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Hikeeba’s Search Function

[sourcecode lang=”c” gist=”1003531″]int search(int alpha, int beta, int depth) { int i, j; //Looping variables int evaluation_score; //The static evaluation int a, b; //Temporary Alpha-beta scores BOOLEAN check = FALSE; //Are we in check? BOOLEAN found_legal_move; //Have we found a legal move?

/*** Return a score only when we are at a quiet position ***/ if(!depth) return(quiesce(alpha, beta));

a = alpha; b = beta;

nodes++; principal_variation_size[ply] = ply;

/*** If we are in check then we want to search deeper in the tree ***/ check = in_check(side);

if(check) depth++;

generate_legal_moves();

if(follow_pv) /* Are we following the principal variation? */ find_principal_variation();

found_legal_move = FALSE;

/*** Loop through the moves ***/ for(i = move_start[ply]; i < move_end[ply]; i++) { find_best_move(i);

 /*** If we can't make the best move then we start over ***/
 if(!make_move(move_stack[i].current_move.description))
   continue;

 found_legal_move = TRUE;

 /***
  * Now that we found our move we have to check for the
  * opponent's reply
  ***/
 evaluation_score = -negascout(-b, -a, depth-1);

 /*** Now that the move's been considered take it back ***/
 take_back();

 if((evaluation_score > a) &&
    (evaluation_score < beta) &&
    (i > move_start[ply]) &&
    (depth < max_depth-1))
 {
    a = -negascout(-beta, -evaluation_score, depth-1);
 }

 a = max_int(a, evaluation_score);

 if(a >= beta)
 {
    /***
     * The current move caused a cutoff so we want to increase the
     * history value so that this move gets ordered high next time
     * that we search it
     ***/
     history[move_stack[i].current_move.description.from] \
            [move_stack[i].current_move.description.to] += depth;

     return(a);
  }

  /*** Update the principal variation ***/
  principal_variation[ply][ply] = move_stack[i].current_move;

  for(j = ply + 1; j < principal_variation_size[ply+1]; j++)
    principal_variation[ply][j] = principal_variation[ply+1][j];

  principal_variation_size[ply] = principal_variation_size[ply+1];

  b = a + 1;
}

return(a); } [/sourcecode]

-m