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evaluate.c
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evaluate.c
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#include "chess.h"
#include "evaluate.h"
#include "data.h"
/* last modified 12/31/15 */
/*
*******************************************************************************
* *
* Evaluate() is used to evaluate the chess board. Broadly, it addresses *
* four (4) distinct areas: (1) material score which is simply a summing of *
* piece types multiplied by piece values; (2) pawn scoring which considers *
* placement of pawns and also evaluates passed pawns, particularly in end- *
* game situations; (3) piece scoring which evaluates the placement of each *
* piece as well as things like piece mobility; (4) king safety which *
* considers the pawn shelter around the king and enemy pieces and how close *
* they are to assist in a king-side attack. *
* *
*******************************************************************************
*/
int Evaluate(TREE * RESTRICT tree, int ply, int wtm, int alpha, int beta) {
PAWN_HASH_ENTRY *ptable;
PXOR *pxtable;
int score, side, can_win = 3, phase, lscore, cutoff;
int full = 0;
uint64_t *etable;
uint64_t temp_hashkey;
/*
*************************************************************
* *
* First thing we do is if -DSKILL was passed in to the *
* compiler, we burn some time to slow the search down, *
* then we fall into the normal evaluation code. *
* *
*************************************************************
*/
#if defined(SKILL)
if (skill < 100) {
int i, j;
for (i = 0; i < burnc[skill / 10] && !abort_search; i++)
for (j = 1; j < 10 && !abort_search; j++)
burner[j - 1] = burner[j - 1] * burner[j];
if (TimeCheck(tree, 1))
abort_search = 1;
}
#endif
/*
************************************************************
* *
* Next we check to see if this position has been handled *
* before. If so, we can skip the work saved in the eval *
* hash table and just return the score found there. Note *
* that we only store FULL evaluations in the evaluation *
* hash, if an early (lazy) exit is taken, nothing is *
* stored. *
* *
************************************************************
*/
temp_hashkey = (wtm) ? HashKey : ~HashKey;
etable = eval_hash_table + (temp_hashkey & eval_hash_mask);
if (*etable >> 16 == temp_hashkey >> 16) {
score = (*etable & 0xffff) - 32768;
return (wtm) ? score : -score;
}
/*
*************************************************************
* *
* First lazy cutoff attempt. If the material score is way *
* below alpha or way above beta (way above means so far *
* above it is very unlikely the positional score can bring *
* the total score back into the alpha / beta window) then *
* we take what is known as a "lazy evaluation exit" and *
* avoid the computational cost of a full evaluation in a *
* position where one side is way ahead or behind. *
* *
*************************************************************
*/
cutoff = (TotalPieces(white, occupied) && TotalPieces(black, occupied))
? KNIGHT_VALUE : ROOK_VALUE;
lscore = MaterialSTM(wtm);
if (lscore + cutoff < alpha)
return alpha;
if (lscore - cutoff > beta)
return beta;
/*
*************************************************************
* *
* Check for draws where one side seems to be ahead, but *
* has no actual winning chances. One simple example is a *
* king, bishop and rook pawn, with the wrong colored *
* bishop and the enemy king too close to the promotion *
* square. *
* *
* The variable "can_win" uses 2 bits. If White can *
* actually win in this position, bit 1 is set. If Black *
* can actually win in this position, bit 0 is set. If *
* both sides can win, both bits are set. This is used *
* later to drag the score closer to a draw score if the *
* side with the better score can't actually win. *
* *
* Note that we only set these bits in minimal material *
* positions (both sides have < 13 points of material *
* total). Otherwise we assume normal scoring should *
* apply. *
* *
*************************************************************
*/
tree->evaluations++;
tree->score_mg = 0;
tree->score_eg = 0;
EvaluateMaterial(tree, wtm);
if (TotalPieces(white, occupied) < 13 && TotalPieces(black, occupied) < 13)
for (side = black; side <= white; side++)
if (!EvaluateWinningChances(tree, side, wtm))
