-- 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
