extensions.c

   1 /*
   2  *      This program is free software; you can redistribute it and/or modify
   3  *      it under the terms of the GNU General Public License as published by
   4  *      the Free Software Foundation; either version 2 of the License, or
   5  *      (at your option) any later version.
   6  *
   7  *      This program is distributed in the hope that it will be useful,
   8  *      but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  *      GNU General Public License for more details.
  11  *
  12  *      You should have received a copy of the GNU General Public License
  13  *      along with this program; if not, write to the Free Software
  14  *      Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  15  */
  16 #include "common.h"
  17 #include "attacks.h"
  18 #include "board.h"
  19 #include "engine.h"
  20 #include "move.h"
  21
  22 #define DEF_LMR_EXTEND_CHECK 1
  23 #define DEF_LMR_REDUCE -1
  24
  25 /* check if we should extend or can reduce search */
  26 int
  27 get_extensions(int move, int in_check, int move_is_check, int depth, int ply)
  28 {
  29         assert(move);
  30         assert(in_check == TRUE || in_check == FALSE);
  31         assert(move_is_check == TRUE || move_is_check == FALSE);
  32         assert(depth >= 0 && depth <= MAX_PLY);
  33         assert(ply >= 0 && ply <= MAX_PLY);
  34
  35         /* extend if we are in check */
  36         if (in_check)
  37                 return DEF_LMR_EXTEND_CHECK;
  38
  39         /* don't reduce checks, tactical moves, killers, moves from transposition
  40            table and all moves at low depth */
  41         if (!e.lmr || move_is_check || depth < 3 || MOVE_IS_TACTICAL(move) || \
  42                         move == killers[ply].killer1 || move == killers[ply].killer2 || \
  43                         move == killers[ply].mate_killer || move == hash_moves[ply])
  44                 return 0;
  45
  46         /* don't reduce passed pawn moves */
  47         if (square64[GET_TO(move)] == PAWN)
  48                 if (!(PAWNS(brd.wtm) & passer_mask[1 ^ brd.wtm][GET_TO(move) + \
  49                                         (brd.wtm ? -8 : 8)]))
  50                         return 0;
  51
  52 #ifdef STATISTIC_COUNTERS
  53         counters.reductions++;
  54 #endif
  55         /* reduce search depth */
  56         return DEF_LMR_REDUCE;
  57 }