Add sf16 WDL model

Author: niklasf

chess/engine.py

@@ -44,7 +44,7 @@
 
 try:
     from typing import Literal
-    _WdlModel = Literal["sf", "sf15.1", "sf15", "sf14", "sf12", "lichess"]
+    _WdlModel = Literal["sf", "sf16", "sf15.1", "sf15", "sf14", "sf12", "lichess"]
 except ImportError:
     # Before Python 3.8.
     _WdlModel = str  # type: ignore
@@ -637,11 +637,20 @@ def __ge__(self, other: object) -> bool:
         else:
             return NotImplemented
 
+def _sf16_wins(cp: int, *, ply: int) -> int:
+    # https://github.com/official-stockfish/Stockfish/blob/sf_16/src/uci.h#L38
+    NormalizeToPawnValue = 328
+    # https://github.com/official-stockfish/Stockfish/blob/sf_16/src/uci.cpp#L200-L224
+    m = min(240, max(ply, 0)) / 64
+    a = (((0.38036525 * m + -2.82015070) * m + 23.17882135) * m) + 307.36768407
+    b = (((-2.29434733 * m + 13.27689788) * m + -14.26828904) * m) + 63.45318330
+    x = min(4000, max(cp * NormalizeToPawnValue / 100, -4000))
+    return int(0.5 + 1000 / (1 + math.exp((a - x) / b)))
 
 def _sf15_1_wins(cp: int, *, ply: int) -> int:
-    # https://github.com/official-stockfish/Stockfish/blob/sf_15.1/src/uci.cpp#L200-L224
     # https://github.com/official-stockfish/Stockfish/blob/sf_15.1/src/uci.h#L38
     NormalizeToPawnValue = 361
+    # https://github.com/official-stockfish/Stockfish/blob/sf_15.1/src/uci.cpp#L200-L224
     m = min(240, max(ply, 0)) / 64
     a = (((-0.58270499 * m + 2.68512549) * m + 15.24638015) * m) + 344.49745382
     b = (((-2.65734562 * m + 15.96509799) * m + -20.69040836) * m) + 73.61029937
@@ -703,9 +712,12 @@ def wdl(self, *, model: _WdlModel = "sf", ply: int = 30) -> Wdl:
         elif model == "sf15":
             wins = _sf15_wins(self.cp, ply=ply)
             losses = _sf15_wins(-self.cp, ply=ply)
-        else:
+        elif model == "sf15.1":
             wins = _sf15_1_wins(self.cp, ply=ply)
             losses = _sf15_1_wins(-self.cp, ply=ply)
+        else:
+            wins = _sf16_wins(self.cp, ply=ply)
+            losses = _sf16_wins(-self.cp, ply=ply)
         draws = 1000 - wins - losses
         return Wdl(wins, draws, losses)
 

test.py

@@ -3002,6 +3002,7 @@ def test_wdl_model(self):
         self.assertEqual(chess.engine.Cp(146).wdl(model="sf14", ply=25), chess.engine.Wdl(601, 398, 1))
         self.assertEqual(chess.engine.Cp(40).wdl(model="sf15", ply=25), chess.engine.Wdl(58, 937, 5))
         self.assertEqual(chess.engine.Cp(100).wdl(model="sf15.1", ply=64), chess.engine.Wdl(497, 503, 0))
+        self.assertEqual(chess.engine.Cp(-52).wdl(model="sf16", ply=63), chess.engine.Wdl(0, 932, 68))
 
     @catchAndSkip(FileNotFoundError, "need stockfish")
     def test_sf_forced_mates(self):