kate/BadFish
1
0
Fork 0
mirror of https://github.com/sockspls/badfish synced 2025-04-30 16:53:09 +00:00
Code Issues Releases Wiki Activity
BadFish/src/syzygy/tbprobe.cpp
Marco Costalba c3e964f35e Run clang-tidy 'modernize' 
Some warnings after a run of:

$ clang-tidy-3.8 -checks='modernize-*' *.cpp syzygy/*.cpp -header-filter=.* -- -std=c++11

I have not fixed all suggestions, for instance I still prefer
to declare the type instead of a spread use of 'auto'. I also
perfer good old 'typedef' to the new 'using' form.

I have not fixed some warnings in the last functions of
syzygy code because those are still the original functions
and need to be completely rewritten anyhow.

Thanks to erbsenzaehler for the original idea.

No functional change.
2017-08-13 05:46:21 -07:00

1695 lines
60 KiB
C++
Raw Blame History

/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (c) 2013 Ronald de Man
Copyright (C) 2016-2017 Marco Costalba, Lucas Braesch
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
#include <deque>
#include <fstream>
#include <iostream>
#include <list>
#include <sstream>
#include <type_traits>
#include "../bitboard.h"
#include "../movegen.h"
#include "../position.h"
#include "../search.h"
#include "../thread_win32.h"
#include "../types.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
#define NOMINMAX
#include <windows.h>
#endif
using namespace Tablebases;
int Tablebases::MaxCardinality;
namespace {
// 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, SingleValue = 128 };
inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
inline Square operator^=(Square& s, int i) { return s = Square(int(s) ^ i); }
inline Square operator^(Square s, int i) { return Square(int(s) ^ i); }
// 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, Value };
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 first byte 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) :
S == Value ? lr[0] : (assert(false), Sym(-1));
}
};
static_assert(sizeof(LR) == 3, "LR tree entry must be 3 bytes");
const int TBPIECES = 6;
struct PairsData {
int flags;
size_t sizeofBlock; // Block size in bytes
size_t span; // About every span values there is a SparseIndex[] entry
int blocksNum; // Number of blocks in the TB file
int maxSymLen; // Maximum length in bits of the Huffman symbols
int minSymLen; // Minimum length in bits of the Huffman symbols
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
int 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)
};
// Helper struct to avoid manually defining entry copy constructor as we
// should because the default one is not compatible with std::atomic_bool.
struct Atomic {
Atomic() = default;
Atomic(const Atomic& e) { ready = e.ready.load(); } // MSVC 2013 wants assignment within body
std::atomic_bool ready;
};
// We define types for the different parts of the WLDEntry and DTZEntry with
// corresponding specializations for pieces or pawns.
struct WLDEntryPiece {
PairsData* precomp;
};
struct WDLEntryPawn {
uint8_t pawnCount[2]; // [Lead color / other color]
WLDEntryPiece file[2][4]; // [wtm / btm][FILE_A..FILE_D]
};
struct DTZEntryPiece {
PairsData* precomp;
uint16_t map_idx[4]; // WDLWin, WDLLoss, WDLCursedWin, WDLBlessedLoss
uint8_t* map;
};
struct DTZEntryPawn {
uint8_t pawnCount[2];
DTZEntryPiece file[4];
uint8_t* map;
};
struct TBEntry : public Atomic {
void* baseAddress;
uint64_t mapping;
Key key;
Key key2;
int pieceCount;
bool hasPawns;
bool hasUniquePieces;
};
// Now the main types: WDLEntry and DTZEntry
struct WDLEntry : public TBEntry {
WDLEntry(const std::string& code);
~WDLEntry();
union {
WLDEntryPiece pieceTable[2]; // [wtm / btm]
WDLEntryPawn pawnTable;
};
};
struct DTZEntry : public TBEntry {
DTZEntry(const WDLEntry& wdl);
~DTZEntry();
union {
DTZEntryPiece pieceTable;
DTZEntryPawn pawnTable;
};
};
typedef decltype(WDLEntry::pieceTable) WDLPieceTable;
typedef decltype(DTZEntry::pieceTable) DTZPieceTable;
