bug#21883: unnecessary bit shifting range limits

[Mark H Weaver]

Stefan Israelsson Tampe <address@hidden> writes:
> how would this slow down the code. just add the correction where you
> throw the exception which should be in a branch outside the hot path.

If you have a suggestion that's simpler than what I did in commits
011aec7e, 9448a078, and 1990aa91, and just as fast in the common cases,
feel free to propose a patch.  The words above are insufficient.

      Mark