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100% accurate PV display

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This gives SF accurate PVs, such that the evaluation of the leaf node in
the PV matches the score backed up to the root (99% of the time.
q-search will use the value stored in the hash table instead of the eval
value sometimes).

One drawback is that fail-high/low only get a minimal 2 move PV.

It doesn't add any additional overhead to the non-PV codepath except an
extra eight bytes to the SearchStack structure in multi-threaded
searches.

A core part of this is not pruning based on TT score in PV nodes. This
was measured as not being a regression at multiple TCs, except for one
exception, fast TC with huge hash, which is not realistic for longer
searches.

STC - 1 thread, 128 mb hash
ELO: 1.42 +-3.1 (95%) LOS: 81.9%
Total: 20000 W: 4078 L: 3996 D: 11926

STC - 3 thread, 128 mb hash
ELO: -3.60 +-2.9 (95%) LOS: 0.8%
Total: 20000 W: 3575 L: 3782 D: 12643

STC - 3 thread, 8 mb hash
ELO: 0.12 +-2.9 (95%) LOS: 53.3%
Total: 20000 W: 3654 L: 3647 D: 12699

LTC - 3 thread, 32mb hash
ELO: 2.29 +-2.0 (95%) LOS: 98.8%
Total: 35740 W: 5618 L: 5382 D: 24740

Bench: 6984058

Resolves #102
This commit is contained in:
Gary Linscott
2014-11-12 16:13:55 -05:00
parent 234344500f
commit 4739037f96
4 changed files with 56 additions and 60 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/search.h
+14 -1
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@@ -32,12 +32,26 @@ struct SplitPoint;
namespace Search {
struct PVEntry {
Move pv[MAX_PLY+1];
void update(Move move, PVEntry* child) {
pv[0] = move;
int i = 1;
for (; child && i < MAX_PLY && child->pv[i - 1] != MOVE_NONE; ++i)
pv[i] = child->pv[i - 1];
pv[i] = MOVE_NONE;
}
};
/// The Stack struct keeps track of the information we need to remember from
/// nodes shallower and deeper in the tree during the search. Each search thread
/// has its own array of Stack objects, indexed by the current ply.
struct Stack {
SplitPoint* splitPoint;
PVEntry* pv;
int ply;
Move currentMove;
Move ttMove;
@@ -62,7 +76,6 @@ struct RootMove {
bool operator<(const RootMove& m) const { return score > m.score; } // Ascending sort
bool operator==(const Move& m) const { return pv[0] == m; }
void extract_pv_from_tt(Position& pos);
void insert_pv_in_tt(Position& pos);
Value score;