typedef decltype(WDLEntry::pawnTable ) WDLPawnTable;
typedef decltype(DTZEntry::pawnTable ) DTZPawnTable;
auto item(WDLPieceTable& e, int stm, int ) -> decltype(e[stm])& { return e[stm]; }
auto item(DTZPieceTable& e, int , int ) -> decltype(e)& { return e; }
auto item(WDLPawnTable& e, int stm, int f) -> decltype(e.file[stm][f])& { return e.file[stm][f]; }
auto item(DTZPawnTable& e, int , int f) -> decltype(e.file[f])& { return e.file[f]; }
template<typename E> struct Ret { typedef int type; };
template<> struct Ret<WDLEntry> { typedef WDLScore type; };
int MapPawns[SQUARE_NB];
int MapB1H1H7[SQUARE_NB];
int MapA1D1D4[SQUARE_NB];
int MapKK[10][SQUARE_NB]; // [MapA1D1D4][SQUARE_NB]
// 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); }
const Value WDL_to_value[] = {
-VALUE_MATE + MAX_PLY + 1,
VALUE_DRAW - 2,
VALUE_DRAW,
VALUE_DRAW + 2,
VALUE_MATE - MAX_PLY - 1
};
const std::string PieceToChar = " PNBRQK pnbrqk";
int Binomial[6][SQUARE_NB]; // [k][n] k elements from a set of n elements
int LeadPawnIdx[5][SQUARE_NB]; // [leadPawnsCnt][SQUARE_NB]
int LeadPawnsSize[5][4]; // [leadPawnsCnt][FILE_A..FILE_D]
enum { BigEndian, LittleEndian };
template<typename T, int Half = sizeof(T) / 2, int End = sizeof(T) - 1>
inline void swap_byte(T& x)
{
char tmp, *c = (char*)&x;
for (int i = 0; i < Half; ++i)
tmp = c[i], c[i] = c[End - i], c[End - i] = tmp;
}
template<> inline void swap_byte<uint8_t, 0, 0>(uint8_t&) {}
template<typename T, int LE> T number(void* addr)
{
const union { uint32_t i; char c[4]; } Le = { 0x01020304 };
const bool IsLittleEndian = (Le.c[0] == 4);
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_byte(v);
return v;
}
class HashTable {
typedef std::pair<WDLEntry*, DTZEntry*> EntryPair;
typedef std::pair<Key, EntryPair> Entry;
static const int TBHASHBITS = 10;
static const int HSHMAX = 5;
Entry hashTable[1 << TBHASHBITS][HSHMAX];
std::deque<WDLEntry> wdlTable;
std::deque<DTZEntry> dtzTable;
void insert(Key key, WDLEntry* wdl, DTZEntry* dtz) {
Entry* entry = hashTable[key >> (64 - TBHASHBITS)];
for (int i = 0; i < HSHMAX; ++i, ++entry)
if (!entry->second.first || entry->first == key) {
*entry = std::make_pair(key, std::make_pair(wdl, dtz));
return;
}
std::cerr << "HSHMAX too low!" << std::endl;
exit(1);
}
public:
template<typename E, int I = std::is_same<E, WDLEntry>::value ? 0 : 1>
E* get(Key key) {
Entry* entry = hashTable[key >> (64 - TBHASHBITS)];
for (int i = 0; i < HSHMAX; ++i, ++entry)
if (entry->first == key)
return std::get<I>(entry->second);
return nullptr;
}
void clear() {
std::memset(hashTable, 0, sizeof(hashTable));
wdlTable.clear();
dtzTable.clear();
}
size_t size() const { return wdlTable.size(); }
void insert(const std::vector<PieceType>& pieces);
};
HashTable EntryTable;
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
const char SepChar = ':';
#else
const 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, const uint8_t* TB_MAGIC) {
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);
fstat(fd, &statbuf);
*mapping = statbuf.st_size;
*baseAddress = mmap(nullptr, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
::close(fd);
if (*baseAddress == MAP_FAILED) {
std::cerr << "Could not mmap() " << fname << std::endl;
exit(1);
}
#else
HANDLE fd = CreateFile(fname.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
DWORD size_high;
DWORD size_low = GetFileSize(fd, &size_high);
HANDLE mmap = CreateFileMapping(fd, nullptr, PAGE_READONLY, size_high, size_low, nullptr);
CloseHandle(fd);
if (!mmap) {
std::cerr << "CreateFileMapping() failed" << std::endl;
exit(1);
}
*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(1);
}
#endif
uint8_t* data = (uint8_t*)*baseAddress;
if ( *data++ != *TB_MAGIC++
|| *data++ != *TB_MAGIC++
|| *data++ != *TB_MAGIC++
|| *data++ != *TB_MAGIC) {
std::cerr << "Corrupted table in file " << fname << std::endl;
unmap(*baseAddress, *mapping);
