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MicroChess.ino
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/**
* MicroChess.ino
*
* the MicroChess project: https://github.com/ripred/MicroChess
*
* version 1.0.0
* written March thru May 2023 - Trent M. Wyatt
*
* version 1.0.7
* February 2025 - Trent M. Wyatt
* Fixed en-passant capture!
*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* TODO:
*
* [ ]
* [ ] Remove all of the stacking sanitizing. Go back to initializing variables where they are declared!!
*
* [ ] Add awareness of other Arduino's on the I2C bus acting as slave devices
* and add the ability to parallel process to moves between all available
* CPU's!
* [ ] Change to use true printf, stdin, stdout and stderr so we don't copy the fmt buffer
* [ ] Add tests that prove that the same moves are chosen when alpha-beta
* pruning is enabled that are chosen when it is disabled and running in brute force?
* [ ] Add optional use of I2C serial RAM to create transposition tables for
* moves that have already been searced during this turn.
* [+] Fix problems with:
* [+] King's in check not being detected or reported correctly
* [+] King's not reacting when in check
* [+] Change skip logic to use the same percentage based logic as the mistakes logic
* [+] Fix alpha-beta bug!
* [+] Finish enabling the en-passant pawn move generation.
* [+] Add a function to display times over 1000 ms as minutes, seconds, and ms
* [+] Add flags to the game to indicate whether each side is human or not
* [+] Add the display of the full game time so far to each show() update
* [+] Enhance to pause the game when a newline is received
* [+] Enhance the game to allow moves to be entered by a human via the serial port
* [+] Change make_move(...) to return MIN_VALUE only if the ply level is 0
* so we don't actually choose it. Otherwise consider taking the King
* worth MAX_VALUE.
* [+] Change to have two sets of option_t in the game, one for each player in order to test
* option settings against each other
*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*
*/
#include <Arduino.h>
#include <math.h>
#include "MicroChess.h"
// #include <Wire.h>
////////////////////////////////////////////////////////////////////////////////////////
// The game board
board_t board;
////////////////////////////////////////////////////////////////////////////////////////
// The currently running game states and flags
game_t game;
// Un-comment the following line to display each move as it is evaluated
// #define SHOW1
////////////////////////////////////////////////////////////////////////////////////////
// Consider a move against the best white move or the best black move
// depending on the color of the piece and set this as the best move
// if it has a higher value (or an equal value when we're using random)
//
// Note: Sanitized stack
void consider_move(piece_gen_t &gen)
{
// Stack Management
// DECLARE ALL LOCAL VARIABLES USED IN THIS CONTEXT HERE AND
// DO NOT MODIFY ANYTHING BEFORE CHECKING THE AVAILABLE STACK
Bool dont_move;
// Check for low stack space
if (check_mem(CONSIDER)) { return; }
dont_move = False;
if (PLAYING != game.state) {
return;
}
// If this is a supplied move that has already been validated then just return:
if (game.supply_valid) {
return;
}
// See if the destination is a king, and if so then don't really make the move
// or evaluate it; Just return MAX or MIN value depending on whose side it is:
if (getType(board.get(gen.move.to)) == King) {
if (gen.whites_turn) {
game.white_king_in_check = True;
gen.move.value = MAX_VALUE;
}
else {
game.black_king_in_check = True;
gen.move.value = MIN_VALUE;
}
show_check();
dont_move = True;
}
// See if the move came from the user or from an opening book:
if (game.book_supplied || game.user_supplied) {
if ((gen.move.from == game.supplied.from) && (gen.move.to == game.supplied.to)) {
game.supply_valid = True;
return;
}
}
// Check for alpha or beta cutoff
if (gen.cutoff) {
#ifdef SHOW1
if (0 == game.ply) {
printf(Debug1, "** ");
}
#endif
dont_move = True;
}
// Recursively generate the move's value
if (!dont_move) {
make_move(gen);
}
if (Pawn == gen.piece) {
// Reward any moves involving a Pawn slightly
gen.move.value += (gen.whites_turn ? +10 : -10);
}
// See if we are in the end game
if (game.piece_count <= END_COUNT) {
if (Pawn == gen.piece) {
// Reward any moves involving a Pawn at this point
gen.move.value += (gen.whites_turn ? +5000 : -5000);
}
else {
// Otherwise make all pieces converge on the opponent's King.
