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Try bad captures before non-captures

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Consider sligtly negative captures as good if at low
depth and far from beta.

After 999 games at 1+0
Mod vs Orig +169 =694 -136  +11 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-02-27 17:09:07 +01:00
parent 68eb7e77f1
commit 14dbeb22dd
3 changed files with 13 additions and 6 deletions
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13
src/movepick.cpp
View file

@ -71,10 +71,11 @@ namespace {
/// move ordering is at the current node. /// move ordering is at the current node.
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
const History& h, SearchStack* ss) : pos(p), H(h) { const History& h, SearchStack* ss, Value beta) : pos(p), H(h) {
int searchTT = ttm; int searchTT = ttm;
ttMoves[0].move = ttm; ttMoves[0].move = ttm;
lastBadCapture = badCaptures; lastBadCapture = badCaptures;
badCaptureThreshold = 0;
pinned = p.pinned_pieces(pos.side_to_move()); pinned = p.pinned_pieces(pos.side_to_move());
@ -90,8 +91,14 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
if (p.is_check()) if (p.is_check())
phasePtr = EvasionsPhaseTable; phasePtr = EvasionsPhaseTable;
else if (d > Depth(0)) else if (d > Depth(0))
{
// Consider sligtly negative captures as good if at low
// depth and far from beta.
if (ss && ss->eval < beta - PawnValueMidgame && d < 3 * OnePly)
badCaptureThreshold = -PawnValueMidgame;
phasePtr = MainSearchPhaseTable; phasePtr = MainSearchPhaseTable;
else if (d == Depth(0)) } else if (d == Depth(0))
phasePtr = QsearchWithChecksPhaseTable; phasePtr = QsearchWithChecksPhaseTable;
else else
{ {
@ -290,7 +297,7 @@ Move MovePicker::get_next_move() {
{ {
// Check for a non negative SEE now // Check for a non negative SEE now
int seeValue = pos.see_sign(move); int seeValue = pos.see_sign(move);
if (seeValue >= 0) if (seeValue >= badCaptureThreshold)
return move; return move;
// Losing capture, move it to the badCaptures[] array, note // Losing capture, move it to the badCaptures[] array, note

4
src/movepick.h
View file

@ -49,7 +49,7 @@ class MovePicker {
MovePicker& operator=(const MovePicker&); // silence a warning under MSVC MovePicker& operator=(const MovePicker&); // silence a warning under MSVC
public: public:
MovePicker(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss = NULL); MovePicker(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss = NULL, Value beta = -VALUE_INFINITE);
Move get_next_move(); Move get_next_move();
int number_of_evasions() const; int number_of_evasions() const;
@ -62,7 +62,7 @@ private:
const Position& pos; const Position& pos;
const History& H; const History& H;
MoveStack ttMoves[2], killers[2]; MoveStack ttMoves[2], killers[2];
int phase; int badCaptureThreshold, phase;
const uint8_t* phasePtr; const uint8_t* phasePtr;
MoveStack *curMove, *lastMove, *lastGoodNonCapture, *lastBadCapture; MoveStack *curMove, *lastMove, *lastGoodNonCapture, *lastBadCapture;
Bitboard pinned; Bitboard pinned;

2
src/search.cpp
View file

@ -1440,7 +1440,7 @@ namespace {
// Loop through all legal moves until no moves remain or a beta cutoff occurs // Loop through all legal moves until no moves remain or a beta cutoff occurs
// Initialize a MovePicker object for the current position // Initialize a MovePicker object for the current position
MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]); MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply], beta);
CheckInfo ci(pos); CheckInfo ci(pos);
while ( bestValue < beta while ( bestValue < beta