Question about Macros

antix · February 2017

I am currently using loads of global variables and when I want to access them I use a line like local globalVar= GLOBALVAR.

If I change to using macros will they be faster than using global vars?

stetso · February 2017

I was wondering about a similar question (maybe I got you wrong, though) so I tried to benchmark it and it turned out no different. Maybe my setup is helpful anyways. Here goes:

--[[
	Benchmarking globals (that are transformed to locals) vs macros
	timing function borrowed from lume.lua - <a href="https://github.com/rxi/lume" rel="nofollow">https://github.com/rxi/lume</a>
--]]
 
local function benchmark(fn, ...)
	local start = os.clock()
	local rtn = {fn(...)}
	return (os.clock() - start), unpack(rtn)
end
 
local function mean(t)
	local sum = 0
	local count= 0
	for k,v in pairs(t) do
		if type(v) == 'number' then
			sum = sum + v
			count = count + 1
		end
	end
	return (sum / count)
end
 
function standardDeviation(t)
  local m
  local vm
  local sum = 0
  local count = 0
  local result
  m = mean(t)
  for k,v in pairs(t) do
    if type(v) == 'number' then
      vm = v - m
      sum = sum + (vm * vm)
      count = count + 1
    end
  end
  result = math.sqrt(sum / (count-1))
  return result
end
 
repeatBenchmarks = 1000 -- repeat the benchmark n times
resultsLocal = {}
resultsMacro = {}
 
 
-- global variable
globalVar = 10
-- macro constant
macroVar @ 10
 
local function localFun()
	local l = globalVar
	local r = 0
	for i = 1,100000 do
		r = r + l
	end
end
 
local function macroFun()
	local r = 0
	for i = 1,100000 do
		r = r + macroVar
	end
end
 
-- repeat the benchmark a couple of times
for r = 1,repeatBenchmarks do
	table.insert(resultsLocal, benchmark(localFun))
	table.insert(resultsMacro, benchmark(macroFun))
end
 
print("MEAN local: "..mean(resultsLocal))
print("SD local:   "..standardDeviation(resultsLocal))
print("MEAN macro: "..mean(resultsMacro))
print("SD macro:   "..standardDeviation(resultsMacro))

There is no difference, so I keep using locals... But it might not be what you were looking for...
O:-)

antix · February 2017

@stetso thanks for the

totebo · February 2017

In addition to this, macros are currently not global. The scope is limited to the file/class in which they were created. This is a bit of a bother, especially since, ironically, each macro variable name has to be unique - globally.

antix · February 2017

Hrmm, then I suppose I will stick with faithful old globals then

SinisterSoft · February 2017

Technically they can be faster, eg:

local leftBorder=10
a=leftBorder+40

a will be tokenised to include the search for leftBorder and the addition of 40.

but...

leftBorder@10
a=leftBorder+40

a will be tokenised directy to a=50. This is because the macro text will be converted to 10 and the byte compiler will see 10+40 and convert this as an optimisation to 50.

So if you have a lot of constants in your code then macros could (overall) speed things up.

The other thing is that locals can be in short supply, macros are a good way of saving local 'space'.

antix · February 2017

Thansk @SinisterSoft. Wow, I can't see how you could run out of locals (limit is 200) unless you made your entire game one giant file (like I used to LOL) b-(

SinisterSoft · February 2017

I use locals whenever I can - they are a lot faster than globals.

I tend to have one big game loop that does virtually everything - with a scenemanager overlayed on top controlling the game state machine.

antix · February 2017

I also use locals everywhere I can. I use globals to enable variables to be used across classes though.

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