PV from TT

[lauriet]

Hi, can someone explain how to get the PV from the TT.
Thanks

Laurie

[Robert Pope]

1. Look up present position in TT and extract best move. If not found, end.
2. Make best move
3. Goto 1.

[lauriet]

Thanks Robert, but we all know goto's are bad practice. Would you like to repost without the goto ?

[Ras]

but we all know goto's are bad practice.

So let's do this in structured programming, including a clean break for every case:

Code: Select all

int state = 0;
do {
    switch (state)
    {
        case 0:
             Look up present position in TT and extract best move.
             If not found, return(something).
             state = 1;
             break;
        case 1:
            Make best move;
            state = 0;
            break;
    }
} while 1;

[lauriet]

How about:


goto 1

1: Look up present position in TT, goto 5

2: goto end.

3: make move goto 1

5: if found then Extract move, goto 3 else goto 2

end.

[Joost Buijs]

You can also try to do it recursively which is IMO the cleanest way to do it.

[Sven]

Thanks Robert, but we all know goto's are bad practice. Would you like to repost without the goto ?

In C++ it might look like this:

Code: Select all

void pvFromTT(Board & b, TTHashTable & tt, PV & pv)
{
    for (TTEntry * e = tt.lookup(b.ttHashKey()); e != 0; e = tt.lookup(b.ttHashKey())) {
        pv.append(e->bestMove);
        b.makeMove(e->bestMove);
    }
    for (int i = int(pv.size()) - 1; i >= 0; i--) {
        b.unmakeMove(pv[i]);
    }
}

[Evert]

Note that you don't actually need to make the move (which should be checked for legality), you just need to update the hash key.

[Volker Annuss]

Don't forget repetitions. They could result in an infinite loop.

Code: Select all

do
{
    Look up present position in TT and extract best move.
    if not found, return(something).
    Make best move;
} while not repetition detected;