Function svn_repos_dated_revision 

pub unsafe extern "C" fn svn_repos_dated_revision(
    revision: *mut svn_revnum_t,
    repos: *mut svn_repos_t,
    tm: apr_time_t,
    pool: *mut apr_pool_t,
) -> *mut svn_error_t

Set @a *revision to the revision number in @a repos’s filesystem that was youngest at time @a tm.