, Mapped = 2, WinPlies = 4, LossPlies = 8, Wide = 16, SingleValue = 128 };
inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
inline Square operator^(Square s, int i) { return Square(int(s) ^ i); }
const std::string PieceToChar = " PNBRQK pnbrqk";
int MapPawns[SQUARE_NB];
int MapB1H1H7[SQUARE_NB];
int MapA1D1D4[SQUARE_NB];
int MapKK[10][SQUARE_NB]; // [MapA1D1D4][SQUARE_NB]
int Binomial[6][SQUARE_NB]; // [k][n] k elements from a set of n elements
int LeadPawnIdx[6][SQUARE_NB]; // [leadPawnsCnt][SQUARE_NB]
int LeadPawnsSize[6][4]; // [leadPawnsCnt][FILE_A..FILE_D]
// Comparison function to sort leading pawns in ascending MapPawns[] order
bool pawns_comp(Square i, Square j) { return MapPawns[i] < MapPawns[j]; }
int off_A1H8(Square sq) { return int(rank_of(sq)) - file_of(sq); }
constexpr Value WDL_to_value[] = {
-VALUE_MATE + MAX_PLY + 1,
VALUE_DRAW - 2,
VALUE_DRAW,
VALUE_DRAW + 2,
VALUE_MATE - MAX_PLY - 1
};
template<typename T, int Half = sizeof(T) / 2, int End = sizeof(T) - 1>
inline void swap_endian(T& x)
{
static_assert(std::is_unsigned<T>::value, "Argument of swap_endian not unsigned");
uint8_t tmp, *c = (uint8_t*)&x;
for (int i = 0; i < Half; ++i)
tmp = c[i], c[i] = c[End - i], c[End - i] = tmp;
}
template<> inline void swap_endian<uint8_t>(uint8_t&) {}
template<typename T, int LE> T number(void* addr)
{
T v;
if ((uintptr_t)addr & (alignof(T) - 1)) // Unaligned pointer (very rare)
std::memcpy(&v, addr, sizeof(T));
else
v = *((T*)addr);
if (LE != IsLittleEndian)
swap_endian(v);
return v;
}
// DTZ tables don't store valid scores for moves that reset the rule50 counter
// like captures and pawn moves but we can easily recover the correct dtz of the
// previous move if we know the position's WDL score.
int dtz_before_zeroing(WDLScore wdl) {
return wdl == WDLWin ? 1 :
wdl == WDLCursedWin ? 101 :
wdl == WDLBlessedLoss ? -101 :
wdl == WDLLoss ? -1 : 0;
}
// Return the sign of a number (-1, 0, 1)
template <typename T> int sign_of(T val) {
return (T(0) < val) - (val < T(0));
}
// Numbers in little endian used by sparseIndex[] to point into blockLength[]
struct SparseEntry {
char block[4]; // Number of block
char offset[2]; // Offset within the block
};
static_assert(sizeof(SparseEntry) == 6, "SparseEntry must be 6 bytes");
typedef uint16_t Sym; // Huffman symbol
struct LR {
enum Side { Left, Right };
uint8_t lr[3]; // The first 12 bits is the left-hand symbol, the second 12
// bits is the right-hand symbol. If symbol has length 1,
// then the left-hand symbol is the stored value.
template<Side S>
Sym get() {
return S == Left ? ((lr[1] & 0xF) << 8) | lr[0] :
S == Right ? (lr[2] << 4) | (lr[1] >> 4) : (assert(false), Sym(-1));
}
};
static_assert(sizeof(LR) == 3, "LR tree entry must be 3 bytes");
// Tablebases data layout is structured as following:
//
// TBFile: memory maps/unmaps the physical .rtbw and .rtbz files
// TBTable: one object for each file with corresponding indexing information
// TBTables: has ownership of TBTable objects, keeping a list and a hash
// class TBFile memory maps/unmaps the single .rtbw and .rtbz files. Files are
// memory mapped for best performance. Files are mapped at first access: at init
// time only existence of the file is checked.
class TBFile : public std::ifstream {
std::string fname;
public:
// Look for and open the file among the Paths directories where the .rtbw
// and .rtbz files can be found. Multiple directories are separated by ";"
// on Windows and by ":" on Unix-based operating systems.
//
// Example:
// C:\tb\wdl345;C:\tb\wdl6;D:\tb\dtz345;D:\tb\dtz6
static std::string Paths;
TBFile(const std::string& f) {
#ifndef _WIN32
constexpr char SepChar = ':';
#else
constexpr char SepChar = ';';
#endif
std::stringstream ss(Paths);
std::string path;
while (std::getline(ss, path, SepChar))
{
fname = path + "/" + f;
std::ifstream::open(fname);
if (is_open())
return;
}
}
// Memory map the file and check it. File should be already open and will be
// closed after mapping.
uint8_t* map(void** baseAddress, uint64_t* mapping, TBType type) {
assert(is_open());
close(); // Need to re-open to get native file descriptor
#ifndef _WIN32
struct stat statbuf;
int fd = ::open(fname.c_str(), O_RDONLY);
if (fd == -1)
return *baseAddress = nullptr, nullptr;
fstat(fd, &statbuf);
if (statbuf.st_size % 64 != 16)
{
std::cerr << "Corrupt tablebase file " << fname << std::endl;
exit(EXIT_FAILURE);
}
*mapping = statbuf.st_size;
*baseAddress = mmap(nullptr, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
#if defined(MADV_RANDOM)
madvise(*baseAddress, statbuf.st_size, MADV_RANDOM);
#endif
::close(fd);
if (*baseAddress == MAP_FAILED)
{
std::cerr << "Could not mmap() " << fname << std::endl;
exit(EXIT_FAILURE);
}
#else
// Note FILE_FLAG_RANDOM_ACCESS is only a hint to Windows and as such may get ignored.
HANDLE fd = CreateFile(fname.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
OPEN_EXISTING, FILE_FLAG_RANDOM_ACCESS, nullptr);
if (fd == INVALID_HANDLE_VALUE)
return *baseAddress = nullptr, nullptr;
DWORD size_high;
DWORD size_low = GetFileSize(fd, &size_high);
if (size_low % 64 != 16)
{
std::cerr << "Corrupt tablebase file " << fname << std::endl;
exit(EXIT_FAILURE);
}
HANDLE mmap = CreateFileMapping(fd, nullptr, PAGE_READONLY, size_high, size_low, nullptr);
CloseHandle(fd);
if (!mmap)
{
std::cerr << "CreateFileMapping() failed" << std::endl;
exit(EXIT_FAILURE);
}
*mapping = (uint64_t)mmap;
*baseAddress = MapViewOfFile(mmap, FILE_MAP_READ, 0, 0, 0);
if (!*baseAddress)
{
std::cerr << "MapViewOfFile() failed, name = " << fname
<< ", error = " << GetLastError() << std::endl;
exit(EXIT_FAILURE);
}
#endif
uint8_t* data = (uint8_t*)*baseAddress;
constexpr uint8_t Magics[][4] = { { 0xD7, 0x66, 0x0C, 0xA5 },
{ 0x71, 0xE8, 0x23, 0x5D } };
if (memcmp(data, Magics[type == WDL], 4))
{
std::cerr << "Corrupted table in file " << fname << std::endl;
unmap(*baseAddress, *mapping);
return *baseAddress = nullptr, nullptr;
}
return data + 4; // Skip Magics's header
}
static void unmap(void* baseAddress, uint64_t mapping) {
#ifndef _WIN32
munmap(baseAddress, mapping);
#else
UnmapViewOfFile(baseAddress);
CloseHandle((HANDLE)mapping);
#endif
}
};
std::string TBFile::Paths;
// struct PairsData contains low level indexing information to access TB data.
