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chess-engine/base.h

2064 lines
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C
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#pragma once
#include "libc-lite.h"
#include "sys.h"
#include <stdint.h>
#ifndef NDEBUG
#define assert(expr) \
((expr) ? 0 : (__builtin_trap(), 0))
#else
#define assert(...) (void)0
#endif
/* BIT MANIPULATION
* ================ */
static inline uint64_t popcount(uint64_t n)
{
// TODO: check of popcountll support
return (uint64_t)__builtin_popcountll(n);
}
static inline uint64_t ctz(uint64_t n)
{
assert(n != 0);
return (uint64_t)__builtin_ctzll(n);
}
/* BITBOARD AND INDEX DATATYPES AND HELPERS
* ========================================= */
typedef uint64_t bitboard;
#define BITBOARD( \
a8,b8,c8,d8,e8,f8,g8,h8, \
a7,b7,c7,d7,e7,f7,g7,h7, \
a6,b6,c6,d6,e6,f6,g6,h6, \
a5,b5,c5,d5,e5,f5,g5,h5, \
a4,b4,c4,d4,e4,f4,g4,h4, \
a3,b3,c3,d3,e3,f3,g3,h3, \
a2,b2,c2,d2,e2,f2,g2,h2, \
a1,b1,c1,d1,e1,f1,g1,h1) \
(bitboard)\
0b##\
h8##g8##f8##e8##d8##c8##b8##a8##\
h7##g7##f7##e7##d7##c7##b7##a7##\
h6##g6##f6##e6##d6##c6##b6##a6##\
h5##g5##f5##e5##d5##c5##b5##a5##\
h4##g4##f4##e4##d4##c4##b4##a4##\
h3##g3##f3##e3##d3##c3##b3##a3##\
h2##g2##f2##e2##d2##c2##b2##a2##\
h1##g1##f1##e1##d1##c1##b1##a1##\
ULL
typedef uint8_t index;
#define INDEX(n) n##ULL
#define RANK_SHIFT_UP(b, n) ((b) << ((index)(n)*8U))
#define RANK_SHIFT_DOWN(b, n) ((b) >> ((index)(n)*8U))
#define FILE_SHIFT_LEFT(b, n) ((b) >> ((index)(n)*1U))
#define FILE_SHIFT_RIGHT(b, n) ((b) << ((index)(n)*1U))
#define INDEX_SHIFT_UP(i, n) ((i) + ((index)(n)*8U))
#define INDEX_SHIFT_DOWN(i, n) ((i) - ((index)(n)*8U))
#define INDEX_SHIFT_LEFT(i, n) ((i) - ((index)(n)*1U))
#define INDEX_SHIFT_RIGHT(i, n) ((i) + ((index)(n)*1U))
#define FILE_MASK(n) FILE_SHIFT_RIGHT((bitboard)0x0101010101010101ULL, n)
#define RANK_MASK(n) RANK_SHIFT_UP((bitboard)0x00000000000000FFULL, n)
#define INDEX_FROM_RF(rank, file) ((index)(8U*(index)(rank) + (index)(file)))
#define SQ_MASK_FROM_INDEX(idx) (((bitboard)1ULL)<<((index)idx))
#define SQ_MASK_FROM_RF(rank, file) (SQ_MASK_FROM_INDEX(INDEX_FROM_RF(rank,file)))
enum file_index : index {
FILE_INDEX_BEGIN,
FILE_INDEX_A = FILE_INDEX_BEGIN,
FILE_INDEX_B,
FILE_INDEX_C,
FILE_INDEX_D,
FILE_INDEX_E,
FILE_INDEX_F,
FILE_INDEX_G,
FILE_INDEX_H,
FILE_INDEX_COUNT,
};
char const file_index_char[FILE_INDEX_COUNT] = {
[FILE_INDEX_A] = 'A',
[FILE_INDEX_B] = 'B',
[FILE_INDEX_C] = 'C',
[FILE_INDEX_D] = 'D',
[FILE_INDEX_E] = 'E',
[FILE_INDEX_F] = 'F',
[FILE_INDEX_G] = 'G',
[FILE_INDEX_H] = 'H',
};
enum rank_index : index {
RANK_INDEX_BEGIN,
RANK_INDEX_1 = RANK_INDEX_BEGIN,
RANK_INDEX_2,
RANK_INDEX_3,
RANK_INDEX_4,
RANK_INDEX_5,
RANK_INDEX_6,
RANK_INDEX_7,
RANK_INDEX_8,
RANK_INDEX_COUNT,
};
char const rank_index_char[RANK_INDEX_COUNT] = {
[RANK_INDEX_1] = '1',
[RANK_INDEX_2] = '2',
[RANK_INDEX_3] = '3',
[RANK_INDEX_4] = '4',
[RANK_INDEX_5] = '5',
[RANK_INDEX_6] = '6',
[RANK_INDEX_7] = '7',
[RANK_INDEX_8] = '8',
};
#define STR(x) #x
#define SQ_MASK_PREFIX SQ_MASK_
#define SQUARES_LIST_BEGIN \
X(A, 1)
#define SQUARES_LIST \
X(A, 1) \
X(A, 2) \
X(A, 3) \
X(A, 4) \
X(A, 5) \
X(A, 6) \
X(A, 7) \
X(A, 8) \
X(B, 1) \
X(B, 2) \
X(B, 3) \
X(B, 4) \
X(B, 5) \
X(B, 6) \
X(B, 7) \
X(B, 8) \
X(C, 1) \
X(C, 2) \
X(C, 3) \
X(C, 4) \
X(C, 5) \
X(C, 6) \
X(C, 7) \
X(C, 8) \
X(D, 1) \
X(D, 2) \
X(D, 3) \
X(D, 4) \
X(D, 5) \
X(D, 6) \
X(D, 7) \
X(D, 8) \
X(E, 1) \
X(E, 2) \
X(E, 3) \
X(E, 4) \
X(E, 5) \
X(E, 6) \
X(E, 7) \
X(E, 8) \
X(F, 1) \
X(F, 2) \
X(F, 3) \
X(F, 4) \
X(F, 5) \
X(F, 6) \
X(F, 7) \
X(F, 8) \
X(G, 1) \
X(G, 2) \
X(G, 3) \
X(G, 4) \
X(G, 5) \
X(G, 6) \
X(G, 7) \
X(G, 8) \
X(H, 1) \
X(H, 2) \
X(H, 3) \
X(H, 4) \
X(H, 5) \
X(H, 6) \
X(H, 7) \
X(H, 8)
/* define mask constants: SQ_MASK_A1, SQ_MASK_A2, ..., SQ_MASK_H8 */
enum : bitboard {
#define X(file, rank) SQ_MASK_##file##rank = SQ_MASK_FROM_RF(RANK_INDEX_##rank, FILE_INDEX_##file),
SQUARES_LIST
#undef X
};
enum square_index : index {
#define X(file, rank) SQ_INDEX_##file##rank = INDEX_FROM_RF(RANK_INDEX_##rank, FILE_INDEX_##file),
SQUARES_LIST
SQ_INDEX_COUNT,
#undef X
/* define iterator begin enum */
#define X(file, rank) SQ_INDEX_BEGIN = SQ_INDEX_##file##rank,
SQUARES_LIST_BEGIN
#undef X
};
static char* const square_index_display[SQ_INDEX_COUNT] = {
#define X(file, rank) \
[SQ_INDEX_##file##rank] = STR(file##rank),
SQUARES_LIST
#undef X
};
static char* const square_index_str[SQ_INDEX_COUNT] = {
#define X(file, rank) \
[SQ_INDEX_##file##rank] = STR(SQ_INDEX_##file##rank),
SQUARES_LIST
#undef X
};
enum : bitboard {
FILE_MASK_A = FILE_MASK(FILE_INDEX_A),
FILE_MASK_B = FILE_MASK(FILE_INDEX_B),
FILE_MASK_C = FILE_MASK(FILE_INDEX_C),
FILE_MASK_D = FILE_MASK(FILE_INDEX_D),
FILE_MASK_E = FILE_MASK(FILE_INDEX_E),
FILE_MASK_F = FILE_MASK(FILE_INDEX_F),
FILE_MASK_G = FILE_MASK(FILE_INDEX_G),
FILE_MASK_H = FILE_MASK(FILE_INDEX_H),
RANK_MASK_1 = RANK_MASK(RANK_INDEX_1),
RANK_MASK_2 = RANK_MASK(RANK_INDEX_2),
RANK_MASK_3 = RANK_MASK(RANK_INDEX_3),
RANK_MASK_4 = RANK_MASK(RANK_INDEX_4),
RANK_MASK_5 = RANK_MASK(RANK_INDEX_5),
RANK_MASK_6 = RANK_MASK(RANK_INDEX_6),
RANK_MASK_7 = RANK_MASK(RANK_INDEX_7),
RANK_MASK_8 = RANK_MASK(RANK_INDEX_8),
FILE_SHIFT_RIGHT_GUARD_0 = ~0ULL,
FILE_SHIFT_RIGHT_GUARD_1 = ~FILE_MASK_H,
FILE_SHIFT_RIGHT_GUARD_2 = ~(FILE_MASK_G | FILE_MASK_H),
FILE_SHIFT_RIGHT_GUARD_3 = ~(FILE_MASK_F | FILE_MASK_G | FILE_MASK_H),
FILE_SHIFT_RIGHT_GUARD_4 = ~(FILE_MASK_E | FILE_MASK_F | FILE_MASK_G | FILE_MASK_H),
FILE_SHIFT_RIGHT_GUARD_5 = ~(FILE_MASK_D | FILE_MASK_E | FILE_MASK_F | FILE_MASK_G | FILE_MASK_H),
FILE_SHIFT_RIGHT_GUARD_6 = ~(FILE_MASK_C | FILE_MASK_D | FILE_MASK_E | FILE_MASK_F | FILE_MASK_G | FILE_MASK_H),
FILE_SHIFT_RIGHT_GUARD_7 = ~(FILE_MASK_B | FILE_MASK_C | FILE_MASK_D | FILE_MASK_E | FILE_MASK_F | FILE_MASK_G | FILE_MASK_H),
FILE_SHIFT_LEFT_GUARD_0 = ~0ULL,
FILE_SHIFT_LEFT_GUARD_1 = ~FILE_MASK_A,
FILE_SHIFT_LEFT_GUARD_2 = ~(FILE_MASK_A | FILE_MASK_B),
FILE_SHIFT_LEFT_GUARD_3 = ~(FILE_MASK_A | FILE_MASK_B | FILE_MASK_C),
FILE_SHIFT_LEFT_GUARD_4 = ~(FILE_MASK_A | FILE_MASK_B | FILE_MASK_C | FILE_MASK_D),
FILE_SHIFT_LEFT_GUARD_5 = ~(FILE_MASK_A | FILE_MASK_B | FILE_MASK_C | FILE_MASK_D | FILE_MASK_E),
FILE_SHIFT_LEFT_GUARD_6 = ~(FILE_MASK_A | FILE_MASK_B | FILE_MASK_C | FILE_MASK_D | FILE_MASK_E | FILE_MASK_F),
