Functions Beyond "+, -, *, /" in Custom Field Formulas

I have encountered multiple instances where logic-based calculations would greatly improve the functionality of my custom fields.  One such instance transpired today where I need to calculate the cost of an item based on 2 different methods.  Based on the result of a simple test, I need my calculated field to use method A or method B.  If I could use the absolute value function, then I can accomplish the rest with the basic "+, -, *, /" operators.

The logic is this:

If x > 0, then use method A, else use method B.

This is accomplished by the following:

(x + |x|) / (2 * x) = 1 or (-x + |-x|) / (2 * -x) = 0

Then I can use this result to multiply one part of the equation by 1 while the other is multiplied by 0, giving the final option needed.

Here is my list of desired functions to add:

absolute value "abs()"

if / then / else statements

sin(), cos(), tan(), arcsin(), arccos(), arctan()

Exponential function " ^ " or "exp()"

I'll think of more and add (and would love to hear from others), but I'm sure you've received this request before.

Thank you kindly!