Depth dependant aspiration window delta

Split delta value in aspiration window so that when
search depth is less than 24 a smaller delta value
is used. The idea is that the search is likely to
be more accurate at lower depths and so we can exclude
more possibilities, 25% to be exact.

Passed STC
LLR: 2.96 (-2.94, 2.94) [-1.50, 4.50]
Total: 20430 W: 3775 L: 3618 D: 13037

And LTC
LLR: 2.96 (-2.94, 2.94) [0.00, 6.00]
Total: 5032 W: 839 L: 715 D: 3478

Bench: 7451319

diff --git a/src/search.cpp b/src/search.cpp
index d7a8379a14e9507d28950ab7b071e456f2f58a46..421d95fe6d7a70786d7c4d31c064a76b9b850521 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -327,7 +327,7 @@ namespace {
             // Reset aspiration window starting size
             if (depth >= 5)
             {
             // Reset aspiration window starting size
             if (depth >= 5)
             {

-                delta = Value(16);
+                delta = Value(depth > 23 ? 16 : 12);

                 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
                 beta  = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
             }
                 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
                 beta  = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
             }