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BadFish/src/syzygy/tbprobe.cpp
Marco Costalba 6f11b0438d Compute KK_idx[] at init time
2016-05-08 14:13:22 +02:00

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/*
Copyright (c) 2013 Ronald de Man
This file may be redistributed and/or modified without restrictions.
tbprobe.cpp contains the Stockfish-specific routines of the
tablebase probing code. It should be relatively easy to adapt
this code to other chess engines.
*/
#include <algorithm>
#include <atomic>
#include <cstdint>
#include <cstring> // For std::memset
#include <deque>
#include <list>
#include <fstream>
#include <iostream>
#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
#define TBPIECES 6
using namespace Tablebases;
int Tablebases::MaxCardinality = 0;
namespace {
inline WDLScore operator-(WDLScore d) { return WDLScore(-int(d)); }
inline WDLScore operator+(WDLScore d1, WDLScore d2) { return WDLScore(int(d1) + int(d2)); }
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); }
struct PairsData {
int blocksize;
int idxbits;
int num_indices;
int real_num_blocks;
int num_blocks;
int max_len;
int min_len;
uint16_t* offset;
uint8_t* sympat;
uint8_t* indextable;
uint16_t* sizetable;
uint8_t* data;
std::vector<uint64_t> base;
std::vector<uint8_t> symlen;
Piece pieces[TBPIECES];
uint64_t factor[TBPIECES];
uint8_t norm[TBPIECES];
};
// Helper struct to avoid manually define WDLEntry copy c'tor as we should
// because default one is not compatible with std::atomic_bool.
struct Atomic {
Atomic() = default;
Atomic(const Atomic& e) : ready(e.ready.load()) {}
std::atomic_bool ready;
};
struct WDLEntry : Atomic {
WDLEntry(const Position& pos, Key keys[]);
~WDLEntry();
bool init(const std::string& fname);
template<typename T> void do_init(T& e, uint8_t* data);
void* baseAddress;
uint64_t mapping;
Key key;
int pieceCount;
bool symmetric;
bool hasPawns;
union {
struct {
typedef int Piece;
bool hasUniquePieces;
PairsData* precomp;
} piece[2];
struct {
uint8_t pawnCount[2];
struct {
typedef int Pawn;
PairsData* precomp;
} file[2][4];
} pawn;
};
};
struct DTZEntry {
enum Flag { STM = 1, Mapped = 2, WinPlies = 4, LossPlies = 8 };
DTZEntry(const WDLEntry& wdl, Key wdlKeys[]);
~DTZEntry();
bool init(const std::string& fname);
template<typename T> void do_init(T& e, uint8_t* data);
void* baseAddress;
uint64_t mapping;
Key key;
Key key2;
int pieceCount;
bool symmetric;
bool hasPawns;
union {
struct {
typedef int Piece;
bool hasUniquePieces;
PairsData* precomp;
uint8_t flags;
uint16_t map_idx[4];
uint8_t* map;
} piece;
struct {
uint8_t pawnCount[2];
struct {
typedef int Pawn;
PairsData* precomp;
uint8_t flags;
uint16_t map_idx[4];
} file[4];
uint8_t* map;
} pawn;
};
};
typedef decltype(WDLEntry::piece) WDLPiece;
typedef decltype(DTZEntry::piece) DTZPiece;
typedef decltype(WDLEntry::pawn ) WDLPawn;
typedef decltype(DTZEntry::pawn ) DTZPawn;
auto item(WDLPiece& e, int stm, int ) -> decltype(e[stm])& { return e[stm]; }
auto item(DTZPiece& e, int , int ) -> decltype(e)& { return e; }
auto item(WDLPawn& e, int stm, int f) -> decltype(e.file[stm][f])& { return e.file[stm][f]; }
auto item(DTZPawn& e, int , int f) -> decltype(e.file[f])& { return e.file[f]; }
const uint8_t MapA1D1D4[64] = {
6, 0, 1, 2, 0, 0, 0, 0,
0, 7, 3, 4, 0, 0, 0, 0,
0, 0, 8, 5, 0, 0, 0, 0,
0, 0, 0, 9
};
const uint8_t MapB1H1H7[] = {
0, 0, 1, 2, 3, 4, 5, 6,
0, 0, 7, 8, 9, 10, 11, 12,
0, 0, 0, 13, 14, 15, 16, 17,
0, 0, 0, 0, 18, 19, 20, 21,
0, 0, 0, 0, 0, 22, 23, 24,
0, 0, 0, 0, 0, 0, 25, 26,
0, 0, 0, 0, 0, 0, 0, 27
};
const uint8_t Flap[] = {
0, 0, 0, 0, 0, 0, 0, 0,
0, 6, 12, 18, 18, 12, 6, 0,
1, 7, 13, 19, 19, 13, 7, 1,
2, 8, 14, 20, 20, 14, 8, 2,
3, 9, 15, 21, 21, 15, 9, 3,
4, 10, 16, 22, 22, 16, 10, 4,
5, 11, 17, 23, 23, 17, 11, 5,
0, 0, 0, 0, 0, 0, 0, 0
};
const uint8_t Ptwist[] = {
0, 0, 0, 0, 0, 0, 0, 0,
47, 35, 23, 11, 10, 22, 34, 46,
45, 33, 21, 9, 8, 20, 32, 44,
43, 31, 19, 7, 6, 18, 30, 42,
41, 29, 17, 5, 4, 16, 28, 40,
39, 27, 15, 3, 2, 14, 26, 38,
37, 25, 13, 1, 0, 12, 24, 36,
0, 0, 0, 0, 0, 0, 0, 0
};
const uint8_t Invflap[] = {
8, 16, 24, 32, 40, 48,
9, 17, 25, 33, 41, 49,
10, 18, 26, 34, 42, 50,
11, 19, 27, 35, 43, 51
};
int KK_idx[10][64];
const uint8_t WDL_MAGIC[] = { 0x71, 0xE8, 0x23, 0x5D };
const uint8_t DTZ_MAGIC[] = { 0xD7, 0x66, 0x0C, 0xA5 };
const int wdl_to_dtz[] = { -1, -101, 0, 101, 1 };
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";
Mutex TB_mutex;
std::string TBPaths;
std::deque<WDLEntry> WDLTable;
std::list<DTZEntry> DTZTable;
int Binomial[6][64];
int Pawnidx[5][24];
int Pfactor[5][4];
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<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 = *((T*)addr);