can_win ^= (1 << side);
/*
*************************************************************
* *
* Determine if this position should be evaluated to force *
* mate (neither side has pawns) or if it should be *
* evaluated normally. *
* *
* Note the special case of no pawns, one side is ahead in *
* total material, but the game is a hopeless draw. KRN vs *
* KR is one example. If EvaluateWinningChances() *
* determines that the side with extra material can not *
* win, the score is pulled closer to a draw although it *
* can not collapse completely to the drawscore as it is *
* possible to lose KRB vs KR if the KR side lets the king *
* get trapped on the edge of the board. *
* *
*************************************************************
*/
tree->all_pawns = Pawns(black) | Pawns(white);
if (!tree->all_pawns) {
if (TotalPieces(white, occupied) > 3 || TotalPieces(black, occupied) > 3) {
if (Material > 0)
EvaluateMate(tree, white);
else if (Material < 0)
EvaluateMate(tree, black);
if (tree->score_eg > DrawScore(1) && !(can_win & 2))
tree->score_eg = tree->score_eg / 16;
if (tree->score_eg < DrawScore(1) && !(can_win & 1))
tree->score_eg = tree->score_eg / 16;
#if defined(SKILL)
if (skill < 100)
tree->score_eg =
skill * tree->score_eg / 100 + ((100 -
skill) * PAWN_VALUE * (uint64_t) Random32() /
0x100000000ull) / 100;
#endif
return (wtm) ? tree->score_eg : -tree->score_eg;
}
}
/*
*************************************************************
* *
* Now evaluate pawns. If the pawn hash signature has not *
* changed from the last entry to Evaluate() then we *
* already have everything we need in the pawn hash entry. *
* In this case, we do not need to call EvaluatePawns() at *
* all. EvaluatePawns() does all of the analysis for *
* information specifically regarding only pawns. In many *
* cases, it merely records the presence/absence of *
* positional pawn features because those features also *
* depends on pieces. *
* *
* Note that anything put into EvaluatePawns() can only *
* consider the placement of pawns. Kings or other pieces *
* can not influence the score because those pieces are not *
* hashed into the pawn hash signature. Violating this *
* principle leads to lots of very difficult and *
* challenging debugging problems. *
* *
*************************************************************
*/
else {
if (PawnHashKey == tree->pawn_score.key) {
tree->score_mg += tree->pawn_score.score_mg;
tree->score_eg += tree->pawn_score.score_eg;
}
/*
*************************************************************
* *
* First check to see if this position has been handled *
* before. If so, we can skip the work saved in the pawn *
* hash table. *
* *
*************************************************************
*/
else {
ptable = pawn_hash_table + (PawnHashKey & pawn_hash_mask);
pxtable = (PXOR *) & (tree->pawn_score);
tree->pawn_score = *ptable;
tree->pawn_score.key ^= pxtable->entry[1] ^ pxtable->entry[2];
if (tree->pawn_score.key != PawnHashKey) {
tree->pawn_score.key = PawnHashKey;
tree->pawn_score.score_mg = 0;
tree->pawn_score.score_eg = 0;
for (side = black; side <= white; side++)
EvaluatePawns(tree, side);
ptable->key =
pxtable->entry[0] ^ pxtable->entry[1] ^ pxtable->entry[2];
memcpy((char *) ptable + 8, (char *) &(tree->pawn_score) + 8,
sizeof(PAWN_HASH_ENTRY) - 8);
}
tree->score_mg += tree->pawn_score.score_mg;
tree->score_eg += tree->pawn_score.score_eg;
}
/*
*************************************************************
* *
* If there are any passed pawns, first call *
* EvaluatePassedPawns() to evaluate them. Then, if one *
* side has a passed pawn and the other side has no pieces, *
* call EvaluatePassedPawnRaces() to see if the passed pawn *
* can be stopped from promoting. *
* *
*************************************************************
*/
if (tree->pawn_score.passed[black] || tree->pawn_score.passed[white]) {
for (side = black; side <= white; side++)
if (tree->pawn_score.passed[side])
EvaluatePassedPawns(tree, side, wtm);
if ((TotalPieces(white, occupied) == 0 &&
tree->pawn_score.passed[black])
|| (TotalPieces(black, occupied) == 0 &&
tree->pawn_score.passed[white]))
EvaluatePassedPawnRaces(tree, wtm);
}
}
/*
*************************************************************
* *
* Call EvaluateCastling() to evaluate castling potential. *
