Módulo:Exponential search

This is a meta module.

This module is meant to be used only by other modules. It should not be invoked in wikitext.

This module provides a generic exponential search algorithm.

Usage

This module should be loaded with require().

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This módulo was adapted from Module:Exponential search on Wikipedia.
Adaptation is noted for reference and attribution only. This módulo may differ from the original in function or in usage.

---

-- This module provides a generic exponential search algorithm.

local checkType = require('libraryUtil').checkType

local function midPoint(lower, upper)
	return math.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 ~= math.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