Handles the sanity check for the parameterisation (P,a,b)

## Usage

`assert_sane_parameterication(P, a, b)`

## Arguments

- P
Modulus used to devide n, iff n is equivalent to (0 mod P).

- a
Factor by which to multiply n.

- b
Value to add to the scaled value of n.

## Details

Required by both the function and reverse function, to assert that they
have sane parameters, otherwise will force stop the execution.