Charcoal, 3236 bytes

×ばつθ⊖η⊖ζ−ζ‹ηζ×ばつθ⊖η⊖ζ−ζ∧‹ηζ›ζ2

Try it online! Try it online! Link is to verbose version of code. Explanation: Not sure that thisNow uses @xnor's correction F<B>2 (my previous correction F<B didn't work in some cases) which is correct but it seemsstill a byte golfier than special-casing F=B; this now makes my answer equivalent to pass alla port of the test caseshis golf to @loopywalt's answer.

Nθ Input `d` as a number
 Nη Input `f` as a number
 Nζ Input `b` as a number
 ζ Input `b`
 X Raised to power
 θ Input `d`
 ×ばつ Multiplied by
 η Input `f`
 ⊖ Decremented
 ÷ Integer divided by
 ζ Input `b`
 ⊖ Decremented
 ⊕ Incremented
 ÷ Integer divided by
 ζ Input `b`
 − Subtract
 η Input `f`
 ‹ Is less than
 ζ Input `b`
 ∧ Logical And
 ζ Input `b`
 › Is greater than
 2 Literal integer `2`
 ×ばつ Multiplied by
 θ Input `d`
 ×ばつ Multiplied by
 η Input `f`
 ⊖ Decremented
 % Modulo
 ζ Input `b`
 ⊖ Decremented
 ⊕ Incremented
 I Cast to string
 Implicitly print