Function tor_llcrypto::util::ct::ct_lookup

pub fn ct_lookup<T, F>(array: &[T], matches: F) -> Option<&T>
where
    F: Fn(&T) -> Choice,

Try to find an item in a slice without leaking where and whether the item was found.

If there is any item x in the array for which matches(x) is true, this function will return a reference to one such item. (We don’t specify which.)

Otherwise, this function returns none.

We evaluate matches on every item of the array, and try not to leak by timing which element (if any) matched. Note that if matches itself has side channels, this function can’t hide them.

Note that this doesn’t necessarily do a constant-time comparison, and that it is not constant-time for the found/not-found case.