"D" suffix simply indicates that the number in use is a double, not a float. Although best I know Java goes the other way; fractional numbers are double by default and floats must be affixed with F, unlike whole numbers which are integers unless specified as long (ie:
). You can check this against the Number:
Number n = 0.85;
Returns Double, while:
Number n = 85;
So in Java, 1.0 = 1.0D.
As for the rest of the equations, there's simply no way to describe them aside from what they do. Its clearly calculating rotation movements, but I can't tell you why or for what.