// There are 8, 4 or 2 PairsData records for each TBTable, according to type of
// table and if positions have pawns or not. It is populated at first access.
struct PairsData {
uint8_t flags; // Table flags, see enum TBFlag
uint8_t maxSymLen; // Maximum length in bits of the Huffman symbols
uint8_t minSymLen; // Minimum length in bits of the Huffman symbols
uint32_t blocksNum; // Number of blocks in the TB file
size_t sizeofBlock; // Block size in bytes
size_t span; // About every span values there is a SparseIndex[] entry
Sym* lowestSym; // lowestSym[l] is the symbol of length l with the lowest value
LR* btree; // btree[sym] stores the left and right symbols that expand sym
uint16_t* blockLength; // Number of stored positions (minus one) for each block: 1..65536
uint32_t blockLengthSize; // Size of blockLength[] table: padded so it's bigger than blocksNum
SparseEntry* sparseIndex; // Partial indices into blockLength[]
size_t sparseIndexSize; // Size of SparseIndex[] table
uint8_t* data; // Start of Huffman compressed data
std::vector<uint64_t> base64; // base64[l - min_sym_len] is the 64bit-padded lowest symbol of length l
std::vector<uint8_t> symlen; // Number of values (-1) represented by a given Huffman symbol: 1..256
Piece pieces[TBPIECES]; // Position pieces: the order of pieces defines the groups
uint64_t groupIdx[TBPIECES+1]; // Start index used for the encoding of the group's pieces
int groupLen[TBPIECES+1]; // Number of pieces in a given group: KRKN -> (3, 1)
uint16_t map_idx[4]; // WDLWin, WDLLoss, WDLCursedWin, WDLBlessedLoss (used in DTZ)
};
// struct TBTable contains indexing information to access the corresponding TBFile.
// There are 2 types of TBTable, corresponding to a WDL or a DTZ file. TBTable
// is populated at init time but the nested PairsData records are populated at
// first access, when the corresponding file is memory mapped.
template<TBType Type>
struct TBTable {
typedef typename std::conditional<Type == WDL, WDLScore, int>::type Ret;
static constexpr int Sides = Type == WDL ? 2 : 1;
std::atomic_bool ready;
void* baseAddress;
uint8_t* map;
uint64_t mapping;
Key key;
Key key2;
int pieceCount;
bool hasPawns;
bool hasUniquePieces;
uint8_t pawnCount[2]; // [Lead color / other color]
PairsData items[Sides][4]; // [wtm / btm][FILE_A..FILE_D or 0]
PairsData* get(int stm, int f) {
return &items[stm % Sides][hasPawns ? f : 0];
}
TBTable() : ready(false), baseAddress(nullptr) {}
explicit TBTable(const std::string& code);
explicit TBTable(const TBTable<WDL>& wdl);
~TBTable() {
if (baseAddress)
TBFile::unmap(baseAddress, mapping);
}
};
template<>
TBTable<WDL>::TBTable(const std::string& code) : TBTable() {
StateInfo st;
Position pos;
key = pos.set(code, WHITE, &st).material_key();
pieceCount = pos.count<ALL_PIECES>();
hasPawns = pos.pieces(PAWN);
hasUniquePieces = false;
for (Color c : { WHITE, BLACK })
for (PieceType pt = PAWN; pt < KING; ++pt)
if (popcount(pos.pieces(c, pt)) == 1)
hasUniquePieces = true;
// Set the leading color. In case both sides have pawns the leading color
// is the side with less pawns because this leads to better compression.
bool c = !pos.count<PAWN>(BLACK)
|| ( pos.count<PAWN>(WHITE)
&& pos.count<PAWN>(BLACK) >= pos.count<PAWN>(WHITE));
pawnCount[0] = pos.count<PAWN>(c ? WHITE : BLACK);
pawnCount[1] = pos.count<PAWN>(c ? BLACK : WHITE);
key2 = pos.set(code, BLACK, &st).material_key();
}
template<>
TBTable<DTZ>::TBTable(const TBTable<WDL>& wdl) : TBTable() {
// Use the corresponding WDL table to avoid recalculating all from scratch
key = wdl.key;
key2 = wdl.key2;
pieceCount = wdl.pieceCount;
hasPawns = wdl.hasPawns;
hasUniquePieces = wdl.hasUniquePieces;
pawnCount[0] = wdl.pawnCount[0];
pawnCount[1] = wdl.pawnCount[1];
}
// class TBTables creates and keeps ownership of the TBTable objects, one for
// each TB file found. It supports a fast, hash based, table lookup. Populated
// at init time, accessed at probe time.
class TBTables {
struct Entry
{
Key key;
TBTable<WDL>* wdl;
TBTable<DTZ>* dtz;
template <TBType Type>
TBTable<Type>* get() const {
return (TBTable<Type>*)(Type == WDL ? (void*)wdl : (void*)dtz);
}
};
static constexpr int Size = 1 << 12; // 4K table, indexed by key's 12 lsb
static constexpr int Overflow = 1; // Number of elements allowed to map to the last bucket
Entry hashTable[Size + Overflow];
std::deque<TBTable<WDL>> wdlTable;
std::deque<TBTable<DTZ>> dtzTable;
void insert(Key key, TBTable<WDL>* wdl, TBTable<DTZ>* dtz) {
uint32_t homeBucket = (uint32_t)key & (Size - 1);
Entry entry{ key, wdl, dtz };
// Ensure last element is empty to avoid overflow when looking up
for (uint32_t bucket = homeBucket; bucket < Size + Overflow - 1; ++bucket) {
Key otherKey = hashTable[bucket].key;
if (otherKey == key || !hashTable[bucket].get<WDL>()) {
hashTable[bucket] = entry;
return;
}
// Robin Hood hashing: If we've probed for longer than this element,
// insert here and search for a new spot for the other element instead.
uint32_t otherHomeBucket = (uint32_t)otherKey & (Size - 1);
if (otherHomeBucket > homeBucket) {
std::swap(entry, hashTable[bucket]);
key = otherKey;
homeBucket = otherHomeBucket;
}
}
std::cerr << "TB hash table size too low!" << std::endl;
exit(EXIT_FAILURE);
}
public:
template<TBType Type>
TBTable<Type>* get(Key key) {
for (const Entry* entry = &hashTable[(uint32_t)key & (Size - 1)]; ; ++entry) {
if (entry->key == key || !entry->get<Type>())
return entry->get<Type>();
}
}
void clear() {
memset(hashTable, 0, sizeof(hashTable));
wdlTable.clear();
dtzTable.clear();
}
size_t size() const { return wdlTable.size(); }
void add(const std::vector<PieceType>& pieces);
};
TBTables TBTables;
// If the corresponding file exists two new objects TBTable<WDL> and TBTable<DTZ>
// are created and added to the lists and hash table. Called at init time.
void TBTables::add(const std::vector<PieceType>& pieces) {
std::string code;
for (PieceType pt : pieces)
code += PieceToChar[pt];
TBFile file(code.insert(code.find('K', 1), "v") + ".rtbw"); // KRK -> KRvK
if (!file.is_open()) // Only WDL file is checked
return;
file.close();
MaxCardinality = std::max((int)pieces.size(), MaxCardinality);
wdlTable.emplace_back(code);
dtzTable.emplace_back(wdlTable.back());
// Insert into the hash keys for both colors: KRvK with KR white and black
insert(wdlTable.back().key , &wdlTable.back(), &dtzTable.back());
insert(wdlTable.back().key2, &wdlTable.back(), &dtzTable.back());
}
// TB tables are compressed with canonical Huffman code. The compressed data is divided into
// blocks of size d->sizeofBlock, and each block stores a variable number of symbols.