if (LE != IsLittleEndian)
swap_byte(v);
return v;
}
class HashTable {
struct Entry {
Key key;
WDLEntry* ptr;
};
static const int TBHASHBITS = 10;
static const int HSHMAX = 5;
Entry table[1 << TBHASHBITS][HSHMAX];
void insert(Key key, WDLEntry* ptr) {
Entry* entry = table[key >> (64 - TBHASHBITS)];
for (int i = 0; i < HSHMAX; ++i, ++entry)
if (!entry->ptr || entry->key == key) {
entry->key = key;
entry->ptr = ptr;
return;
}
std::cerr << "HSHMAX too low!" << std::endl;
exit(1);
}
public:
WDLEntry* operator[](Key key) {
Entry* entry = table[key >> (64 - TBHASHBITS)];
for (int i = 0; i < HSHMAX; ++i, ++entry)
if (entry->key == key)
return entry->ptr;
return nullptr;
}
void clear() { std::memset(table, 0, sizeof(table)); }
void insert(const std::vector<PieceType>& pieces);
};
HashTable WDLHash;
class TBFile : public std::ifstream {
std::string fname;
public:
// Open the file with the given name found among the TBPaths. TBPaths stores
// the paths to 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
TBFile(const std::string& f) {
#ifndef _WIN32
const char SepChar = ':';
#else
const char SepChar = ';';
#endif
std::stringstream ss(TBPaths);
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[]) {
if (!is_open()) {
std::cerr << "Could not find " << fname << std::endl;
*baseAddress = nullptr;
return nullptr;
}
close();
#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[0]
|| *data++ != TB_MAGIC[1]
|| *data++ != TB_MAGIC[2]
|| *data++ != TB_MAGIC[3]) {
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
}
};
WDLEntry::WDLEntry(const Position& pos, Key keys[])
{
memset(this, 0, sizeof(WDLEntry));
key = keys[WHITE];
pieceCount = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
symmetric = (keys[WHITE] == keys[BLACK]);
hasPawns = pos.pieces(PAWN);
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 a better compression.
bool c = !pos.count<PAWN>(BLACK)
|| ( pos.count<PAWN>(WHITE)
&& pos.count<PAWN>(BLACK) >= pos.count<PAWN>(WHITE));
pawn.pawnCount[0] = pos.count<PAWN>(c ? WHITE : BLACK);
pawn.pawnCount[1] = pos.count<PAWN>(c ? BLACK : WHITE);
} else
for (Color c = WHITE; c <= BLACK; ++c)
for (PieceType pt = PAWN; pt < KING; ++pt)
if (popcount(pos.pieces(c, pt)) == 1)
piece[0].hasUniquePieces = piece[1].hasUniquePieces = true;
}
WDLEntry::~WDLEntry()
{
if (baseAddress)
TBFile::unmap(baseAddress, mapping);
if (hasPawns)
for (File f = FILE_A; f <= FILE_D; ++f) {
delete pawn.file[0][f].precomp;
delete pawn.file[1][f].precomp;
}
else {
delete piece[0].precomp;
delete piece[1].precomp;
}
}
DTZEntry::DTZEntry(const WDLEntry& wdl, Key wdlKeys[])
{
memset(this, 0, sizeof(DTZEntry));
key = wdlKeys[0];
key2 = wdlKeys[1];
assert(key == wdl.key);
pieceCount = wdl.pieceCount;
symmetric = wdl.symmetric;
hasPawns = wdl.hasPawns;
if (hasPawns) {
pawn.pawnCount[0] = wdl.pawn.pawnCount[0];
pawn.pawnCount[1] = wdl.pawn.pawnCount[1];
} else
piece.hasUniquePieces = wdl.piece[0].hasUniquePieces;
}
DTZEntry::~DTZEntry()
{
if (baseAddress)
TBFile::unmap(baseAddress, mapping);
if (hasPawns)
for (File f = FILE_A; f <= FILE_D; ++f)
delete pawn.file[f].precomp;
else
delete piece.precomp;
}
// Given a position with 6 or fewer pieces, produce a text string
// of the form KQPvKRP, where "KQP" represents the white pieces if
// mirror == false and the black pieces if mirror == true.
std::string file_name(const Position& pos, bool mirror)
{
std::string 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]);
}
return mirror ? b + 'v' + w : w + 'v' + b;
}
void HashTable::insert(const std::vector<PieceType>& pieces)
{
StateInfo st;
Position pos;
std::string code;
for (PieceType pt : pieces)
code += PieceToChar[pt];
int bk = code.find('K', 1); // Black king
TBFile f(code.substr(0, bk) + 'v' + code.substr(bk) + ".rtbw");
if (!f.is_open())
return;
f.close();
if (int(pieces.size()) > Tablebases::MaxCardinality)
Tablebases::MaxCardinality = pieces.size();
Key keys[] = { pos.set(code, WHITE, &st).material_key(),
pos.set(code, BLACK, &st).material_key() };
WDLTable.push_back(WDLEntry(pos.set(code, WHITE, &st), keys));
insert(keys[WHITE], &WDLTable.back());
insert(keys[BLACK], &WDLTable.back());
}
int decompress_pairs(PairsData* d, uint64_t idx)
{
if (!d->idxbits)
return d->min_len;
// idx = blockidx | litidx where litidx is a signed number of lenght d->idxbits
uint32_t blockidx = (uint32_t)(idx >> d->idxbits);
int litidx = (idx & ((1ULL << d->idxbits) - 1)) - (1ULL << (d->idxbits - 1));
// indextable points to an array of blocks of 6 bytes representing numbers in
// little endian. The low 4 bytes are the block, the high 2 bytes the idxOffset.
