Rate index   mod first   new   org
index 1109/s    --  -24%  -38%  -48%  -52% # moved @mult out loop and used index
mod   1464/s   32%    --  -18%  -31%  -36% # Your mod
first 1780/s   61%   22%    --  -16%  -22% # The original long code
new   2116/s   91%   45%   19%    --   -8% # my version, but inline += * shift for reverse split
org   2288/s  106%   56%   29%    8%    -- # my original update s/(\d+)-//; and split