Code Optimisation

Introduction

This article will try to be a general guide about improving your code and its performance.

The first part (Rules) will focus on having a clean, readable and maintainable code.
The second part (Code optimisation) is about improving performance, sometimes trading it against code readability.
The third part (Equivalent commands performance) mentions commands that in appearance have identical effects but may differ in terms of performance according to the use you may have of them.
The fourth part (Conversion from earlier versions) is a hopefully helpful, short guide about useful new commands or syntaxes to replace the old ways.

Rules

In the domain of development, any rule is a rule of thumb. If a rule states for example that it is better that a line of code doesn't go over 80 characters, it doesn't mean that any line must not go over 80 characters; sometimes, the situation needs it. If you have a good structure, do not change your code to enforce a single arbitrary rule. If you break many of them, you may have to change something. Again, this is according to your judgement.

With that being said, here are the three basic rules to get yourself in the clear:

Make it work
Make it readable
Optimise then

Make it work

Template:note Your first goal when coding is to make your code do what you want it does. A good way to reach this objective is to read and getting inspired by other people's code. If you understand it by reading it once, it is probably a good source of inspiration.

When starting from scratch if you know what you want but miss the specific steps to get to your point, it is a good practice to write down in your native language what you want to do. E.g Get all the units near the city, and for each west soldier in them, add 30% damage.
Use -showScriptErrors startup parameter and make sure your code doesn't throw errors. Not only will your code run slower but it may also not work at all. Be sure to read the error, isolate the issue and sort it out thanks to this Wiki.
Read your Arma RPT (report) to read more details about the error that happened in your code.

Make it readable

Whether you are cleaning your code or a different person's, you must understand the code without twisting your brain:

While SQF is (non-noticeably) impacted by variable name length, this should not take precedence on the fact that code must be readable by a human being. Variables like _u instead of _uniform should not be present.
One-lining (putting everything in one statement) memory improvement is most of the time not worth the headache it gives when trying to read it. Don't overuse it.
Indentation is important for the human mind, and space is too. Space is free, use it.
Same goes for line return; it helps to see a code block wrapping multiple common instructions instead of having to guess where it starts and stops.
Do you see the same code multiple times, only with different parameters? Now is the time to write a function!
If you have a lot of if..else, you may want to look at a switch condition, or again break your code in smaller functions.
Is your function code far too long? Break it in understandable-sized bites for your own sanity.
Finally, camel-casing (namingLikeThis) your variables and commands will naturally make the code more readable, especially for long names.

ⓘ

_i is an accepted variable standard for a for..do iteration

See the following code:

_w=[]; {_w pushbackunique primaryweapon _x} foreach((allunits+alldeadmen) select{_x call bis_fnc_objectside==east});

The same example is far more readable with proper spacing, good variable names and intermediate results:

_weaponNames = [];
_allUnitsAliveAndDead = allUnits + allDeadMen;
_allEastAliveAndDead = _allUnitsAliveAndDead select { _x call BIS_fnc_objectSide == east };
{ _weaponNames pushBackUnique primaryWeapon _x } forEach _allEastAliveAndDead;

Constants

Using a hard coded constant more than once? Use preprocessor directives rather than storing it in memory or cluttering your code with numbers. Such as:

a = _x + 1.053;
b = _y + 1.053;

And

_buffer = 1.053;
a = _x + _buffer;
b = _y + _buffer;

Becomes

#define BUFFER 1.053 // note: no semicolon
_a = _x + BUFFER;
_b = _y + BUFFER;

This also allows quick modifying of code; with the obvious loss of dynamics, but in that case it isn't a constant anymore.

Optimise then

Once you know what is what, you can understand your code better.

Use private variables instead of global variables (preceded with an underscore) as much as possible
You were iterating multiple times on the same array?
- You should be able to spot your issue now.
Are you using execVM on the same file, many times?
- Store your function in memory to avoid file reading every call with _myFunction = compile preprocessFileLineNumbers "myFile.sqf";
Is your variable name far too long?
- Find a smaller name, according to the variable scope:

e.g

{ _opforUnitUniform = uniform _x; systemChat _opforUnitUniform; } forEach _allOpforUnits;

becomes

{ _uniform = uniform _x; systemChat _uniform; } forEach _allopforUnits;

Code optimisation

⚠

Please note: Tests and benchmarks were done with the latest Arma 3 version at the time

1.82 with Tank DLC. Game engine performance may have changed since.
Benchmark result in milliseconds (ms) is an average for 10000 iterations.

ⓘ

Template:colorball means you must change your ways today, or with us you will ride…

Template:colorball means you may want to look at it if you are targeting pure performance

Template:colorball means the gain is little to insignificant. Going through your code for this replacement is not worth it. You may only consider it for future code.

Scheduled and unscheduled environment

There are two code environment types, scheduled and unscheduled.

