(surprising) speed test: (global) integer constants vs strings as constants

keszegh

following other programming languages' conventions i thought that maybe i should change my string constants to integer values to speed up the code. by that i mean that an object of mine has several states, so (self.)state has value "STRING1" or "STRING2" or etc. and i changed these so that i defined global STRING1=1, STRING2=2 etc. and used these. suprisingly the code became slower. making these constants local sped up the things, a bit faster than with strings, but still only approx. to the same speed as the string solution.
it is a bit surprising for me, and the conclusion is that in lua you don't need to optimize this (as many other things, e.g. sin tables).

summary:
constants vs local constants vs strings
pc:
2.1765020517934 vs 1.2641564022966 vs 1.2715337009151
android:
6.2562990000006 vs 4.3186989999958 vs 4.6480369999917

test code:

TOUCHED=1 RELEASED=2   something=TOUCHED startTime=os.timer() for i = 1, 10000000 do if something==TOUCHED then something=RELEASED elseif something==RELEASED then something=TOUCHED end end print(os.timer()-startTime)   local TOUCHED=1 local RELEASED=2   something=TOUCHED startTime=os.timer() for i = 1, 10000000 do if something==TOUCHED then something=RELEASED elseif something==RELEASED then something=TOUCHED end end print(os.timer()-startTime)   something="TOUCHED" startTime=os.timer() for i = 1, 10000000 do if something=="TOUCHED" then something="RELEASED" elseif something=="RELEASED" then something="TOUCHED" end end print(os.timer()-startTime)

ar2rsawseen

Yes in lua local optimization should give much more
From types stand of point, then any variable can be any type and can change type, so in weakly typed languages in most cases, changing type won't give you a better performance, only may take less memory in some cases

keszegh

apparently.
i expected that checking the equality/setting value of strings will take significantly longer than checking the equality/setting the value of integers (even together with the lookup time of the global integer constants).

john26

One thing to note is Lua has no integers! Just (floating point) numbers.