Function bitcoin_muhash::mulnadd3

pub fn mulnadd3(
    c0: &mut Limb,
    c1: &mut Limb,
    c2: &mut Limb,
    d0: &mut Limb,
    d1: &mut Limb,
    d2: &mut Limb,
    n: &Limb
)

| [c0,c1,c2] += n * [d0,d1,d2]. c2 is 0 | initially |