Fibonacci sequence algorithms comparison recursive vs loop

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This is a small script that compares two fibonacci sequence algorithms.
One is the classic school example of a recursive algorithm and the second one is one I wrote that is using a loop instead.

Here is the results I got after some testing:
The slow version starts to slow down at about fibN = 35 (2 seconds) and increases fast (15 seconds at 40, 30 minutes at 50)
The fast one finishes in under a second for fibN = 200, the problem here is the variables overflow and starts to return negative results after 161

]]
local arg = {...}

if tonumber(arg[1]) then
  fibN = tonumber(arg[1])
 else
  error("Invalid parameter, give witch fibonacci number ot calculate")
 end

function fib(n)
  if n==0 then return 0 end
  if n==1 then return 1 end
  return fib(n-1) + fib(n-2)
end

function fib2(n)
  if n==0 then return 0 end
  if n==1 then return 1 end

  local v1, v2, v3, m = 0, 1, 1, 1
  while (m < n) do
    v3 = v2 + v1
    v1 = v2
    v2 = v3
    m = m + 1
  end
  return v3
end


print ("calculating " .. fibN .."th fibonacci number..")

local start = os.time()
print("Fast version: " ..fib2(fibN))
print("time: " .. os.time() - start)

if arg[2] then
  print("Skipping slow version.")
else
  start = os.time()
  print("Slow version: " .. fib(fibN))
  print("time: " .. os.time() - start)
end