If we want to store a value of type VALUE_TYPE_EVAL for
a given position and we found an already exsisting entry
for the same position then we skip.
We don't want to overwrite a more valuable score with a
lesser one. Note that also in case the exsisting entry is
of VALUE_TYPE_EVAL type the overwrite is unuseful because
we would store the same score again.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
When the stored TT value equals the static value set a
proper flag so to not call evaluation() if we hit the
same position again but use the stored TT value instead.
This is another trick to avoid calling costly evaluation()
in qsearch.
No functional change.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Fix a bug in the way a move is stored and read in a TT entry.
We use a mask of 19 bits insteaad of 17 so that the last
two bits in the TT entry end up to be random data.
This bug will bite us when we will use these two until now
unused bits.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Instead of just drop evaluation score after stand pat
logic save it in TT so to be reused if the same position
occurs again.
Note that we NEVER use the cached value apart to avoid an
evaluation call, in particulary we never return to caller
after a succesful tt hit.
To accomodate this a new value type VALUE_TYPE_EVAL has been
introduced so that ok_to_use_TT() always returns false.
With this patch we cut about 15% of total evaluation calls.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
We implicitly considered the minimum depth stored in TT
to be Depth(0), but because we store values in TT also in
qsearch() where depth is < 0, we need to use a negative
number as minimum depth.
Bug spotted by Joona Kiiski.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Note that some pawns and material info has been switched
to int from int8_t.
This is a waste of space but it is not clear if we have a
faster or slower code (or nothing changed), some test should be
needed.
Few warnings still are alive.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
We don't backup anymore but use the renamed StateInfo
argument passed in do_move() to store the new position
state when doing a move.
Backup is now just revert to previous StateInfo that we know
because we store a pointer to it.
Note that now backing store is up to the caller, Position is
stateless in that regard, state is accessed through a pointer.
This patch will let us remove all the backup/restore copying,
just a pointer switch is now necessary.
Note that do_null_move() still uses StateInfo as backup.
No functional change.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Make the logic work as advertised in the function
description.
Still a fallback from TT cleanup.
This should be less serious then the one in retrieve(),
but it's still a bug.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
