137?
so, let's golf it a bit.
107 sounds a lot better:
Code:

Function b($)
 do
  If $+0=$
   $b = iif($ mod 2,'1','0') + $b
   $ = $ / 2
  else
   $b = 2*$b + left($,1)
   $ = right($,~)
  endif
 Until $ = .
EndFunction