pub fn modf(x: f64) -> (f64, f64) {

    let rv2: f64;

    let mut u = x.to_bits();

    let mask: u64;

    let e = ((u >> 52 & 0x7ff) as i32) - 0x3ff;

    /* no fractional part */

    if e >= 52 {

        rv2 = x;

        if e == 0x400 && (u << 12) != 0 {

            /* nan */

            return (x, rv2);

        }

        u &= 1 << 63;

        return (f64::from_bits(u), rv2);

    }

    /* no integral part*/

    if e < 0 {

        u &= 1 << 63;

        rv2 = f64::from_bits(u);

        return (x, rv2);

    }

    mask = ((!0) >> 12) >> e;

    if (u & mask) == 0 {

        rv2 = x;

        u &= 1 << 63;

        return (f64::from_bits(u), rv2);

    }

    u &= !mask;

    rv2 = f64::from_bits(u);

    return (x - rv2, rv2);

}