FILE_SHIFT_LEFT_GUARD_7 = ~(FILE_MASK_A | FILE_MASK_B | FILE_MASK_C | FILE_MASK_D | FILE_MASK_E | FILE_MASK_F | FILE_MASK_G),
};
#define _FILE_SHIFT_RIGHT_GUARDED(b, n) \
(((bitboard)(b) & FILE_SHIFT_RIGHT_GUARD_##n) << (index)(n))
#define _FILE_SHIFT_LEFT_GUARDED(b, n) \
(((bitboard)(b) & FILE_SHIFT_LEFT_GUARD_##n) >> (index)(n))
/* FILE_SHIFT_RIGHT_n shifts the bitboard right by n ranks without wrapping */
#define FILE_SHIFT_RIGHT_1(b) _FILE_SHIFT_RIGHT_GUARDED(b, 1)
#define FILE_SHIFT_RIGHT_2(b) _FILE_SHIFT_RIGHT_GUARDED(b, 2)
#define FILE_SHIFT_RIGHT_3(b) _FILE_SHIFT_RIGHT_GUARDED(b, 3)
#define FILE_SHIFT_RIGHT_4(b) _FILE_SHIFT_RIGHT_GUARDED(b, 4)
#define FILE_SHIFT_RIGHT_5(b) _FILE_SHIFT_RIGHT_GUARDED(b, 5)
#define FILE_SHIFT_RIGHT_6(b) _FILE_SHIFT_RIGHT_GUARDED(b, 6)
#define FILE_SHIFT_RIGHT_7(b) _FILE_SHIFT_RIGHT_GUARDED(b, 7)
#define FILE_SHIFT_RIGHT_8(b) _FILE_SHIFT_RIGHT_GUARDED(b, 8)
/* FILE_SHIFT_LEFT_n shifts the bitboard left by n ranks without wrapping */
#define FILE_SHIFT_LEFT_1(b) _FILE_SHIFT_LEFT_GUARDED(b, 1)
#define FILE_SHIFT_LEFT_2(b) _FILE_SHIFT_LEFT_GUARDED(b, 2)
#define FILE_SHIFT_LEFT_3(b) _FILE_SHIFT_LEFT_GUARDED(b, 3)
#define FILE_SHIFT_LEFT_4(b) _FILE_SHIFT_LEFT_GUARDED(b, 4)
#define FILE_SHIFT_LEFT_5(b) _FILE_SHIFT_LEFT_GUARDED(b, 5)
#define FILE_SHIFT_LEFT_6(b) _FILE_SHIFT_LEFT_GUARDED(b, 6)
#define FILE_SHIFT_LEFT_7(b) _FILE_SHIFT_LEFT_GUARDED(b, 7)
#define FILE_SHIFT_LEFT_8(b) _FILE_SHIFT_LEFT_GUARDED(b, 8)
/* RANK_SHIFT_UP_n shifts the bitboard up by n ranks without wrapping */
#define RANK_SHIFT_UP_1(b) RANK_SHIFT_UP(b, 1)
#define RANK_SHIFT_UP_2(b) RANK_SHIFT_UP(b, 2)
#define RANK_SHIFT_UP_3(b) RANK_SHIFT_UP(b, 3)
#define RANK_SHIFT_UP_4(b) RANK_SHIFT_UP(b, 4)
#define RANK_SHIFT_UP_5(b) RANK_SHIFT_UP(b, 5)
#define RANK_SHIFT_UP_6(b) RANK_SHIFT_UP(b, 6)
#define RANK_SHIFT_UP_7(b) RANK_SHIFT_UP(b, 7)
#define RANK_SHIFT_UP_8(b) RANK_SHIFT_UP(b, 8)
/* RANK_SHIFT_DOWN_n shifts the bitboard down by n ranks without wrapping */
#define RANK_SHIFT_DOWN_1(b) RANK_SHIFT_DOWN(b, 1)
#define RANK_SHIFT_DOWN_2(b) RANK_SHIFT_DOWN(b, 2)
#define RANK_SHIFT_DOWN_3(b) RANK_SHIFT_DOWN(b, 3)
#define RANK_SHIFT_DOWN_4(b) RANK_SHIFT_DOWN(b, 4)
#define RANK_SHIFT_DOWN_5(b) RANK_SHIFT_DOWN(b, 5)
#define RANK_SHIFT_DOWN_6(b) RANK_SHIFT_DOWN(b, 6)
#define RANK_SHIFT_DOWN_7(b) RANK_SHIFT_DOWN(b, 7)
#define RANK_SHIFT_DOWN_8(b) RANK_SHIFT_DOWN(b, 8)
/*
* Player
* ===========
* */
enum player : uint8_t {
PLAYER_BEGIN,
PLAYER_WHITE = PLAYER_BEGIN,
PLAYER_BLACK,
PLAYER_COUNT,
};
static inline enum player opposite_player(enum player p)
{
return (p == PLAYER_WHITE ? PLAYER_BLACK : PLAYER_WHITE);
}
static char const* player_str[PLAYER_COUNT] = {
[PLAYER_WHITE] = "PLAYER_WHITE",
[PLAYER_BLACK] = "PLAYER_BLACK",
};
/*
* Piece
* ===========
* */
/* enum value white char white unicode black char black unicode */
#define PIECES \
X(PIECE_PAWN, 1.0, 'P', 0x2659, 'p', 0x265F) \
X(PIECE_KING, 5.0, 'K', 0x2654, 'k', 0x265A) \
X(PIECE_QUEEN, 9.0, 'Q', 0x2655, 'q', 0x265B) \
X(PIECE_BISHOP, 3.0, 'B', 0x2657, 'b', 0x265D) \
X(PIECE_ROOK, 5.0, 'R', 0x2656, 'r', 0x265C) \
X(PIECE_KNIGHT, 3.0, 'N', 0x2658, 'n', 0x265E)
enum piece : uint8_t {
#define X(e, v, wc, wu, bc, bu) e,
PIECES
PIECE_COUNT,
PIECE_BEGIN = 0,
#undef X
};
static double piece_value[PIECE_COUNT] = {
#define X(e, v, wc, wu, bc, bu) [e] = v,
PIECES
#undef X
};
static char const* piece_str[PIECE_COUNT] = {
#define X(e, v, wc, wu, bc, bu) [e] = STR(e),
PIECES
#undef X
};
struct piece_player {enum piece piece; enum player player;} const piece_and_player_from_char[256] = {
#define X(e, v, wc, wu, bc, bu) \
[(uint8_t)bc] = {.piece = e, .player = PLAYER_BLACK}, \
[(uint8_t)wc] = {.piece = e, .player = PLAYER_WHITE},
PIECES
#undef X
};
static char const piece_char[PLAYER_COUNT][PIECE_COUNT] = {
[PLAYER_WHITE] = {
#define X(e, v, wc, wu, bc, bu) [e] = wc,
PIECES
#undef X
},
[PLAYER_BLACK] = {
#define X(e, v, wc, wu, bc, bu) [e] = bc,
PIECES
#undef X
}
};
static int const piece_unicode[PLAYER_COUNT][PIECE_COUNT] = {
[PLAYER_WHITE] = {
#define X(e, v, wc, wu, bc, bu) [e] = wu,
PIECES
#undef X
},
[PLAYER_BLACK] = {
#define X(e, v, wc, wu, bc, bu) [e] = bu,
PIECES
#undef X
}
};
/* MISC
* ============*/
/* TODO: Put these struct definition in a sensible category */
/* `struct magic` is used by magic bitboard lookups, see
* rook_attacks_from_index and bishop_attacks_from_index */
struct magic {
bitboard mask;
bitboard magic;
};
/* BITBOARD PRIMITIVES
* ======================== */
static enum square_index bitboard_lsb(bitboard p)
{
return (enum square_index)__builtin_ffsll((int64_t)p) - 1;
}
static enum square_index bitboard_pop_lsb(bitboard* p)
{
index const lsb = bitboard_lsb(*p);
*p &= ~(1ULL<<(lsb));
return lsb;
}
static uint64_t bitboard_popcount(bitboard b)
{
return (uint64_t)__builtin_popcountll(b);
}
static inline enum file_index index_to_file(enum square_index p)
{
return p % 8ULL;
}
static inline enum rank_index index_to_rank(enum square_index p)
{
return p / 8ULL;
}
static bitboard cardinals_from_index(enum square_index p)
{
/* might benefit from a lookup table */
return (FILE_MASK(index_to_file(p)) | RANK_MASK(index_to_rank(p)))
& ~SQ_MASK_FROM_INDEX(p);
}
static bitboard diagonals_from_index(enum square_index sq)
{
enum rank_index const rank = index_to_rank(sq);
enum file_index const file = index_to_file(sq);
bitboard mask = 0ULL;
/* Ensure signed-underflow detection rules match your style */
_Static_assert(((enum rank_index)-1) > 0, "rank_index must be unsigned");
_Static_assert(((enum file_index)-1) > 0, "file_index must be unsigned");
enum rank_index r;
enum file_index f;
for (r = rank+1, f = file+1;
r <= RANK_INDEX_8 && f <= FILE_INDEX_H;
++r, ++f)
{
mask |= SQ_MASK_FROM_RF(r, f);
}
/* NW (rank+1, file-1) */
for (r = rank+1, f = file-1;
r <= RANK_INDEX_8 && f <= FILE_INDEX_H;
++r, --f)
{
mask |= SQ_MASK_FROM_RF(r, f);
}
/* SE (rank-1, file+1) */
for (r = rank-1, f = file+1;
r <= RANK_INDEX_8 && f <= FILE_INDEX_H;
--r, ++f)
{
mask |= SQ_MASK_FROM_RF(r, f);
}
/* SW (rank-1, file-1) */
for (r = rank-1, f = file-1;
r <= RANK_INDEX_8 && f <= FILE_INDEX_H;
--r, --f)
{
mask |= SQ_MASK_FROM_RF(r, f);
}
return mask;
}
/* PIECE ATTACKS
* ==================
*
* All piece attack functions rely on the caller masking their own pieces.
