Depth is already dependent on the actual value
of ONE_PLY, in particular can be expressed like:
Depth = n * ONE_PLY
And because formula is used to calculate R that is
also dependent on the value of ONE_PLY and can be
expressed like:
R = x * ONE_PLY
We don't want to divide depth by a 'ply' value but
directly by an integer number.
Spotted by sf-x
No functional change.
// Null move dynamic reduction based on depth and value
Depth R = 3 * ONE_PLY
- + depth / (2 * ONE_PLY)
+ + depth / 4
+ int(eval - beta) / PawnValueMg * ONE_PLY;
pos.do_null_move(st);