Function acf_approx_dot 

pub unsafe extern "C" fn acf_approx_dot(
    res: *mut acf_struct,
    initial: *const acf_struct,
    subtract: c_int,
    x: acf_srcptr,
    xstep: slong,
    y: acf_srcptr,
    ystep: slong,
    len: slong,
    prec: slong,
    rnd: arf_rnd_t,
)