pdep failure

[drtconway]

Great library, thanks for making it!

I am writing succinct data structure code using pdep to implement select on 64-bit words:

pub fn select64(x: u64, idx: usize) -> u64 {
    (1u64 << idx).pdep(x).trailing_zeros() as u64
}

However, the following test is failing:

fn test_select64_2() {
    let x:u64 = 18446744073709551615u64;
    assert_eq!(select64(x, 0), 0);
}

Note that x is 111....111 (i.e. -1).

The error message I'm seeing is:

thread 'words::tests::test_select64_2' panicked at 'attempt to add with overflow', /<path-to-my-home-directory>/.cargo/registry/src/github.com-1ecc6299db9ec823/bitintr-0.3.0/src/pdep.rs:107:17

I'm willing to be convinced that my code is somehow bad, but I think this might be a bug in the library. I'm on an X86_64 Mac.