// Get the location of the opponent's King
index_t kingloc = (gen.whites_turn ? game.bking : game.wking);
index_t king_col = kingloc % 8;
index_t king_row = kingloc / 8;
// Get the difference between our destination and the opponent's king
index_t delta_col = abs((gen.move.to % 8) - king_col);
index_t delta_row = abs((gen.move.to / 8) - king_row);
gen.move.value = (14 - (delta_col + delta_row)) +
(gen.whites_turn ? game.black_king_in_check : game.white_king_in_check) * 10;
}
}
if (gen.whites_turn && game.white_king_in_check) {
gen.move.value = MIN_VALUE;
}
if (!gen.whites_turn && game.black_king_in_check) {
gen.move.value = MAX_VALUE;
}
// Penalize the move if it would cause us to lose by move repetition
if (would_repeat(gen.move)) {
gen.move.value = gen.whites_turn ? MIN_VALUE : MAX_VALUE;
}
// See if this move is equal to OR greater than the best move we've seen so far
if (gen.whites_turn) {
if ((gen.move.value == gen.wbest.value) && random(2)) {
gen.wbest = gen.move;
}
else if (gen.move.value > gen.wbest.value) {
gen.wbest = gen.move;
}
}
else {
if ((gen.move.value == gen.bbest.value) && random(2)) {
gen.bbest = gen.move;
}
else if (gen.move.value < gen.bbest.value) {
gen.bbest = gen.move;
}
}
// Debugging output
#ifdef SHOW1
if (0 == game.ply) {
show_move(gen.move, True);
}
#endif
} // consider_move(piece_gen_t &gen)
////////////////////////////////////////////////////////////////////////////////////////
// Move a piece on the board, taking a piece if necessary. Evaluate the value of the
// board after the move. Optionally restore the board back to it's original state after
// evaluating the value of the move.
//
// This is a big and complicated function.
// It performs 5 major steps:
//
// 1) Identify the piece being moved
// 2) Identify any piece being captured and remove it if so
// 3) Place the piece being moved at the destination
// 4) Evaluate the board score after making the move
// 5) If we are just considering the move then put everything back
//
// returns the value of the board after the move was made
//
// Note: Sanitized stack
long make_move(piece_gen_t & gen)
{
// Stack Management
// DECLARE ALL LOCAL VARIABLES USED IN THIS CONTEXT HERE AND
// DO NOT MODIFY ANYTHING BEFORE CHECKING THE AVAILABLE STACK
struct local_t {
uint8_t
op : 6,
book_supplied : 1,
user_supplied : 1, // 8
board_rook : 6,
last_was_pawn_promotion : 1,
last_was_en_passant : 1, // 16
place_piece : 6,
white_king_in_check : 1,
black_king_in_check : 1, // 24
captured_piece : 6,
last_was_castle : 1,
quiescent : 1, // 32
to_col : 3,
supply_valid : 1,
to_row : 3,
oside : 1, // 40
wking : 6,
bking : 6,
white_taken_count : 5,
black_taken_count : 5,
otype : 3; // 65 bits (9 bytes)
} vars;
index_t taken_index, captured, castly_rook, hist_count;
game_t::history_t history[MAX_REPS * 2 - 1];
move_t last_move, wbest, bbest;
int32_t recurse_value;
// Check for low stack space
if (check_mem(MAKE)) { return gen.whites_turn ? MIN_VALUE : MAX_VALUE; }
// Now we can alter local variables! 😎
// The value of the board.
// Default to the worst value for our side.
// i.e: Don't make the move whatever it is
gen.move.value = gen.whites_turn ? MIN_VALUE : MAX_VALUE;
/// Step 1: Identify the piece being moved
vars.to_col = uint8_t(gen.move.to % 8);
vars.to_row = uint8_t(gen.move.to / 8);
vars.op = board.get(gen.move.to);
vars.otype = getType(vars.op);
vars.oside = getSide(vars.op);
// Save the current last 5 moves in the game history
hist_count = game.hist_count;
// Save the current king locations
vars.wking = game.wking;
vars.bking = game.bking;
// Save the current number of taken pieces
vars.white_taken_count = game.white_taken_count;
vars.black_taken_count = game.black_taken_count;
// Save the current last move and move flags
vars.last_was_pawn_promotion = game.last_was_pawn_promotion;
vars.last_was_en_passant = game.last_was_en_passant;
vars.last_was_castle = game.last_was_castle;
last_move = game.last_move;
// Save the user supplied and book supplied flags
vars.book_supplied = game.book_supplied;
vars.user_supplied = game.user_supplied;
vars.supply_valid = game.supply_valid;
if (gen.evaluating) {
memmove(history, game.history, sizeof(history));
game.stats.inc_moves_count();
}
// Save the state of whether or not the kings are in check.