*baseAddress = nullptr;
return nullptr;
}
return data;
}
static void unmap(void* baseAddress, uint64_t mapping) {
#ifndef _WIN32
munmap(baseAddress, mapping);
#else
UnmapViewOfFile(baseAddress);
CloseHandle((HANDLE)mapping);
#endif
}
};
std::string TBFile::Paths;
WDLEntry::WDLEntry(const std::string& code) {
StateInfo st;
Position pos;
memset(this, 0, sizeof(WDLEntry));
ready = false;
key = pos.set(code, WHITE, &st).material_key();
pieceCount = popcount(pos.pieces());
hasPawns = pos.pieces(PAWN);
for (Color c = WHITE; c <= BLACK; ++c)
for (PieceType pt = PAWN; pt < KING; ++pt)
if (popcount(pos.pieces(c, pt)) == 1)
hasUniquePieces = true;
if (hasPawns) {
// 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));
pawnTable.pawnCount[0] = pos.count<PAWN>(c ? WHITE : BLACK);
pawnTable.pawnCount[1] = pos.count<PAWN>(c ? BLACK : WHITE);
}
key2 = pos.set(code, BLACK, &st).material_key();
}
WDLEntry::~WDLEntry() {
if (baseAddress)
TBFile::unmap(baseAddress, mapping);
for (int i = 0; i < 2; ++i)
if (hasPawns)
for (File f = FILE_A; f <= FILE_D; ++f)
delete pawnTable.file[i][f].precomp;
else
delete pieceTable[i].precomp;
}
DTZEntry::DTZEntry(const WDLEntry& wdl) {
memset(this, 0, sizeof(DTZEntry));
ready = false;
key = wdl.key;
key2 = wdl.key2;
pieceCount = wdl.pieceCount;
hasPawns = wdl.hasPawns;
hasUniquePieces = wdl.hasUniquePieces;
if (hasPawns) {
pawnTable.pawnCount[0] = wdl.pawnTable.pawnCount[0];
pawnTable.pawnCount[1] = wdl.pawnTable.pawnCount[1];
}
}
DTZEntry::~DTZEntry() {
if (baseAddress)
TBFile::unmap(baseAddress, mapping);
if (hasPawns)
for (File f = FILE_A; f <= FILE_D; ++f)
delete pawnTable.file[f].precomp;
else
delete pieceTable.precomp;
}
void HashTable::insert(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())
return;
file.close();
MaxCardinality = std::max((int)pieces.size(), MaxCardinality);
wdlTable.emplace_back(code);
dtzTable.emplace_back(wdlTable.back());
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 = 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 + 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 = (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::Value>();
}
bool check_dtz_stm(WDLEntry*, int, File) { return true; }
bool check_dtz_stm(DTZEntry* entry, int stm, File f) {
int flags = entry->hasPawns ? entry->pawnTable.file[f].precomp->flags
: entry->pieceTable.precomp->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(WDLEntry*, File, int value, WDLScore) { return WDLScore(value - 2); }
int map_score(DTZEntry* entry, File f, int value, WDLScore wdl) {
const int WDLMap[] = { 1, 3, 0, 2, 0 };
int flags = entry->hasPawns ? entry->pawnTable.file[f].precomp->flags
: entry->pieceTable.precomp->flags;
uint8_t* map = entry->hasPawns ? entry->pawnTable.map
: entry->pieceTable.map;
uint16_t* idx = entry->hasPawns ? entry->pawnTable.file[f].map_idx
: entry->pieceTable.map_idx;
if (flags & TBFlag::Mapped)
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 Entry, typename T = typename Ret<Entry>::type>
T do_probe_table(const Position& pos, Entry* entry, WDLScore wdl, ProbeState* result) {
const bool IsWDL = std::is_same<Entry, WDLEntry>::value;
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) * 070;
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(item(entry->pawnTable, 0, 0).precomp->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_of(squares[0]);
if (tbFile > FILE_D)
tbFile = file_of(squares[0] ^ 7); // Horizontal flip: SQ_H1 -> SQ_A1
d = item(entry->pawnTable , stm, tbFile).precomp;
} else
d = item(entry->pieceTable, stm, tbFile).precomp;
// 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 (!IsWDL && !check_dtz_stm(entry, stm, tbFile))
return *result = CHANGE_STM, T();
// 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);
// Then we reorder the pieces to have the same sequence as the one stored
// in precomp->pieces[i]: the sequence that ensures the best compression.
