Issue #22 proposed fix.

[snakehand]

Avoid performing logical and on !mask as this will cause a clippy lint error if result is 0.

Reformulate boolean check to os logial or opereations instead.

[wrenger]

Thanks for the PR. This check, however, does not entirely catch all cases. Take the following as an example:

#[test]
#[should_panic]
fn negative_pos_overflow() {
    #[bitfield(u32)]
    struct MyBitfield {
        #[bits(3)]
        negative: i32,
        #[bits(29)]
        __: (),
    }
    // 4 is too large for a 3bit singed integer
    MyBitfield::new().with_negative(4); 
}

As for fixing #24, I had to redesign the bounds check entirely.