tactics/1lib.c

   1 #include <assert.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4
   5 #define DEBUG
   6 #include "board.h"
   7 #include "debug.h"
   8 #include "mq.h"
   9 #include "tactics/1lib.h"
  10 #include "tactics/ladder.h"
  11 #include "tactics/selfatari.h"
  12
  13
  14 /* Whether to avoid capturing/atariing doomed groups (this is big
  15  * performance hit and may reduce playouts balance; it does increase
  16  * the strength, but not quite proportionally to the performance). */
  17 //#define NO_DOOMED_GROUPS
  18
  19
  20 static bool
  21 can_play_on_lib(struct board *b, group_t g, enum stone to_play)
  22 {
  23         coord_t capture = board_group_info(b, g).lib[0];
  24         if (DEBUGL(6))
  25                 fprintf(stderr, "can capture group %d (%s)?\n",
  26                         g, coord2sstr(capture, b));
  27         /* Does playing on the liberty usefully capture the group? */
  28         if (board_is_valid_play(b, to_play, capture)
  29             && !is_bad_selfatari(b, to_play, capture))
  30                 return true;
  31
  32         return false;
  33 }
  34
  35 /* For given position @c, decide if this is a group that is in danger from
  36  * @capturer and @to_play can do anything about it (play at the last
  37  * liberty to either capture or escape). */
  38 /* Note that @to_play is important; e.g. consider snapback, it's good
  39  * to play at the last liberty by attacker, but not defender. */
  40 static inline __attribute__((always_inline)) bool
  41 capturable_group(struct board *b, enum stone capturer, coord_t c,
  42                  enum stone to_play)
  43 {
  44         group_t g = group_at(b, c);
  45         if (likely(board_at(b, c) != stone_other(capturer)
  46                    || board_group_info(b, g).libs > 1))
  47                 return false;
  48
  49         return can_play_on_lib(b, g, to_play);
  50 }
  51
  52 bool
  53 can_countercapture(struct board *b, enum stone owner, group_t g,
  54                    enum stone to_play, struct move_queue *q, int tag)
  55 {
  56         if (b->clen < 2)
  57                 return false;
  58
  59         unsigned int qmoves_prev = q ? q->moves : 0;
  60
  61         foreach_in_group(b, g) {
  62                 foreach_neighbor(b, c, {
  63                         if (!capturable_group(b, owner, c, to_play))
  64                                 continue;
  65
  66                         if (!q) {
  67                                 return true;
  68                         }
  69                         mq_add(q, board_group_info(b, group_at(b, c)).lib[0], tag);
  70                         mq_nodup(q);
  71                 });
  72         } foreach_in_group_end;
  73
  74         bool can = q ? q->moves > qmoves_prev : false;
  75         return can;
  76 }
  77
  78 #ifdef NO_DOOMED_GROUPS
  79 static bool
  80 can_be_rescued(struct board *b, group_t group, enum stone color, int tag)
  81 {
  82         /* Does playing on the liberty rescue the group? */
  83         if (can_play_on_lib(b, group, color))
  84                 return true;
  85
  86         /* Then, maybe we can capture one of our neighbors? */
  87         return can_countercapture(b, color, group, color, NULL, tag);
  88 }
  89 #endif
  90
  91 void
  92 group_atari_check(unsigned int alwaysccaprate, struct board *b, group_t group, enum stone to_play,
  93                   struct move_queue *q, coord_t *ladder, bool middle_ladder, int tag)
  94 {
  95         enum stone color = board_at(b, group_base(group));
  96         coord_t lib = board_group_info(b, group).lib[0];
  97
  98         assert(color != S_OFFBOARD && color != S_NONE);
  99         if (DEBUGL(5))
 100                 fprintf(stderr, "[%s] atariiiiiiiii %s of color %d\n",
 101                         coord2sstr(group, b), coord2sstr(lib, b), color);
 102         assert(board_at(b, lib) == S_NONE);
 103
 104         if (to_play != color) {
 105                 /* We are the attacker! In that case, do not try defending
 106                  * our group, since we can capture the culprit. */
 107 #ifdef NO_DOOMED_GROUPS
 108                 /* Do not remove group that cannot be saved by the opponent. */
 109                 if (!can_be_rescued(b, group, color, tag))
 110                         return;
 111 #endif
 112                 if (can_play_on_lib(b, group, to_play)) {
 113                         mq_add(q, lib, tag);
 114                         mq_nodup(q);
 115                 }
 116                 return;
 117         }
 118
 119         /* Can we capture some neighbor? */
 120         bool ccap = can_countercapture(b, color, group, to_play, q, tag);
 121         if (ccap && !ladder && alwaysccaprate > fast_random(100))
 122                 return;
 123
 124         /* Otherwise, do not save kos. */
 125         if (group_is_onestone(b, group)
 126             && neighbor_count_at(b, lib, color) + neighbor_count_at(b, lib, S_OFFBOARD) == 4) {
 127                 /* Except when the ko is for an eye! */
 128                 bool eyeconnect = false;
 129                 foreach_diag_neighbor(b, lib) {
 130                         if (board_at(b, c) == S_NONE && neighbor_count_at(b, c, color) + neighbor_count_at(b, c, S_OFFBOARD) == 4) {
 131                                 eyeconnect = true;
 132                                 break;
 133                         }
 134                 } foreach_diag_neighbor_end;
 135                 if (!eyeconnect)
 136                         return;
 137         }
 138
 139         /* Do not suicide... */
 140         if (!can_play_on_lib(b, group, to_play))
 141                 return;
 142         if (DEBUGL(6))
 143                 fprintf(stderr, "...escape route valid\n");
 144
 145         /* ...or play out ladders (unless we can counter-capture anytime). */
 146         if (!ccap) {
 147                 if (is_ladder(b, lib, group, middle_ladder)) {
 148                         /* Sometimes we want to keep the ladder move in the
 149                          * queue in order to discourage it. */
 150                         if (!ladder)
 151                                 return;
 152                         else
 153                                 *ladder = lib;
 154                 } else if (DEBUGL(6))
 155                         fprintf(stderr, "...no ladder\n");
 156         }
 157
 158         mq_add(q, lib, tag);
 159         mq_nodup(q);
 160 }