From 14f7d9a6292ac7c2e92d9bcab7dd7186eb151c02 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 25 Jan 2015 11:07:43 +0100
Subject: [PATCH] Re-arrange Skill struct

Instead of swapping sub-optimal move in Skill
d'tor, make it explicitly at the end of the search.

Also streamline and clarify relation with multiPV
and pass it directly instead of relying on the hacky
'candidates' member.

No functional change.
---
 src/search.cpp | 58 ++++++++++++++++++++++++--------------------------
 1 file changed, 28 insertions(+), 30 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index a15f259e..4515bba0 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -105,22 +105,14 @@ namespace {
   string uci_pv(const Position& pos, Depth depth, Value alpha, Value beta);
 
   struct Skill {
-    Skill(int l, size_t rootSize) : level(l),
-                                    candidates(l < 20 ? std::min(4, (int)rootSize) : 0),
-                                    best(MOVE_NONE) {}
-   ~Skill() {
-      if (candidates) // Swap best PV line with the sub-optimal one
-          std::swap(RootMoves[0], *std::find(RootMoves.begin(),
-                    RootMoves.end(), best ? best : pick_move()));
-    }
-
-    size_t candidates_size() const { return candidates; }
+    Skill(int l) : level(l) {}
+    bool enabled() const { return level < 20; }
     bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
-    Move pick_move();
+    Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
+    Move pick_best(size_t multiPV);
 
     int level;
-    size_t candidates;
-    Move best;
+    Move best = MOVE_NONE;
   };
 
 } // namespace
@@ -309,11 +301,14 @@ namespace {
     Followupmoves.clear();
 
     size_t multiPV = Options["MultiPV"];
-    Skill skill(Options["Skill Level"], RootMoves.size());
+    Skill skill(Options["Skill Level"]);
 
-    // Do we have to play with skill handicap? In this case enable MultiPV search
-    // that we will use behind the scenes to retrieve a set of possible moves.
-    multiPV = std::max(multiPV, skill.candidates_size());
+    // When playing with strength handicap enable MultiPV search that we will
+    // use behind the scenes to retrieve a set of possible moves.
+    if (skill.enabled())
+        multiPV = std::max(multiPV, (size_t)4);
+
+    multiPV = std::min(multiPV, RootMoves.size());
 
     // Iterative deepening loop until requested to stop or target depth reached
     while (++depth < DEPTH_MAX && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
@@ -327,7 +322,7 @@ namespace {
             rm.previousScore = rm.score;
 
         // MultiPV loop. We perform a full root search for each PV line
-        for (PVIdx = 0; PVIdx < std::min(multiPV, RootMoves.size()) && !Signals.stop; ++PVIdx)
+        for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
         {
             // Reset aspiration window starting size
             if (depth >= 5 * ONE_PLY)
@@ -399,14 +394,13 @@ namespace {
                 sync_cout << "info nodes " << RootPos.nodes_searched()
                           << " time " << Time::now() - SearchTime << sync_endl;
 
-            else if (   PVIdx + 1 == std::min(multiPV, RootMoves.size())
-                     || Time::now() - SearchTime > 3000)
+            else if (PVIdx + 1 == multiPV || Time::now() - SearchTime > 3000)
                 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
         }
 
-        // If skill levels are enabled and time is up, pick a sub-optimal best move
-        if (skill.candidates_size() && skill.time_to_pick(depth))
-            skill.pick_move();
+        // If skill level is enabled and time is up, pick a sub-optimal best move
+        if (skill.enabled() && skill.time_to_pick(depth))
+            skill.pick_best(multiPV);
 
         // Have we found a "mate in x"?
         if (   Limits.mate
@@ -435,6 +429,11 @@ namespace {
             }
         }
     }
+
+    // If skill level is enabled, swap best PV line with the sub-optimal one
+    if (skill.enabled())
+        std::swap(RootMoves[0], *std::find(RootMoves.begin(),
+                  RootMoves.end(), skill.best_move(multiPV)));
   }
 
 
@@ -1370,24 +1369,23 @@ moves_loop: // When in check and at SpNode search starts from here
   }
 
 
-  // When playing with a strength handicap, choose best move among the first 'candidates'
-  // RootMoves using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
+  // When playing with strength handicap, choose best move among a set of RootMoves
+  // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
 
-  Move Skill::pick_move() {
+  Move Skill::pick_best(size_t multiPV) {
 
     // PRNG sequence should be non-deterministic, so we seed it with the time at init
     static PRNG rng(Time::now());
 
     // RootMoves are already sorted by score in descending order
-    int variance = std::min(RootMoves[0].score - RootMoves[candidates - 1].score, PawnValueMg);
+    int variance = std::min(RootMoves[0].score - RootMoves[multiPV - 1].score, PawnValueMg);
     int weakness = 120 - 2 * level;
     int maxScore = -VALUE_INFINITE;
-    best = MOVE_NONE;
 
     // Choose best move. For each move score we add two terms both dependent on
-    // weakness. One deterministic and bigger for weaker moves, and one random,
+    // weakness. One deterministic and bigger for weaker levels, and one random,
     // then we choose the move with the resulting highest score.
-    for (size_t i = 0; i < candidates; ++i)
+    for (size_t i = 0; i < multiPV; ++i)
     {
         int score = RootMoves[i].score;
 
-- 
2.39.2