uint32_t block = number<uint32_t, LittleEndian>(d->indextable + 6 * blockidx);
litidx += number<uint16_t, LittleEndian>(d->indextable + 6 * blockidx + 4);
while (litidx < 0)
litidx += d->sizetable[--block] + 1;
while (litidx > d->sizetable[block])
litidx -= d->sizetable[block++] + 1;
uint32_t* ptr = (uint32_t*)(d->data + (block << d->blocksize));
uint64_t code = number<uint64_t, BigEndian>(ptr);
int m = d->min_len;
uint16_t *offset = d->offset;
int sym, bitcnt;
ptr += 2;
bitcnt = 0; // number of "empty bits" in code
for (;;) {
int l = m;
while (code < d->base[l - d->min_len])
++l;
sym = number<uint16_t, LittleEndian>(offset + l);
sym += (int)((code - d->base[l - d->min_len]) >> (64 - l));
if (litidx < (int)d->symlen[sym] + 1)
break;
litidx -= (int)d->symlen[sym] + 1;
code <<= l;
bitcnt += l;
if (bitcnt >= 32) {
bitcnt -= 32;
code |= (uint64_t)number<uint32_t, BigEndian>(ptr++) << bitcnt;
}
}
uint8_t *sympat = d->sympat;
while (d->symlen[sym] != 0) {
uint8_t* w = sympat + (3 * sym);
int s1 = ((w[1] & 0xf) << 8) | w[0];
if (litidx < (int)d->symlen[s1] + 1)
sym = s1;
else {
litidx -= (int)d->symlen[s1] + 1;
sym = (w[2] << 4) | (w[1] >> 4);
}
}
return sympat[3 * sym];
}
template<typename Entry>
bool check_dtz_stm(Entry*, File, int) { return true; }
template<>
bool check_dtz_stm(DTZEntry* entry, File f, int stm) {
uint8_t flags = entry->hasPawns ? entry->pawn.file[f].flags
: entry->piece.flags;
return (flags & DTZEntry::Flag::STM) == stm
|| (entry->symmetric && !entry->hasPawns);
}
// DTZ scores are sorted by frequency of occurrence and then assigned the
// values 0, 1, 2, 3, ... in order of decreasing frequency. This is done
// in each of the four ranges. The mapping information necessary to
// reconstruct the original values is stored in the TB file and used to
// initialise the map[] array during initialisation of the TB.
template<typename Entry>
int map_score(Entry*, File, int value, WDLScore) { return value - 2; }
template<>
int map_score(DTZEntry* entry, File f, int value, WDLScore wdl) {
const int WDLMap[] = { 1, 3, 0, 2, 0 };
uint8_t flags = entry->hasPawns ? entry->pawn.file[f].flags
: entry->piece.flags;
uint8_t* map = entry->hasPawns ? entry->pawn.map
: entry->piece.map;
uint16_t* idx = entry->hasPawns ? entry->pawn.file[f].map_idx
: entry->piece.map_idx;
if (flags & DTZEntry::Flag::Mapped)
value = map[idx[WDLMap[wdl + 2]] + value];
// DTZ tables store distance to zero in number of moves but
// under some conditions we want to return plies, so we have
// to multiply score by 2.
if ( (wdl == WDLWin && !(flags & DTZEntry::Flag::WinPlies))
|| (wdl == WDLLoss && !(flags & DTZEntry::Flag::LossPlies))
|| wdl == WDLCursedWin
|| wdl == WDLCursedLoss)
value *= 2;
return value;
}
int off_A1H8(Square sq) { return int(rank_of(sq)) - file_of(sq); }
template<typename Entry>
uint64_t probe_table(const Position& pos, Entry* entry, WDLScore wdl = WDLDraw, int* success = nullptr)
{
Square squares[TBPIECES];
Piece pieces[TBPIECES];
uint64_t idx;
int stm, next = 0, flipColor = 0, flipSquares = 0, size = 0, leadPawnsCnt = 0;
bool hasUniquePieces;
PairsData* precomp;
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 we have a symmetric material and the
// keys are equal. The stored TB entry is calculated always with WHITE side
// to move and if the position to lookup has instead BLACK to move, we need
// to switch color and flip the squares before the lookup:
if (entry->symmetric) {
flipColor = pos.side_to_move() * 8; // Switch color
flipSquares = pos.side_to_move() * 070; // Vertical flip: SQ_A8 -> SQ_A1
stm = WHITE;
}
// In case of sides with different pieces, if the position to look up has a
// different key form the stored one (entry->key), then we have to switch
// color and flip the squares:
else {
flipColor = (pos.material_key() != entry->key) * 8;
flipSquares = (pos.material_key() != entry->key) * 070;
// TB entry is stored with WHITE as stronger side, so side to move has
// to be flipped accordingly, for example Kvkr (white to move) maps to
// KRvk (black to move).
stm = (pos.material_key() != entry->key) ^ pos.side_to_move();
}
// For pawns, TB files store separate tables according if leading pawn is on
// file a, b, c or d after reordering. To determine which of the 4 tables
// must be probed we need to extract the position's leading pawns then order
// them according to Flap table, in ascending order and finally pick the file
// of the pawn with minimum Flap[]. The new pawn order should be preserved
// because needed for next steps.
