UC r,i=1;WH(r+=c&i?r++:r,i+=i);RT r;

I am afraid that this is non-conforming code, because in the section "r+=c&i?r++:r", the variable "r" is modified twice between sequence points. Perhaps "r+=c&i?r+1:r", although this introduces an additional constant.

Not to matter because I've taken your idea and extended it to:

UC r,i=1;WH(r+=r+c/i%2,i+=i);RT r;