* Note we only do this when that side has not castled at *
* the root. *
* *
*************************************************************
*/
for (side = black; side <= white; side++)
if (Castle(1, side) > 0)
EvaluateCastling(tree, ply, side);
/*
*************************************************************
* *
* The "dangerous" flag simply indicates whether that side *
* has enough material to whip up a mating attack if the *
* other side is careless (Q + minor or better, or RR + two *
* minors or better). *
* *
*************************************************************
*/
tree->dangerous[white] = (Queens(white) && TotalPieces(white, occupied) > 9)
|| (TotalPieces(white, rook) > 1 && TotalPieces(white, occupied) > 15);
tree->dangerous[black] = (Queens(black) && TotalPieces(black, occupied) > 9)
|| (TotalPieces(black, rook) > 1 && TotalPieces(black, occupied) > 15);
/*
*************************************************************
* *
* Second lazy evaluation test. We have computed the large *
* positional scores (except for king safety). If the *
* score is too far outside the alpha/beta window, we skip *
* the piece scoring which is the most expensive of all the *
* evaluation terms, and simply use what we have at this *
* point. *
* *
*************************************************************
*/
phase =
Min(62, TotalPieces(white, occupied) + TotalPieces(black, occupied));
score = ((tree->score_mg * phase) + (tree->score_eg * (62 - phase))) / 62;
lscore = (wtm) ? score : -score;
int w_mat = (2 * TotalPieces(white, rook)) + TotalPieces(white,
knight) + TotalPieces(white, bishop);
int b_mat = (2 * TotalPieces(black, rook)) + TotalPieces(black,
knight) + TotalPieces(black, bishop);
cutoff = 72 + (w_mat + b_mat) * 8 + abs(w_mat - b_mat) * 16;
if (tree->dangerous[white] || tree->dangerous[black])
cutoff += 35;
/*
*************************************************************
* *
* Then evaluate pieces if the lazy eval test fails. *
* *
* Note: We MUST evaluate kings last, since their scoring *
* depends on the tropism scores computed by the other *
* piece evaluators. Do NOT try to collapse the following *
* loops into one loop. That will break things since it *
* would violate the kings last rule. More importantly *
* there is no benefit as the loops below are unrolled by *
* the compiler anyway. *
* *
*************************************************************
*/
if (lscore + cutoff > alpha && lscore - cutoff < beta) {
tree->tropism[white] = 0;
tree->tropism[black] = 0;
for (side = black; side <= white; side++)
EvaluateKnights(tree, side);
for (side = black; side <= white; side++)
EvaluateBishops(tree, side);
for (side = black; side <= white; side++)
EvaluateRooks(tree, side);
for (side = black; side <= white; side++)
EvaluateQueens(tree, side);
for (side = black; side <= white; side++)
EvaluateKing(tree, ply, side);
full = 1;
}
/*
*************************************************************
* *
* Caclulate the final score, which is interpolated between *
* the middlegame score and endgame score based on the *
* material left on the board. *
* *
* Adjust the score if one side can't win, but the score *
* actually favors that side significantly. *
* *
*************************************************************
*/
score = ((tree->score_mg * phase) + (tree->score_eg * (62 - phase))) / 62;
score = EvaluateDraws(tree, ply, can_win, score);
#if defined(SKILL)
if (skill < 100)
score =
skill * score / 100 + ((100 -
skill) * PAWN_VALUE * (uint64_t) Random32() / 0x100000000ull) /
100;
#endif
if (full)
*etable = (temp_hashkey & 0xffffffffffff0000) + score + 32768;
return (wtm) ? score : -score;
}
/* last modified 10/19/15 */
/*
*******************************************************************************
* *
* EvaluateBishops() is used to evaluate bishops. *
* *
*******************************************************************************
*/
void EvaluateBishops(TREE * RESTRICT tree, int side) {
uint64_t temp, moves;
int square, special, i, mobility;
int score_eg = 0, score_mg = 0, enemy = Flip(side), tpawns;
/*
************************************************************
* *
* First, locate each bishop and add in its piece/square *
* table score. *
* *
************************************************************
*/
for (temp = Bishops(side); temp; temp &= temp - 1) {