if (entry->hasPawns) {
Piece pc = Piece(item(entry->pawn, 0, 0).precomp->pieces[0] ^ flipColor);
assert(type_of(pc) == PAWN);
leadPawns = b = pos.pieces(color_of(pc), PAWN);
while (b)
squares[size++] = pop_lsb(&b) ^ flipSquares;
leadPawnsCnt = size;
auto flap = [] (Square i, Square j) { return Flap[i] < Flap[j]; };
std::sort(squares, squares + size, flap);
tbFile = file_of(squares[0]);
if (tbFile > FILE_D)
tbFile = file_of(squares[0] ^ 7); // Horizontal flip: SQ_H1 -> SQ_A1
precomp = item(entry->pawn, stm, tbFile).precomp;
} else
precomp = item(entry->piece, stm, 0).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 ( std::is_same<Entry, DTZEntry>::value
&& !check_dtz_stm(entry, tbFile, stm)) {
*success = -1;
return 0;
}
// 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;
for ( ; b; ++size) {
Square sq = pop_lsb(&b);
squares[size] = sq ^ flipSquares;
pieces[size] = Piece(pos.piece_on(sq) ^ flipColor);
}
// Then we reorder the pieces to have the same sequence as the one stored
// in precomp->pieces[i], this is important for the next step. The sequence
// stored is the one that ensures the best compression.
for (int i = leadPawnsCnt; i < size; ++i)
for (int j = i; j < size; ++j)
if (precomp->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. We take care that the condition on the diagonal
// flip is checked after horizontal and vertical flips are already done.
if (file_of(squares[0]) > FILE_D)
for (int i = 0; i < size; ++i)
squares[i] ^= 7; // Horizontal flip: SQ_H1 -> SQ_A1
// Reorder the leading pawns according to Ptwist table, in descending order,
// and encode them.
if (entry->hasPawns) {
auto ptwist = [] (Square i, Square j) { return Ptwist[i] > Ptwist[j]; };
std::sort(squares + 1, squares + leadPawnsCnt, ptwist);
idx = Pawnidx[leadPawnsCnt - 1][Flap[squares[0]]];
for (int i = 1; i < leadPawnsCnt; ++i)
idx += Binomial[i][Ptwist[squares[i]]];
next = leadPawnsCnt;
goto encode_remaining; // With pawns we have finished special treatments
}
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 not on the A1-D4 diagonal and ensure it is
// mapped below the diagonal.
hasUniquePieces = item(entry->piece, stm, 0).hasUniquePieces;
for (int i = 0; i < size; ++i) {
if (!off_A1H8(squares[i]))
continue;
if (off_A1H8(squares[i]) > 0 && i < (hasUniquePieces ? 3 : 2))
for (int j = i; j < size; ++j) // A1-H8 diagonal flip: SQ_A3 -> SQ_C3
squares[j] = Square(((squares[j] >> 3) | (squares[j] << 3)) & 63);
break;
}
// The encoding function maps a position to its index into the table.
// 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 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.
// In case we have at least 3 unique pieces (inlcuded kings) we encode them
// together.
if (hasUniquePieces) {
int adjust1 = squares[1] > squares[0];
int adjust2 = (squares[2] > squares[0]) + (squares[2] > squares[1]);
// 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 * 62
+ (squares[1] - adjust1) * 62
+ squares[2] - adjust2;
// First piece is on diagonal: map to 6, rank_of() maps a1-d4 diagonal
// to 0...3 and MapB1H1H7[] maps the b1-h1-h7 triangle to 0..27
else if (off_A1H8(squares[1]))
idx = 6 * 63 * 62
+ rank_of(squares[0]) * 28 * 62
+ MapB1H1H7[squares[1]] * 62
+ squares[2] - adjust2;
// First 2 pieces are on the diagonal a1-h8
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);
next = 3; // Continue encoding form piece[3]
} else {
// We don't have at least 3 unique pieces, like in KRRvKBB, just map
// the kings and set next to 2.
idx = KK_idx[MapA1D1D4[squares[0]]][squares[1]];
next = 2;
}
encode_remaining:
idx *= precomp->factor[0];
// Reorder remainig pawns then pieces according to square, in ascending order
int remainingPawns = entry->hasPawns ? entry->pawn.pawnCount[1] : 0;
while (next < size) {
int end = next + (remainingPawns ? remainingPawns : precomp->norm[next]);
std::sort(squares + next, squares + end);
uint64_t s = 0;
// Map squares to lower index if "come later" than previous (as done earlier for pieces)
for (int i = next; i < end; ++i) {
int adjust = 0;
for (int j = 0; j < next; ++j)
adjust += squares[i] > squares[j];
s += Binomial[i - next + 1][squares[i] - adjust - (remainingPawns ? 8 : 0)];
}
remainingPawns = 0;
idx += s * precomp->factor[next];
next = end;
}
// Now that we have the index, decompress the pair and get the score
return map_score(entry, tbFile, decompress_pairs(precomp, idx), wdl);
}
template<typename T>
int get_pfactor(const T& p, File, typename T::Piece = 0)
{ return p.hasUniquePieces ? 31332 : 462; }
template<typename T>
int get_pfactor(const T& p, File f, typename T::Pawn = 0)
{ return Pfactor[p.precomp->norm[0] - 1][f]; }
