Reduce history 4 times instead of 2 when reach the maximum

This gives more weight to newer entries.

After 999 games at 1'+ 0" we have:

Mod vs Orig +233/-208/=558 51.25% +9 ELO

Confirmed by another session of 437 games:

Mod vs Orig +109/-92/=236 51.95% +14 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/history.cpp b/src/history.cpp
index 6fe222feb4dfe7bec169d177bbb4b985ff350bc7..edd5cdb7c500a6e86166705c3eb47097db982fb1 100644 (file)
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -64,7 +64,7 @@ void History::success(Piece p, Square to, Depth d) {
   if (history[p][to] >= HistoryMax)
       for (int i = 0; i < 16; i++)
           for (int j = 0; j < 64; j++)
-              history[i][j] /= 2;
+              history[i][j] /= 4;
 }