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Increase null reduction at high depths

Linear rule, less aggressive then Dann's one.

It seems it scales well with depth. We will need to
verify against weaker engine if it keeps the score.

After 999 games at 1+0 on my Dual Core
Mod vs Orig +232 =534 -207  +9 ELO

After 1000 games by Martin Thoresen on his QUAD at 1+0
Mod vs Orig 521/479 52.10%

Functionality Signature: 17655312

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
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1 parent d11af1d commit 860260c3b1c8da9906fddd2385fe127c6f5d10f1 @mcostalba committed Dec 31, 2009
Showing with 1 addition and 1 deletion.
  1. +1 −1 src/search.cpp
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2 src/search.cpp
@@ -1376,7 +1376,7 @@ namespace {
pos.do_null_move(st);
// Null move dynamic reduction based on depth
- int R = (depth >= 5 * OnePly ? 4 : 3);
+ int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
// Null move dynamic reduction based on value
if (approximateEval - beta > PawnValueMidgame)

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