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Tweak backward pawns definition 

Advanced pawns cannot be backward. Also lower the backward penalty in
endgame.

Passed STC:
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 18534 W: 3588 L: 3433 D: 11513

and LTC:
LLR: 2.96 (-2.94,2.94) [0.00,6.00]
Total: 21319 W: 3415 L: 3217 D: 14687

Bench: 7271152

Resolves #359
pull/359/merge
Stéphane Nicolet 2015-06-02 12:06:46 -07:00 committed by Gary Linscott
parent 2795aedbc3
commit 4502a1934f
1 changed files with 4 additions and 3 deletions
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7
src/pawns.cpp
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@ -44,7 +44,7 @@ namespace {
S(40, 35), S(40, 35), S(36, 35), S(25, 30) } };
// Backward pawn penalty by opposed flag
const Score Backward[2] = { S(67, 56), S(49, 40) };
const Score Backward[2] = { S(67, 42), S(49, 24) };
// Connected pawn bonus by opposed, phalanx, twice supported and rank
Score Connected[2][2][2][RANK_NB];
@ -147,9 +147,10 @@ namespace {
// Test for backward pawn.
// If the pawn is passed, isolated, lever or connected it cannot be
// backward. If there are friendly pawns behind on adjacent files
// it cannot be backward either.
// or if it is sufficiently advanced, it cannot be backward either.
if ( (passed | isolated | lever | connected)
|| (ourPawns & pawn_attack_span(Them, s)))
|| (ourPawns & pawn_attack_span(Them, s))
|| (relative_rank(Us, s) >= RANK_5))
backward = false;
else
{