From 1f9404434dcfd1013e20266a79dfed5d0271294a Mon Sep 17 00:00:00 2001
From: Carlos Esparza <ca2010es@gmail.com>
Date: Sun, 24 Nov 2024 16:17:42 -0800
Subject: [PATCH] Simplify picking of evasion moves

Sort evasions before we start returning them in next_move() (just like
every other kind of move) instead of looking for the biggest element on
every call to next_move(). The bench number changes because the old
method is not equivalent to a stable sort.

Passed STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 132064 W: 34318 L: 34204 D: 63542
Ptnml(0-2): 392, 15522, 34106, 15604, 408
https://tests.stockfishchess.org/tests/view/6743fee086d5ee47d953f9ca

Passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 97542 W: 24899 L: 24757 D: 47886
Ptnml(0-2): 63, 10646, 27193, 10824, 45
https://tests.stockfishchess.org/tests/view/674509cd86d5ee47d953fb96

closes https://github.com/official-stockfish/Stockfish/pull/5700

Bench: 1094825
---
 AUTHORS          |  1 +
 src/movepick.cpp | 29 ++++++++++-------------------
 src/movepick.h   |  7 +------
 3 files changed, 12 insertions(+), 25 deletions(-)

diff --git a/AUTHORS b/AUTHORS
index 31a64c17..ddc53ec0 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -45,6 +45,7 @@ Bruno de Melo Costa (BM123499)
 Bruno Pellanda (pellanda)
 Bryan Cross (crossbr)
 candirufish
+Carlos Esparza Sánchez (ces42)
 Chess13234
 Chris Cain (ceebo)
 Ciekce
diff --git a/src/movepick.cpp b/src/movepick.cpp
index df722ece..96f03171 100644
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -18,11 +18,9 @@
 
 #include "movepick.h"
 
-#include <algorithm>
 #include <array>
 #include <cassert>
 #include <limits>
-#include <utility>
 
 #include "bitboard.h"
 #include "position.h"
@@ -199,19 +197,13 @@ void MovePicker::score() {
 
 // Returns the next move satisfying a predicate function.
 // This never returns the TT move, as it was emitted before.
-template<MovePicker::PickType T, typename Pred>
+template<typename Pred>
 Move MovePicker::select(Pred filter) {
 
-    while (cur < endMoves)
-    {
-        if constexpr (T == Best)
-            std::swap(*cur, *std::max_element(cur, endMoves));
-
+    for (; cur < endMoves; ++cur)
         if (*cur != ttMove && filter())
             return *cur++;
 
-        cur++;
-    }
     return Move::none();
 }
 
@@ -245,7 +237,7 @@ top:
         goto top;
 
     case GOOD_CAPTURE :
-        if (select<Next>([&]() {
+        if (select([&]() {
                 // Move losing capture to endBadCaptures to be tried later
                 return pos.see_ge(*cur, -cur->value / 18) ? true
                                                           : (*endBadCaptures++ = *cur, false);
@@ -269,7 +261,7 @@ top:
         [[fallthrough]];
 
     case GOOD_QUIET :
-        if (!skipQuiets && select<Next>([]() { return true; }))
+        if (!skipQuiets && select([]() { return true; }))
         {
             if ((cur - 1)->value > -7998 || (cur - 1)->value <= quiet_threshold(depth))
                 return *(cur - 1);
@@ -286,7 +278,7 @@ top:
         [[fallthrough]];
 
     case BAD_CAPTURE :
-        if (select<Next>([]() { return true; }))
+        if (select([]() { return true; }))
             return *(cur - 1);
 
         // Prepare the pointers to loop over the bad quiets
@@ -298,7 +290,7 @@ top:
 
     case BAD_QUIET :
         if (!skipQuiets)
-            return select<Next>([]() { return true; });
+            return select([]() { return true; });
 
         return Move::none();
 
@@ -307,17 +299,16 @@ top:
         endMoves = generate<EVASIONS>(pos, cur);
 
         score<EVASIONS>();
+        partial_insertion_sort(cur, endMoves, std::numeric_limits<int>::min());
         ++stage;
         [[fallthrough]];
 
     case EVASION :
-        return select<Best>([]() { return true; });
+    case QCAPTURE :
+        return select([]() { return true; });
 
     case PROBCUT :
-        return select<Next>([&]() { return pos.see_ge(*cur, threshold); });
-
-    case QCAPTURE :
-        return select<Next>([]() { return true; });
+        return select([&]() { return pos.see_ge(*cur, threshold); });
     }
 
     assert(false);
diff --git a/src/movepick.h b/src/movepick.h
index 0278b70e..ab4e832f 100644
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -35,11 +35,6 @@ class Position;
 // a cut-off first.
 class MovePicker {
 
-    enum PickType {
-        Next,
-        Best
-    };
-
    public:
     MovePicker(const MovePicker&)            = delete;
     MovePicker& operator=(const MovePicker&) = delete;
@@ -57,7 +52,7 @@ class MovePicker {
     void skip_quiet_moves();
 
    private:
-    template<PickType T, typename Pred>
+    template<typename Pred>
     Move select(Pred);
     template<GenType>
     void     score();