square = LSB(temp);
score_mg += bval[mg][side][square];
score_eg += bval[eg][side][square];
/*
************************************************************
* *
* Evaluate for "outposts" which is a bishop that can't be *
* driven off by an enemy pawn, and which is supported by *
* a friendly pawn. *
* *
* If the enemy has NO minor to take this bishop, then *
* increase the bonus. *
* *
************************************************************
*/
special = bishop_outpost[side][square];
if (special) {
if (!(mask_pattacks[enemy][square] & Pawns(enemy))) {
if (pawn_attacks[enemy][square] & Pawns(side)) {
special += special / 2;
if (!Knights(enemy) && !(Color(square) & Bishops(enemy)))
special += bishop_outpost[side][square];
}
score_eg += special;
score_mg += special;
}
}
/*
************************************************************
* *
* Next we count the number of friendly pawns on the same *
* color squares as the bishop. This is a bad thing since *
* it restricts the bishop's ability to move. We only do *
* this if there is only one bishop for this side. *
* *
************************************************************
*/
if (TotalPieces(side, bishop) == 1) {
if (dark_squares & SetMask(square))
tpawns = PopCnt(dark_squares & Pawns(side));
else
tpawns = PopCnt(~dark_squares & Pawns(side));
score_mg -= tpawns * bishop_pawns_on_color[mg];
score_eg -= tpawns * bishop_pawns_on_color[eg];
}
/*
************************************************************
* *
* Mobility counts the number of squares the bishop *
* attacks, excluding squares with friendly pieces, and *
* weighs each square according to centralization. *
* *
************************************************************
*/
mobility = BishopMobility(square, OccupiedSquares);
if (mobility < 0 && (pawn_attacks[enemy][square] & Pawns(side))
&& (File(square) == FILEA || File(square) == FILEH))
mobility -= 8;
score_mg += mobility;
score_eg += mobility;
/*
************************************************************
* *
* Check for pawns on both wings, which makes a bishop *
* even more valuable against an enemy knight *
* *
************************************************************
*/
if (tree->all_pawns & mask_fgh && tree->all_pawns & mask_abc) {
score_mg += bishop_wing_pawns[mg];
score_eg += bishop_wing_pawns[eg];
}
/*
************************************************************
* *
* Adjust the tropism count for this piece. *
* *
************************************************************
*/
if (tree->dangerous[side]) {
moves = king_attacks[KingSQ(enemy)];
i = ((bishop_attacks[square] & moves) &&
((BishopAttacks(square, OccupiedSquares & ~Queens(side))) & moves))
? 1 : Distance(square, KingSQ(enemy));
tree->tropism[side] += king_tropism_b[i];
}
}
/*
************************************************************
* *
* Add a bonus if this side has a pair of bishops, which *
* can become very strong in open positions. *
* *
************************************************************
*/
if (TotalPieces(side, bishop) > 1) {
score_mg += bishop_pair[mg];
score_eg += bishop_pair[eg];
}
tree->score_mg += sign[side] * score_mg;
tree->score_eg += sign[side] * score_eg;
}
/* last modified 01/03/15 */
/*
*******************************************************************************
* *
* EvaluateCastling() is called when "side" has not castled at the root. *
* Its main purpose is to determine if it has either castled somewhere in *
* the tree, or else has lost all (or some) castling rights, which reduces *
* options significantly. *
* *
*******************************************************************************
*/
void EvaluateCastling(TREE * RESTRICT tree, int ply, int side) {
int enemy = Flip(side), oq, score_mg = 0;;
/*
************************************************************
* *
* If the king castled during the search, we are done and *
* we leave it to EvaluateKing() to figure out how safe it *
* is. If it has not castled, we give a significant *
* penalty if the king moves since that loses all castling *
* rights, otherwise we give a smaller penalty for moving *
* a rook and giving up castling rights to that side of *
* the board. The penalty is always increased if the *
* opponent has a queen since the position is much more *
* dangerous. *
* *