// Each symbol represents either a WDL or a (remapped) DTZ value, or a pair of other symbols
// (recursively). If you keep expanding the symbols in a block, you end up with up to 65536
// WDL or DTZ values. Each symbol represents up to 256 values and will correspond after
// Huffman coding to at least 1 bit. So a block of 32 bytes corresponds to at most
// 32 x 8 x 256 = 65536 values. This maximum is only reached for tables that consist mostly
// of draws or mostly of wins, but such tables are actually quite common. In principle, the
// blocks in WDL tables are 64 bytes long (and will be aligned on cache lines). But for
// mostly-draw or mostly-win tables this can leave many 64-byte blocks only half-filled, so
// in such cases blocks are 32 bytes long. The blocks of DTZ tables are up to 1024 bytes long.
// The generator picks the size that leads to the smallest table. The "book" of symbols and
// Huffman codes is the same for all blocks in the table. A non-symmetric pawnless TB file
// will have one table for wtm and one for btm, a TB file with pawns will have tables per
// file a,b,c,d also in this case one set for wtm and one for btm.
int decompress_pairs(PairsData* d, uint64_t idx) {
// Special case where all table positions store the same value
if (d->flags & TBFlag::SingleValue)
return d->minSymLen;
// First we need to locate the right block that stores the value at index "idx".
// Because each block n stores blockLength[n] + 1 values, the index i of the block
// that contains the value at position idx is:
//
// for (i = -1, sum = 0; sum <= idx; i++)
// sum += blockLength[i + 1] + 1;
//
// This can be slow, so we use SparseIndex[] populated with a set of SparseEntry that
// point to known indices into blockLength[]. Namely SparseIndex[k] is a SparseEntry
// that stores the blockLength[] index and the offset within that block of the value
// with index I(k), where:
//
// I(k) = k * d->span + d->span / 2 (1)
// First step is to get the 'k' of the I(k) nearest to our idx, using definition (1)
uint32_t k = uint32_t(idx / d->span);
// Then we read the corresponding SparseIndex[] entry
uint32_t block = number<uint32_t, LittleEndian>(&d->sparseIndex[k].block);
int offset = number<uint16_t, LittleEndian>(&d->sparseIndex[k].offset);
// Now compute the difference idx - I(k). From definition of k we know that
//
// idx = k * d->span + idx % d->span (2)
//
// So from (1) and (2) we can compute idx - I(K):
int diff = idx % d->span - d->span / 2;
// Sum the above to offset to find the offset corresponding to our idx
offset += diff;
// Move to previous/next block, until we reach the correct block that contains idx,
// that is when 0 <= offset <= d->blockLength[block]
while (offset < 0)
offset += d->blockLength[--block] + 1;
while (offset > d->blockLength[block])
offset -= d->blockLength[block++] + 1;
// Finally, we find the start address of our block of canonical Huffman symbols
uint32_t* ptr = (uint32_t*)(d->data + ((uint64_t)block * d->sizeofBlock));
// Read the first 64 bits in our block, this is a (truncated) sequence of
// unknown number of symbols of unknown length but we know the first one
// is at the beginning of this 64 bits sequence.
uint64_t buf64 = number<uint64_t, BigEndian>(ptr); ptr += 2;
int buf64Size = 64;
Sym sym;
while (true)
{
int len = 0; // This is the symbol length - d->min_sym_len
// Now get the symbol length. For any symbol s64 of length l right-padded
// to 64 bits we know that d->base64[l-1] >= s64 >= d->base64[l] so we
// can find the symbol length iterating through base64[].
while (buf64 < d->base64[len])
++len;
// All the symbols of a given length are consecutive integers (numerical
// sequence property), so we can compute the offset of our symbol of
// length len, stored at the beginning of buf64.
sym = Sym((buf64 - d->base64[len]) >> (64 - len - d->minSymLen));
// Now add the value of the lowest symbol of length len to get our symbol
sym += number<Sym, LittleEndian>(&d->lowestSym[len]);
// If our offset is within the number of values represented by symbol sym
// we are done...
if (offset < d->symlen[sym] + 1)
break;
// ...otherwise update the offset and continue to iterate
offset -= d->symlen[sym] + 1;
len += d->minSymLen; // Get the real length
buf64 <<= len; // Consume the just processed symbol
buf64Size -= len;
if (buf64Size <= 32) { // Refill the buffer
buf64Size += 32;
buf64 |= (uint64_t)number<uint32_t, BigEndian>(ptr++) << (64 - buf64Size);
}
}
// Ok, now we have our symbol that expands into d->symlen[sym] + 1 symbols.
// We binary-search for our value recursively expanding into the left and
// right child symbols until we reach a leaf node where symlen[sym] + 1 == 1
// that will store the value we need.
while (d->symlen[sym])
{
Sym left = d->btree[sym].get<LR::Left>();
// If a symbol contains 36 sub-symbols (d->symlen[sym] + 1 = 36) and
// expands in a pair (d->symlen[left] = 23, d->symlen[right] = 11), then
// we know that, for instance the ten-th value (offset = 10) will be on
// the left side because in Recursive Pairing child symbols are adjacent.
if (offset < d->symlen[left] + 1)
sym = left;
else {
offset -= d->symlen[left] + 1;
sym = d->btree[sym].get<LR::Right>();
}
}
return d->btree[sym].get<LR::Left>();
}
bool check_dtz_stm(TBTable<WDL>*, int, File) { return true; }
bool check_dtz_stm(TBTable<DTZ>* entry, int stm, File f) {
auto flags = entry->get(stm, f)->flags;
return (flags & TBFlag::STM) == stm
|| ((entry->key == entry->key2) && !entry->hasPawns);
}
// DTZ scores are sorted by frequency of occurrence and then assigned the
// values 0, 1, 2, ... in order of decreasing frequency. This is done for each
// of the four WDLScore values. The mapping information necessary to reconstruct
// the original values is stored in the TB file and read during map[] init.
