UCI_Elo implementation (#2225)

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index df19108fb2db4dd28642c1ef20b34f49aa5f2a53..2c2321ee9ca0bb5f48bd99b4fc068986a8d2a297 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -271,7 +271,7 @@ void MainThread::search() {
   // Check if there are threads with a better score than main thread
   if (    Options["MultiPV"] == 1
       && !Limits.depth
-      && !Skill(Options["Skill Level"]).enabled()
+      && !(Skill(Options["Skill Level"]).enabled() || Options["UCI_LimitStrength"])
       &&  rootMoves[0].pv[0] != MOVE_NONE)
   {
       std::map<Move, int64_t> votes;
@@ -335,11 +335,18 @@ void Thread::search() {
   beta = VALUE_INFINITE;
 
   multiPV = Options["MultiPV"];
+
   // Pick integer skill levels, but non-deterministically round up or down
   // such that the average integer skill corresponds to the input floating point one.
+  // UCI_Elo is converted to a suitable fractional skill level, using anchoring
+  // to CCRL Elo (goldfish 1.13 = 2000) and a fit through Ordo derived Elo
+  // for match (TC 60+0.6) results spanning a wide range of k values.
   PRNG rng(now());
-  int intLevel = int(Options["Skill Level"]) +
-        ((Options["Skill Level"] - int(Options["Skill Level"])) * 1024 > rng.rand<unsigned>() % 1024  ? 1 : 0);
+  double floatLevel = Options["UCI_LimitStrength"] ?
+                        clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
+                        double(Options["Skill Level"]);
+  int intLevel = int(floatLevel) +
+                 ((floatLevel - int(floatLevel)) * 1024 > rng.rand<unsigned>() % 1024  ? 1 : 0);
   Skill skill(intLevel);
 
   // When playing with strength handicap enable MultiPV search that we will