for (int i = leadPawnsCnt; i < size; ++i)
for (int j = i; 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] ^= 7; // Horizontal flip: SQ_H1 -> SQ_A1
// Encode leading pawns starting with the one with minimum MapPawns[] and
// proceeding in ascending order.
if (entry->hasPawns) {
idx = LeadPawnIdx[leadPawnsCnt][squares[0]];
std::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] ^= 070; // Vertical flip: SQ_A8 -> SQ_A1
// 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_C3
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->pawnTable.pawnCount[1];
while (d->groupLen[++next])
{
std::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.pawnTable.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 = (tbSize + d->span - 1) / d->span; // Round up
int 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 http://www.eecs.harvard.edu/~michaelm/E210/huffman.pdf
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 comrpession 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);
}
template<typename T>
uint8_t* set_dtz_map(WDLEntry&, T&, uint8_t*, File) { return nullptr; }
template<typename T>
uint8_t* set_dtz_map(DTZEntry&, T& p, uint8_t* data, File maxFile) {
p.map = data;
for (File f = FILE_A; f <= maxFile; ++f) {
if (item(p, 0, f).precomp->flags & TBFlag::Mapped)
for (int i = 0; i < 4; ++i) { // Sequence like 3,x,x,x,1,x,0,2,x,x
item(p, 0, f).map_idx[i] = (uint16_t)(data - p.map + 1);
data += *data + 1;
}
}
return data += (uintptr_t)data & 1; // Word alignment
}
template<typename Entry, typename T>
void do_init(Entry& e, T& p, uint8_t* data) {
const bool IsWDL = std::is_same<Entry, WDLEntry>::value;
PairsData* d;
enum { Split = 1, HasPawns = 2 };
assert(e.hasPawns == !!(*data & HasPawns));
assert((e.key != e.key2) == !!(*data & Split));
data++; // First byte stores flags
const int Sides = IsWDL && (e.key != e.key2) ? 2 : 1;
const File MaxFile = e.hasPawns ? FILE_D : FILE_A;
bool pp = e.hasPawns && e.pawnTable.pawnCount[1]; // Pawns on both sides
assert(!pp || e.pawnTable.pawnCount[0]);
for (File f = FILE_A; f <= MaxFile; ++f) {
for (int i = 0; i < Sides; i++)
item(p, i, f).precomp = new 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++)
item(p, i, f).precomp->pieces[k] = Piece(i ? *data >> 4 : *data & 0xF);
for (int i = 0; i < Sides; ++i)
set_groups(e, item(p, i, f).precomp, 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(item(p, i, f).precomp, data);
if (!IsWDL)
data = set_dtz_map(e, p, data, MaxFile);
for (File f = FILE_A; f <= MaxFile; ++f)
for (int i = 0; i < Sides; i++) {
(d = item(p, i, f).precomp)->sparseIndex = (SparseEntry*)data;
data += d->sparseIndexSize * sizeof(SparseEntry);
}
for (File f = FILE_A; f <= MaxFile; ++f)
for (int i = 0; i < Sides; i++) {
(d = item(p, i, f).precomp)->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 = item(p, i, f).precomp)->data = data;
data += d->blocksNum * d->sizeofBlock;
}
}
template<typename Entry>
void* init(Entry& e, const Position& pos) {
const bool IsWDL = std::is_same<Entry, WDLEntry>::value;
static Mutex mutex;
// Avoid a thread reads 'ready' == true while another is still in do_init(),
// this could happen due to compiler reordering.
