Handling of Ko Moves in Class GoBoard

Default Settings

By default moves violating the Ko rule are illegal. That means that GoBoard::IsLegal will return false. If they are played anyway, GoBoard::LastMoveInfo will return true for GO_MOVEFLAG_ILLEGAL and GO_MOVEFLAG_REPETITION.

Allowing Ko Moves

During searches, Ko moves can be made legal with GoBoard::AllowKoRepetition. In addition, a ko loser has to be set with GoBoard::SetKoLoser. Then, Ko moves are legal (the GO_MOVEFLAG_REPETITION flag is still set). GoBoard::KoLevel returns the number of (now legal) Ko moves played by the Ko winner so far. If GoBoard::KoModifiesHash is true, only up to GoBoard::MAX_KOLEVEL Ko moves will be legal.

Oddities in the Current Implementation

• AllowAnyRepetition overrides AllowKoRepetition.

• GoBoard::KoModifiesHash has an effect only if AllowKoRepetition.

• GoBoard::KoLevel is updated both if AllowKoRepetition and AllowAnyRepetition (does some code rely on this?)

• GoBoard::KoColor is updated only if AllowKoRepetition (does some code rely on this?)

• AllowKoRepetition does not allow two non-alternating Ko moves by the same player in a row (does some code rely on this?)