tactics.h

   1 #ifndef ZZGO_TACTICS_H
   2 #define ZZGO_TACTICS_H
   3
   4 /* Advanced tactical checks non-essential to the board implementation. */
   5
   6 #include "board.h"
   7
   8 /* Check if this move is undesirable self-atari (resulting group would have
   9  * only single liberty and not capture anything; ko is allowed); we mostly
  10  * want to avoid these moves. The function actually does a rather elaborate
  11  * tactical check, allowing self-atari moves that are nakade, eye falsification
  12  * or throw-ins. */
  13 static bool is_bad_selfatari(struct board *b, enum stone color, coord_t to);
  14
  15 /* Check if escaping on this liberty by given group in atari would play out
  16  * a simple ladder. */
  17 /* Two ways of ladder reading can be enabled separately; simple first-line
  18  * ladders and trivial middle-board ladders. */
  19 static bool is_ladder(struct board *b, coord_t coord, group_t laddered,
  20                       bool border_ladders, bool middle_ladders);
  21
  22 /* Checks if there are any stones in n-vincinity of coord. */
  23 bool board_stone_radar(struct board *b, coord_t coord, int distance);
  24
  25 /* Construct a "common fate graph" from given coordinate; that is, a weighted
  26  * graph of intersections where edges between all neighbors have weight 1,
  27  * but edges between neighbors of same color have weight 0. Thus, this is
  28  * "stone chain" metric in a sense. */
  29 /* The output are distanes from start stored in given [board_size2()] array;
  30  * intersections further away than maxdist have all distance maxdist+1 set. */
  31 void cfg_distances(struct board *b, coord_t start, int *distances, int maxdist);
  32
  33 /* Compute an extra komi describing the "effective handicap" black receives
  34  * (returns 0 for even game with 7.5 komi). */
  35 /* This is just an approximation since in reality, handicap seems to be usually
  36  * non-linear. */
  37 float board_effective_handicap(struct board *b);
  38
  39
  40 bool is_bad_selfatari_slow(struct board *b, enum stone color, coord_t to);
  41 static inline bool
  42 is_bad_selfatari(struct board *b, enum stone color, coord_t to)
  43 {
  44         /* More than one immediate liberty, thumbs up! */
  45         if (immediate_liberty_count(b, to) > 1)
  46                 return false;
  47         if (board_playing_ko_threat(b))
  48                 return false; // all is fair in a ko
  49
  50         return is_bad_selfatari_slow(b, color, to);
  51 }
  52
  53 bool is_border_ladder(struct board *b, coord_t coord, enum stone lcolor);
  54 bool is_middle_ladder(struct board *b, coord_t coord, enum stone lcolor);
  55 static inline bool
  56 is_ladder(struct board *b, coord_t coord, group_t laddered,
  57           bool border_ladders, bool middle_ladders)
  58 {
  59         if (board_playing_ko_threat(b))
  60                 return false; // all is fair in a ko
  61
  62         enum stone lcolor = board_at(b, group_base(laddered));
  63
  64         if (DEBUGL(6))
  65                 fprintf(stderr, "ladder check - does %s play out %s's laddered group %s?\n",
  66                         coord2sstr(coord, b), stone2str(lcolor), coord2sstr(laddered, b));
  67
  68         /* First, special-case first-line "ladders". This is a huge chunk
  69          * of ladders we actually meet and want to play. */
  70         if (border_ladders
  71             && neighbor_count_at(b, coord, S_OFFBOARD) == 1
  72             && neighbor_count_at(b, coord, lcolor) == 1)
  73                 return is_border_ladder(b, coord, lcolor);
  74
  75         if (middle_ladders)
  76                 return is_middle_ladder(b, coord, lcolor);
  77
  78         return false;
  79 }
  80
  81 #endif