************************************************************
*/
oq = (Queens(enemy)) ? 3 : 1;
if (Castle(ply, side) != Castle(1, side)) {
if (Castle(ply, side) == 0)
score_mg -= oq * development_losing_castle;
else if (Castle(ply, side) > 0)
score_mg -= (oq * development_losing_castle) / 2;
} else
score_mg -= oq * development_not_castled;
tree->score_mg += sign[side] * score_mg;
}
/* last modified 01/03/15 */
/*
*******************************************************************************
* *
* EvaluateDraws() is used to adjust the score based on whether the side *
* that appears to be better according the computed score can actually win *
* the game or not. If the answer is "no" then the score is reduced *
* significantly to reflect the lack of winning chances. *
* *
*******************************************************************************
*/
int EvaluateDraws(TREE * RESTRICT tree, int ply, int can_win, int score) {
/*
************************************************************
* *
* If the ending has only bishops of opposite colors, the *
* score is pulled closer to a draw. *
* *
* If this is a pure BOC ending, it is very drawish unless *
* one side has at least 4 pawns. More pawns makes it *
* harder for a bishop and king to stop them all from *
* advancing. *
* *
* If the following are both true: *
* *
* black and white have less than a queen left (pieces *
* only). *
* *
* both have one bishop and they are opposite colored. *
* *
* then either *
* *
* (a) both have just one bishop, both have less than 4 *
* pawns or one side has only one more pawn than the *
* other side then score is divided by 2 with draw score *
* added in; or *
* *
* (b) pieces are equal, then score is reduced by 25% *
* with draw score added in. *
* *
************************************************************
*/
if (TotalPieces(white, occupied) <= 8 && TotalPieces(black, occupied) <= 8) {
if (TotalPieces(white, bishop) == 1 && TotalPieces(black, bishop) == 1)
if (square_color[LSB(Bishops(black))] !=
square_color[LSB(Bishops(white))]) {
if (TotalPieces(white, occupied) == 3 &&
TotalPieces(black, occupied) == 3 &&
((TotalPieces(white, pawn) < 4 && TotalPieces(black, pawn) < 4)
|| Abs(TotalPieces(white, pawn) - TotalPieces(black,
pawn)) < 2))
score = score / 2 + DrawScore(1);
else if (TotalPieces(white, occupied) == TotalPieces(black, occupied))
score = 3 * score / 4 + DrawScore(1);
}
}
/*
************************************************************
* *
* Final score adjustment. If the score says white is *
* better, but can_win says white can not win, or if the *
* score says black is better, but can_win says black can *
* not win, then we divide the score by 16, and then add *
* in the draw score. If the can_win says neither side *
* can win, we just set the score to draw score and exit. *
* *
************************************************************
*/
if (can_win != 3) {
if (can_win & 1) {
if (score > DrawScore(1))
score = score / 16 + DrawScore(1);
} else if (can_win & 2) {
if (score < DrawScore(1))
score = score / 16 + DrawScore(1);
} else
score = DrawScore(1);
}
/*
************************************************************
* *
* If we are running into the 50-move rule, then start *
* dragging the score toward draw. This is the idea of a *
* "weariness factor" as mentioned by Dave Slate many *
* times. This avoids slamming into a draw at move 50 and *
* having to move something quickly, rather than slowly *
* discovering that the score is dropping and that pushing *
* a pawn or capturing something will cause it to go back *
* to its correct value a bit more smoothly. *
* *
************************************************************
*/
if (Reversible(ply) > 80) {
int closeness = 101 - Reversible(ply);
score = DrawScore(1) + score * closeness / 20;
}
return score;
}
/* last modified 01/03/15 */
/*
*******************************************************************************
* *
* EvaluateHasOpposition() is used to determine if one king stands in *
* "opposition" to the other. If the kings are opposed on the same file or *
* else are opposed on the same diagonal, then the side not-to-move has the *
* opposition and the side-to-move must give way. *
* *
*******************************************************************************
*/
int EvaluateHasOpposition(int on_move, int king, int enemy_king) {