WDLScore map_score(TBTable<WDL>*, File, int value, WDLScore) { return WDLScore(value - 2); }
int map_score(TBTable<DTZ>* entry, File f, int value, WDLScore wdl) {
constexpr int WDLMap[] = { 1, 3, 0, 2, 0 };
auto flags = entry->get(0, f)->flags;
uint8_t* map = entry->map;
uint16_t* idx = entry->get(0, f)->map_idx;
if (flags & TBFlag::Mapped) {
if (flags & TBFlag::Wide)
value = ((uint16_t *)map)[idx[WDLMap[wdl + 2]] + value];
else
value = map[idx[WDLMap[wdl + 2]] + value];
}
// DTZ tables store distance to zero in number of moves or plies. We
// want to return plies, so we have convert to plies when needed.
if ( (wdl == WDLWin && !(flags & TBFlag::WinPlies))
|| (wdl == WDLLoss && !(flags & TBFlag::LossPlies))
|| wdl == WDLCursedWin
|| wdl == WDLBlessedLoss)
value *= 2;
return value + 1;
}
// Compute a unique index out of a position and use it to probe the TB file. To
// encode k pieces of same type and color, first sort the pieces by square in
// ascending order s1 <= s2 <= ... <= sk then compute the unique index as:
//
// idx = Binomial[1][s1] + Binomial[2][s2] + ... + Binomial[k][sk]
//
template<typename T, typename Ret = typename T::Ret>
Ret do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result) {
Square squares[TBPIECES];
Piece pieces[TBPIECES];
uint64_t idx;
int next = 0, size = 0, leadPawnsCnt = 0;
PairsData* d;
Bitboard b, leadPawns = 0;
File tbFile = FILE_A;
// A given TB entry like KRK has associated two material keys: KRvk and Kvkr.
// If both sides have the same pieces keys are equal. In this case TB tables
// only store the 'white to move' case, so if the position to lookup has black
// to move, we need to switch the color and flip the squares before to lookup.
bool symmetricBlackToMove = (entry->key == entry->key2 && pos.side_to_move());
// TB files are calculated for white as stronger side. For instance we have
// KRvK, not KvKR. A position where stronger side is white will have its
// material key == entry->key, otherwise we have to switch the color and
// flip the squares before to lookup.
bool blackStronger = (pos.material_key() != entry->key);
int flipColor = (symmetricBlackToMove || blackStronger) * 8;
int flipSquares = (symmetricBlackToMove || blackStronger) * 56;
int stm = (symmetricBlackToMove || blackStronger) ^ pos.side_to_move();
// For pawns, TB files store 4 separate tables according if leading pawn is on
// file a, b, c or d after reordering. The leading pawn is the one with maximum
// MapPawns[] value, that is the one most toward the edges and with lowest rank.
if (entry->hasPawns) {
// In all the 4 tables, pawns are at the beginning of the piece sequence and
// their color is the reference one. So we just pick the first one.
Piece pc = Piece(entry->get(0, 0)->pieces[0] ^ flipColor);
assert(type_of(pc) == PAWN);
leadPawns = b = pos.pieces(color_of(pc), PAWN);
do
squares[size++] = pop_lsb(b) ^ flipSquares;
while (b);
leadPawnsCnt = size;
std::swap(squares[0], *std::max_element(squares, squares + leadPawnsCnt, pawns_comp));
tbFile = File(edge_distance(file_of(squares[0])));
}
// DTZ tables are one-sided, i.e. they store positions only for white to
// move or only for black to move, so check for side to move to be stm,
// early exit otherwise.
if (!check_dtz_stm(entry, stm, tbFile))
return *result = CHANGE_STM, Ret();
// Now we are ready to get all the position pieces (but the lead pawns) and
// directly map them to the correct color and square.
b = pos.pieces() ^ leadPawns;
do {
Square s = pop_lsb(b);
squares[size] = s ^ flipSquares;
pieces[size++] = Piece(pos.piece_on(s) ^ flipColor);
} while (b);
assert(size >= 2);
d = entry->get(stm, tbFile);
// Then we reorder the pieces to have the same sequence as the one stored
// in pieces[i]: the sequence that ensures the best compression.
for (int i = leadPawnsCnt; i < size - 1; ++i)
for (int j = i + 1; j < size; ++j)
if (d->pieces[i] == pieces[j])
{
std::swap(pieces[i], pieces[j]);
std::swap(squares[i], squares[j]);
break;
}
// Now we map again the squares so that the square of the lead piece is in
// the triangle A1-D1-D4.
if (file_of(squares[0]) > FILE_D)
for (int i = 0; i < size; ++i)
squares[i] = flip_file(squares[i]);
// Encode leading pawns starting with the one with minimum MapPawns[] and
// proceeding in ascending order.
if (entry->hasPawns) {
idx = LeadPawnIdx[leadPawnsCnt][squares[0]];
std::stable_sort(squares + 1, squares + leadPawnsCnt, pawns_comp);
for (int i = 1; i < leadPawnsCnt; ++i)
idx += Binomial[i][MapPawns[squares[i]]];
goto encode_remaining; // With pawns we have finished special treatments
}
// In positions withouth pawns, we further flip the squares to ensure leading
// piece is below RANK_5.
if (rank_of(squares[0]) > RANK_4)
for (int i = 0; i < size; ++i)
squares[i] = flip_rank(squares[i]);
// Look for the first piece of the leading group not on the A1-D4 diagonal
// and ensure it is mapped below the diagonal.
for (int i = 0; i < d->groupLen[0]; ++i) {
if (!off_A1H8(squares[i]))
continue;
if (off_A1H8(squares[i]) > 0) // A1-H8 diagonal flip: SQ_A3 -> SQ_C1
for (int j = i; j < size; ++j)
squares[j] = Square(((squares[j] >> 3) | (squares[j] << 3)) & 63);
break;
}
// Encode the leading group.
//
// Suppose we have KRvK. Let's say the pieces are on square numbers wK, wR
// and bK (each 0...63). The simplest way to map this position to an index
// is like this:
//
// index = wK * 64 * 64 + wR * 64 + bK;
//
// But this way the TB is going to have 64*64*64 = 262144 positions, with
// lots of positions being equivalent (because they are mirrors of each
// other) and lots of positions being invalid (two pieces on one square,
// adjacent kings, etc.).
// Usually the first step is to take the wK and bK together. There are just
// 462 ways legal and not-mirrored ways to place the wK and bK on the board.
// Once we have placed the wK and bK, there are 62 squares left for the wR
// Mapping its square from 0..63 to available squares 0..61 can be done like:
//
// wR -= (wR > wK) + (wR > bK);
//
// In words: if wR "comes later" than wK, we deduct 1, and the same if wR
// "comes later" than bK. In case of two same pieces like KRRvK we want to
// place the two Rs "together". If we have 62 squares left, we can place two
// Rs "together" in 62 * 61 / 2 ways (we divide by 2 because rooks can be
// swapped and still get the same position.)