* e.g. `knight_attacks(knights) & ~our_occupied`
* */
static bitboard knight_attacks(bitboard p)
{
bitboard const l1 = FILE_SHIFT_RIGHT_1(p /*& ~FILE_MASK_H*/);
bitboard const l2 = FILE_SHIFT_RIGHT_2(p /*& ~(FILE_MASK_G | FILE_MASK_H)*/);
bitboard const r1 = FILE_SHIFT_LEFT_1 (p /*& ~FILE_MASK_A*/);
bitboard const r2 = FILE_SHIFT_LEFT_2 (p /*& ~(FILE_MASK_A | FILE_MASK_B)*/);
bitboard const h1 = l1 | r1;
bitboard const h2 = l2 | r2;
return RANK_SHIFT_UP_2(h1)
| RANK_SHIFT_DOWN_2(h1)
| RANK_SHIFT_UP_1(h2)
| RANK_SHIFT_DOWN_1(h2);
}
static bitboard rook_attacks_from_index(enum square_index sq, bitboard occ)
{
#ifdef CODEGEN
enum rank_index const rank = index_to_rank(sq);
enum file_index const file = index_to_file(sq);
bitboard atk = 0ULL;
/* following loops assume rank and file types are unsigned, which relies on C23 enums */
_Static_assert(((enum rank_index)-1) > 0, "rank_index must be unsigned");
_Static_assert(((enum file_index)-1) > 0, "file_index must be unsigned");
for (enum rank_index walk_rank = rank+1; walk_rank <= RANK_INDEX_8; ++walk_rank) {
bitboard const sq = SQ_MASK_FROM_RF(walk_rank, file);
atk |= sq;
if (occ & sq) {
break;
}
}
for (enum rank_index walk_rank = rank-1; walk_rank <= RANK_INDEX_8; --walk_rank) {
bitboard const sq = SQ_MASK_FROM_RF(walk_rank, file);
atk |= sq;
if (occ & sq) {
break;
}
}
for (enum file_index walk_file = file+1; walk_file <= FILE_INDEX_H; ++walk_file) {
bitboard const sq = SQ_MASK_FROM_RF(rank, walk_file);
atk |= sq;
if (occ & sq) {
break;
}
}
for (enum file_index walk_file = file-1; walk_file <= FILE_INDEX_H; --walk_file) {
bitboard const sq = SQ_MASK_FROM_RF(rank, walk_file);
atk |= sq;
if (occ & sq) {
break;
}
}
return atk;
#else
#if ! __has_include("mbb_rook.h")
#error "compile with -DCODEGEN and run once to generate required header files"
#else
/* defines
- `mbb_rook[SQ_INDEX_COUNT]`
- `bitboard rook_attacks[SQ_INDEX_COUNT][1<<12ULL] */
#include "mbb_rook.h"
struct magic const m = mbb_rook[sq];
occ &= m.mask;
occ *= m.magic;
occ >>= (64ULL-12ULL);
assert(rook_attacks[sq][occ] != SQ_MASK_FROM_INDEX(sq));
return rook_attacks[sq][occ];
#endif
#endif
}
static bitboard rook_attacks(bitboard p, bitboard occ)
{
bitboard b = 0ULL;
while (p) {
index const lsb = bitboard_pop_lsb(&p);
b |= rook_attacks_from_index(lsb, occ);
}
return b;
}
static bitboard bishop_attacks_from_index(enum square_index sq, bitboard occ)
{
#ifdef CODEGEN
enum rank_index const rank = index_to_rank(sq);
enum file_index const file = index_to_file(sq);
bitboard atk = 0ULL;
/* following loops assume rank and file types are unsigned, which relies on C23 enums */
_Static_assert(((enum rank_index)-1) > 0, "rank_index must be unsigned");
_Static_assert(((enum file_index)-1) > 0, "file_index must be unsigned");
enum rank_index walk_rank;
enum file_index walk_file;
for (walk_rank = rank+1, walk_file = file+1;
walk_rank <= RANK_INDEX_8 && walk_file <= FILE_INDEX_H;
++walk_rank, ++walk_file) {
bitboard const sq = SQ_MASK_FROM_RF(walk_rank, walk_file);
atk |= sq;
if (occ & sq) {
break;
}
}
for (walk_rank = rank+1, walk_file = file-1;
walk_rank <= RANK_INDEX_8 && walk_file <= FILE_INDEX_H;
++walk_rank, --walk_file) {
bitboard const sq = SQ_MASK_FROM_RF(walk_rank, walk_file);
atk |= sq;
if (occ & sq) {
break;
}
}
for (walk_rank = rank-1, walk_file = file+1;
walk_rank <= RANK_INDEX_8 && walk_file <= FILE_INDEX_H;
--walk_rank, ++walk_file) {
bitboard const sq = SQ_MASK_FROM_RF(walk_rank, walk_file);
atk |= sq;
if (occ & sq) {
break;
}
}
for (walk_rank = rank-1, walk_file = file-1;
walk_rank <= RANK_INDEX_8 && walk_file <= FILE_INDEX_H;
--walk_rank, --walk_file) {
bitboard const sq = SQ_MASK_FROM_RF(walk_rank, walk_file);
atk |= sq;
if (occ & sq) {
break;
}
}
return atk;
#else
#if ! __has_include("mbb_bishop.h")
#error "compile with -DCODEGEN and run once to generate required header files"
#else
/* defines
- `mbb_bishop[SQ_INDEX_COUNT]`
- `bitboard bishop_attacks[SQ_INDEX_COUNT][1<<9ULL] */
#include "mbb_bishop.h"
assert(sq < SQ_INDEX_COUNT);
struct magic const m = mbb_bishop[sq];
occ &= m.mask;
occ *= m.magic;
occ >>= (64ULL-9ULL);
return bishop_attacks[sq][occ];
#endif
#endif
}
static bitboard bishop_attacks(bitboard p, bitboard occ)
{
bitboard b = 0ULL;
while (p) {
index const lsb = bitboard_pop_lsb(&p);
b |= bishop_attacks_from_index(lsb, occ);
}
return b;
}
static bitboard queen_attacks_from_index(enum square_index sq, bitboard occ)
{
return bishop_attacks_from_index(sq, occ) | rook_attacks_from_index(sq, occ);
}
static bitboard queen_attacks(bitboard p, bitboard occ)
{
bitboard b = 0ULL;
while (p) {
index const lsb = bitboard_pop_lsb(&p);
b |= queen_attacks_from_index(lsb, occ);
}
return b;
}
static inline bitboard pawn_moves_white(bitboard p, bitboard empty)
{
/* Assumptions:
- empty = ~(black_occupied | white_occupied);
*/
bitboard const single_push = RANK_SHIFT_UP_1(p) & empty;
bitboard const double_push =
RANK_SHIFT_UP_1(single_push & RANK_MASK_3) & empty;
return (single_push | double_push);
}
static inline bitboard pawn_attacks_white(bitboard p)
{
bitboard const up = RANK_SHIFT_UP_1(p);
bitboard const captures_right = FILE_SHIFT_RIGHT_1(up);
bitboard const captures_left = FILE_SHIFT_LEFT_1(up);
return (captures_right | captures_left);
}
static inline bitboard pawn_moves_black(bitboard p, bitboard empty)
{
/* Assumptions:
- empty = ~(black_occupied | white_occupied);
*/
bitboard const single_push = RANK_SHIFT_DOWN_1(p) & empty;
bitboard const double_push =
RANK_SHIFT_DOWN_1(single_push & RANK_MASK_6) & empty;
return (single_push | double_push);
}
static inline bitboard pawn_attacks_black(bitboard p)
{
bitboard const down = RANK_SHIFT_DOWN_1(p);
bitboard const captures_right = FILE_SHIFT_RIGHT_1(down);
bitboard const captures_left = FILE_SHIFT_LEFT_1(down);
return (captures_right | captures_left);
}
/* temporary solution, annoying branch */
static inline bitboard pawn_moves_dispatch(bitboard p, bitboard empty, enum player attacker)
{
if (attacker == PLAYER_WHITE) {
return pawn_moves_white(p, empty);
} else {
return pawn_moves_black(p, empty);
}
}
/* temporary solution, annoying branch */
static inline bitboard pawn_attacks_dispatch(bitboard p, enum player attacker)
{
if (attacker == PLAYER_WHITE) {
return pawn_attacks_white(p);
} else {
return pawn_attacks_black(p);
}
}
static bitboard king_attacks(bitboard sq)
{
/* potential untested improvements:
* - lookup table
* - union of three files, three ranks and ~sq */