int file_distance, rank_distance;
file_distance = FileDistance(king, enemy_king);
rank_distance = RankDistance(king, enemy_king);
if (rank_distance < 2)
return 1;
if (on_move) {
if (rank_distance & 1)
rank_distance--;
if (file_distance & 1)
file_distance--;
}
if (!(file_distance & 1) && !(rank_distance & 1))
return 1;
return 0;
}
/* last modified 01/03/15 */
/*
*******************************************************************************
* *
* EvaluateKing() is used to evaluate a king. *
* *
*******************************************************************************
*/
void EvaluateKing(TREE * RESTRICT tree, int ply, int side) {
int score_eg = 0, score_mg = 0, defects;
int ksq = KingSQ(side), enemy = Flip(side);
/*
************************************************************
* *
* First, check for where the king should be if this is an *
* endgame. The basic idea is to centralize unless the *
* king is needed to deal with a passed enemy pawn. *
* *
************************************************************
*/
score_eg += kval[side][ksq];
/*
************************************************************
* *
* Do castle scoring, if the king has castled, the pawns *
* in front are important. If not castled yet, the pawns *
* on the kingside should be preserved for this. *
* *
************************************************************
*/
if (tree->dangerous[enemy]) {
defects = 0;
if (Castle(ply, side) <= 0) {
if (File(ksq) > FILEE)
defects = tree->pawn_score.defects_k[side];
else if (File(ksq) < FILED)
defects = tree->pawn_score.defects_q[side];
else
defects = tree->pawn_score.defects_m[side];
} else {
if (Castle(ply, side) == 3)
defects =
Min(Min(tree->pawn_score.defects_k[side],
tree->pawn_score.defects_m[side]),
tree->pawn_score.defects_q[side]);
else if (Castle(ply, side) == 1)
defects =
Min(tree->pawn_score.defects_k[side],
tree->pawn_score.defects_m[side]);
else
defects =
Min(tree->pawn_score.defects_q[side],
tree->pawn_score.defects_m[side]);
if (defects < 3)
defects = 3;
}
/*
************************************************************
* *
* Fold in the king tropism and king pawn shelter scores *
* together. *
* *
************************************************************
*/
if (tree->tropism[enemy] < 0)
tree->tropism[enemy] = 0;
else if (tree->tropism[enemy] > 15)
tree->tropism[enemy] = 15;
if (defects > 15)
defects = 15;
score_mg -= king_safety[defects][tree->tropism[enemy]];
}
tree->score_mg += sign[side] * score_mg;
tree->score_eg += sign[side] * score_eg;
}
/* last modified 01/03/15 */
/*
*******************************************************************************
* *
* EvaluateKingsFile computes defects for a file, based on whether the file *
* is open or half-open. If there are friendly pawns still on the file, *
* they are penalized for advancing in front of the king. *
* *
*******************************************************************************
*/
int EvaluateKingsFile(TREE * RESTRICT tree, int side, int first, int last) {
int defects = 0, file, enemy = Flip(side);
for (file = first; file <= last; file++)
if (!(file_mask[file] & tree->all_pawns))
defects += open_file[file];
else {
if (!(file_mask[file] & Pawns(enemy)))
defects += half_open_file[file] / 2;
else
defects +=
pawn_defects[side][Rank(MostAdvanced(enemy,
file_mask[file] & Pawns(enemy)))];
if (!(file_mask[file] & Pawns(side)))
defects += half_open_file[file];
else if (!(Pawns(side) & SetMask(sqflip[side][A2] + file))) {
defects++;
if (!(Pawns(side) & SetMask(sqflip[side][A3] + file)))
defects++;
}
}
return defects;
}
/* last modified 10/19/15 */
/*
*******************************************************************************
* *
* EvaluateKnights() is used to evaluate knights. *
* *
*******************************************************************************
*/
void EvaluateKnights(TREE * RESTRICT tree, int side) {
uint64_t temp;
int square, special, i, score_eg = 0, score_mg = 0, enemy = Flip(side);
/*
************************************************************
* *
* First fold in centralization score from the piece/ *
* square table "nval". *
* *
************************************************************
*/
for (temp = Knights(side); temp; temp &= temp - 1) {
square = LSB(temp);
score_mg += nval[mg][side][square];
