Lua global lookups overhead

lua-global-lookups.lua

-- do global lookups matter?
require "os"

f = function() return end

run = function(n)
  start = os.clock()
  for i=1,n do f() end
  stop = os.clock()
  return (stop - start) 
end

run2 = function(n)
  local g = f
  start = os.clock()
  for i=1,n do g() end
  stop = os.clock()
  return (stop - start) 
end

for i=3,9 do
  j = math.pow(10,i)
  s1 = run(j)
  s2 = run2(j)
  d = s1 - s2
  print(string.format("%u: %g / %g (%g)",i,s1,s2,d))
end

-- RESULTS:
-- 3: 8.1e-05 / 6.1e-05 (2e-05)
-- 4: 0.000803 / 0.000597 (0.000206)
-- 5: 0.007189 / 0.004677 (0.002512)
-- 6: 0.0621 / 0.047847 (0.014253)
-- 7: 0.61813 / 0.47468 (0.14345)
-- 8: 6.17794 / 4.74395 (1.43399)
-- 9: 61.8233 / 47.4341 (14.3892)