Introduce Optimism

[stockfish] / src / misc.h

diff --git a/src/misc.h b/src/misc.h
index 718e5558178fafbca9edba04fbb64d0fb03e4c9a..c17441306c1a5a621579233b25441342712e68e0 100644 (file)
--- a/src/misc.h
+++ b/src/misc.h
@@ -138,6 +138,33 @@ private:
   std::size_t size_ = 0;
 };
 
+
+/// sigmoid(t, x0, y0, C, P, Q) implements a sigmoid-like function using only integers,
+/// with the following properties:
+/// 
+///  -  sigmoid is centered in (x0, y0)
+///  -  sigmoid has amplitude [-P/Q , P/Q] instead of [-1 , +1]
+///  -  limit is (y0 - P/Q) when t tends to -infinity
+///  -  limit is (y0 + P/Q) when t tends to +infinity
+///  -  the slope can be adjusted using C > 0, smaller C giving a steeper sigmoid
+///  -  the slope of the sigmoid when t = x0 is P/(Q*C)
+///  -  sigmoid is increasing with t when P > 0 and Q > 0
+///  -  to get a decreasing sigmoid, call with -t, or change sign of P
+///  -  mean value of the sigmoid is y0
+///
+/// Use <https://www.desmos.com/calculator/jhh83sqq92> to draw the sigmoid
+
+inline int64_t sigmoid(int64_t t, int64_t x0,
+                                  int64_t y0,
+                                  int64_t  C,
+                                  int64_t  P,
+                                  int64_t  Q)
+{
+   assert(C > 0);
+   return y0 + P * (t-x0) / (Q * (std::abs(t-x0) + C)) ;
+}
+
+
 /// xorshift64star Pseudo-Random Number Generator
 /// This class is based on original code written and dedicated
 /// to the public domain by Sebastiano Vigna (2014).