//
// In case we have at least 3 unique pieces (inlcuded kings) we encode them
// together.
if (entry->hasUniquePieces) {
int adjust1 = squares[1] > squares[0];
int adjust2 = (squares[2] > squares[0]) + (squares[2] > squares[1]);
// First piece is below a1-h8 diagonal. MapA1D1D4[] maps the b1-d1-d3
// triangle to 0...5. There are 63 squares for second piece and and 62
// (mapped to 0...61) for the third.
if (off_A1H8(squares[0]))
idx = ( MapA1D1D4[squares[0]] * 63
+ (squares[1] - adjust1)) * 62
+ squares[2] - adjust2;
// First piece is on a1-h8 diagonal, second below: map this occurence to
// 6 to differentiate from the above case, rank_of() maps a1-d4 diagonal
// to 0...3 and finally MapB1H1H7[] maps the b1-h1-h7 triangle to 0..27.
else if (off_A1H8(squares[1]))
idx = ( 6 * 63 + rank_of(squares[0]) * 28
+ MapB1H1H7[squares[1]]) * 62
+ squares[2] - adjust2;
// First two pieces are on a1-h8 diagonal, third below
else if (off_A1H8(squares[2]))
idx = 6 * 63 * 62 + 4 * 28 * 62
+ rank_of(squares[0]) * 7 * 28
+ (rank_of(squares[1]) - adjust1) * 28
+ MapB1H1H7[squares[2]];
// All 3 pieces on the diagonal a1-h8
else
idx = 6 * 63 * 62 + 4 * 28 * 62 + 4 * 7 * 28
+ rank_of(squares[0]) * 7 * 6
+ (rank_of(squares[1]) - adjust1) * 6
+ (rank_of(squares[2]) - adjust2);
} else
// We don't have at least 3 unique pieces, like in KRRvKBB, just map
// the kings.
idx = MapKK[MapA1D1D4[squares[0]]][squares[1]];
encode_remaining:
idx *= d->groupIdx[0];
Square* groupSq = squares + d->groupLen[0];
// Encode remainig pawns then pieces according to square, in ascending order
bool remainingPawns = entry->hasPawns && entry->pawnCount[1];
while (d->groupLen[++next])
{
std::stable_sort(groupSq, groupSq + d->groupLen[next]);
uint64_t n = 0;
// Map down a square if "comes later" than a square in the previous
// groups (similar to what done earlier for leading group pieces).
for (int i = 0; i < d->groupLen[next]; ++i)
{
auto f = [&](Square s) { return groupSq[i] > s; };
auto adjust = std::count_if(squares, groupSq, f);
n += Binomial[i + 1][groupSq[i] - adjust - 8 * remainingPawns];
}
remainingPawns = false;
idx += n * d->groupIdx[next];
groupSq += d->groupLen[next];
}
// Now that we have the index, decompress the pair and get the score
return map_score(entry, tbFile, decompress_pairs(d, idx), wdl);
}
// Group together pieces that will be encoded together. The general rule is that
// a group contains pieces of same type and color. The exception is the leading
// group that, in case of positions withouth pawns, can be formed by 3 different
// pieces (default) or by the king pair when there is not a unique piece apart
// from the kings. When there are pawns, pawns are always first in pieces[].
//
// As example KRKN -> KRK + N, KNNK -> KK + NN, KPPKP -> P + PP + K + K
//
// The actual grouping depends on the TB generator and can be inferred from the
// sequence of pieces in piece[] array.
template<typename T>
void set_groups(T& e, PairsData* d, int order[], File f) {
int n = 0, firstLen = e.hasPawns ? 0 : e.hasUniquePieces ? 3 : 2;
d->groupLen[n] = 1;
// Number of pieces per group is stored in groupLen[], for instance in KRKN
// the encoder will default on '111', so groupLen[] will be (3, 1).
for (int i = 1; i < e.pieceCount; ++i)
if (--firstLen > 0 || d->pieces[i] == d->pieces[i - 1])
d->groupLen[n]++;
else
d->groupLen[++n] = 1;
d->groupLen[++n] = 0; // Zero-terminated
// The sequence in pieces[] defines the groups, but not the order in which
// they are encoded. If the pieces in a group g can be combined on the board
// in N(g) different ways, then the position encoding will be of the form:
//
// g1 * N(g2) * N(g3) + g2 * N(g3) + g3
//
// This ensures unique encoding for the whole position. The order of the
// groups is a per-table parameter and could not follow the canonical leading
// pawns/pieces -> remainig pawns -> remaining pieces. In particular the
// first group is at order[0] position and the remaining pawns, when present,
// are at order[1] position.
bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
int next = pp ? 2 : 1;
int freeSquares = 64 - d->groupLen[0] - (pp ? d->groupLen[1] : 0);
uint64_t idx = 1;
for (int k = 0; next < n || k == order[0] || k == order[1]; ++k)
if (k == order[0]) // Leading pawns or pieces
{
d->groupIdx[0] = idx;
idx *= e.hasPawns ? LeadPawnsSize[d->groupLen[0]][f]
: e.hasUniquePieces ? 31332 : 462;
}
else if (k == order[1]) // Remaining pawns
{
d->groupIdx[1] = idx;
idx *= Binomial[d->groupLen[1]][48 - d->groupLen[0]];
}
else // Remainig pieces
{
d->groupIdx[next] = idx;
idx *= Binomial[d->groupLen[next]][freeSquares];
freeSquares -= d->groupLen[next++];
}
d->groupIdx[n] = idx;
}
// In Recursive Pairing each symbol represents a pair of childern symbols. So
// read d->btree[] symbols data and expand each one in his left and right child
// symbol until reaching the leafs that represent the symbol value.
uint8_t set_symlen(PairsData* d, Sym s, std::vector<bool>& visited) {
visited[s] = true; // We can set it now because tree is acyclic
Sym sr = d->btree[s].get<LR::Right>();
if (sr == 0xFFF)
return 0;
Sym sl = d->btree[s].get<LR::Left>();
if (!visited[sl])
d->symlen[sl] = set_symlen(d, sl, visited);
if (!visited[sr])
d->symlen[sr] = set_symlen(d, sr, visited);
return d->symlen[sl] + d->symlen[sr] + 1;
}
uint8_t* set_sizes(PairsData* d, uint8_t* data) {
d->flags = *data++;
if (d->flags & TBFlag::SingleValue) {
d->blocksNum = d->blockLengthSize = 0;
d->span = d->sparseIndexSize = 0; // Broken MSVC zero-init
d->minSymLen = *data++; // Here we store the single value
return data;
}
// groupLen[] is a zero-terminated list of group lengths, the last groupIdx[]
// element stores the biggest index that is the tb size.
uint64_t tbSize = d->groupIdx[std::find(d->groupLen, d->groupLen + 7, 0) - d->groupLen];
d->sizeofBlock = 1ULL << *data++;
d->span = 1ULL << *data++;
d->sparseIndexSize = size_t((tbSize + d->span - 1) / d->span); // Round up
auto padding = number<uint8_t, LittleEndian>(data++);
d->blocksNum = number<uint32_t, LittleEndian>(data); data += sizeof(uint32_t);
d->blockLengthSize = d->blocksNum + padding; // Padded to ensure SparseIndex[]
// does not point out of range.
d->maxSymLen = *data++;
d->minSymLen = *data++;
d->lowestSym = (Sym*)data;
d->base64.resize(d->maxSymLen - d->minSymLen + 1);
// The canonical code is ordered such that longer symbols (in terms of
// the number of bits of their Huffman code) have lower numeric value,
// so that d->lowestSym[i] >= d->lowestSym[i+1] (when read as LittleEndian).
// Starting from this we compute a base64[] table indexed by symbol length
// and containing 64 bit values so that d->base64[i] >= d->base64[i+1].