template<typename T>
uint64_t set_factors(T& p, int num, int order[], File f)
{
PairsData* d = p.precomp;
int i = d->norm[0];
if (order[1] < 0xF)
i += d->norm[i];
int n = 64 - i;
uint64_t size = 1;
for (int k = 0; i < num || k == order[0] || k == order[1]; ++k)
if (k == order[0]) {
d->factor[0] = size;
size *= get_pfactor(p, f);
} else if (k == order[1]) {
d->factor[d->norm[0]] = size;
size *= Binomial[d->norm[d->norm[0]]][48 - d->norm[0]];
} else {
d->factor[i] = size;
size *= Binomial[d->norm[i]][n];
n -= d->norm[i];
i += d->norm[i];
}
return size;
}
template<typename T>
void set_norms(T* p, int num, const uint8_t pawns[])
{
p->norm[0] = pawns[0];
if (pawns[1])
p->norm[pawns[0]] = pawns[1];
for (int i = pawns[0] + pawns[1]; i < num; i += p->norm[i])
for (int j = i; j < num && p->pieces[j] == p->pieces[i]; ++j)
++p->norm[i];
}
void calc_symlen(PairsData* d, size_t s, std::vector<uint8_t>& tmp)
{
int s1, s2;
uint8_t* w = d->sympat + 3 * s;
s2 = (w[2] << 4) | (w[1] >> 4);
if (s2 == 0xFFF)
d->symlen[s] = 0;
else {
s1 = ((w[1] & 0xF) << 8) | w[0];
if (!tmp[s1])
calc_symlen(d, s1, tmp);
if (!tmp[s2])
calc_symlen(d, s2, tmp);
d->symlen[s] = d->symlen[s1] + d->symlen[s2] + 1;
}
tmp[s] = 1;
}
uint8_t* set_sizes(PairsData* d, uint8_t* data, uint64_t tb_size)
{
if (*data++ & 0x80) {
d->min_len = *data++;
return data;
}
d->blocksize = *data++;
d->idxbits = *data++;
d->num_indices = (tb_size + (1ULL << d->idxbits) - 1) >> d->idxbits; // Divide and round upward, like ceil()
d->num_blocks = number<uint8_t, LittleEndian>(data++);
d->real_num_blocks = number<uint32_t, LittleEndian>(data); data += sizeof(uint32_t);
d->num_blocks += d->real_num_blocks;
d->max_len = *data++;
d->min_len = *data++;
d->offset = (uint16_t*)data;
d->base.resize(d->max_len - d->min_len + 1);
for (int i = d->base.size() - 2; i >= 0; --i)
d->base[i] = (d->base[i + 1] + number<uint16_t, LittleEndian>(d->offset + i)
- number<uint16_t, LittleEndian>(d->offset + i + 1)) / 2;
for (size_t i = 0; i < d->base.size(); ++i)
d->base[i] <<= (64 - d->min_len) - i;
d->offset -= d->min_len;
data += d->base.size() * sizeof(*d->offset);
d->symlen.resize(number<uint16_t, LittleEndian>(data)); data += sizeof(uint16_t);
d->sympat = data;
std::vector<uint8_t> tmp(d->symlen.size());
for (size_t i = 0; i < d->symlen.size(); ++i)
if (!tmp[i])
calc_symlen(d, i, tmp);
return data + 3 * d->symlen.size() + (d->symlen.size() & 1);
}
template<typename T>
void WDLEntry::do_init(T& e, uint8_t* data)
{
PairsData* d;
uint64_t tb_size[8];
enum { Split = 1, HasPawns = 2 };
uint8_t flags = *data++;
int split = (flags & Split);
File maxFile = (flags & HasPawns) ? FILE_D : FILE_A;
assert(hasPawns == !!(flags & HasPawns));
assert(symmetric != !!(flags & Split));
bool pp = (flags & HasPawns) && pawn.pawnCount[1]; // Pawns on both sides
assert(!pp || pawn.pawnCount[0]);
for (File f = FILE_A; f <= maxFile; ++f) {
for (int k = 0; k < 2; k++)
item(e, k, 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 i = 0; i < pieceCount; ++i, ++data) {
item(e, 0, f).precomp->pieces[i] = Piece(*data & 0xF);
item(e, 1, f).precomp->pieces[i] = Piece(*data >> 4);
}
uint8_t pn[] = { uint8_t(piece[0].hasUniquePieces ? 3 : 2), 0 };
for (int i = 0; i < 2; ++i) {
set_norms(item(e, i, f).precomp, pieceCount, (flags & HasPawns) ? pawn.pawnCount : pn);
tb_size[2 * f + i] = set_factors(item(e, i, f), pieceCount, order[i], f);
}
}
data += (uintptr_t)data & 1; // Word alignment
for (File f = FILE_A; f <= maxFile; ++f)
for (int k = 0; k <= split; k++)
data = set_sizes(item(e, k, f).precomp, data, tb_size[2 * f + k]);
for (File f = FILE_A; f <= maxFile; ++f)
for (int k = 0; k <= split; k++) {
(d = item(e, k, f).precomp)->indextable = data;
data += 6ULL * d->num_indices;
}
for (File f = FILE_A; f <= maxFile; ++f)
for (int k = 0; k <= split; k++) {
(d = item(e, k, f).precomp)->sizetable = (uint16_t*)data;
data += 2ULL * d->num_blocks;
}
for (File f = FILE_A; f <= maxFile; ++f)
for (int k = 0; k <= split; k++) {
data = (uint8_t*)(((uintptr_t)data + 0x3F) & ~0x3F); // 64 byte alignment
(d = item(e, k, f).precomp)->data = data;
data += (1ULL << d->blocksize) * d->real_num_blocks;
}
}
bool WDLEntry::init(const std::string& fname)
{
uint8_t* data = TBFile(fname).map(&baseAddress, &mapping, WDL_MAGIC);
if (!data)
return false;
hasPawns ? do_init(pawn, data) : do_init(piece, data);
return true;
}
template<typename T>
void DTZEntry::do_init(T& e, uint8_t* data)
{
PairsData* d;
uint64_t tb_size[8];
enum { Split = 1, HasPawns = 2 };
uint8_t flags = *data++;
File maxFile = (flags & HasPawns) ? FILE_D : FILE_A;
assert(hasPawns == !!(flags & HasPawns));
assert(symmetric != !!(flags & Split));
