Encourage rook lift to third rank

This change to the Rook psqt encourages rook lifts to the third rank
on the two center files.

STC 10+0.1 th 1 :
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 40654 W: 9028 L: 8704 D: 22922
http://tests.stockfishchess.org/tests/view/5d885da60ebc5906dd3e9fcd

LTC 60+0.6 th 1 :
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 56963 W: 9530 L: 9196 D: 38237
http://tests.stockfishchess.org/tests/view/5d88618c0ebc5906dd3ea45f

Thanks to @snicolet for mentioning that Komodo does this a lot and
Stockfish doesn't, which gave me the idea for this patch, and to
@noobpwnftw for providing cores to fishtest which allowed very quick
testing.

Future work: perhaps this can be refined somehow to encourage this
on other files, my attempts have failed.

Closes https://github.com/official-stockfish/Stockfish/pull/2322

Bench: 3950249

diff --git a/src/psqt.cpp b/src/psqt.cpp
index 36d99feb7e05280ce9ee6aacc9ab84aec8ebd8d8..2b06931c6f9ed87b69347dbe052b1a5b5cebbe47 100644 (file)
--- a/src/psqt.cpp
+++ b/src/psqt.cpp
@@ -61,7 +61,7 @@ constexpr Score Bonus[][RANK_NB][int(FILE_NB) / 2] = {
   { // Rook
    { S(-24, -2), S(-13,-6), S(-7, -3), S( 2,-2) },
    { S(-18,-10), S(-10,-7), S(-5,  1), S( 9, 0) },
-   { S(-21, 10), S( -7,-4), S( 3,  2), S(-1,-2) },
+   { S(-21, 10), S( -7,-4), S( 3,  2), S( 7,-2) },
    { S(-13, -5), S( -5, 2), S(-4, -8), S(-6, 8) },
    { S(-24, -8), S(-12, 5), S(-1,  4), S( 6,-9) },
    { S(-24,  3), S( -4,-2), S( 4,-10), S(10, 7) },