tactics/1lib.c

   1 #include <assert.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4
   5 #define QUICK_BOARD_CODE
   6
   7 #define DEBUG
   8 #include "board.h"
   9 #include "debug.h"
  10 #include "mq.h"
  11 #include "tactics/1lib.h"
  12 #include "tactics/ladder.h"
  13 #include "tactics/selfatari.h"
  14
  15
  16 static inline bool
  17 capturing_group_is_snapback(struct board *b, group_t group)
  18 {
  19         coord_t lib = board_group_info(b, group).lib[0];
  20
  21         if (immediate_liberty_count(b, lib) > 0 ||
  22             group_stone_count(b, group, 2) > 1)
  23                 return false;
  24
  25         enum stone to_play = stone_other(board_at(b, group));
  26         enum stone other = stone_other(to_play);
  27         if (board_is_eyelike(b, lib, other))
  28                 return false;
  29
  30         foreach_neighbor(b, lib, {
  31                         group_t g = group_at(b, c);
  32                         if (board_at(b, c) == S_OFFBOARD || g == group)
  33                                 continue;
  34
  35                         if (board_at(b, c) == other &&
  36                             board_group_info(b, g).libs == 1)  // capture more than one group
  37                                 return false;
  38                         if (board_at(b, c) == to_play &&
  39                             board_group_info(b, g).libs > 1)
  40                                 return false;
  41                 });
  42         return true;
  43 }
  44
  45 /* Whether to avoid capturing/atariing doomed groups (this is big
  46  * performance hit and may reduce playouts balance; it does increase
  47  * the strength, but not quite proportionally to the performance). */
  48 //#define NO_DOOMED_GROUPS
  49
  50
  51 static inline bool
  52 can_capture(struct board *b, group_t g, enum stone to_play)
  53 {
  54         coord_t capture = board_group_info(b, g).lib[0];
  55         if (DEBUGL(6))
  56                 fprintf(stderr, "can capture group %d (%s)?\n",
  57                         g, coord2sstr(capture, b));
  58         /* Does playing on the liberty usefully capture the group? */
  59         if (board_is_valid_play(b, to_play, capture)
  60             && !capturing_group_is_snapback(b, g))
  61                 return true;
  62
  63         return false;
  64 }
  65
  66 static inline bool
  67 can_play_on_lib(struct board *b, group_t g, enum stone to_play)
  68 {
  69         coord_t capture = board_group_info(b, g).lib[0];
  70         if (DEBUGL(6))
  71                 fprintf(stderr, "can capture group %d (%s)?\n",
  72                         g, coord2sstr(capture, b));
  73         /* Does playing on the liberty usefully capture the group? */
  74         if (board_is_valid_play(b, to_play, capture)
  75             && !is_bad_selfatari(b, to_play, capture))
  76                 return true;
  77
  78         return false;
  79 }
  80
  81 /* Checks snapbacks */
  82 bool
  83 can_countercapture(struct board *b, group_t group, struct move_queue *q, int tag)
  84 {
  85         enum stone color = board_at(b, group);
  86         enum stone other = stone_other(color);
  87         assert(color == S_BLACK || color == S_WHITE);
  88         // Not checking b->clen, not maintained by board_quick_play()
  89
  90         unsigned int qmoves_prev = q ? q->moves : 0;
  91
  92         foreach_in_group(b, group) {
  93                 foreach_neighbor(b, c, {
  94                         group_t g = group_at(b, c);
  95                         if (likely(board_at(b, c) != other
  96                                    || board_group_info(b, g).libs > 1) ||
  97                             !can_capture(b, g, color))
  98                                 continue;
  99
 100                         if (!q)
 101                                 return true;
 102                         mq_add(q, board_group_info(b, group_at(b, c)).lib[0], tag);
 103                         mq_nodup(q);
 104                 });
 105         } foreach_in_group_end;
 106
 107         bool can = q ? q->moves > qmoves_prev : false;
 108         return can;
 109 }
 110
 111 bool
 112 can_countercapture_any(struct board *b, group_t group, struct move_queue *q, int tag)
 113 {
 114         enum stone color = board_at(b, group);
 115         enum stone other = stone_other(color);
 116         assert(color == S_BLACK || color == S_WHITE);
 117         // Not checking b->clen, not maintained by board_quick_play()
 118
 119         unsigned int qmoves_prev = q ? q->moves : 0;
 120
 121         foreach_in_group(b, group) {
 122                 foreach_neighbor(b, c, {
 123                         group_t g = group_at(b, c);
