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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

4
src/tt.h
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@@ -40,7 +40,7 @@ struct TTEntry {
Move move() const { return (Move )move16; }
Value value() const { return (Value)value16; }
Value eval() const { return (Value)eval16; }
Depth depth() const { return (Depth)(depth8 * int(ONE_PLY)); }
Depth depth() const { return (Depth)(depth8 * int(ONE_PLY)) + DEPTH_NONE; }
bool is_pv() const { return (bool)(genBound8 & 0x4); }
Bound bound() const { return (Bound)(genBound8 & 0x3); }
void save(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev);
@@ -53,7 +53,7 @@ private:
int16_t value16;
int16_t eval16;
uint8_t genBound8;
int8_t depth8;
uint8_t depth8;
};