// We do this AFTER we've had a chance to set the 'king-in-check'
// flags above so that this move leaves the flags behind after evaluation
vars.white_king_in_check = game.white_king_in_check;
vars.black_king_in_check = game.black_king_in_check;
/// Step 2: Identify any piece being captured and remove it if so.
//
// * NOTE BELOW *
// Once any changes have been made to the board or game state we MUST NOT return
// without passing through the "if (gen.evaluating) { ... }" restoration logic.
// The game.pieces[] index being captured (if any, -1 if none)
taken_index = -1;
// The board index being captured (if any, -1 if none)
captured = -1;
vars.captured_piece = Empty;
// Check for en-passant capture
if (Pawn == gen.type && isEmpty(vars.otype) && gen.col != vars.to_col) {
game.last_was_en_passant = True;
captured = vars.to_col + gen.row * 8u;
vars.captured_piece = board.get(captured);
}
else {
// See if the destination is not empty and not a piece on our side.
// i.e. an opponent's piece.
if (Empty != vars.otype && gen.side != vars.oside) {
captured = gen.move.to;
vars.captured_piece = board.get(captured);
}
}
// If a piece was taken, make the change on the board and to the game.pieces[] list
if (-1 != captured) {
// Remember the piece index of the piece being taken
taken_index = game.find_piece(captured);
// Change the spot on the board for the taken piece to Empty
board.set(captured, Empty);
// Soft-delete the piece taken in the piece list!
game.pieces[taken_index] = { -1, -1 };
// Add the piece to the list of taken pieces
if (gen.whites_turn) {
game.taken_by_white[game.white_taken_count++].piece = vars.captured_piece;
}
else {
game.taken_by_black[game.black_taken_count++].piece = vars.captured_piece;
}
}
/// Step 3: Place the piece being moved at the destination
// Set the 'moved' flag on the piece that we place on the board
vars.place_piece = setMoved(gen.piece, True);
// Promote a Pawn to a Queen if it reaches the back row
if (Pawn == gen.type && (vars.to_row == (gen.whites_turn ? index_t(0) : index_t(7)))) {
vars.place_piece = setType(vars.place_piece, Queen);
game.last_was_pawn_promotion = True;
}
// Move the piece to the destination on the board
board.set(gen.move.from, Empty);
board.set(gen.move.to, vars.place_piece);
// Update the piece list to reflect the piece's new location
game.pieces[gen.piece_index] = { index_t(vars.to_col), index_t(vars.to_row) };
// Check for castling
castly_rook = -1;
// If the piece being moved is a King
if (King == gen.type) {
// Update this side's king location
((White == gen.side) ? game.wking : game.bking) = gen.move.to;
// Get the horizontal distance the king is
// moving and see if it is a Castling move
if (abs(vars.to_col - (gen.move.from % 8)) > 1) {
// see which side we're castling on
if (2 == abs(vars.to_col - (gen.move.from % 8))) {
// Castle on the King's side
vars.board_rook = 7 + gen.row * 8u;
castly_rook = game.find_piece(vars.board_rook);
board.set(vars.board_rook, setMoved(board.get(vars.board_rook), True));
game.pieces[castly_rook].x = 5;
game.last_was_castle = True;
}
else if (3 == abs(vars.to_col - (gen.move.from % 8))) {
// Castle on the Queen's side
vars.board_rook = 0 + gen.row * 8u;
castly_rook = game.find_piece(vars.board_rook);
board.set(vars.board_rook, setMoved(board.get(vars.board_rook), True));
game.pieces[castly_rook].x = 3;
game.last_was_castle = True;
}
}
}
/// Step 4: Evaluate the board score after making the move
// Get the value of the current board
gen.move.value = evaluate(gen);
// Control the percentage of moves that the engine makes a mistake on
if (0 != game.options.mistakes) {
if (random(100) <= game.options.mistakes) {
gen.move.value -= gen.whites_turn ? +5000 : -5000;
}
}
// set our move as the last move
game.last_move = gen.move;
////////////////////////////////////////////////////////////////////////////////////////
// The move has been made and we have the value for the updated board.
