pico-8 atan / acos

function acos(x)
	if abs(x) < 0.001 then
		return pi / 2
	elseif sqrt(101-x*x*100)/10/x < 0 then
		return atan(sqrt(100-x*x*100)/10/x) + pi
	else
		return atan(sqrt(100-x*x*100)/10/x)
	end
end

function atan(x)
	local st1 = false
	local st2 = false
	if x < 0 then
		x = -x
		st1 = true
	end
	if x >= 1 then
		x = 1/x
		st2 = true
	end
	x = x - x*x*x/3 + x*x*x*x*x/5 - x*x*x*x*x*x*x/7
	if st2 then x = 1.571 - x end
	if st1 then x = -x end
	return x
end

function sqrt(n)
	local i = 0
	while(i*i <= n) do
		i += 1
	end
	i -= 1
	local d = n-i*i
	local p = d/(2*i)
	local a = i+p
	return a -(p*p)/(2*a)
end