// See https://en.wikipedia.org/wiki/Huffman_coding
for (int i = d->base64.size() - 2; i >= 0; --i) {
d->base64[i] = (d->base64[i + 1] + number<Sym, LittleEndian>(&d->lowestSym[i])
- number<Sym, LittleEndian>(&d->lowestSym[i + 1])) / 2;
assert(d->base64[i] * 2 >= d->base64[i+1]);
}
// Now left-shift by an amount so that d->base64[i] gets shifted 1 bit more
// than d->base64[i+1] and given the above assert condition, we ensure that
// d->base64[i] >= d->base64[i+1]. Moreover for any symbol s64 of length i
// and right-padded to 64 bits holds d->base64[i-1] >= s64 >= d->base64[i].
for (size_t i = 0; i < d->base64.size(); ++i)
d->base64[i] <<= 64 - i - d->minSymLen; // Right-padding to 64 bits
data += d->base64.size() * sizeof(Sym);
d->symlen.resize(number<uint16_t, LittleEndian>(data)); data += sizeof(uint16_t);
d->btree = (LR*)data;
// The compression scheme used is "Recursive Pairing", that replaces the most
// frequent adjacent pair of symbols in the source message by a new symbol,
// reevaluating the frequencies of all of the symbol pairs with respect to
// the extended alphabet, and then repeating the process.
// See http://www.larsson.dogma.net/dcc99.pdf
std::vector<bool> visited(d->symlen.size());
for (Sym sym = 0; sym < d->symlen.size(); ++sym)
if (!visited[sym])
d->symlen[sym] = set_symlen(d, sym, visited);
return data + d->symlen.size() * sizeof(LR) + (d->symlen.size() & 1);
}
uint8_t* set_dtz_map(TBTable<WDL>&, uint8_t* data, File) { return data; }
uint8_t* set_dtz_map(TBTable<DTZ>& e, uint8_t* data, File maxFile) {
e.map = data;
for (File f = FILE_A; f <= maxFile; ++f) {
auto flags = e.get(0, f)->flags;
if (flags & TBFlag::Mapped) {
if (flags & TBFlag::Wide) {
data += (uintptr_t)data & 1; // Word alignment, we may have a mixed table
for (int i = 0; i < 4; ++i) { // Sequence like 3,x,x,x,1,x,0,2,x,x
e.get(0, f)->map_idx[i] = (uint16_t)((uint16_t *)data - (uint16_t *)e.map + 1);
data += 2 * number<uint16_t, LittleEndian>(data) + 2;
}
}
else {
for (int i = 0; i < 4; ++i) {
e.get(0, f)->map_idx[i] = (uint16_t)(data - e.map + 1);
data += *data + 1;
}
}
}
}
return data += (uintptr_t)data & 1; // Word alignment
}
// Populate entry's PairsData records with data from the just memory mapped file.
// Called at first access.
template<typename T>
void set(T& e, uint8_t* data) {
PairsData* d;
enum { Split = 1, HasPawns = 2 };
assert(e.hasPawns == bool(*data & HasPawns));
assert((e.key != e.key2) == bool(*data & Split));
data++; // First byte stores flags
const int sides = T::Sides == 2 && (e.key != e.key2) ? 2 : 1;
const File maxFile = e.hasPawns ? FILE_D : FILE_A;
bool pp = e.hasPawns && e.pawnCount[1]; // Pawns on both sides
assert(!pp || e.pawnCount[0]);
for (File f = FILE_A; f <= maxFile; ++f) {
for (int i = 0; i < sides; i++)
*e.get(i, f) = PairsData();
int order[][2] = { { *data & 0xF, pp ? *(data + 1) & 0xF : 0xF },
{ *data >> 4, pp ? *(data + 1) >> 4 : 0xF } };
data += 1 + pp;
for (int k = 0; k < e.pieceCount; ++k, ++data)
for (int i = 0; i < sides; i++)
e.get(i, f)->pieces[k] = Piece(i ? *data >> 4 : *data & 0xF);
for (int i = 0; i < sides; ++i)
set_groups(e, e.get(i, f), order[i], f);
}
data += (uintptr_t)data & 1; // Word alignment
for (File f = FILE_A; f <= maxFile; ++f)
for (int i = 0; i < sides; i++)
data = set_sizes(e.get(i, f), data);
data = set_dtz_map(e, data, maxFile);
for (File f = FILE_A; f <= maxFile; ++f)
for (int i = 0; i < sides; i++) {
(d = e.get(i, f))->sparseIndex = (SparseEntry*)data;
data += d->sparseIndexSize * sizeof(SparseEntry);
}
for (File f = FILE_A; f <= maxFile; ++f)
for (int i = 0; i < sides; i++) {
(d = e.get(i, f))->blockLength = (uint16_t*)data;
data += d->blockLengthSize * sizeof(uint16_t);
}
for (File f = FILE_A; f <= maxFile; ++f)
for (int i = 0; i < sides; i++) {
data = (uint8_t*)(((uintptr_t)data + 0x3F) & ~0x3F); // 64 byte alignment
(d = e.get(i, f))->data = data;
data += d->blocksNum * d->sizeofBlock;
}
}
// If the TB file corresponding to the given position is already memory mapped
// then return its base address, otherwise try to memory map and init it. Called
// at every probe, memory map and init only at first access. Function is thread
// safe and can be called concurrently.
template<TBType Type>
void* mapped(TBTable<Type>& e, const Position& pos) {
static std::mutex mutex;
// Use 'acquire' to avoid a thread reading 'ready' == true while
// another is still working. (compiler reordering may cause this).
if (e.ready.load(std::memory_order_acquire))
return e.baseAddress; // Could be nullptr if file does not exist
std::scoped_lock<std::mutex> lk(mutex);
if (e.ready.load(std::memory_order_relaxed)) // Recheck under lock
return e.baseAddress;
// Pieces strings in decreasing order for each color, like ("KPP","KR")
std::string fname, w, b;
for (PieceType pt = KING; pt >= PAWN; --pt) {
w += std::string(popcount(pos.pieces(WHITE, pt)), PieceToChar[pt]);
b += std::string(popcount(pos.pieces(BLACK, pt)), PieceToChar[pt]);
}
fname = (e.key == pos.material_key() ? w + 'v' + b : b + 'v' + w)
+ (Type == WDL ? ".rtbw" : ".rtbz");
uint8_t* data = TBFile(fname).map(&e.baseAddress, &e.mapping, Type);
if (data)
set(e, data);
e.ready.store(true, std::memory_order_release);
return e.baseAddress;
}
template<TBType Type, typename Ret = typename TBTable<Type>::Ret>
Ret probe_table(const Position& pos, ProbeState* result, WDLScore wdl = WDLDraw) {
if (pos.count<ALL_PIECES>() == 2) // KvK
return Ret(WDLDraw);
TBTable<Type>* entry = TBTables.get<Type>(pos.material_key());
if (!entry || !mapped(*entry, pos))
return *result = FAIL, Ret();
return do_probe_table(pos, entry, wdl, result);
}
// For a position where the side to move has a winning capture it is not necessary
// to store a winning value so the generator treats such positions as "don't cares"
// and tries to assign to it a value that improves the compression ratio. Similarly,
// if the side to move has a drawing capture, then the position is at least drawn.
// If the position is won, then the TB needs to store a win value. But if the
// position is drawn, the TB may store a loss value if that is better for compression.
// All of this means that during probing, the engine must look at captures and probe
// their results and must probe the position itself. The "best" result of these
// probes is the correct result for the position.