// Recursively look-ahead and accumulatively update the value here.
//
if (gen.evaluating) {
// flag indicating whether we are traversing into quiescent moves
vars.quiescent = ((-1 != captured) && (game.ply < (game.options.max_quiescent_ply)) && (game.ply < game.options.max_max_ply));
if (((game.ply < game.options.maxply) || vars.quiescent)) {
if (!timeout()) {
// Indicate whether we are on a quiescent search or not
if (vars.quiescent) {
show_quiescent_search();
}
else {
direct_write(DEBUG2_PIN, LOW);
}
if ((0 == game.options.randskip) || (random(100) > game.options.randskip)) {
// Explore The Future! (plies)
game.ply++;
game.turn = !game.turn;
if (game.ply > game.stats.move_stats.depth) {
game.stats.move_stats.depth = game.ply;
}
wbest = { -1, -1, game.alpha };
bbest = { -1, -1, game.beta };
reset_turn_flags();
choose_best_moves(wbest, bbest, consider_move);
game.turn = !game.turn;
game.ply--;
if (gen.whites_turn) {
if (-1 != gen.wbest.from && -1 != gen.wbest.to) {
if (game.options.alpha_beta_pruning) {
recurse_value = max(gen.move.value, gen.wbest.value);
gen.move.value = game.options.integrate ? (gen.move.value + recurse_value) : recurse_value;
if (gen.move.value > game.beta) {
gen.cutoff = True;
}
else {
game.alpha = max((long) game.alpha, (long) gen.move.value);
}
}
else {
gen.move.value = game.options.integrate ? (gen.move.value + gen.wbest.value) : gen.wbest.value;
}
}
}
else {
if (-1 != gen.bbest.from && -1 != gen.bbest.to) {
if (game.options.alpha_beta_pruning) {
recurse_value = min(gen.move.value, gen.bbest.value);
gen.move.value = game.options.integrate ? (gen.move.value + recurse_value) : recurse_value;
if (gen.move.value < game.alpha) {
gen.cutoff = True;
}
else {
game.beta = min((long) game.beta, (long) gen.move.value);
}
}
else {
gen.move.value = game.options.integrate ? (gen.move.value + gen.bbest.value) : gen.bbest.value;
}
}
}
// We're finished calling into the future moves, and setting the new alpha and
// beta boundaries. Now make sure this move didn't place our king in check
// if (gen.whites_turn) {
// if (game.white_king_in_check) {
// gen.move.value = MIN_VALUE;
// }
// }
// else {
// if (game.black_king_in_check) {
// gen.move.value = MAX_VALUE;
// }
// }
if (game.ply > 0) {
game.white_king_in_check = vars.white_king_in_check;
game.black_king_in_check = vars.black_king_in_check;
}
}
}
}
} // if (gen.evaluating)
/// Step 5: If we are just considering the move then put everything back
if (gen.evaluating) {
if (-1 == captured) {
board.set(gen.move.to, vars.op);
} else {
// restore the captured board changes and
// set it's "in-check" flag
vars.captured_piece = setCheck(vars.captured_piece, True);
board.set(captured, vars.captured_piece);
// restore the captured piece list changes
game.pieces[taken_index] = { index_t(captured % 8), index_t(captured / 8) };
}
// restore the taken pieces list changes
game.white_taken_count = vars.white_taken_count;
game.black_taken_count = vars.black_taken_count;
// restore the changes made to the moves history
memmove(game.history, history, sizeof(history));
game.hist_count = hist_count;
// restore the moved piece board changes
board.set(gen.move.from, gen.piece);
// restore the moved piece pieces list changes
game.pieces[gen.piece_index] = { index_t(gen.col), index_t(gen.row) };
// restore the last move made
game.last_move = last_move;
// restore the last move flags
game.last_was_en_passant = vars.last_was_en_passant;
game.last_was_castle = vars.last_was_castle;
game.last_was_pawn_promotion = vars.last_was_pawn_promotion;