if (e.ready.load(std::memory_order_acquire))
return e.baseAddress;
std::unique_lock<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]);
}
const uint8_t TB_MAGIC[][4] = { { 0xD7, 0x66, 0x0C, 0xA5 },
{ 0x71, 0xE8, 0x23, 0x5D } };
fname = (e.key == pos.material_key() ? w + 'v' + b : b + 'v' + w)
+ (IsWDL ? ".rtbw" : ".rtbz");
uint8_t* data = TBFile(fname).map(&e.baseAddress, &e.mapping, TB_MAGIC[IsWDL]);
if (data)
e.hasPawns ? do_init(e, e.pawnTable, data) : do_init(e, e.pieceTable, data);
e.ready.store(true, std::memory_order_release);
return e.baseAddress;
}
template<typename E, typename T = typename Ret<E>::type>
T probe_table(const Position& pos, ProbeState* result, WDLScore wdl = WDLDraw) {
if (!(pos.pieces() ^ pos.pieces(KING)))
return T(WDLDraw); // KvK
E* entry = EntryTable.get<E>(pos.material_key());
if (!entry || !init(*entry, pos))
return *result = FAIL, T();
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 table don't 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 = false>
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(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<WDLEntry>(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
void Tablebases::init(const std::string& paths) {
EntryTable.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.push_back(std::make_pair(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 6-men TB we
// can have up to 4 leading pawns (KPPPPK).
for (int leadPawnsCnt = 1; leadPawnsCnt <= 4; ++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[sq ^ 7] = availableSquares--; // Horizontal flip
}
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;
}
for (PieceType p1 = PAWN; p1 < KING; ++p1) {
EntryTable.insert({KING, p1, KING});
for (PieceType p2 = PAWN; p2 <= p1; ++p2) {
EntryTable.insert({KING, p1, p2, KING});
EntryTable.insert({KING, p1, KING, p2});
for (PieceType p3 = PAWN; p3 < KING; ++p3)
EntryTable.insert({KING, p1, p2, KING, p3});
for (PieceType p3 = PAWN; p3 <= p2; ++p3) {
EntryTable.insert({KING, p1, p2, p3, KING});
for (PieceType p4 = PAWN; p4 <= p3; ++p4)
EntryTable.insert({KING, p1, p2, p3, p4, KING});
for (PieceType p4 = PAWN; p4 < KING; ++p4)
EntryTable.insert({KING, p1, p2, p3, KING, p4});
}
for (PieceType p3 = PAWN; p3 <= p1; ++p3)
for (PieceType p4 = PAWN; p4 <= (p1 == p3 ? p2 : p3); ++p4)
EntryTable.insert({KING, p1, p2, KING, p3, p4});
}
}
sync_cout << "info string Found " << EntryTable.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(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)
// 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-movecounter <= 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<DTZEntry>(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(pos, result))
: -probe_dtz(pos, result);
pos.undo_move(move);
if (*result == FAIL)
return 0;
// 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;
}
// Special handle a mate position, when there are no legal moves, in this
// case return value is somewhat arbitrary, so stick to the original TB code
// that returns -1 in this case.
return minDTZ == 0xFFFF ? -1 : minDTZ;
}
// Check whether there has been at least one repetition of positions
// since the last capture or pawn move.
static int has_repeated(StateInfo *st)
{
while (1) {
int i = 4, e = std::min(st->rule50, st->pliesFromNull);
if (e < i)
return 0;
StateInfo *stp = st->previous->previous;
do {
stp = stp->previous->previous;
if (stp->key == st->key)
return 1;
i += 2;
} while (i <= e);
st = st->previous;
}
}
// Use the DTZ tables to filter out moves that don't preserve the win or draw.
// If the position is lost, but DTZ is fairly high, only keep moves that
// maximise DTZ.
