* %$2^n$%, say, we'll end up with %$-d$% (or would do, if we weren't
* sticking to unsigned arithmetic for good performance). So instead, we
* rewrite this as %$2^n - 2^{n-1} + d$% and everything will be good.
* %$2^n$%, say, we'll end up with %$-d$% (or would do, if we weren't
* sticking to unsigned arithmetic for good performance). So instead, we
* rewrite this as %$2^n - 2^{n-1} + d$% and everything will be good.