// game.white_king_in_check = vars.white_king_in_check;
// game.black_king_in_check = vars.black_king_in_check;
game.book_supplied = vars.book_supplied;
game.user_supplied = vars.user_supplied;
game.supply_valid = vars.supply_valid;
// Don't take the move if it leaves us in check
if (gen.whites_turn) {
if (game.white_king_in_check) {
gen.move.value = MIN_VALUE;
}
}
else {
if (game.black_king_in_check) {
gen.move.value = MAX_VALUE;
}
}
// restore the king's locations
game.wking = vars.wking;
game.bking = vars.bking;
// restore any rook moved during a castle move
game.last_was_castle = vars.last_was_castle;
if (-1 != castly_rook) {
if (3 == game.pieces[castly_rook].x) {
game.pieces[castly_rook].x = 0;
}
else {
game.pieces[castly_rook].x = 7;
}
board.set((game.pieces[castly_rook].x + game.pieces[castly_rook].y * 8),
setMoved(board.get((game.pieces[castly_rook].x + game.pieces[castly_rook].y * 8)), False));
}
} // if (gen.evaluating)
return gen.move.value;
} // make_move(piece_gen_t & gen)
////////////////////////////////////////////////////////////////////////////////////////
// Evaluate the identity (score) of the board state.
// Positive scores indicate an advantage for white and
// Negative scores indicate an advantage for black.
// Uses pre-computed material bonus tables for speed.
//
// returns the score/value of the current board
//
// Note: Sanitized stack
long evaluate(piece_gen_t &gen)
{
// Stack Management
// DECLARE ALL LOCAL VARIABLES USED IN THIS CONTEXT HERE AND
// DO NOT MODIFY ANYTHING BEFORE CHECKING THE AVAILABLE STACK
long materialTotal, mobilityTotal, centerTotal, kingTotal, score;
index_t col, row, piece_index, kloc, col_dist, row_dist, proximity;
Piece p, ptype;
Color pside;
// Check for low stack space
if (check_mem(MAKE)) { return 0; }
// Now we can alter local variables! 😎
// Calculate the value of the board:
materialTotal = 0L;
mobilityTotal = 0L;
centerTotal = 0L;
kingTotal = 0L;
score = 0L;
for (piece_index = 0; piece_index < game.piece_count; piece_index++) {
col = game.pieces[piece_index].x;
row = game.pieces[piece_index].y;
if (-1 == col || -1 == row) continue;
p = board.get(col + row * 8);
ptype = getType(p);
pside = getSide(p);
if (Empty == ptype) continue;
// Material Bonus
materialTotal += pgm_read_dword(&game.material_bonus[ptype][pside]) * game.options.materialBonus;
// In-Check Penalty
if (inCheck(p)) {
if (White == ptype) {
materialTotal -= ptype;
}
else {
materialTotal += ptype;
}
}
// Let's not encourage the King to wander to
// the center of the board mmkay?
if (King == ptype) {
continue;
}
// Center Bonus
centerTotal +=
pgm_read_dword(&game.center_bonus[col][ptype][pside]) +
pgm_read_dword(&game.center_bonus[row][ptype][pside]);
// Proximity to opponent's King Bonus
kloc = (White == pside) ? game.bking : game.wking;
col_dist = (col > (kloc % 8)) ? (col - (kloc % 8)) : ((kloc % 8) - col);
row_dist = (row > (kloc / 8)) ? (row - (kloc / 8)) : ((kloc / 8) - row);
proximity = 14 - (col_dist + row_dist);
if (White == pside) {
kingTotal += proximity;
}
else {
kingTotal -= proximity;
}
}
kingTotal *= game.options.kingBonus;
// Mobility Bonus
if (gen.whites_turn) {
mobilityTotal += static_cast<long>(gen.num_wmoves * game.options.mobilityBonus);
}
else {
mobilityTotal -= static_cast<long>(gen.num_bmoves * game.options.mobilityBonus);
}
score = kingTotal + materialTotal + centerTotal + mobilityTotal;
// printf(Debug4,
// "evaluation: %ld = centerTotal: %ld materialTotal: %ld mobilityTotal: %ld\n",
// score, centerTotal, materialTotal, mobilityTotal);
return score;
} // evaluate(...)