score_eg += nval[eg][side][square];
/*
************************************************************
* *
* Evaluate for "outposts" which is a knight that can't *
* be driven off by an enemy pawn, and which is supported *
* by a friendly pawn. *
* *
* If the enemy has NO minor to take this knight, then *
* increase the bonus. *
* *
************************************************************
*/
special = knight_outpost[side][square];
if (special && !(mask_pattacks[enemy][square] & Pawns(enemy))) {
if (pawn_attacks[enemy][square] & Pawns(side)) {
special += special / 2;
if (!Knights(enemy) && !(Color(square) & Bishops(enemy)))
special += knight_outpost[side][square];
}
score_eg += special;
score_mg += special;
}
/*
************************************************************
* *
* Adjust the tropism count for this piece. *
* *
************************************************************
*/
if (tree->dangerous[side]) {
i = Distance(square, KingSQ(enemy));
tree->tropism[side] += king_tropism_n[i];
}
}
tree->score_mg += sign[side] * score_mg;
tree->score_eg += sign[side] * score_eg;
}
/* last modified 03/30/15 */
/*
*******************************************************************************
* *
* EvaluateMate() is used to evaluate positions where neither side has pawns *
* and one side has enough material to force checkmate. It simply trys to *
* force the losing king to the edge of the board, and then to the corner *
* where mates are easier to find. *
* *
*******************************************************************************
*/
void EvaluateMate(TREE * RESTRICT tree, int side) {
int mate_score = 0, enemy = Flip(side);
/*
************************************************************
* *
* If the winning side has a bishop + knight and the other *
* side has no pieces or pawns, then use the special *
* bishop_knight scoring board for the losing king to *
* force it to the right corner for mate. *
* *
************************************************************
*/
if (!TotalPieces(enemy, occupied) && TotalPieces(side, bishop) == 1 &&
TotalPieces(side, knight) == 1) {
if (dark_squares & Bishops(side))
mate_score = b_n_mate_dark_squares[KingSQ(enemy)];
else
mate_score = b_n_mate_light_squares[KingSQ(enemy)];
}
/*
************************************************************
* *
* The winning side has to force the losing king to the *
* edge of the board. *
* *
************************************************************
*/
else
mate_score = mate[KingSQ(enemy)];
/*
************************************************************
* *
* And for either, it is important to bring the winning *
* king to help force mate. *
* *
************************************************************
*/
mate_score -= Distance(KingSQ(side), KingSQ(enemy)) * king_king_tropism;
tree->score_eg += sign[side] * mate_score;
}
/* last modified 10/19/15 */
/*
*******************************************************************************
* *
* EvaluateMaterial() is used to evaluate material on the board. It really *
* accomplishes detecting cases where one side has made a 'bad trade' as the *
* comments below show. *
* *
*******************************************************************************
*/
void EvaluateMaterial(TREE * RESTRICT tree, int wtm) {
int score_mg, score_eg, majors, minors;
/*
*************************************************************
* *
* We start with the raw Material balance for the current *
* position, then adjust this with a small bonus for the *
* side on move. *
* *
*************************************************************
*/
score_mg = Material + ((wtm) ? wtm_bonus[mg] : -wtm_bonus[mg]);
score_eg = Material + ((wtm) ? wtm_bonus[eg] : -wtm_bonus[eg]);
/*
*************************************************************
* *
* test 1. if Majors or Minors are not balanced, then if *
* one side is only an exchange up or down, we give a *
* penalty to the side that is an exchange down, but not as *
* big a penalty as the bad trade case below. *
* *
* test 2. if Majors or Minors are not balanced, then if *
* one side has more piece material points than the other *
* (using normal piece values of 3, 3, 5, 9 for N, B, R *
* and Q) then the side that is behind in piece material *
* gets a penalty. *
* *
*************************************************************
*/