bitboard const n = RANK_SHIFT_UP_1(sq);
bitboard const s = RANK_SHIFT_DOWN_1(sq);
bitboard const w = FILE_SHIFT_LEFT_1(sq);
bitboard const e = FILE_SHIFT_RIGHT_1(sq);
bitboard const nw = FILE_SHIFT_LEFT_1(n);
bitboard const ne = FILE_SHIFT_RIGHT_1(n);
bitboard const sw = FILE_SHIFT_LEFT_1(s);
bitboard const se = FILE_SHIFT_RIGHT_1(s);
return (n | s | w | e | nw | ne | sw | se);
}
static bitboard piece_attacks(enum piece piece,
enum player player,
bitboard ep_targets,
bitboard p,
bitboard occ,
bitboard their_occ)
{
switch (piece) {
case PIECE_PAWN: {
return pawn_attacks_dispatch(p, player) & (their_occ | ep_targets);
} break;
case PIECE_KNIGHT: {
return knight_attacks(p);
} break;
case PIECE_BISHOP: {
return bishop_attacks(p, occ);
} break;
case PIECE_ROOK: {
return rook_attacks(p, occ);
} break;
case PIECE_QUEEN: {
return queen_attacks(p, occ);
} break;
case PIECE_KING: {
return king_attacks(p);
} break;
#ifndef NDEBUG
default: {
__builtin_trap();
__builtin_unreachable();
} break;
#endif
}
}
static bitboard piece_moves(enum piece piece,
enum player player,
bitboard ep_targets,
bitboard p,
bitboard occ,
bitboard their_occ)
{
bitboard x = 0ULL;
if (piece == PIECE_PAWN) {
x |= pawn_moves_dispatch(p, ~occ, player);
}
x |= piece_attacks(piece, player, ep_targets, p, occ, their_occ);
return x;
}
/* BOARD
* ================= */
enum castle_direction {
CASTLE_BEGIN,
CASTLE_KINGSIDE = CASTLE_BEGIN,
CASTLE_QUEENSIDE,
CASTLE_COUNT,
};
enum {
MATTR_CAPTURE = 1<<0,
MATTR_PROMOTE = 1<<1,
MATTR_CHECK = 1<<2,
MATTR_CASTLE_KINGSIDE = 1<<3,
MATTR_CASTLE_QUEENSIDE = 1<<4,
};
struct move {
index from;
index to;
uint8_t attr;
#define APPEAL_MAX UINT8_MAX
uint8_t appeal;
};
_Static_assert(sizeof(struct move) == 4,
"this static assert is here to check when sizeof(move) changes");
struct search_option {
/* TODO: optimize order of fields and size */
double score;
struct move move;
uint64_t hash;
uint8_t init : 1;
enum tt_flag {TT_EXACT, TT_LOWER, TT_UPPER} flag : 3;
int8_t depth : 4;
};
#define TT_ADDRESS_BITS 24
#define TT_ENTRIES (1ULL<<TT_ADDRESS_BITS)
struct tt {
struct search_option* entries/*[TT_ENTRIES]*/; /* must be initialized somewhere */
#ifndef NDEBUG
/* stats */
uint64_t collisions;
uint64_t hits;
uint64_t probes;
uint64_t overwritten;
uint64_t insertions;
#endif
};
struct board {
struct pos {
bitboard pieces[PLAYER_COUNT][PIECE_COUNT];
enum player player;
bool castling_illegal[PLAYER_COUNT][CASTLE_COUNT];
bitboard ep_targets;
bitboard occupied[PLAYER_COUNT];
int halfmoves; /* FIXME: this duplicates the hist.length value */
int fullmoves;
uint64_t hash;
} pos;
struct tt tt;
/* used for repeated board state detection only */
struct history {
struct pos items[64];
size_t length;
} hist;
/* Used only for square->piece lookups, not central to logic. Does not
* store which player owns the square piece, and checking non-occupied
* squares is undefined
*
* TODO: make mailbox smaller, only 3 bits are needed per piece
* */
enum piece mailbox[SQ_INDEX_COUNT];
};
static void move_compute_appeal(struct move* m,
struct pos const* pos,
enum player us,
enum piece mailbox[restrict static SQ_INDEX_COUNT])
{
enum player them = opposite_player(us);
/* MVV-LVA: https://www.chessprogramming.org/MVV-LVA */
enum piece const atk = mailbox[m->from];
uint8_t n = 1;
if (SQ_MASK_FROM_INDEX(m->to) & pos->occupied[them]) {
n += (uint8_t)piece_value[mailbox[m->to]];
}
m->appeal = 16*n - (uint8_t)piece_value[atk];
}
#define BOARD_INIT (struct board) { \
.pos = { \
.fullmoves = 1, \
.pieces = { \
[PLAYER_WHITE] = { \
[PIECE_PAWN] = RANK_MASK_2, \
[PIECE_ROOK] = SQ_MASK_A1 | SQ_MASK_H1, \
[PIECE_KNIGHT] = SQ_MASK_B1 | SQ_MASK_G1, \
[PIECE_BISHOP] = SQ_MASK_C1 | SQ_MASK_F1, \
[PIECE_QUEEN] = SQ_MASK_D1, \
[PIECE_KING] = SQ_MASK_E1, \
}, \
[PLAYER_BLACK] = { \
[PIECE_PAWN] = RANK_MASK_7, \
[PIECE_ROOK] = SQ_MASK_A8 | SQ_MASK_H8, \
[PIECE_KNIGHT] = SQ_MASK_B8 | SQ_MASK_G8, \
[PIECE_BISHOP] = SQ_MASK_C8 | SQ_MASK_F8, \
[PIECE_QUEEN] = SQ_MASK_D8, \
[PIECE_KING] = SQ_MASK_E8, \
} \
}, \
.occupied = { \
[PLAYER_WHITE] = \
RANK_MASK_2 | SQ_MASK_A1 | SQ_MASK_H1 | \
SQ_MASK_B1 | SQ_MASK_G1 | SQ_MASK_C1 | \
SQ_MASK_F1 | SQ_MASK_D1 | SQ_MASK_E1, \
[PLAYER_BLACK] = \
RANK_MASK_7 | SQ_MASK_A8 | SQ_MASK_H8 | \
SQ_MASK_B8 | SQ_MASK_G8| SQ_MASK_C8 | \
SQ_MASK_F8| SQ_MASK_D8| SQ_MASK_E8, \
}, \
.hash = ~0ULL, \
}, \
.mailbox = { \
[SQ_INDEX_A1] = PIECE_ROOK, \
[SQ_INDEX_B1] = PIECE_KNIGHT, \
[SQ_INDEX_C1] = PIECE_BISHOP, \
[SQ_INDEX_D1] = PIECE_QUEEN, \
[SQ_INDEX_E1] = PIECE_KING, \
[SQ_INDEX_F1] = PIECE_BISHOP, \
[SQ_INDEX_G1] = PIECE_KNIGHT, \
[SQ_INDEX_H1] = PIECE_ROOK, \
[SQ_INDEX_A2] = PIECE_PAWN, \
[SQ_INDEX_B2] = PIECE_PAWN, \
[SQ_INDEX_C2] = PIECE_PAWN, \
[SQ_INDEX_D2] = PIECE_PAWN, \
[SQ_INDEX_E2] = PIECE_PAWN, \
[SQ_INDEX_F2] = PIECE_PAWN, \
[SQ_INDEX_G2] = PIECE_PAWN, \
[SQ_INDEX_H2] = PIECE_PAWN, \
[SQ_INDEX_A7] = PIECE_PAWN, \
[SQ_INDEX_B7] = PIECE_PAWN, \
[SQ_INDEX_C7] = PIECE_PAWN, \
[SQ_INDEX_D7] = PIECE_PAWN, \
[SQ_INDEX_E7] = PIECE_PAWN, \
[SQ_INDEX_F7] = PIECE_PAWN, \
[SQ_INDEX_G7] = PIECE_PAWN, \
[SQ_INDEX_H7] = PIECE_PAWN, \
[SQ_INDEX_A8] = PIECE_ROOK, \
[SQ_INDEX_B8] = PIECE_KNIGHT, \
[SQ_INDEX_C8] = PIECE_BISHOP, \
[SQ_INDEX_D8] = PIECE_QUEEN, \
[SQ_INDEX_E8] = PIECE_KING, \
[SQ_INDEX_F8] = PIECE_BISHOP, \
[SQ_INDEX_G8] = PIECE_KNIGHT, \
[SQ_INDEX_H8] = PIECE_ROOK, \
}, \
.hist = {0}, \
}
static bool board_load_fen_unsafe(struct board* b, char const* fen_str)
{
/* TODO: this function is not tested for malicious/corrupted inputs */
struct {
char const* buf;
size_t i;
size_t len;
} fen = {
.buf = fen_str,
.i = 0,
.len = strlen(fen_str),
};
#define BUF_GETCHAR(x) (assert(x.i < x.len), x.buf[x.i++])
my_memset(&b->pos, 0, sizeof b->pos);
b->pos.hash = ~0ULL;
for (enum rank_index ri = RANK_INDEX_8; ri < RANK_INDEX_COUNT; --ri) {
for (enum file_index fi = FILE_INDEX_BEGIN; fi < FILE_INDEX_COUNT; ++fi) {
char const ch = BUF_GETCHAR(fen);
if (my_isdigit(ch)) {
if (ch == '0') {
__builtin_trap();
}
fi += ch - '0' - 1;
} else {
struct piece_player const p = piece_and_player_from_char[(uint8_t)ch];
bitboard const sq_mask = SQ_MASK_FROM_RF(ri, fi);
b->pos.pieces[p.player][p.piece] |= sq_mask;
b->pos.occupied[p.player] |= sq_mask;
b->mailbox[INDEX_FROM_RF(ri, fi)] = p.piece;
}
}
(void)BUF_GETCHAR(fen); /* discard '/' or ' ' */
}
{ /* active color */
char const ch = BUF_GETCHAR(fen);
if (ch == 'w') {
b->pos.player = PLAYER_WHITE;
} else if (ch == 'b') {
b->pos.player = PLAYER_BLACK;
