binary_search_index.rb

def bsearch_index(ary)
  low = 0
  high = ary.length
  smaller = 0
  satisfied = 0

  while low < high
     mid = low + ((high - low) / 2)
     val = ary[mid]
     begin
     v = yield val
     rescue
       val = ary[mid+1]
       retry
     end

     if v == true
       satisfied = 1
       smaller = 1
     elsif v == false || v == nil
       smaller = 0
     else
       raise TypeError, "wrong argument type #{v.class} (must be numeric, true, false or nil)"
     end

     if smaller > 0
       high = mid
     else
       low = mid + 1
     end
  end

  return nil if low == ary.length
  return nil unless satisfied
  return low
end