My point is that if I'm going to optimize anything, this is the sub to spend my time on. The other two candidates I've already tweaked, and even if I doubled their performance I'd still get only a modest gain. A clever insight on this sub could make a much bigger difference.

%Time ExclSec CumulS #Calls sec/call Csec/c  Name
 48.8   20.83 20.710 130000   0.0002 0.0002  FTS::printto
 17.5   7.499  7.490  10000   0.0007 0.0007  FTS::addstring
 15.3   6.569  6.450 120000   0.0001 0.0001  FTS::assign
 6.77   2.892 42.220  10000   0.0003 0.0042  main::__ANON__
 2.55   1.090 43.310  10002   0.0001 0.0043  Benchmark::__ANON__
 2.44   1.040  1.030  10000   0.0001 0.0001  main::cleverlinks
 2.20   0.940  8.410  10000   0.0001 0.0008  FTS::parsehandle
 1.45   0.620  0.610  10000   0.0001 0.0001  IO::File::open
 1.38   0.590  1.650  10000   0.0001 0.0002  IO::File::new
 1.38   0.590 10.620  10000   0.0001 0.0011  FTS::parsefile
 1.03   0.440 11.410  10000   0.0000 0.0011  FTS::new_fromfile
 0.94   0.400  0.390  10000   0.0000 0.0000  FTS::new
 0.77   0.330  0.320  10000   0.0000 0.0000  Symbol::gensym
 0.42   0.180  0.480  10000   0.0000 0.0000  IO::Handle::new
 0.07   0.030  0.010  20000   0.0000 0.0000  IO::Handle::DESTROY