} else {
__builtin_trap();
}
}
{ /* castling */
char ch = BUF_GETCHAR(fen);
if (ch != ' ') {
__builtin_trap();
}
b->pos.castling_illegal[PLAYER_WHITE][CASTLE_KINGSIDE] = true;
b->pos.castling_illegal[PLAYER_WHITE][CASTLE_QUEENSIDE] = true;
b->pos.castling_illegal[PLAYER_BLACK][CASTLE_KINGSIDE] = true;
b->pos.castling_illegal[PLAYER_BLACK][CASTLE_QUEENSIDE] = true;
do {
ch = BUF_GETCHAR(fen);
switch (ch) {
case 'K': b->pos.castling_illegal[PLAYER_WHITE][CASTLE_KINGSIDE] = false; break;
case 'Q': b->pos.castling_illegal[PLAYER_WHITE][CASTLE_QUEENSIDE] = false; break;
case 'k': b->pos.castling_illegal[PLAYER_BLACK][CASTLE_KINGSIDE] = false; break;
case 'q': b->pos.castling_illegal[PLAYER_BLACK][CASTLE_QUEENSIDE] = false; break;
case ' ': break;
case '-': break;
default: {
__builtin_trap();
} break;
}
} while (ch != ' ');
}
{ /* en passent */
char const ch = BUF_GETCHAR(fen);
if (ch != '-') {
__builtin_trap();
}
}
{ /* halfmoves */
b->pos.halfmoves = 0;
char ch = BUF_GETCHAR(fen);
while (ch != ' ') {
b->pos.halfmoves *= 10;
b->pos.halfmoves += ch-'0';
ch = BUF_GETCHAR(fen);
}
}
{ /* fullmoves */
b->pos.fullmoves = 0;
char ch = BUF_GETCHAR(fen);
while (ch != ' ') {
b->pos.fullmoves *= 10;
b->pos.fullmoves += ch-'0';
ch = BUF_GETCHAR(fen);
}
}
#undef BUF_GETCHAR
return true;
}
static bitboard all_threats_from_player(struct pos const * pos, enum player player)
{
bitboard const occ = pos->occupied[PLAYER_WHITE] | pos->occupied[PLAYER_BLACK];
bitboard const* p = pos->pieces[player];
bitboard t = 0ULL;
t |= pawn_attacks_dispatch(p[PIECE_PAWN], player);
t |= knight_attacks(p[PIECE_KNIGHT]);
t |= bishop_attacks(p[PIECE_BISHOP], occ);
t |= rook_attacks(p[PIECE_ROOK], occ);
t |= queen_attacks(p[PIECE_QUEEN], occ);
t |= king_attacks(p[PIECE_KING]);
return t;
}
static bitboard between_mask(enum square_index a, enum square_index b)
{
#ifdef CODEGEN
enum rank_index const ra = index_to_rank(a);
enum file_index const fa = index_to_file(a);
enum rank_index const rb = index_to_rank(b);
enum file_index const fb = index_to_file(b);
/* directional differences */
int const dr = (int)rb - (int)ra;
int const df = (int)fb - (int)fa;
int step_r = 0;
int step_f = 0;
if (df == 0 && dr != 0) {
step_r = (dr > 0) ? 1 : -1;
step_f = 0;
}
else if (dr == 0 && df != 0) {
step_r = 0;
step_f = (df > 0) ? 1 : -1;
}
else if (dr != 0 && (dr > 0 ? dr : -dr) == (df > 0 ? df : -df)) {
step_r = (dr > 0) ? 1 : -1;
step_f = (df > 0) ? 1 : -1;
}
else {
return 0ULL;
}
bitboard mask = 0ULL;
enum rank_index r = (enum rank_index)((int)ra + step_r);
enum file_index f = (enum file_index)((int)fa + step_f);
while (r != rb || f != fb) {
mask |= SQ_MASK_FROM_RF(r, f);
r = (enum rank_index)((int)r + step_r);
f = (enum file_index)((int)f + step_f);
}
return mask;
#else
#if ! __has_include("between_lookup.h")
#error "compile codegen.c and run once to generate required header files"
#else
/* defines static between_lookup[SQUARE_INDEX_COUNT][SQUARE_INDEX_COUNT] */
#include "between_lookup.h"
return between_lookup[a][b];
#endif
#endif
}
static bitboard attacks_to(struct pos const* pos,
bitboard target_square,
bitboard pretend_occupied,
bitboard pretend_empty)
{
bitboard const occ_orig = pos->occupied[PLAYER_WHITE] | pos->occupied[PLAYER_BLACK];
bitboard const occ = (occ_orig & ~pretend_empty) | pretend_occupied;
bitboard const* pw = pos->pieces[PLAYER_WHITE];
bitboard const* pb = pos->pieces[PLAYER_BLACK];
bitboard const wps = pw[PIECE_PAWN];
bitboard const bps = pb[PIECE_PAWN];
bitboard const ns = (pw[PIECE_KNIGHT]
| pb[PIECE_KNIGHT])
;
bitboard const ks = (pw[PIECE_KING]
| pb[PIECE_KING])
;
bitboard const qs = (pw[PIECE_QUEEN]
| pb[PIECE_QUEEN])
;
bitboard const qrs = (pw[PIECE_ROOK]
| pb[PIECE_ROOK]
| qs)
;
bitboard const qbs = (pw[PIECE_BISHOP]
| pb[PIECE_BISHOP]
| qs)
;
enum square_index target_index = bitboard_lsb(target_square);
return ((bps & pawn_attacks_white(target_square))
| (wps & pawn_attacks_black(target_square))
| (ns & knight_attacks(target_square))
| (qbs & bishop_attacks_from_index(target_index, occ))
| (qrs & rook_attacks_from_index(target_index, occ))
| (ks & king_attacks(target_square)))
& ~pretend_occupied;
}
#define MOVE_CASTLE_KINGSIDE_WHITE (struct move) \
{.from = SQ_INDEX_E1, .to = SQ_INDEX_G1, .attr = MATTR_CASTLE_KINGSIDE}
#define MOVE_CASTLE_QUEENSIDE_WHITE \
(struct move){.from = SQ_INDEX_E1, .to = SQ_INDEX_C1, .attr = MATTR_CASTLE_QUEENSIDE}
#define MOVE_CASTLE_KINGSIDE_BLACK (struct move) \
{.from = SQ_INDEX_E8, .to = SQ_INDEX_G8, .attr = MATTR_CASTLE_KINGSIDE}
#define MOVE_CASTLE_QUEENSIDE_BLACK \
(struct move){.from = SQ_INDEX_E8, .to = SQ_INDEX_C8, .attr = MATTR_CASTLE_QUEENSIDE}
struct move move_make(struct pos const* pos, enum piece piece, index from, index to, uint8_t add_attr)
{
enum player const us = pos->player;
enum player const them = opposite_player(us);
bitboard const their_occ = pos->occupied[them];
bitboard const tomask = SQ_MASK_FROM_INDEX(to);
bitboard const finishline = (us == PLAYER_WHITE ? RANK_MASK_8 : RANK_MASK_1);
uint8_t attr = 0ULL;
#define MASK_IF8(x) ((~(uint8_t)0U) + (uint8_t)!(x))
attr |= MATTR_CAPTURE & MASK_IF8(tomask & their_occ);
attr |= MATTR_CAPTURE & MASK_IF8((piece == PIECE_PAWN) && tomask & pos->ep_targets);
attr |= MATTR_PROMOTE & MASK_IF8((piece == PIECE_PAWN) && (tomask & finishline));
attr |= add_attr;
#undef MASK_IF8
return (struct move){.from = from, .to = to, .attr = attr};
}
#define MOVE_MAX 128
static void all_moves_from_piece(struct pos const* restrict pos,
enum piece piece,
enum player us,
enum square_index from,
bitboard allowed,
size_t* restrict out_count,
struct move out[restrict static MOVE_MAX])
{
/* TODO: this function is terrible, needs major rework
*
* instead of dispatching to a generalized `piece_moves`, this can be specialized for each
* piece
* */
assert(piece != PIECE_KING);
enum player const them = opposite_player(us);
bitboard const our_occ = pos->occupied[us];
bitboard const their_occ = pos->occupied[them];
bitboard const all_occ = pos->occupied[PLAYER_WHITE] | pos->occupied[PLAYER_BLACK];
bitboard const from_mask = SQ_MASK_FROM_INDEX(from);
bitboard move_mask =
piece_moves(piece, us, pos->ep_targets, from_mask, all_occ, their_occ)
& ~our_occ
/*& allowed*/
;
while (move_mask) {
enum square_index const to = bitboard_pop_lsb(&move_mask);
bitboard const to_mask = SQ_MASK_FROM_INDEX(to);
bitboard const king_attackers =
attacks_to(pos, pos->pieces[us][PIECE_KING], to_mask, from_mask) & ~(our_occ | to_mask);
