From: Stéphane Nicolet <cassio@free.fr>
Date: Fri, 8 May 2020 08:32:52 +0000 (+0200)
Subject: Move 50 moves counter to initiative.
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=cca643669db016f20c6e91f50892a0b44f297a48;hp=d4763424d2728fe2dfd0a6fe747666feb6a2fdbb

Move 50 moves counter to initiative.

simplify the usage of the 50 moves counter,
moving it frome the scale factor to initiative.

This patch was inspired by recent games where a blocked or semi-blocked position
was 'blundered', by moving a pawn, into a lost endgame. This patch improves this situation,
finding a more robust move more often.

for example (1s searches with many threads):
```
FEN 8/p3kp2/Pp2p3/1n2PpP1/5P2/1Kp5/8/R7 b - - 68 143

master:
      6 bestmove b5c7
      6 bestmove e7e8
     12 bestmove e7d8
    176 bestmove e7d7
patch:
      3 bestmove b5c7
      5 bestmove e7d8
    192 bestmove e7d7
```

fixes https://github.com/official-stockfish/Stockfish/issues/2620

the patch also tests well

passed STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 50168 W: 9508 L: 9392 D: 31268
Ptnml(0-2): 818, 5873, 11616, 5929, 848
https://tests.stockfishchess.org/tests/view/5ebb07287dd5693aad4e680b

passed LTC
LLR: 2.93 (-2.94,2.94) {-1.50,0.50}
Total: 7520 W: 981 L: 870 D: 5669
Ptnml(0-2): 49, 647, 2256, 760, 48
https://tests.stockfishchess.org/tests/view/5ebbff747dd5693aad4e6858

closes https://github.com/official-stockfish/Stockfish/pull/2666

Bench: 4395562
---

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index e663f21f..d972db5a 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -739,6 +739,7 @@ namespace {
                     + 24 * infiltration
                     + 51 * !pos.non_pawn_material()
                     - 43 * almostUnwinnable
+                    -  2 * pos.rule50_count()
                     -110 ;
 
     Value mg = mg_value(score);
@@ -778,8 +779,6 @@ namespace {
         }
         else
             sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
-
-        sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
     }
 
     return ScaleFactor(sf);
@@ -856,7 +855,8 @@ namespace {
         Trace::add(TOTAL, score);
     }
 
-    return  (pos.side_to_move() == WHITE ? v : -v) + Tempo; // Side to move point of view
+    // Side to move point of view
+    return (pos.side_to_move() == WHITE ? v : -v) + Tempo;
   }
 
 } // namespace