Add log depth as term to reduction factors.
Replace most reduction factors with a linear term of the form X + Y * msb(depth) (using msb(depth) as simple and fast approximation for log(depth))
and tune the weights with following SPSA test: https://tests.stockfishchess.org/tests/view/689903860049e8ccef9d6415.
Here the tuned values of X[8] and Y[8] were ignored because a simple test with this parameters alone failed badly (https://tests.stockfishchess.org/tests/view/68992b350049e8ccef9d6482).
Passed STC:
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 32448 W: 8651 L: 8342 D: 15455
Ptnml(0-2): 81, 3695, 8408, 3914, 126
https://tests.stockfishchess.org/tests/view/6899489b0049e8ccef9d64ad
Passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 73854 W: 19042 L: 18649 D: 36163
Ptnml(0-2): 37, 7908, 20659, 8271, 52
https://tests.stockfishchess.org/tests/view/689abbe7fd8719b088c8d514
closes https://github.com/official-stockfish/Stockfish/pull/6229
Bench: 3151102