if (king_attackers == 0ULL) {
out[(*out_count)++] = move_make(pos, piece, from, to, 0);
}
}
}
static void all_moves_from_king(struct pos const* restrict pos,
enum player us,
enum square_index from,
size_t* restrict out_count,
struct move out[restrict static MOVE_MAX])
{
enum player const them = opposite_player(us);
bitboard const our_occ = pos->occupied[us];
bitboard const all_occ = pos->occupied[PLAYER_WHITE] | pos->occupied[PLAYER_BLACK];
bitboard const from_mask = SQ_MASK_FROM_INDEX(from);
bitboard const threats = all_threats_from_player(pos, them);
bitboard move_mask = king_attacks(from_mask) & ~(threats | our_occ);
/* general moves */
while (move_mask) {
enum square_index const to = bitboard_pop_lsb(&move_mask);
bitboard const to_mask = SQ_MASK_FROM_INDEX(to);
bitboard const king_attackers = attacks_to(pos, to_mask, to_mask, from_mask) & ~(our_occ | to_mask);
if (king_attackers == 0ULL) {
out[(*out_count)++] = move_make(pos, PIECE_KING, from, to, 0);
}
}
/* castling */
if (from_mask & ~threats) {
bool kingside_free, queenside_free;
if (us == PLAYER_WHITE) {
kingside_free = !((threats | all_occ) & (SQ_MASK_F1 | SQ_MASK_G1))
&& (pos->pieces[us][PIECE_ROOK] & SQ_MASK_H1);
queenside_free = !((threats | all_occ) & (SQ_MASK_B1 | SQ_MASK_C1 | SQ_MASK_D1))
&& (pos->pieces[us][PIECE_ROOK] & SQ_MASK_A1);
} else {
kingside_free = !((threats | all_occ) & (SQ_MASK_F8 | SQ_MASK_G8))
&& (pos->pieces[us][PIECE_ROOK] & SQ_MASK_H8);
queenside_free = !((threats | all_occ) & (SQ_MASK_B8 | SQ_MASK_C8 | SQ_MASK_D8))
&& (pos->pieces[us][PIECE_ROOK] & SQ_MASK_A8);
}
if (!pos->castling_illegal[us][CASTLE_KINGSIDE] && kingside_free)
{
out[(*out_count)++] = us == PLAYER_WHITE
? MOVE_CASTLE_KINGSIDE_WHITE
: MOVE_CASTLE_KINGSIDE_BLACK;
}
if (!pos->castling_illegal[us][CASTLE_QUEENSIDE] && queenside_free)
{
out[(*out_count)++] = us == PLAYER_WHITE
? MOVE_CASTLE_QUEENSIDE_WHITE
: MOVE_CASTLE_QUEENSIDE_BLACK;
}
}
}
static void all_moves(struct pos const* restrict pos,
enum player us,
size_t* restrict out_count,
struct move out[restrict static MOVE_MAX])
{
*out_count = 0ULL;
bitboard const myking = pos->pieces[us][PIECE_KING];
assert(myking);
enum square_index const myking_index = bitboard_lsb(myking);
bitboard const attackers = attacks_to(pos, myking, 0ULL, 0ULL) & ~pos->occupied[us];
bitboard allowed = ~0ULL;
uint64_t const natk = bitboard_popcount(attackers);
//if (natk == 1) {
// enum square_index const attacker_index = bitboard_lsb(attackers);
// allowed = between_mask(myking_index, attacker_index) | attackers;
//} else {
// bitboard const pinners = pinning_lines(pos, us, myking_index);
//}
/* king */
{
all_moves_from_king(pos, us, myking_index, out_count, out);
}
if (natk >= 2) {
/* no other piece can fix check if the king has two attackers or more */
return;
}
/* pawns */
{
bitboard ps = pos->pieces[us][PIECE_PAWN];
while (ps) {
enum square_index const from = bitboard_pop_lsb(&ps);
all_moves_from_piece(pos, PIECE_PAWN, us, from, allowed, out_count, out);
}
}
/* knights */
{
bitboard ns = pos->pieces[us][PIECE_KNIGHT];
while (ns) {
index const from = bitboard_pop_lsb(&ns);
all_moves_from_piece(pos, PIECE_KNIGHT, us, from, allowed, out_count, out);
}
}
/* bishops */
{
bitboard bs = pos->pieces[us][PIECE_BISHOP];
while (bs) {
index const from = bitboard_pop_lsb(&bs);
all_moves_from_piece(pos, PIECE_BISHOP, us, from, allowed, out_count, out);
}
}
/* rooks */
{
bitboard rs = pos->pieces[us][PIECE_ROOK];
while (rs) {
index const from = bitboard_pop_lsb(&rs);
all_moves_from_piece(pos, PIECE_ROOK, us, from, allowed, out_count, out);
}
}
/* queens */
{
bitboard qs = pos->pieces[us][PIECE_QUEEN];
while (qs) {
index const from = bitboard_pop_lsb(&qs);
all_moves_from_piece(pos, PIECE_QUEEN, us, from, allowed, out_count, out);
}
}
}
struct zobrist {
uint64_t piece_keys[SQ_INDEX_COUNT][PLAYER_COUNT][PIECE_COUNT];
uint64_t ep_targets[SQ_INDEX_COUNT];
uint64_t castling_keys[PLAYER_COUNT][CASTLE_COUNT];
bool init;
};
static struct zobrist zobrist;
static void init_zobrist()
{
for (enum square_index sq = SQ_INDEX_BEGIN; sq < SQ_INDEX_COUNT; ++sq) {
for (enum player pl = PLAYER_BEGIN; pl < PLAYER_COUNT; ++pl) {
for (enum piece piece = PIECE_BEGIN; piece < PIECE_COUNT; ++piece) {
zobrist.piece_keys[sq][pl][piece] = my_rand64();
}
}
zobrist.ep_targets[sq] = my_rand64();
}
for (enum player pl = PLAYER_BEGIN; pl < PLAYER_COUNT; ++pl) {
for (enum castle_direction d = CASTLE_BEGIN; d < CASTLE_COUNT; ++d) {
zobrist.castling_keys[pl][d] = my_rand64();
}
}
zobrist.init = true;
}
static inline uint64_t tt_hash_update(uint64_t hash,
enum square_index sq,
enum player us,
enum piece piece)
{
if (!zobrist.init) {
init_zobrist();
}
return hash ^ zobrist.piece_keys[sq][us][piece];
}
static inline uint64_t tt_hash_update_castling_rights(uint64_t hash,
enum player us,
enum castle_direction dir)
{
if (!zobrist.init) {
init_zobrist();
}
return hash ^ zobrist.castling_keys[us][dir];
}
static inline uint64_t tt_hash_update_ep_targets(uint64_t hash, enum square_index sq)
{
if (!zobrist.init) {
init_zobrist();
}
assert(sq < SQ_INDEX_COUNT);
return hash ^ zobrist.ep_targets[sq];
}
static inline uint64_t tt_hash_switch_player(uint64_t hash)
{
if (!zobrist.init) {
init_zobrist();
}
return ~hash;
}
static inline struct search_option tt_get(struct tt* tt, uint64_t hash)
{
uint64_t const addr = hash % TT_ENTRIES;
struct search_option tte = tt->entries[addr];
#ifndef NDEBUG
tt->probes += 1;
if (tte.init && tte.hash == hash) {
tt->hits += 1;
} else if (tte.init && tte.hash != hash) {
tt->collisions += 1;
}
#endif
return tte;
}
static inline void tt_insert(struct tt* tt, uint64_t hash, struct search_option so)
{
uint64_t const addr = hash % TT_ENTRIES;
so.init = true;
tt->entries[addr] = so;
#ifndef NDEBUG
tt->insertions += 1;
#endif
}
enum move_result {
MR_NORMAL,
MR_CHECK,
MR_REPEATS, /* this board state has been observed before */
MR_STALEMATE,
MR_CHECKMATE,
};
/* does not check validity */
static enum move_result board_move(struct pos* restrict pos,
struct history* restrict hist,
enum piece mailbox[restrict static SQ_INDEX_COUNT],
struct move move)
{
enum player const us = pos->player;
enum player const them = opposite_player(us);
enum piece const from_piece = mailbox[move.from];
enum piece const to_piece = mailbox[move.to];
bitboard const from_mask = SQ_MASK_FROM_INDEX(move.from);
bitboard const to_mask = SQ_MASK_FROM_INDEX(move.to);
