From 154b8d3ecb19d0b3fa9ec11cc3a1e666dfe0d2ce Mon Sep 17 00:00:00 2001
From: Stefan Geschwentner <stgeschwentner@gmail.com>
Date: Tue, 19 Sep 2023 09:08:58 +0200
Subject: [PATCH] Remove VALUE_KNOWN_WIN.

After removing classic evaluation VALUE_KNOWN_WIN is not anymore returned explicit evaluation. So remove and replace it with VALUE_TB_WIN_IN_MAX_PLY.

Measurement on my big bench (bench 16 1 16 pos1000.fen) verifies that at least with current net the calculated evaluation lies always in the open interval  (-VALUE_KNOWN_WIN, VALUE_KNOWN_WIN).
So i consider this a non-functional change. But to be safe i tested this also at LTC as requested by Stephane Nicolet.

STC:
https://tests.stockfishchess.org/tests/view/64f9db40eaf01be8259a6ed5
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 455296 W: 115981 L: 116217 D: 223098
Ptnml(0-2): 1415, 50835, 123420, 50527, 1451

LTC:
https://tests.stockfishchess.org/tests/view/650bfd867ca0d3f7bbf25feb
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 35826 W: 9170 L: 8973 D: 17683
Ptnml(0-2): 12, 3523, 10645, 3722, 11

closes https://github.com/official-stockfish/Stockfish/pull/4792

Bench: 1603079
---
 src/search.cpp | 10 +++++-----
 src/types.h    |  1 -
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 936aa0db..3e19000a 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -778,7 +778,7 @@ namespace {
         &&  depth < 9
         &&  eval - futility_margin(depth, cutNode && !ss->ttHit, improving) - (ss-1)->statScore / 306 >= beta
         &&  eval >= beta
-        &&  eval < 24923) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
+        &&  eval < 24923) // smaller than TB wins
         return eval;
 
     // Step 9. Null move search with verification search (~35 Elo)
@@ -908,8 +908,8 @@ moves_loop: // When in check, search starts here
         && (tte->bound() & BOUND_LOWER)
         && tte->depth() >= depth - 4
         && ttValue >= probCutBeta
-        && abs(ttValue) <= VALUE_KNOWN_WIN
-        && abs(beta) <= VALUE_KNOWN_WIN)
+        && abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY
+        && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY)
         return probCutBeta;
 
     const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
@@ -1050,7 +1050,7 @@ moves_loop: // When in check, search starts here
               &&  move == ttMove
               && !excludedMove // Avoid recursive singular search
            /* &&  ttValue != VALUE_NONE Already implicit in the next condition */
-              &&  abs(ttValue) < VALUE_KNOWN_WIN
+              &&  abs(ttValue) < VALUE_TB_WIN_IN_MAX_PLY
               && (tte->bound() & BOUND_LOWER)
               &&  tte->depth() >= depth - 3)
           {
@@ -1541,7 +1541,7 @@ moves_loop: // When in check, search starts here
             // Futility pruning and moveCount pruning (~10 Elo)
             if (   !givesCheck
                 &&  to_sq(move) != prevSq
-                &&  futilityBase > -VALUE_KNOWN_WIN
+                &&  futilityBase > VALUE_TB_LOSS_IN_MAX_PLY
                 &&  type_of(move) != PROMOTION)
             {
                 if (moveCount > 2)
diff --git a/src/types.h b/src/types.h
index f81d30fe..340c47a5 100644
--- a/src/types.h
+++ b/src/types.h
@@ -161,7 +161,6 @@ enum Bound {
 enum Value : int {
   VALUE_ZERO      = 0,
   VALUE_DRAW      = 0,
-  VALUE_KNOWN_WIN = 10000,
   VALUE_MATE      = 32000,
   VALUE_INFINITE  = 32001,
   VALUE_NONE      = 32002,
-- 
2.39.2