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Allow for higher depths. (#2147)

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High rootDepths, selDepths and generally searches are increasingly
common with long time control games, analysis, and improving hardware.
In this case, depths of MAX_DEPTH/MAX_PLY (128) can be reached,
and the search tree is truncated.

In principle MAX_PLY can be easily increased, except for a technicality
of storing depths in a signed 8 bit int in the TT. This patch increases
MAX_PLY by storing the depth in an unsigned 8 bit, after shifting by the
most negative depth stored in TT (DEPTH_NONE).

No regression at STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 42235 W: 9565 L: 9484 D: 23186
http://tests.stockfishchess.org/tests/view/5cdb35360ebc5925cf0595e1

Verified to reach high depths on
k1b5/1p1p4/pP1Pp3/K2pPp2/1P1p1P2/3P1P2/5P2/8 w - -
info depth 142 seldepth 154 multipv 1 score cp 537 nodes 26740713110 ...

No bench change.
This commit is contained in:
Joost VandeVondele
2019-05-15 09:52:27 +02:00
committed by Marco Costalba
parent 7df832fea6
commit 893a08a8c2
3 changed files with 6 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
src/tt.cpp
View File

@@ -43,14 +43,15 @@ void TTEntry::save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev)
// Overwrite less valuable entries
if ( (k >> 48) != key16
|| d / ONE_PLY > depth8 - 4
|| d / ONE_PLY + 10 > depth8
|| b == BOUND_EXACT)
{
key16 = (uint16_t)(k >> 48);
value16 = (int16_t)v;
eval16 = (int16_t)ev;
genBound8 = (uint8_t)(TT.generation8 | uint8_t(pv) << 2 | b);
depth8 = (int8_t)(d / ONE_PLY);
assert((d - DEPTH_NONE) / ONE_PLY >= 0);
depth8 = (uint8_t)((d - DEPTH_NONE) / ONE_PLY);
}
}