bool pp = (flags & HasPawns) && pawn.pawnCount[1]; // Pawns on both sides
assert(!pp || pawn.pawnCount[0]);
for (File f = FILE_A; f <= maxFile; ++f) {
item(e, 0, 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 i = 0; i < pieceCount; ++i, ++data)
item(e, 0, f).precomp->pieces[i] = Piece(*data & 0xF);
uint8_t pn[] = { uint8_t(piece.hasUniquePieces ? 3 : 2), 0 };
set_norms(item(e, 0, f).precomp, pieceCount, (flags & HasPawns) ? pawn.pawnCount : pn);
tb_size[f] = set_factors(item(e, 0, f), pieceCount, order[0], f);
}
data += (uintptr_t)data & 1; // Word alignment
for (File f = FILE_A; f <= maxFile; ++f) {
assert(!(*data & 0x80));
item(e, 0, f).flags = *data;
data = set_sizes(item(e, 0, f).precomp, data, tb_size[f]);
}
e.map = data;
for (File f = FILE_A; f <= maxFile; ++f) {
if (item(e, 0, f).flags & 2)
for (int i = 0; i < 4; ++i) { // Sequence like 3,x,x,x,1,x,0,2,x,x
item(e, 0, f).map_idx[i] = (uint16_t)(data - e.map + 1);
data += *data + 1;
}
}
data += (uintptr_t)data & 1;
for (File f = FILE_A; f <= maxFile; ++f) {
(d = item(e, 0, f).precomp)->indextable = data;
data += 6ULL * d->num_indices;
}
for (File f = FILE_A; f <= maxFile; ++f) {
(d = item(e, 0, f).precomp)->sizetable = (uint16_t*)data;
data += 2ULL * d->num_blocks;
}
for (File f = FILE_A; f <= maxFile; ++f) {
data = (uint8_t*)(((uintptr_t)data + 0x3F) & ~0x3F); // 64 byte alignment
(d = item(e, 0, f).precomp)->data = data;
data += (1ULL << d->blocksize) * d->real_num_blocks;
}
}
bool DTZEntry::init(const std::string& fname)
{
uint8_t* data = TBFile(fname).map(&baseAddress, &mapping, DTZ_MAGIC);
if (!data)
return false;
hasPawns ? do_init(pawn, data) : do_init(piece, data);
return true;
}
WDLScore probe_wdl_table(Position& pos, int* success)
{
Key key = pos.material_key();
if (!(pos.pieces() ^ pos.pieces(KING)))
return WDLDraw; // KvK
WDLEntry* entry = WDLHash[key];
if (!entry) {
*success = 0;
return WDLDraw;
}
// Init table at first access attempt. Special care to avoid
// one thread reads ready == 1 while the other is still in
// init(), this could happen due to compiler reordering.
if (!entry->ready.load(std::memory_order_acquire)) {
std::unique_lock<Mutex> lk(TB_mutex);
if (!entry->ready.load(std::memory_order_relaxed)) {
std::string fname = file_name(pos, entry->key != key) + ".rtbw";
if (!entry->init(fname)) {
// Was ptr2->key = 0ULL; Just leave !ptr->ready condition
*success = 0;
return WDLDraw;
}
entry->ready.store(1, std::memory_order_release);
}
}
assert(key == entry->key || !entry->symmetric);
return (WDLScore)probe_table(pos, entry);
}
int probe_dtz_table(const Position& pos, WDLScore wdl, int *success)
{
Key key = pos.material_key();
if (DTZTable.front().key != key && DTZTable.front().key2 != key) {
// Enforce "Most Recently Used" (MRU) order for DTZ list
for (auto it = DTZTable.begin(); it != DTZTable.end(); ++it)
if (it->key == key) {
// Move to front without deleting the element
DTZTable.splice(DTZTable.begin(), DTZTable, it);
break;
}
// If still not found, add a new one
if (DTZTable.front().key != key) {
WDLEntry* wdlEntry = WDLHash[key];
if (!wdlEntry) {
*success = 0;
return 0;
}
StateInfo st;
Position p;
std::string wdlCode = file_name(pos, wdlEntry->key != key);
std::string fname = wdlCode + ".rtbz";
wdlCode.erase(wdlCode.find('v'), 1);
Key wdlKeys[] = { p.set(wdlCode, WHITE, &st).material_key(),
p.set(wdlCode, BLACK, &st).material_key() };
DTZTable.push_front(DTZEntry(*wdlEntry, wdlKeys));
if (!DTZTable.front().init(fname)) {
// In case file is not found init() fails, but we leave
// the entry so to avoid rechecking at every probe (same
// functionality as WDL case).
// FIXME: This is different form original functionality!
/* DTZTable.pop_front(); */
*success = 0;
return 0;
}
// Keep list size within 64 entries
// FIXME remove it when we will know what we are doing
if (DTZTable.size() > 64)
DTZTable.pop_back();
}
}
if (!DTZTable.front().baseAddress) {
*success = 0;
return 0;
}
return probe_table(pos, &DTZTable.front(), wdl, success);
}
// Add underpromotion captures to list of captures.
ExtMove *add_underprom_caps(Position& pos, ExtMove *stack, ExtMove *end)
{
ExtMove *moves, *extra = end;
for (moves = stack; moves < end; ++moves) {
Move move = moves->move;
if (type_of(move) == PROMOTION && !pos.empty(to_sq(move))) {
(*extra++).move = (Move)(move - (1 << 12));
(*extra++).move = (Move)(move - (2 << 12));
(*extra++).move = (Move)(move - (3 << 12));
}
}
return extra;
}
WDLScore probe_ab(Position& pos, WDLScore alpha, WDLScore beta, int *success)
{
WDLScore value;
ExtMove stack[64];
ExtMove *moves, *end;
StateInfo st;
// Generate (at least) all legal non-ep captures including (under)promotions.
