Evaluation

Overview

The evaluation function returns a score in centipawns from the perspective of the side to move. Positive scores favor the side to move.

Material

Piece	Value (centipawns)
Pawn	100
Knight	300
Bishop	350
Rook	500
Queen	1000
King	10000

Piece values in Kirin

Positional Factors

Piece-Square Tables

Each piece type has a positional bonus table. Example for pawns:

const int pawnScore[64] = {
    90,  90,  90,  90,  90,  90,  90,  90,
    30,  30,  30,  40,  40,  30,  30,  30,
    20,  20,  20,  30,  30,  30,  20,  20,
    10,  10,  10,  20,  20,  10,  10,  10,
     5,   5,  10,  20,  20,   5,   5,   5,
     0,   0,   0,   5,   5,   0,   0,   0,
     0,   0,   0, -10, -10,   0,   0,   0,
     0,   0,   0,   0,   0,   0,   0,   0
};

Knight Positioning

Knights are rewarded for central placement:

const int knightScore[64] = {
    -5,   0,   0,   0,   0,   0,   0,  -5,
    -5,   0,   0,  10,  10,   0,   0,  -5,
    -5,   5,  20,  20,  20,  20,   5,  -5,
    -5,  10,  20,  30,  30,  20,  10,  -5,
    -5,  10,  20,  30,  30,  20,  10,  -5,
    -5,   5,  20,  10,  10,  20,   5,  -5,
    -5,   0,   0,   0,   0,   0,   0,  -5,
    -5, -10,   0,   0,   0,   0, -10,  -5
};

Pawn Structure

Double Pawns

Doubled pawns receive a penalty:

const int doublePawnPenalty = -10;

doublePawns = countBits(bitboards[P] & fileMasks[square]);
if(doublePawns > 1) score += doublePawns * doublePawnPenalty;

Isolated Pawns

Pawns with no friendly pawns on adjacent files are penalized:

const int isolatedPawnPenalty = -10;

if((bitboards[P] & isolatedMasks[square]) == 0) 
    score += isolatedPawnPenalty;

Passed Pawns

Passed pawns receive bonuses based on how advanced they are:

const int passedPawnBonus[8] = { 0, 10, 30, 50, 75, 100, 150, 200 };

if((passedWhiteMasks[square] & bitboards[p]) == 0) 
    score += passedPawnBonus[getRank[square]];