////////////////////////////////////////////////////////////////////////////////////////
// Evaluate all of the available moves for both sides.
// The best moves are stored in wbest and bbest.
// The callback is called for each move, implementing the visitor pattern.
//
// This function is the top of the recursive call chain:
//
// choose_best_move(...)
// add_xxxx_moves(...)
// consider_move(...)
// make_move(...)
// choose_best_move(...)
//
// Note: Sanitized stack
void choose_best_moves(move_t &wbest, move_t &bbest, generator_t const callback)
{
// Stack Management
// DECLARE ALL LOCAL VARIABLES USED IN THIS CONTEXT HERE AND
// DO NOT MODIFY ANYTHING BEFORE CHECKING THE AVAILABLE STACK
// Check for low stack space
if (check_mem(CHOOSE)) { return; }
// Now we can alter local variables!
else {
static uint32_t last_led_update;
index_t move_count;
move_t move = { -1, -1, 0 };
piece_gen_t gen(move, wbest, bbest, callback, True);
gen.num_wmoves = 0;
gen.num_bmoves = 0;
// Turn off the 'King in check' LED
direct_write(DEBUG4_PIN, LOW);
// Walk through the game.pieces[] list and evaluate the moves for each one
for (gen.piece_index = 0; gen.piece_index < game.piece_count; gen.piece_index++) {
if (game.supply_valid || (PLAYING != game.state)) {
return;
}
if (check_serial()) {
return;
}
else {
gen.col = game.pieces[gen.piece_index].x;
if (-1 == gen.col) { continue; }
// Construct a move_t object with the starting location
gen.row = game.pieces[gen.piece_index].y;
gen.move.from = gen.col + gen.row * 8u;
gen.move.to = -1;
gen.piece = board.get(gen.move.from);
gen.type = getType(gen.piece);
gen.side = getSide(gen.piece);
gen.whites_turn = gen.side; // same as White == gen.side
gen.move.value = gen.whites_turn ? MIN_VALUE : MAX_VALUE;
if (Empty == gen.type) {
continue;
}
// Periodically update the LED strip display and progress indicator if enabled
if (game.options.live_update
// && (game.ply < game.options.max_max_ply)
// && (game.ply <= game.options.maxply)
) {
if ((millis() - last_led_update) >= 10)
{
last_led_update = millis();
set_led_strip(gen.move.from);
}
}
// Keep track of the location of the Kings
if (King == gen.type) {
(gen.whites_turn ? game.wking : game.bking) = gen.move.from;
}
// Check for move timeout (only if we're at ply level 2 or above,
// this happens internally in the timeout() function)
if (timeout()) {
break;
}
move_count = 0;
// Evaluate the moves for this Piece Type and get the highest value move
switch (gen.type) {
default: printf(Always, "bad type: line %d\n", __LINE__); break;
case Pawn: move_count = add_pawn_moves(gen); break;
case Knight: move_count = add_knight_moves(gen); break;
case Bishop: move_count = add_bishop_moves(gen); break;
case Rook: move_count = add_rook_moves(gen); break;
case Queen: move_count = add_queen_moves(gen); break;
case King:
move_count = add_king_moves(gen);
// if (0 == move_count) {
// if (White == gen.side && game.white_king_in_check) {
// game.state = BLACK_CHECKMATE;
// return;
// }
// if (Black == gen.side && game.black_king_in_check) {
// game.state = WHITE_CHECKMATE;
// return;
// }
// }
break;
}
// Keep track of the total number of moves for this side
(gen.whites_turn ? gen.num_wmoves : gen.num_bmoves) += move_count;
// Check for alpha or beta cuttoff
if (gen.cutoff) {
break;
}
// Check for move timeout if we've finished ply level 1
if (game.timeout1) {
break;
}
}
} // for each piece on both sides
// See if the game is over
if (0 == game.ply) {
// See if we only have the two kings on either side:
if (2 == game.piece_count) {
game.state = STALEMATE;
}
if ((0 == gen.num_wmoves) && (0 == gen.num_bmoves)) {
game.state = STALEMATE;
}
if ((0 == gen.num_wmoves) && game.white_king_in_check) {
game.state = BLACK_CHECKMATE;
}
if ((0 == gen.num_bmoves) && game.black_king_in_check) {
game.state = WHITE_CHECKMATE;
}
}
}
} // choose_best_moves(...)