// It is OK to generate more, as long as they are filtered out below.
if (!pos.checkers()) {
end = generate<CAPTURES>(pos, stack);
// Since underpromotion captures are not included, we need to add them.
end = add_underprom_caps(pos, stack, end);
} else
end = generate<EVASIONS>(pos, stack);
CheckInfo ci(pos);
for (moves = stack; moves < end; ++moves) {
Move capture = moves->move;
if ( !pos.capture(capture)
|| type_of(capture) == ENPASSANT
|| !pos.legal(capture, ci.pinned))
continue;
pos.do_move(capture, st, pos.gives_check(capture, ci));
value = -probe_ab(pos, -beta, -alpha, success);
pos.undo_move(capture);
if (*success == 0)
return WDLDraw;
if (value > alpha) {
if (value >= beta) {
*success = 2;
return value;
}
alpha = value;
}
}
value = probe_wdl_table(pos, success); // FIXME why this is not at the beginning?
if (*success == 0)
return WDLDraw;
if (alpha >= value) {
*success = 1 + (alpha > 0);
return alpha;
} else {
*success = 1;
return value;
}
}
int probe_dtz(Position& pos, int *success);
// This routine treats a position with en passant captures as one without.
int probe_dtz_no_ep(Position& pos, int *success)
{
int dtz;
WDLScore wdl = probe_ab(pos, WDLLoss, WDLWin, success);
if (!*success)
return 0;
if (wdl == WDLDraw)
return 0;
if (*success == 2)
return wdl == WDLWin ? 1 : 101;
ExtMove stack[MAX_MOVES];
ExtMove *moves, *end = nullptr;
StateInfo st;
CheckInfo ci(pos);
if (wdl > 0) {
// Generate at least all legal non-capturing pawn moves
// including non-capturing promotions.
if (!pos.checkers())
end = generate<NON_EVASIONS>(pos, stack);
else
end = generate<EVASIONS>(pos, stack);
for (moves = stack; moves < end; ++moves) {
Move move = moves->move;
if ( type_of(pos.moved_piece(move)) != PAWN
|| pos.capture(move)
|| !pos.legal(move, ci.pinned))
continue;
pos.do_move(move, st, pos.gives_check(move, ci));
WDLScore v = -probe_ab(pos, WDLLoss, -wdl + WDLCursedWin, success);
pos.undo_move(move);
if (*success == 0) return 0;
if (v == wdl)
return v == WDLWin ? 1 : 101;
}
}
dtz = 1 + probe_dtz_table(pos, wdl, success);
if (*success >= 0) {
if (wdl & 1) dtz += 100;
return wdl >= 0 ? dtz : -dtz;
}
if (wdl > 0) {
int best = 0xffff;
for (moves = stack; moves < end; ++moves) {
Move move = moves->move;
if (pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN
|| !pos.legal(move, ci.pinned))
continue;
pos.do_move(move, st, pos.gives_check(move, ci));
int v = -probe_dtz(pos, success);
pos.undo_move(move);
if (*success == 0)
return 0;
if (v > 0 && v + 1 < best)
best = v + 1;
}
return best;
} else {
int best = -1;
if (!pos.checkers())
end = generate<NON_EVASIONS>(pos, stack);
else
end = generate<EVASIONS>(pos, stack);
for (moves = stack; moves < end; ++moves) {
int v;
Move move = moves->move;
if (!pos.legal(move, ci.pinned))
continue;
pos.do_move(move, st, pos.gives_check(move, ci));
if (st.rule50 == 0) {
if (wdl == -2) v = -1;
else {
v = probe_ab(pos, WDLCursedWin, WDLWin, success);
v = (v == 2) ? 0 : -101;
}
} else {
v = -probe_dtz(pos, success) - 1;
}
pos.undo_move(move);
if (*success == 0)
return 0;
if (v < best)
best = v;
}
return best;
}
}
// Probe the DTZ table for a particular position.
// If *success != 0, 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 probe_dtz(Position& pos, int *success)
{
*success = 1;
int v = probe_dtz_no_ep(pos, success);
if (pos.ep_square() == SQ_NONE)
return v;
if (*success == 0)
return 0;
// Now handle en passant.
int v1 = -3;
ExtMove stack[MAX_MOVES];
ExtMove *moves, *end;
StateInfo st;
if (!pos.checkers())
end = generate<CAPTURES>(pos, stack);
else
end = generate<EVASIONS>(pos, stack);
CheckInfo ci(pos);
for (moves = stack; moves < end; ++moves) {
Move capture = moves->move;
if (type_of(capture) != ENPASSANT
|| !pos.legal(capture, ci.pinned))
continue;
pos.do_move(capture, st, pos.gives_check(capture, ci));
WDLScore v0 = -probe_ab(pos, WDLLoss, WDLWin, success);
pos.undo_move(capture);
if (*success == 0)
return 0;
if (v0 > v1) v1 = v0;
}
if (v1 > -3) {
v1 = wdl_to_dtz[v1 + 2];
if (v < -100) {
if (v1 >= 0)
v = v1;
} else if (v < 0) {
if (v1 >= 0 || v1 < -100)
v = v1;
} else if (v > 100) {
if (v1 > 0)
v = v1;
} else if (v > 0) {
if (v1 == 1)
v = v1;
} else if (v1 >= 0) {
v = v1;
} else {
for (moves = stack; moves < end; ++moves) {
Move move = moves->move;
if (type_of(move) == ENPASSANT) continue;
if (pos.legal(move, ci.pinned))
break;
}
if (moves == end && !pos.checkers()) {
end = generate<QUIETS>(pos, end);
for (; moves < end; ++moves) {
Move move = moves->move;
if (pos.legal(move, ci.pinned))
break;
}
}
if (moves == end)
v = v1;
}
}
return v;
}
} // namespace
void Tablebases::init(const std::string& paths)
{
DTZTable.clear();
WDLTable.clear();
WDLHash.clear();
MaxCardinality = 0;
TBPaths = paths;
if (TBPaths.empty() || TBPaths == "<empty>")
return;
// Fill binomial[] with the Binomial Coefficents using Pascal triangle
Binomial[0][0] = 1;
for (int n = 1; n < 64; n++)
for (int k = 0; k < 6 && k <= n; ++k)
Binomial[k][n] = (k > 0 ? Binomial[k-1][n-1] : 0)
+ (k < n ? Binomial[k][n-1] : 0);
for (int i = 0; i < 5; ++i) {
int k = 0;
for (int j = 1; j <= 4; ++j) {
int s = 0;
for ( ; k < 6 * j; ++k) {
Pawnidx[i][k] = s;
s += Binomial[i][Ptwist[Invflap[k]]];
}
Pfactor[i][j - 1] = s;
}
}
// Compute KK_idx[] that encodes all the 461 possible legal positions of a couple of
// kings where first king is on a1-d1-d4 triangle. When first king is on the a1-d4
// diagonal, second king is assumed not to be above the a1-h8 diagonal.
