From: protonspring <mike@whiteley.org>
Date: Sun, 14 Jul 2019 12:46:10 +0000 (-0600)
Subject: Remove std::pow from reduction. (#2234)
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=650aeaf2420bdac00de03963132d82a415193a1c

Remove std::pow from reduction. (#2234)

This is a functional simplification that removes the std::pow from reduction. The resulting reduction values are within 1% of master.

This is a simplification because i believe an fp addition and multiplication is much faster than a call to std::pow() which is historically slow and performance varies widely on different architectures.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 23471 W: 5245 L: 5127 D: 13099
http://tests.stockfishchess.org/tests/view/5d27ac1b0ebc5925cf0d476b

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 51533 W: 8736 L: 8665 D: 34132
http://tests.stockfishchess.org/tests/view/5d27b74e0ebc5925cf0d493c

Bench 3765158
---

diff --git a/src/search.cpp b/src/search.cpp
index bd5ae75e..df19108f 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -503,7 +503,7 @@ void Thread::search() {
 
           // If the bestMove is stable over several iterations, reduce time accordingly
           timeReduction = lastBestMoveDepth + 10 * ONE_PLY < completedDepth ? 1.95 : 1.0;
-          double reduction = std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction;
+          double reduction = (1.25 + mainThread->previousTimeReduction) / (2.25 * timeReduction);
 
           // Use part of the gained time from a previous stable move for the current move
           for (Thread* th : Threads)