-- This module provides a generic exponential search algorithm.  local checkType = require('libraryUtil').checkType local floor = math.floor  local function midPoint(lower, upper)  return floor(lower + (upper - lower) / 2) end  local function search(testFunc, i, lower, upper)  if testFunc(i) then  if i + 1 == upper then  return i  end  lower = i  if upper then  i = midPoint(lower, upper)  else  i = i * 2  end  return search(testFunc, i, lower, upper)  else  upper = i  i = midPoint(lower, upper)  return search(testFunc, i, lower, upper)  end end  return function (testFunc, init)  checkType('Exponential search', 1, testFunc, 'function')  checkType('Exponential search', 2, init, 'number', true)  if init and (init < 1 or init ~= floor(init) or init == math.huge) then  error(string.format(  "invalid init value '%s' detected in argument #2 to " ..  "'Exponential search' (init value must be a positive integer)",  tostring(init)  ), 2)  end  init = init or 2  if not testFunc(1) then  return nil  end  return search(testFunc, init, 1, nil) end