enum square_index const krook = (us == PLAYER_WHITE) ? SQ_INDEX_H1 : SQ_INDEX_H8;
enum square_index const qrook = (us == PLAYER_WHITE) ? SQ_INDEX_A1 : SQ_INDEX_A8;
enum square_index const krook_to = (us == PLAYER_WHITE) ? SQ_INDEX_F1 : SQ_INDEX_F8;
enum square_index const qrook_to = (us == PLAYER_WHITE) ? SQ_INDEX_D1 : SQ_INDEX_D8;
enum square_index const ksq = (us == PLAYER_WHITE) ? SQ_INDEX_E1 : SQ_INDEX_E8;
enum square_index const kcast_sq = (us == PLAYER_WHITE) ? SQ_INDEX_G1 : SQ_INDEX_G8;
enum square_index const qcast_sq = (us == PLAYER_WHITE) ? SQ_INDEX_C1 : SQ_INDEX_C8;
enum square_index const their_krook = (us != PLAYER_WHITE) ? SQ_INDEX_H1 : SQ_INDEX_H8;
enum square_index const their_qrook = (us != PLAYER_WHITE) ? SQ_INDEX_A1 : SQ_INDEX_A8;
#define POS_MOVE(player, piece, from, to) \
do { \
bitboard const x = SQ_MASK_FROM_INDEX(from) | SQ_MASK_FROM_INDEX(to); \
pos->pieces[player][piece] ^= x; \
pos->occupied[player] ^= x; \
pos->hash = tt_hash_update(pos->hash, from, player, piece); \
pos->hash = tt_hash_update(pos->hash, to, player, piece); \
mailbox[to] = piece; \
if (piece == PIECE_PAWN) pos->halfmoves = 0; \
} while (0)
#define POS_REMOVE(owner, piece, at) \
do { \
bitboard const x = SQ_MASK_FROM_INDEX(at); \
pos->pieces[owner][piece] &= ~x; \
pos->occupied[owner] &= ~x; \
pos->hash = tt_hash_update(pos->hash, at, owner, piece); \
hist->length = 0; \
pos->halfmoves = 0; \
} while (0)
#define POS_ADD(owner, piece, at) \
do { \
bitboard const x = SQ_MASK_FROM_INDEX(at); \
pos->pieces[owner][piece] |= x; \
pos->occupied[owner] |= x; \
pos->hash = tt_hash_update(pos->hash, at, owner, piece); \
mailbox[at] = piece; \
pos->halfmoves = 0; \
hist->length = 0; \
} while (0)
bitboard const ep_targets_now = pos->ep_targets;
if (ep_targets_now) {
pos->hash = tt_hash_update_ep_targets(pos->hash, bitboard_lsb(ep_targets_now));
}
pos->ep_targets = 0ULL;
/* castle kingside, legality is checked by the caller */
/**/ if (from_piece == PIECE_KING && move.from == ksq && move.to == kcast_sq) {
POS_MOVE(us, PIECE_KING, ksq, kcast_sq);
POS_MOVE(us, PIECE_ROOK, krook, krook_to);
}
/* castle queenside, legality is checked by the caller */
else if (from_piece == PIECE_KING && move.from == ksq && move.to == qcast_sq) {
POS_MOVE(us, PIECE_KING, ksq, qcast_sq);
POS_MOVE(us, PIECE_ROOK, qrook, qrook_to);
}
/* regular move / capture */
else {
POS_MOVE(us, from_piece, move.from, move.to);
/* capture */
/**/ if (to_mask & pos->occupied[them]) {
POS_REMOVE(them, to_piece, move.to);
}
else if (from_piece == PIECE_PAWN) {
bitboard const finishline = (us == PLAYER_WHITE ? RANK_MASK_8 : RANK_MASK_1);
/* en passent */
/**/ if (to_mask & ep_targets_now) {
enum square_index const ti =
(us == PLAYER_WHITE)
? INDEX_SHIFT_DOWN(move.to, 1)
: INDEX_SHIFT_UP(move.to, 1);
POS_REMOVE(them, PIECE_PAWN, ti);
}
/* pawn double push -> new ep_target */
else if (us == PLAYER_WHITE && (from_mask & RANK_MASK_2) && (to_mask & RANK_MASK_4)) {
pos->ep_targets |= RANK_SHIFT_UP_1(from_mask);
pos->hash = tt_hash_update_ep_targets(pos->hash, INDEX_SHIFT_UP(move.from, 1));
}
else if (us == PLAYER_BLACK && (from_mask & RANK_MASK_7) && (to_mask & RANK_MASK_5)) {
pos->ep_targets |= RANK_SHIFT_DOWN_1(from_mask);
pos->hash = tt_hash_update_ep_targets(pos->hash, INDEX_SHIFT_DOWN(move.from, 1));
}
else if (to_mask & finishline) {
/* already moved to `move.to` */
POS_REMOVE(us, PIECE_PAWN, move.to);
POS_ADD(us, PIECE_QUEEN, move.to);
}
}
}
/* castling rights */
if (!pos->castling_illegal[us][CASTLE_KINGSIDE]) {
if (move.from == ksq || move.from == krook) {
pos->castling_illegal[us][CASTLE_KINGSIDE] = true;
pos->hash = tt_hash_update_castling_rights(pos->hash, us, CASTLE_KINGSIDE);
}
}
if (!pos->castling_illegal[us][CASTLE_QUEENSIDE]) {
if (move.from == ksq || move.from == qrook) {
pos->castling_illegal[us][CASTLE_QUEENSIDE] = true;
pos->hash = tt_hash_update_castling_rights(pos->hash, us, CASTLE_QUEENSIDE);
}
}
if (move.to == their_krook) {
if (!pos->castling_illegal[them][CASTLE_KINGSIDE]) {
pos->castling_illegal[them][CASTLE_KINGSIDE] = true;
pos->hash = tt_hash_update_castling_rights(pos->hash, them, CASTLE_KINGSIDE);
}
}
if (move.to == their_qrook) {
if (!pos->castling_illegal[them][CASTLE_QUEENSIDE]) {
pos->castling_illegal[them][CASTLE_QUEENSIDE] = true;
pos->hash = tt_hash_update_castling_rights(pos->hash, them, CASTLE_QUEENSIDE);
}
}
pos->hash = tt_hash_switch_player(pos->hash);
pos->player = them;
pos->fullmoves += (pos->player == PLAYER_BLACK);
pos->halfmoves += 1;
assert(hist->length < 64);
int repetitions = 0;
for (size_t i = 0; i < hist->length; ++i) {
_Static_assert(sizeof *pos == sizeof hist->items[i]);
if (!my_memcmp(&hist->items[i].pieces, &pos->pieces, sizeof pos->pieces)
&& !my_memcmp(&hist->items[i].castling_illegal, &pos->castling_illegal, sizeof pos->castling_illegal)
&& hist->items[i].player == pos->player
&& hist->items[i].ep_targets == pos->ep_targets)
{
repetitions += 1;
}
}
hist->items[hist->length++] = *pos;
if (repetitions >= 3 || pos->halfmoves > 50) {
return MR_STALEMATE;
}
else if (repetitions > 0) {
return MR_REPEATS;
}
else if (pos->halfmoves > 50) {
return MR_STALEMATE;
}
else if (attacks_to(pos, pos->pieces[them][PIECE_KING], 0ULL, 0ULL)
& ~pos->occupied[them]) {
return MR_CHECK;
}
else {
return MR_NORMAL;
}
}
static enum move_result board_move_2(struct board* b, struct move move)
{
return board_move(&b->pos,
&b->hist,
b->mailbox,
move);
}
/*
* Placeholder heuristic
*
* */
static double board_score_heuristic(struct pos const* pos)
{
/* this function always evaluates from white's perspective before
eventually flipping the sign */
double score = 0.0;
/* evaluations.h defines:
- POSITIONAL_MODIFIER_COUNT
- static struct {bitboard const area; double const val} const
positional_modifier[PLAYER_COUNT][POSITIONAL_MODIFIER_COUNT][PIECE_COUNT];
* */
#include "evaluations.h"
for (enum piece p = PIECE_BEGIN; p < PIECE_COUNT; ++p) {
/* raw material value */
score += piece_value[p] *
((double)bitboard_popcount(pos->pieces[PLAYER_WHITE][p]) -
(double)bitboard_popcount(pos->pieces[PLAYER_BLACK][p]));
/* pawns defending pieces are desired */
score += 0.05 * (
(double)bitboard_popcount(
pawn_attacks_white(pos->pieces[PLAYER_WHITE][PIECE_PAWN])
& pos->pieces[PLAYER_WHITE][p]
)
- (double)bitboard_popcount(
pawn_attacks_black(pos->pieces[PLAYER_WHITE][PIECE_PAWN])
& pos->pieces[PLAYER_WHITE][p]
)
);
/* positional bonus, see evaluations.h */
for (size_t i = 0; i < POSITIONAL_MODIFIER_COUNT; ++i) {