majors =
TotalPieces(white, rook) + 2 * TotalPieces(white,
queen) - TotalPieces(black, rook) - 2 * TotalPieces(black, queen);
minors =
TotalPieces(white, knight) + TotalPieces(white,
bishop) - TotalPieces(black, knight) - TotalPieces(black, bishop);
if (majors || minors) {
if (Abs(TotalPieces(white, occupied) - TotalPieces(black, occupied)) != 2
&& TotalPieces(white, occupied) - TotalPieces(black, occupied) != 0) {
score_mg +=
Sign(TotalPieces(white, occupied) - TotalPieces(black,
occupied)) * bad_trade;
score_eg +=
Sign(TotalPieces(white, occupied) - TotalPieces(black,
occupied)) * bad_trade;
}
}
tree->score_mg += score_mg;
tree->score_eg += score_eg;
}
/* last modified 11/27/15 */
/*
*******************************************************************************
* *
* EvaluatePassedPawns() is used to evaluate passed pawns and the danger *
* they produce. This code considers pieces as well, so it MUST NOT be done *
* in the normal EvaluatePawns() code since that hashes information based *
* only on the position of pawns. *
* *
* This is a significant rewrite of passed pawn evaluation, with the primary *
* change being to collect the passed pawn scoring into one place, rather *
* than have it scattered around all over the place. One example is the old *
* rook_behind_passed_pawn scoring term that was done in rook scoring. It *
* is now done here along with other passed pawn terms such as blockaded and *
* the ability to advance or not. *
* *
*******************************************************************************
*/
void EvaluatePassedPawns(TREE * RESTRICT tree, int side, int wtm) {
uint64_t behind, forward, backward, attacked, defended, thispawn;
int file, square, score, score_mg = 0, score_eg = 0, next_sq;
int pawns, rank, mg_base, eg_base, bonus, enemy = Flip(side);
uint64_t fsliders = Queens(side) | Rooks(side);
uint64_t esliders = Queens(enemy) | Rooks(enemy);
/*
************************************************************
* *
* Initialize. The base value "passed_pawn[rank]" is *
* almost the "square" of the rank. That got a bit too *
* big, so a hand-tuned set of values, one per rank, *
* proved to be a better value. *
* *
************************************************************
*/
for (pawns = tree->pawn_score.passed[side]; pawns; pawns &= pawns - 1) {
file = LSB8Bit(pawns);
thispawn = Pawns(side) & file_mask[file];
if (thispawn) {
square = MostAdvanced(side, thispawn);
rank = rankflip[side][Rank(square)];
score = passed_pawn[rank];
/*
************************************************************
* *
* For endgame only, we add in a bonus based on how close *
* our king is to this pawn and a penalty based on how *
* close the enemy king is. We also try to keep our king *
* ahead of the pawn so it can escort it to promotion. We *
* only do this for passed pawns whose base score value is *
* greater than zero (ie pawns on ranks 4-7 since those *
* are the ones threatening to become a major problem.) *
* Also, if you happen to think that a small bonus for a *
* passed pawn on the 3rd rank might be useful, consider *
* speed. If the 3rd rank score is non-zero, that will *
* trigger a significant amount of work below. In testing *
* the additional cost more than offset the gain and so it *
* is basically ignored unless rank > 3. *
* *
************************************************************
*/
if (score) {
mg_base = score * passed_pawn_base[mg];
eg_base = score * passed_pawn_base[eg];
next_sq = square + direction[side];
eg_base +=
Distance(KingSQ(enemy),
next_sq) * 2 * score - Distance(KingSQ(side), next_sq) * score;
if (rank < RANK7)
eg_base -=
Distance(KingSQ(side), next_sq + direction[side]) * score / 2;
/*
************************************************************
* *
* If the pawn is not blockaded, we need to see whether it *
* can actually advance or not. Note that this directly *
* gives a bonus for blockading a passed pawn since the *
* mobility evaluation below will not be applied when the *
* pawn is blockaded by any piece. *
* *
* Step one is to determine if the squares in front of the *
* pawn are attacked by the enemy. If not, we add in a *
* significant score bonus. If some are attacked, we look *
* to see if at least the square directly in front of the *
* pawn is not attacked so that we can advance one square, *