-// Marcel van Kervink's cuckoo algorithm for fast detection of "upcoming repetition"/
-// "no progress" situations. Description of the algorithm in the following paper:
+// Marcel van Kervinck's cuckoo algorithm for fast detection of "upcoming repetition"
+// situations. Description of the algorithm in the following paper:
// https://marcelk.net/2013-04-06/paper/upcoming-rep-v2.pdf
// First and second hash functions for indexing the cuckoo tables
// https://marcelk.net/2013-04-06/paper/upcoming-rep-v2.pdf
// First and second hash functions for indexing the cuckoo tables
{
Move move = make_move(s1, s2);
Key key = Zobrist::psq[pc][s1] ^ Zobrist::psq[pc][s2] ^ Zobrist::side;
{
Move move = make_move(s1, s2);
Key key = Zobrist::psq[pc][s1] ^ Zobrist::psq[pc][s2] ^ Zobrist::side;
- // "originalKey == " detects upcoming repetition, "progressKey == " detects no-progress
- if ( originalKey == (progressKey ^ stp->key)
- || progressKey == Zobrist::side)
+ Key moveKey = originalKey ^ stp->key;
+ if ( (j = H1(moveKey), cuckoo[j] == moveKey)
+ || (j = H2(moveKey), cuckoo[j] == moveKey))
- Key moveKey = originalKey ^ stp->key;
- if ( (j = H1(moveKey), cuckoo[j] == moveKey)
- || (j = H2(moveKey), cuckoo[j] == moveKey))
+ Move move = cuckooMove[j];
+ Square from = from_sq(move);
+ Square to = to_sq(move);
+
+ if (!(between_bb(from, to) & pieces()))
- Move m = Move(cuckooMove[j]);
- if (!(between_bb(from_sq(m), to_sq(m)) & pieces()))
- {
- if (ply > i)
- return true;
+ // Take care to reverse the move in the no-progress case (opponent to move)
+ if (empty(from))
+ move = make_move(to, from);
- // For repetitions before or at the root, require one more
- StateInfo* next_stp = stp;
- for (int k = i + 2; k <= end; k += 2)
- {
- next_stp = next_stp->previous->previous;
- if (next_stp->key == stp->key)
- return true;
- }
+ if (ply > i)
+ return true;
+
+ // For repetitions before or at the root, require one more
+ StateInfo* next_stp = stp;
+ for (int k = i + 2; k <= end; k += 2)
+ {
+ next_stp = next_stp->previous->previous;
+ if (next_stp->key == stp->key)
+ return true;