EasyMove is cleared after every iteration of the
search if the 3rd move in the PV of the main thread
changes from the previous iteration. Therefore,
clearing EasyMove during a search iteration may be
excessive. The tests show that this is indeed unnecessary.
In the new version the EasyMove variable is used only in
the Thread::search function.
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 47719 W: 8438 L: 8362 D: 30919
LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 122841 W: 15448 L: 15457 D: 91936
bench: 5468995
This patch fixed bugs #859 and #882.
At initialization we generate a new random key (Zobrist::noPawns).
It's added to the pawn key of all positions, so that the pawn key
of a pawnless position is no longer 0.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 21307 W: 3738 L: 3618 D: 13951
LTC:
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 45270 W: 5737 L: 5648 D: 33885
No functional change.
A position can never repeat the one on the previous move.
Thus we can start searching for a repetition from the 4th
ply behind. In the case:
std::min(st->rule50, st->pliesFromNull) < 4
We don't need to do any more calculations. This case happens
very often - in more than a half of all calls of the function.
No functional change.
In 10 of 12 calls total to Position::do_move()the givesCheck argument is
simply gives_check(m). So it's reasonable to make an overload without
this parameter, which wraps the existing version.
No functional change.