score += positional_modifier[PLAYER_WHITE][i][p].val *
(
(double)bitboard_popcount(
pos->pieces[PLAYER_WHITE][p]
& positional_modifier[PLAYER_WHITE][i][p].area
)
- (double)bitboard_popcount(
pos->pieces[PLAYER_BLACK][p]
& positional_modifier[PLAYER_BLACK][i][p].area
)
);
}
}
/* stacked pawns are bad */
const double k = 0.30;
for (enum file_index fi = FILE_INDEX_BEGIN; fi < FILE_INDEX_COUNT; ++fi) {
uint64_t wstk = bitboard_popcount(pos->pieces[PLAYER_WHITE][PIECE_PAWN] & FILE_MASK(fi));
uint64_t bstk = bitboard_popcount(pos->pieces[PLAYER_BLACK][PIECE_PAWN] & FILE_MASK(fi));
score -= k * (double)(wstk - (wstk == 1));
score += k * (double)(bstk - (bstk == 1));
}
double sign = (pos->player == PLAYER_WHITE) ? 1.0 : -1.0;
return sign*score;
}
static inline struct move moves_linear_search(struct move moves[restrict static MOVE_MAX],
size_t* restrict move_count)
{
size_t best = 0;
assert(*move_count > 0);
for (size_t i = 0; i < *move_count; ++i) {
if (moves[i].appeal > moves[best].appeal) {
best = i;
}
}
struct move m = moves[best];
moves[best] = moves[(*move_count) - 1];
*move_count -= 1;
return m;
}
/* quiescence is a deep search that only considers captures */
double quiesce(struct pos const* pos,
enum piece mailbox[restrict static SQ_INDEX_COUNT],
enum player us,
double alpha,
double beta,
int8_t depth)
{
enum player const them = opposite_player(us);
double score = board_score_heuristic(pos);
double highscore = score;
if (highscore >= beta) {
return highscore;
}
if (highscore > alpha) {
alpha = highscore;
}
size_t move_count = 0;
struct move moves[MOVE_MAX];
all_moves(pos, us, &move_count, moves);
if (move_count == 0) {
/* TODO: detect stalemate */
return -(999.0 + (double)depth);
}
for (size_t i = 0; i < move_count; ++i) {
move_compute_appeal(&moves[i], pos, us, mailbox);
}
while (move_count) {
struct move m = moves_linear_search(moves, &move_count);
if ((m.attr & MATTR_CAPTURE) == 0ULL) {
continue;
}
struct pos poscpy = *pos;
enum piece mailbox_cpy[SQ_INDEX_COUNT];
my_memcpy(mailbox_cpy, mailbox, sizeof (enum piece[SQ_INDEX_COUNT]));
/* history is irrelevant when all moves are captures */
static struct history hist;
hist.length = 0;
(void)board_move(&poscpy, &hist, mailbox_cpy, m);
score = -quiesce(&poscpy, mailbox_cpy, them, -beta, -alpha, depth - 1);
if (score >= beta) {
highscore = score;
break;
}
if (score > highscore) {
highscore = score;
}
if (score > alpha) {
alpha = score;
}
}
return highscore;
}
static
struct search_option alphabeta_search(struct pos const* pos,
struct history* hist,
struct tt* tt,
enum piece mailbox[restrict static SQ_INDEX_COUNT],
enum player us,
int8_t depth,
uint64_t mattr_filter,
double alpha,
double beta)
{
if (depth <= 0) {
return (struct search_option) {
.score = quiesce(pos, mailbox, us, alpha, beta, 0),
/*.score = board_score_heuristic(pos),*/
.move = (struct move){0},
.depth = 0,
.hash = pos->hash,
.init = true,
.flag = TT_EXACT,
};
}
double const alpha_orig = alpha;
struct search_option tte = tt_get(tt, pos->hash);
if (tte.init && tte.hash == pos->hash && tte.depth >= depth) {
if (tte.flag == TT_EXACT) {
return tte;
} else if (tte.flag == TT_LOWER) {
if (tte.score > alpha) alpha = tte.score;
} else if (tte.flag == TT_UPPER) {
if (tte.score < beta) beta = tte.score;
}
if (alpha >= beta) {
return tte;
}
}
struct move moves[MOVE_MAX];
size_t move_count = 0ULL;
all_moves(pos, us, &move_count, moves);
if (move_count == 0) {
/* TODO: reusing mate distances correctly needs ply normalization */
double score = 0;
if (attacks_to(pos, pos->pieces[us][PIECE_KING], 0ULL, 0ULL) != 0ULL) {
score = -(999.0 + (double)depth);
}
return (struct search_option) {
.score = score,
.move = (struct move){0},
.depth = depth,
.hash = pos->hash,
.init = true,
.flag = TT_EXACT,
};
}
for (size_t i = 0; i < move_count; ++i) {
move_compute_appeal(&moves[i], pos, us, mailbox);
}
/* if TT had a best move for this position, search it first. */
if (tte.init && tte.hash == pos->hash) {
for (size_t i = 0; i < move_count; ++i) {
if (moves[i].from == tte.move.from && moves[i].to == tte.move.to) {
moves[i].appeal = APPEAL_MAX;
break;
}
}
}
double best_score = -1e300;
struct move best_move = moves[0];
while (move_count) {
struct move m = moves_linear_search(moves, &move_count);
if (mattr_filter && !(m.attr & mattr_filter)) {
continue;
}
/* TODO: make lean apply/undo mechanism instead of copying */
struct pos poscpy = *pos;
enum piece mailbox_cpy[SQ_INDEX_COUNT];
my_memcpy(mailbox_cpy, mailbox, sizeof mailbox_cpy);
size_t old_hist_length = hist->length;
enum move_result const r = board_move(&poscpy, hist, mailbox_cpy, m);
double score;
if (r == MR_STALEMATE || r == MR_REPEATS) {
score = 0.0;
} else {
score = -alphabeta_search(&poscpy,
hist,
tt,
mailbox_cpy,
opposite_player(us),
depth - 1,
mattr_filter,
-beta,
-alpha).score;
}
hist->length = old_hist_length;
if (score > best_score) {
best_score = score;
best_move = m;
}
if (score > alpha) {
alpha = score;
}
if (alpha >= beta) {
struct search_option out = {
.score = alpha,
.move = best_move,
.depth = depth,
.hash = pos->hash,
.init = true,
.flag = TT_LOWER,
};
tt_insert(tt, pos->hash, out);
return out;
}
}
enum tt_flag flag = TT_EXACT;
if (best_score <= alpha_orig) flag = TT_UPPER;
struct search_option out = {
.score = best_score,
.move = best_move,
.depth = depth,
.hash = pos->hash,
.init = true,
.flag = flag,
};
tt_insert(tt, pos->hash, out);
return out;
}
static struct search_result {struct move move; double score;}
search(struct board* b, enum player us, int8_t max_depth)
{
#if 1
if (b->tt.entries == NULL) {
b->tt.entries = sys_mmap_anon_shared(TT_ENTRIES * sizeof b->tt.entries[0],
SYS_PROT_READ | SYS_PROT_WRITE,
SYS_MADV_RANDOM);
if (b->tt.entries == NULL) {
__builtin_trap();
}
}
#endif
struct move best_move = {0};
double score = 0.0;
#define SCORE_INF 1e80
for (int8_t d = 1; d <= max_depth; ++d) {
double window = 2.0;
double alpha = score - window;
double beta = score + window;
while (true) {
struct search_option so =
alphabeta_search(&b->pos, &b->hist, &b->tt, b->mailbox, us, d, 0, alpha, beta);
if (so.score > alpha && so.score < beta) {
score = so.score;
best_move = so.move;
break;
}
window *= 2;
alpha = score - window;
beta = score + window;
if (so.score <= alpha) {
alpha = -SCORE_INF;
} else {
beta = SCORE_INF;
}
}
}
#undef SCORE_INF
return (struct search_result){.move = best_move, .score = score};
}
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