//
// A return value false indicates that not all probes were successful and that
// no moves were filtered out.
bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, Value& score)
{
assert(rootMoves.size());
ProbeState result;
int dtz = probe_dtz(pos, &result);
if (result == FAIL)
return false;
StateInfo st;
// Probe each move
for (size_t i = 0; i < rootMoves.size(); ++i) {
Move move = rootMoves[i].pv[0];
pos.do_move(move, st);
int v = 0;
if (pos.checkers() && dtz > 0) {
ExtMove s[MAX_MOVES];
if (generate<LEGAL>(pos, s) == s)
v = 1;
}
if (!v) {
if (st.rule50 != 0) {
v = -probe_dtz(pos, &result);
if (v > 0)
++v;
else if (v < 0)
--v;
} else {
v = -probe_wdl(pos, &result);
v = dtz_before_zeroing(WDLScore(v));
}
}
pos.undo_move(move);
if (result == FAIL)
return false;
rootMoves[i].score = (Value)v;
}
// Obtain 50-move counter for the root position.
// In Stockfish there seems to be no clean way, so we do it like this:
int cnt50 = st.previous ? st.previous->rule50 : 0;
// Use 50-move counter to determine whether the root position is
// won, lost or drawn.
WDLScore wdl = WDLDraw;
if (dtz > 0)
wdl = (dtz + cnt50 <= 100) ? WDLWin : WDLCursedWin;
else if (dtz < 0)
wdl = (-dtz + cnt50 <= 100) ? WDLLoss : WDLBlessedLoss;
// Determine the score to report to the user.
score = WDL_to_value[wdl + 2];
// If the position is winning or losing, but too few moves left, adjust the
// score to show how close it is to winning or losing.
// NOTE: int(PawnValueEg) is used as scaling factor in score_to_uci().
if (wdl == WDLCursedWin && dtz <= 100)
score = (Value)(((200 - dtz - cnt50) * int(PawnValueEg)) / 200);
else if (wdl == WDLBlessedLoss && dtz >= -100)
score = -(Value)(((200 + dtz - cnt50) * int(PawnValueEg)) / 200);
// Now be a bit smart about filtering out moves.
size_t j = 0;
if (dtz > 0) { // winning (or 50-move rule draw)
int best = 0xffff;
for (size_t i = 0; i < rootMoves.size(); ++i) {
int v = rootMoves[i].score;
if (v > 0 && v < best)
best = v;
}
int max = best;
// If the current phase has not seen repetitions, then try all moves
// that stay safely within the 50-move budget, if there are any.
if (!has_repeated(st.previous) && best + cnt50 <= 99)
max = 99 - cnt50;
for (size_t i = 0; i < rootMoves.size(); ++i) {
int v = rootMoves[i].score;
if (v > 0 && v <= max)
rootMoves[j++] = rootMoves[i];
}
} else if (dtz < 0) { // losing (or 50-move rule draw)
int best = 0;
for (size_t i = 0; i < rootMoves.size(); ++i) {
int v = rootMoves[i].score;
if (v < best)
best = v;
}
// Try all moves, unless we approach or have a 50-move rule draw.
if (-best * 2 + cnt50 < 100)
return true;
for (size_t i = 0; i < rootMoves.size(); ++i) {
if (rootMoves[i].score == best)
rootMoves[j++] = rootMoves[i];
}
} else { // drawing
// Try all moves that preserve the draw.
for (size_t i = 0; i < rootMoves.size(); ++i) {
if (rootMoves[i].score == 0)
rootMoves[j++] = rootMoves[i];
}
}
rootMoves.resize(j, Search::RootMove(MOVE_NONE));
return true;
}
// Use the WDL tables to filter out moves that don't preserve the win or draw.
// 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 and that
// no moves were filtered out.
bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves, Value& score)
{
ProbeState result;
WDLScore wdl = Tablebases::probe_wdl(pos, &result);
if (result == FAIL)
return false;
score = WDL_to_value[wdl + 2];
StateInfo st;
int best = WDLLoss;
// Probe each move
for (size_t i = 0; i < rootMoves.size(); ++i) {
Move move = rootMoves[i].pv[0];
pos.do_move(move, st);
WDLScore v = -Tablebases::probe_wdl(pos, &result);
pos.undo_move(move);
if (result == FAIL)
return false;
rootMoves[i].score = (Value)v;
if (v > best)
best = v;
}
size_t j = 0;
for (size_t i = 0; i < rootMoves.size(); ++i) {
if (rootMoves[i].score == best)
rootMoves[j++] = rootMoves[i];
}
rootMoves.resize(j, Search::RootMove(MOVE_NONE));
return true;
}
Reference in a new issue View git blame Copy permalink