[gnugo-devel] Superko and suicide

[Gunnar Farnebäck]

Prompted by the use of New Zealand rules in the Computer Olympiad I
have at long last implemented superko detection and working suicide
options. See tickets #132 and #134 at http://trac.gnugo.org/gnugo for
more information and the patch.

After the patch there are four different ko rule options

  --simple-ko, only forbid immediate recapture of a normal ko (default),
  --no-ko, allow any kind of board repetition,
  --positional-superko, forbid repetition of a previous position,
  --situational-superko, forbid repetition of a previous position with
    the same player to move, 

and three different suicide options

  --forbid-suicide, all suicide moves forbidden (default),
  --allow-suicide, allow suicide but not of single stones,
  --allow-all-suicide, allow all suicide moves.

GNU Go itself still won't generate suicide moves, neither will it
recapture a simple ko with --no-ko. It may play superko repetitions
when such rules are not used, however.

Summary of changes:
- new static functions really_do_trymove() and is_superko_violation()
  in board.c 
- store board hashes in the move history
- is_legal() does no longer depend on allow_suicide
- new function is_allowed_move() to determine legality with respect to
  current suicide and ko rules 
- new global variables suicide_rule and ko_rule
- replace illegal moves with passes near the end of do_genmove()
- reevaluate_ko_threats() revised
- look for ko threats also if best move is a superko violation,
  assuming superko rules are used 
- new suicide options --forbid-suicide (default) and
  --allow-all-suicide, in addition to the earlier --allow-suicide
- new ko rule options --simple-ko (default), --no-ko,
  positional-superko, and --situational-superko
- use is_allowed_move() instead of is_legal() in play_gtp.c,
  play_ascii.c, and play_solo.c 

/Gunnar