Function floor_power_sum 

pub fn floor_power_sum<R>(
    x: R::T,
    y: R::T,
    n: u64,
    a: u64,
    b: u64,
    m: u64,
) -> R::T
where
    R: SemiRing,

$$\sum_{i=0}^{n-1}x^iy^{\left\lfloor\frac{a\times i+b}{m}\right\rfloor}$$