FLT is not FTL
 
 Experimental Pango module with m17n-lib shows FLT is 4 to 5 times slower than the original C codes.  Why?
  inefficient interface between m17n-lib and Pango
      M17n-lib provides only high level API.
  slowness of FLT interpreter
      The current code is very naive.
      Lot's of room for tuning up.
  slowness of OTF handling
      We are now using libotf.
      Using HarfBuzz will improve it a lot.
  slowness of FLT's algorithm
      Redundant regexp matching.
      Unnecessary stages.