////////////////////////////////////////////////////////////////////////////////////////
// Set the per-side options. This allows testing feature choices against each other
void set_per_side_options() {
if (game.turn) {
// White's turn
}
else {
// Black's turn
}
}
////////////////////////////////////////////////////////////////////////////////////////
// reset the various move tracking flags
//
// Note: Sanitized stack
void reset_turn_flags()
{
// Stack Management
// DECLARE ALL LOCAL VARIABLES USED IN THIS CONTEXT HERE AND
// DO NOT MODIFY ANYTHING BEFORE CHECKING THE AVAILABLE STACK
index_t index;
// Check for low stack space
if (check_mem(CHOOSE)) { return; }
// Now we can alter local variables! 😎
for (index = 0; index < game.piece_count; index++) {
if (-1 == game.pieces[index].x) { continue; }
board.set( game.pieces[index].x + game.pieces[index].y * 8,
setCheck(board.get(game.pieces[index].x + game.pieces[index].y * 8), False));
}
// reset the king-in-check flags
game.white_king_in_check = False;
game.black_king_in_check = False;
game.last_was_en_passant = False;
game.last_was_castle = False;
game.timeout1 = False;
game.timeout2 = False;
game.last_was_pawn_promotion = False;
game.book_supplied = False;
game.user_supplied = False;
game.supply_valid = False;
set_per_side_options();
} // reset_turn_flags()
////////////////////////////////////////////////////////////////////////////////////////
// Make the next move in the game
void take_turn()
{
// Turn off the LED move indicators
direct_write(DEBUG1_PIN, LOW);
direct_write(DEBUG2_PIN, LOW);
direct_write(DEBUG3_PIN, LOW);
direct_write(DEBUG4_PIN, LOW);
// See if we've hit the move limit and return if so
if (game.move_num >= game.options.move_limit) {
game.state = MOVE_LIMIT;
return;
}
// The best white and black moves
move_t wmove = { -1, -1, MIN_VALUE };
move_t bmove = { -1, -1, MAX_VALUE };
// Reset the flags for this turn
game.stats.start_move_stats();
game.stats.move_stats.depth = 0;
reset_turn_flags();
// Set the alpha and beta edges to the worst case (brute force)
// O(N) based on whose turn it is. Math is so freakin cool..
game.alpha = wmove.value;
game.beta = bmove.value;
Bool const whites_turn = game.turn; // same as (White == game.turn) ? True : False;
move_t move = { -1, -1, whites_turn ? MIN_VALUE : MAX_VALUE };
// See if we have an opening book move
check_book();
if (game.options.shuffle_pieces) {
game.sort_pieces(game.turn);
game.shuffle_pieces(SHUFFLE);
}
// Choose the best moves for both sides
choose_best_moves(wmove, bmove, consider_move);
// Gather the move statistics for this turn
game.stats.stop_move_stats();
printf(Debug1, "\nMove #%d: ", game.move_num + 1);
// If we have a user or a book move that's been validated then use it
if (game.supply_valid) {
(whites_turn ? wmove : bmove) = game.supplied;
game.last_move = game.supplied;
if (game.book_supplied) {
printf(Debug1, "Book: ");
}
if (game.user_supplied) {
printf(Debug1, "User: ");
}
}
move = (whites_turn ? wmove : bmove);
// Display the move that we chose * Before Modifying the Board *
show_move(move);
// Save the number of pieces in the game before we make the move
// in order to see if any pieces were taken
index_t const piece_count = game.piece_count;
// Make the move:
piece_gen_t gen(move, wmove, bmove, consider_move, False);
gen.move = move;
gen.init(board, game);
make_move(gen);
// Set the 'king-in-check' flags
check_kings();
// Check for move repetition
if ((PLAYING == game.state) && add_to_history(gen.move)) {
game.state = whites_turn ? WHITE_3_MOVE_REP : BLACK_3_MOVE_REP;
}
if (game.last_was_en_passant) {
printf(Debug1, " - en passant capture ")
}
if (game.last_was_pawn_promotion) {
printf(Debug1, " - pawn promoted ")
}