int code = 0;
std::vector<std::pair<int, Square>> bothOnDiagonal;
for (int idx = 0; idx < 10; idx++)
for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
if (idx == MapA1D1D4[s1] && (idx || s1 == SQ_B1)) // SQ_B1 is mapped to 0
for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
{
if ((StepAttacksBB[KING][s1] | s1) & s2) // Illegal position
KK_idx[idx][s2] = -1;
else if (!off_A1H8(s1) && off_A1H8(s2) > 0)
KK_idx[idx][s2] = -1; // First king on diagonal, second above
else if (!off_A1H8(s1) && !off_A1H8(s2))
bothOnDiagonal.push_back(std::make_pair(idx, s2));
else
KK_idx[idx][s2] = code++;
}
// Legal positions with both kings on diagonal are encoded as last ones
for (auto p : bothOnDiagonal)
KK_idx[p.first][p.second] = code++;
for (PieceType p1 = PAWN; p1 < KING; ++p1) {
WDLHash.insert({KING, p1, KING});
for (PieceType p2 = PAWN; p2 <= p1; ++p2) {
WDLHash.insert({KING, p1, p2, KING});
WDLHash.insert({KING, p1, KING, p2});
for (PieceType p3 = PAWN; p3 < KING; ++p3)
WDLHash.insert({KING, p1, p2, KING, p3});
for (PieceType p3 = PAWN; p3 <= p2; ++p3) {
WDLHash.insert({KING, p1, p2, p3, KING});
for (PieceType p4 = PAWN; p4 <= p3; ++p4)
WDLHash.insert({KING, p1, p2, p3, p4, KING});
for (PieceType p4 = PAWN; p4 < KING; ++p4)
WDLHash.insert({KING, p1, p2, p3, KING, p4});
}
for (PieceType p3 = PAWN; p3 <= p1; ++p3)
for (PieceType p4 = PAWN; p4 <= (p1 == p3 ? p2 : p3); ++p4)
WDLHash.insert({KING, p1, p2, KING, p3, p4});
}
}
std::cerr << "info string Found " << WDLTable.size() << " tablebases" << std::endl;
}
// Probe the WDL table for a particular position.
// If *success != 0, 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, int *success)
{
*success = 1;
WDLScore v = probe_ab(pos, WDLLoss, WDLWin, success);
// If en passant is not possible, we are done.
if (pos.ep_square() == SQ_NONE)
return v;
if (*success == 0)
return WDLDraw;
// Now handle en passant.
WDLScore v1 = WDLScore(-3); // FIXME use a proper enum value here
// Generate (at least) all legal en passant captures.
ExtMove stack[MAX_MOVES];
ExtMove *moves, *end;
StateInfo st;
if (!pos.checkers())
end = generate<CAPTURES>(pos, stack);
else
end = generate<EVASIONS>(pos, stack);
CheckInfo ci(pos);
for (moves = stack; moves < end; ++moves) {
Move capture = moves->move;
if (type_of(capture) != ENPASSANT
|| !pos.legal(capture, ci.pinned))
continue;
pos.do_move(capture, st, pos.gives_check(capture, ci));
WDLScore v0 = -probe_ab(pos, WDLLoss, WDLWin, success);
pos.undo_move(capture);
if (*success == 0)
return WDLDraw;
if (v0 > v1) v1 = v0;
}
if (v1 > -3) {
if (v1 >= v) v = v1;
else if (v == 0) {
// Check whether there is at least one legal non-ep move.
for (moves = stack; moves < end; ++moves) {
Move capture = moves->move;
if (type_of(capture) == ENPASSANT) continue;
if (pos.legal(capture, ci.pinned))
break;
}
if (moves == end && !pos.checkers()) {
end = generate<QUIETS>(pos, end);
for (; moves < end; ++moves) {
Move move = moves->move;
if (pos.legal(move, ci.pinned))
break;
}
}
// If not, then we are forced to play the losing ep capture.
if (moves == end)
v = v1;
}
}
return v;
}
// 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)
{
int success;
int dtz = probe_dtz(pos, &success);
if (!success)
return false;
StateInfo st;
CheckInfo ci(pos);
// Probe each move
for (size_t i = 0; i < rootMoves.size(); ++i) {
Move move = rootMoves[i].pv[0];
pos.do_move(move, st, pos.gives_check(move, ci));
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, &success);
if (v > 0)
++v;
else if (v < 0)
--v;
} else {
v = -probe_wdl(pos, &success);
v = wdl_to_dtz[v + 2];
}
}
pos.undo_move(move);
if (!success)
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->rule50;
// Use 50-move counter to determine whether the root position is
// won, lost or drawn.
int wdl = 0;
if (dtz > 0)
wdl = (dtz + cnt50 <= 100) ? 2 : 1;
else if (dtz < 0)
wdl = (-dtz + cnt50 <= 100) ? -2 : -1;
// 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 == 1 && dtz <= 100)
score = (Value)(((200 - dtz - cnt50) * int(PawnValueEg)) / 200);
else if (wdl == -1 && 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)
{
int success;
WDLScore wdl = Tablebases::probe_wdl(pos, &success);
if (!success)
return false;
score = WDL_to_value[wdl + 2];
StateInfo st;
CheckInfo ci(pos);
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, pos.gives_check(move, ci));
WDLScore v = -Tablebases::probe_wdl(pos, &success);
pos.undo_move(move);
if (!success)
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;
}
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