 124                         if (likely(board_at(b, c) != other
 125                                    || board_group_info(b, g).libs > 1))
 126                                 continue;
 127                         coord_t lib = board_group_info(b, g).lib[0];
 128                         if (!board_is_valid_play(b, color, lib))
 129                                 continue;
 130
 131                         if (!q)
 132                                 return true;
 133                         mq_add(q, board_group_info(b, group_at(b, c)).lib[0], tag);
 134                         mq_nodup(q);
 135                 });
 136         } foreach_in_group_end;
 137
 138         bool can = q ? q->moves > qmoves_prev : false;
 139         return can;
 140 }
 141
 142
 143 #ifdef NO_DOOMED_GROUPS
 144 static bool
 145 can_be_rescued(struct board *b, group_t group, enum stone color, int tag)
 146 {
 147         /* Does playing on the liberty rescue the group? */
 148         if (can_play_on_lib(b, group, color))
 149                 return true;
 150
 151         /* Then, maybe we can capture one of our neighbors? */
 152         return can_countercapture(b, group, NULL, tag);
 153 }
 154 #endif
 155
 156 void
 157 group_atari_check(unsigned int alwaysccaprate, struct board *b, group_t group, enum stone to_play,
 158                   struct move_queue *q, coord_t *ladder, bool middle_ladder, int tag)
 159 {
 160         enum stone color = board_at(b, group_base(group));
 161         coord_t lib = board_group_info(b, group).lib[0];
 162
 163         assert(color != S_OFFBOARD && color != S_NONE);
 164         if (DEBUGL(5))
 165                 fprintf(stderr, "[%s] atariiiiiiiii %s of color %d\n",
 166                         coord2sstr(group, b), coord2sstr(lib, b), color);
 167         assert(board_at(b, lib) == S_NONE);
 168
 169         if (to_play != color) {
 170                 /* We are the attacker! In that case, do not try defending
 171                  * our group, since we can capture the culprit. */
 172 #ifdef NO_DOOMED_GROUPS
 173                 /* Do not remove group that cannot be saved by the opponent. */
 174                 if (!can_be_rescued(b, group, color, tag))
 175                         return;
 176 #endif
 177                 if (can_play_on_lib(b, group, to_play)) {
 178                         mq_add(q, lib, tag);
 179                         mq_nodup(q);
 180                 }
 181                 return;
 182         }
 183
 184         /* Can we capture some neighbor? */
 185         /* XXX Attempts at using new can_countercapture() here failed so far.
 186          *     Could be because of a bug / under the stones situations
 187          *     (maybe not so uncommon in moggy ?) / it upsets moggy's balance somehow
 188          *     (there's always a chance opponent doesn't capture after taking snapback) */
 189         bool ccap = can_countercapture_any(b, group, q, tag);
 190         if (ccap && !ladder && alwaysccaprate > fast_random(100))
 191                 return;
 192
 193         /* Otherwise, do not save kos. */
 194         if (group_is_onestone(b, group)
 195             && neighbor_count_at(b, lib, color) + neighbor_count_at(b, lib, S_OFFBOARD) == 4) {
 196                 /* Except when the ko is for an eye! */
 197                 bool eyeconnect = false;
 198                 foreach_diag_neighbor(b, lib) {
 199                         if (board_at(b, c) == S_NONE && neighbor_count_at(b, c, color) + neighbor_count_at(b, c, S_OFFBOARD) == 4) {
 200                                 eyeconnect = true;
 201                                 break;
 202                         }
 203                 } foreach_diag_neighbor_end;
 204                 if (!eyeconnect)
 205                         return;
 206         }
 207
 208         /* Do not suicide... */
 209         if (!can_play_on_lib(b, group, to_play))
 210                 return;
 211         if (DEBUGL(6))
 212                 fprintf(stderr, "...escape route valid\n");
 213
 214         /* ...or play out ladders (unless we can counter-capture anytime). */
 215         if (!ccap) {
 216                 if (is_ladder(b, lib, group, middle_ladder)) {
 217                         /* Sometimes we want to keep the ladder move in the
 218                          * queue in order to discourage it. */
 219                         if (!ladder)
 220                                 return;
 221                         else
 222                                 *ladder = lib;
 223                 } else if (DEBUGL(6))
 224                         fprintf(stderr, "...no ladder\n");
 225         }
 226
 227         mq_add(q, lib, tag);
 228         mq_nodup(q);
 229 }