// DTZ tables do not store values when a following move is a zeroing winning move
// (winning capture or winning pawn move). Also DTZ store wrong values for positions
// where the best move is an ep-move (even if losing). So in all these cases set
// the state to ZEROING_BEST_MOVE.
template<bool CheckZeroingMoves>
WDLScore search(Position& pos, ProbeState* result) {
WDLScore value, bestValue = WDLLoss;
StateInfo st;
auto moveList = MoveList<LEGAL>(pos);
size_t totalCount = moveList.size(), moveCount = 0;
for (const Move move : moveList)
{
if ( !pos.capture(move)
&& (!CheckZeroingMoves || type_of(pos.moved_piece(move)) != PAWN))
continue;
moveCount++;
pos.do_move(move, st);
value = -search<false>(pos, result);
pos.undo_move(move);
if (*result == FAIL)
return WDLDraw;
if (value > bestValue)
{
bestValue = value;
if (value >= WDLWin)
{
*result = ZEROING_BEST_MOVE; // Winning DTZ-zeroing move
return value;
}
}
}
// In case we have already searched all the legal moves we don't have to probe
// the TB because the stored score could be wrong. For instance TB tables
// do not contain information on position with ep rights, so in this case
// the result of probe_wdl_table is wrong. Also in case of only capture
// moves, for instance here 4K3/4q3/6p1/2k5/6p1/8/8/8 w - - 0 7, we have to
// return with ZEROING_BEST_MOVE set.
bool noMoreMoves = (moveCount && moveCount == totalCount);
if (noMoreMoves)
value = bestValue;
else
{
value = probe_table<WDL>(pos, result);
if (*result == FAIL)
return WDLDraw;
}
// DTZ stores a "don't care" value if bestValue is a win
if (bestValue >= value)
return *result = ( bestValue > WDLDraw
|| noMoreMoves ? ZEROING_BEST_MOVE : OK), bestValue;
return *result = OK, value;
}
} // namespace
/// Tablebases::init() is called at startup and after every change to
/// "SyzygyPath" UCI option to (re)create the various tables. It is not thread
/// safe, nor it needs to be.
void Tablebases::init(const std::string& paths) {
TBTables.clear();
MaxCardinality = 0;
TBFile::Paths = paths;
if (paths.empty() || paths == "<empty>")
return;
// MapB1H1H7[] encodes a square below a1-h8 diagonal to 0..27
int code = 0;
for (Square s = SQ_A1; s <= SQ_H8; ++s)
if (off_A1H8(s) < 0)
MapB1H1H7[s] = code++;
// MapA1D1D4[] encodes a square in the a1-d1-d4 triangle to 0..9
std::vector<Square> diagonal;
code = 0;
for (Square s = SQ_A1; s <= SQ_D4; ++s)
if (off_A1H8(s) < 0 && file_of(s) <= FILE_D)
MapA1D1D4[s] = code++;
else if (!off_A1H8(s) && file_of(s) <= FILE_D)
diagonal.push_back(s);
// Diagonal squares are encoded as last ones
for (auto s : diagonal)
MapA1D1D4[s] = code++;
// MapKK[] encodes all the 461 possible legal positions of two kings where
// the first is in the a1-d1-d4 triangle. If the first king is on the a1-d4
// diagonal, the other one shall not to be above the a1-h8 diagonal.
std::vector<std::pair<int, Square>> bothOnDiagonal;
code = 0;
for (int idx = 0; idx < 10; idx++)
for (Square s1 = SQ_A1; s1 <= SQ_D4; ++s1)
if (MapA1D1D4[s1] == idx && (idx || s1 == SQ_B1)) // SQ_B1 is mapped to 0
{
for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
if ((PseudoAttacks[KING][s1] | s1) & s2)
continue; // Illegal position
else if (!off_A1H8(s1) && off_A1H8(s2) > 0)
continue; // First on diagonal, second above
else if (!off_A1H8(s1) && !off_A1H8(s2))
bothOnDiagonal.emplace_back(idx, s2);
else
MapKK[idx][s2] = code++;
}
// Legal positions with both kings on diagonal are encoded as last ones
for (auto p : bothOnDiagonal)
MapKK[p.first][p.second] = code++;
// Binomial[] stores the Binomial Coefficents using Pascal rule. There
// are Binomial[k][n] ways to choose k elements from a set of n elements.
Binomial[0][0] = 1;
for (int n = 1; n < 64; n++) // Squares
for (int k = 0; k < 6 && k <= n; ++k) // Pieces
Binomial[k][n] = (k > 0 ? Binomial[k - 1][n - 1] : 0)
+ (k < n ? Binomial[k ][n - 1] : 0);
// MapPawns[s] encodes squares a2-h7 to 0..47. This is the number of possible
// available squares when the leading one is in 's'. Moreover the pawn with
// highest MapPawns[] is the leading pawn, the one nearest the edge and,
// among pawns with same file, the one with lowest rank.
int availableSquares = 47; // Available squares when lead pawn is in a2
// Init the tables for the encoding of leading pawns group: with 7-men TB we
// can have up to 5 leading pawns (KPPPPPK).
for (int leadPawnsCnt = 1; leadPawnsCnt <= 5; ++leadPawnsCnt)
for (File f = FILE_A; f <= FILE_D; ++f)
{
// Restart the index at every file because TB table is splitted
// by file, so we can reuse the same index for different files.
int idx = 0;
// Sum all possible combinations for a given file, starting with
// the leading pawn on rank 2 and increasing the rank.
for (Rank r = RANK_2; r <= RANK_7; ++r)
{
Square sq = make_square(f, r);
// Compute MapPawns[] at first pass.
// If sq is the leading pawn square, any other pawn cannot be
// below or more toward the edge of sq. There are 47 available
// squares when sq = a2 and reduced by 2 for any rank increase
// due to mirroring: sq == a3 -> no a2, h2, so MapPawns[a3] = 45
if (leadPawnsCnt == 1)
{
MapPawns[sq] = availableSquares--;
MapPawns[flip_file(sq)] = availableSquares--;
}
LeadPawnIdx[leadPawnsCnt][sq] = idx;
idx += Binomial[leadPawnsCnt - 1][MapPawns[sq]];
}
// After a file is traversed, store the cumulated per-file index
LeadPawnsSize[leadPawnsCnt][f] = idx;
}
// Add entries in TB tables if the corresponding ".rtbw" file exists
for (PieceType p1 = PAWN; p1 < KING; ++p1) {
TBTables.add({KING, p1, KING});
for (PieceType p2 = PAWN; p2 <= p1; ++p2) {
TBTables.add({KING, p1, p2, KING});
TBTables.add({KING, p1, KING, p2});
for (PieceType p3 = PAWN; p3 < KING; ++p3)
TBTables.add({KING, p1, p2, KING, p3});
for (PieceType p3 = PAWN; p3 <= p2; ++p3) {
TBTables.add({KING, p1, p2, p3, KING});
for (PieceType p4 = PAWN; p4 <= p3; ++p4) {
TBTables.add({KING, p1, p2, p3, p4, KING});
for (PieceType p5 = PAWN; p5 <= p4; ++p5)
TBTables.add({KING, p1, p2, p3, p4, p5, KING});
for (PieceType p5 = PAWN; p5 < KING; ++p5)
TBTables.add({KING, p1, p2, p3, p4, KING, p5});
}
for (PieceType p4 = PAWN; p4 < KING; ++p4) {
TBTables.add({KING, p1, p2, p3, KING, p4});
for (PieceType p5 = PAWN; p5 <= p4; ++p5)
TBTables.add({KING, p1, p2, p3, KING, p4, p5});
}
}
for (PieceType p3 = PAWN; p3 <= p1; ++p3)
for (PieceType p4 = PAWN; p4 <= (p1 == p3 ? p2 : p3); ++p4)
TBTables.add({KING, p1, p2, KING, p3, p4});
}
}
sync_cout << "info string Found " << TBTables.size() << " tablebases" << sync_endl;
}
// Probe the WDL table for a particular position.
