Pi Calculator

--Made by TurtleHunter

--bigInt from http://www.computercraft.info/forums2/index.php?/topic/12137-bigint-arbitrary-precision-unsigned-integers/  KillaVanilla

local yieldTime
local function yield() --http://www.computercraft.info/forums2/index.php?/topic/11245-avoiding-too-long-without-yielding-the-efficient-way  modified to sleep(so you can see the result) instead of pulling a event
    if yieldTime then
        if os.clock() - yieldTime > 2 then
            print("Yielding...")
            sleep(2)
            yieldTime = nil
        end
    else
        yieldTime = os.clock() -- store the time
    end
end
function download(name, url)
	term.write("Downloading "..name)
	local sResponse = http.get(url)
	if fs.exists(name) then error("Download: File exist", 0) end
	local file = fs.open(name, "w")
	file.write(sResponse.readAll())
	sResponse.close()
	file.close()
	term.write("   Done")
end

if not fs.exists("bigInt") then download("bigInt", "http://www.pastebin.com/raw.php?i=th3Vrppb") end

os.loadAPI("bigInt")

function pi(precision) --localized :P ported to cclua and bigInt from http://powdertoy.co.uk/Discussions/Thread/View.html?Thread=16546
	local pival = 1
 	local isNegative = 1
 	local k = 0
 	local calc = 3
 	while k < precision do
 		pival = bigInt.mul(bigInt.sub(pival, bigInt.div(1, calc)), isNegative)
 		calc = bigInt.add(calc, 2)
 		isNegative = -isNegative
 		k = k+1
 		if k==precision then
	 		term.clear()
	 		term.setCursorPos(1,1)
	 		print("Finished")
		 	print(bigInt.toStr(bigInt.mul(pival, 4)))
	 	else
	 		term.clear()
	 		term.setCursorPos(1,1)
		 	print(bigInt.toStr(bigInt.mul(pival, 4)))
		end
	 	yield()
 	end
end

print("Precision(How many times to run): ")
local a = read()
pi(tonumber(a))