// If *result != FAIL, the probe was successful.
// The return value is from the point of view of the side to move:
// -2 : loss
// -1 : loss, but draw under 50-move rule
// 0 : draw
// 1 : win, but draw under 50-move rule
// 2 : win
WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) {
*result = OK;
return search<false>(pos, result);
}
// Probe the DTZ table for a particular position.
// If *result != FAIL, the probe was successful.
// The return value is from the point of view of the side to move:
// n < -100 : loss, but draw under 50-move rule
// -100 <= n < -1 : loss in n ply (assuming 50-move counter == 0)
// -1 : loss, the side to move is mated
// 0 : draw
// 1 < n <= 100 : win in n ply (assuming 50-move counter == 0)
// 100 < n : win, but draw under 50-move rule
//
// The return value n can be off by 1: a return value -n can mean a loss
// in n+1 ply and a return value +n can mean a win in n+1 ply. This
// cannot happen for tables with positions exactly on the "edge" of
// the 50-move rule.
//
// This implies that if dtz > 0 is returned, the position is certainly
// a win if dtz + 50-move-counter <= 99. Care must be taken that the engine
// picks moves that preserve dtz + 50-move-counter <= 99.
//
// If n = 100 immediately after a capture or pawn move, then the position
// is also certainly a win, and during the whole phase until the next
// capture or pawn move, the inequality to be preserved is
// dtz + 50-move-counter <= 100.
//
// In short, if a move is available resulting in dtz + 50-move-counter <= 99,
// then do not accept moves leading to dtz + 50-move-counter == 100.
int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
*result = OK;
WDLScore wdl = search<true>(pos, result);
if (*result == FAIL || wdl == WDLDraw) // DTZ tables don't store draws
return 0;
// DTZ stores a 'don't care' value in this case, or even a plain wrong
// one as in case the best move is a losing ep, so it cannot be probed.
if (*result == ZEROING_BEST_MOVE)
return dtz_before_zeroing(wdl);
int dtz = probe_table<DTZ>(pos, result, wdl);
if (*result == FAIL)
return 0;
if (*result != CHANGE_STM)
return (dtz + 100 * (wdl == WDLBlessedLoss || wdl == WDLCursedWin)) * sign_of(wdl);
// DTZ stores results for the other side, so we need to do a 1-ply search and
// find the winning move that minimizes DTZ.
StateInfo st;
int minDTZ = 0xFFFF;
for (const Move move : MoveList<LEGAL>(pos))
{
bool zeroing = pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN;
pos.do_move(move, st);
// For zeroing moves we want the dtz of the move _before_ doing it,
// otherwise we will get the dtz of the next move sequence. Search the
// position after the move to get the score sign (because even in a
// winning position we could make a losing capture or going for a draw).
dtz = zeroing ? -dtz_before_zeroing(search<false>(pos, result))
: -probe_dtz(pos, result);
// If the move mates, force minDTZ to 1
if (dtz == 1 && pos.checkers() && MoveList<LEGAL>(pos).size() == 0)
minDTZ = 1;
// Convert result from 1-ply search. Zeroing moves are already accounted
// by dtz_before_zeroing() that returns the DTZ of the previous move.
if (!zeroing)
dtz += sign_of(dtz);
// Skip the draws and if we are winning only pick positive dtz
if (dtz < minDTZ && sign_of(dtz) == sign_of(wdl))
minDTZ = dtz;
pos.undo_move(move);
if (*result == FAIL)
return 0;
}
// When there are no legal moves, the position is mate: we return -1
return minDTZ == 0xFFFF ? -1 : minDTZ;
}
// Use the DTZ tables to rank root moves.
//
// A return value false indicates that not all probes were successful.
bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
ProbeState result;
StateInfo st;
// Obtain 50-move counter for the root position
int cnt50 = pos.rule50_count();
// Check whether a position was repeated since the last zeroing move.
bool rep = pos.has_repeated();
int dtz, bound = Options["Syzygy50MoveRule"] ? 900 : 1;
// Probe and rank each move
for (auto& m : rootMoves)
{
pos.do_move(m.pv[0], st);
// Calculate dtz for the current move counting from the root position
if (pos.rule50_count() == 0)
{
// In case of a zeroing move, dtz is one of -101/-1/0/1/101
WDLScore wdl = -probe_wdl(pos, &result);
dtz = dtz_before_zeroing(wdl);
}
else if (pos.is_draw(1))
{
// In case a root move leads to a draw by repetition or
// 50-move rule, we set dtz to zero. Note: since we are
// only 1 ply from the root, this must be a true 3-fold
// repetition inside the game history.
dtz = 0;
}
else
{
// Otherwise, take dtz for the new position and correct by 1 ply
dtz = -probe_dtz(pos, &result);
dtz = dtz > 0 ? dtz + 1
: dtz < 0 ? dtz - 1 : dtz;
}
// Make sure that a mating move is assigned a dtz value of 1
if ( pos.checkers()
&& dtz == 2
&& MoveList<LEGAL>(pos).size() == 0)
dtz = 1;
pos.undo_move(m.pv[0]);
if (result == FAIL)
return false;
// Better moves are ranked higher. Certain wins are ranked equally.
// Losing moves are ranked equally unless a 50-move draw is in sight.
int r = dtz > 0 ? (dtz + cnt50 <= 99 && !rep ? 1000 : 1000 - (dtz + cnt50))
: dtz < 0 ? (-dtz * 2 + cnt50 < 100 ? -1000 : -1000 + (-dtz + cnt50))
: 0;
m.tbRank = r;
// Determine the score to be displayed for this move. Assign at least
// 1 cp to cursed wins and let it grow to 49 cp as the positions gets
// closer to a real win.
m.tbScore = r >= bound ? VALUE_MATE - MAX_PLY - 1
: r > 0 ? Value((std::max( 3, r - 800) * int(PawnValueEg)) / 200)
: r == 0 ? VALUE_DRAW
: r > -bound ? Value((std::min(-3, r + 800) * int(PawnValueEg)) / 200)
: -VALUE_MATE + MAX_PLY + 1;
}
return true;
}
// Use the WDL tables to rank root moves.
// This is a fallback for the case that some or all DTZ tables are missing.
//
// A return value false indicates that not all probes were successful.
bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves) {
static const int WDL_to_rank[] = { -1000, -899, 0, 899, 1000 };
ProbeState result;
StateInfo st;
WDLScore wdl;
bool rule50 = Options["Syzygy50MoveRule"];
// Probe and rank each move
for (auto& m : rootMoves)
{
pos.do_move(m.pv[0], st);
if (pos.is_draw(1))
wdl = WDLDraw;
else
wdl = -probe_wdl(pos, &result);
pos.undo_move(m.pv[0]);
if (result == FAIL)
return false;
m.tbRank = WDL_to_rank[wdl + 2];
if (!rule50)
wdl = wdl > WDLDraw ? WDLWin
: wdl < WDLDraw ? WDLLoss : WDLDraw;
m.tbScore = WDL_to_value[wdl + 2];
}
return true;
}
} // namespace Stockfish
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