A scheduled script has an execution time limit of 3 ms before being suspended to the benefit of another script until its turn comes back. It is a bit slower than unscheduled but suspending (sleep, waitUntil) is allowed.
An unscheduled script is not watched and will run without limitations. It is recommended for time-critical scripts, but suspending (sleep, waitUntil) is not allowed!

Template:note

Template:colorball Lazy evaluation

private _myVar = [33, 66] select (false);										// 0.0013 ms
private _myVar = if (false) then { 33; } else { 66; };							// 0.0020 ms
private "_myVar"; if (false) then { _myVar = 33; } else { _myVar = 66; };	 	// 0.0025 ms

Template:colorball Successive condition check

In SQF the following code will check all and every condition, even if one fail:

if (condition1 && condition2 && condition3) then { /* thenCode */ };

This code will check condition1, and if it is not true condition2 and condition3 will execute anyway. To avoid this behaviour, you can either imbricate ifs or use lazy evaluation such as the following:

if (condition1 && { condition2 } && { condition3 }) then { /* thenCode */ };

This method will stop condition evaluation on the first false statement.

Using lazy evaluation is not always the best way as it could speed up the code as well as slow it down, depending on the current condition being evaluated:

["true  || {{false} || {false}}", nil, 100000] call BIS_fnc_codePerformance;	// 0.00080 ms
["true  ||  {false} || {false }", nil, 100000] call BIS_fnc_codePerformance;	// 0.00105 ms
["false ||   false  ||  false  ", nil, 100000] call BIS_fnc_codePerformance;	// 0.00123 ms
["true  ||   false  ||  false  ", nil, 100000] call BIS_fnc_codePerformance;	// 0.00128 ms
["false ||  {false} || {false} ", nil, 100000] call BIS_fnc_codePerformance;	// 0.00200 ms

Template:colorball Concatenating multiple small strings together

myString = myString + otherString works fine for small strings, however the bigger the string gets the slower the operation becomes:

myString = ""; for "_i" from 1 to 10000 do { myString = myString + "123" };		// 290 ms

The solution is to use a string array that you will concatenate later:

strings = [];
for "_i" from 1 to 10000 do {strings pushBack "123"};
strings = strings joinString "";												// 30 ms

Template:colorball Manipulating arrays

Adding elements

New commands append and pushBack hold the best score.

_array = [0,1,2,3]; _array append [4,5,6];										// 0.0020 ms
_array = [0,1,2,3]; _array = _array + [4,5,6];									// 0.0023 ms
_array = [0,1,2,3]; { _array set [count _array, _x]; } forEach [4,5,6];			// 0.0080 ms

_array = [0,1,2,3]; _array pushBack 4;											// 0.0016 ms
_array = [0,1,2,3]; _array = _array + [4];										// 0.0021 ms
_array = [0,1,2,3]; _array set [count _array, _x]; 								// 0.0022 ms

Removing elements

_array = [0,1,2,3]; _array deleteAt 0;															// 0.0015 ms
_array = [0,1,2,3]; _array set [0, objNull]; _array = _array - [objNull];						// 0.0038 ms

_array = [0,1,2,3]; _array deleteRange [1, 2];													// 0.0018 ms
_array = [0,1,2,3]; { _array set [_x, objNull] } forEach [1,2]; _array = _array - [objNull];	// 0.0078 ms

Template:colorball Multiplayer recommendations

Do not saturate the network with information: publicVariable or public setVariable shouldn't be used at high frequency, else everyone's performance experience is at risk!
The server is supposed to have a good CPU and a lot of memory, use it: store functions, run them from it, send only the result to the clients
publicVariable and setVariable variable name length impacts network, be sure to send well-named, understandable variables
(and not playerNameBecauseThePlayerIsImportantAndWeNeedToKnowWhoTheyAreAllTheTimeEspeciallyInsideThisImpressiveFunction)
Use, use and use remoteExec & remoteExecCall. Ditch BIS_fnc_MP for good!

Equivalent commands performance

Template:colorball if

if..then { /* thenCode */ };											// 0.0011 ms
if..exitWith { /* exitCode */ };										// 0.0014 ms
if..then { /* thenCode */ } else { /* elseCode */ };					// 0.0015 ms
if..then [{ /* thenCode */ }, { /* elseCode */ }]						// 0.0016 ms

Template:colorball if and select

Use [array] select Boolean instead of the lazy-evaluated if.

_result = ["false result", "true result"] select true;					// 0.0011 ms
_result = if (true) then { "true result"; } else { "false result"; };	// 0.0017 ms

Template:colorball if and switch

_result = call {
	if (false) exitWith {};
	if (false) exitWith {};
	if (true)  exitWith {};
	if (false) exitWith {};
	if (false) exitWith {};
};							// 0.0032 ms

_result = switch (true) do {
	case (false): {};
	case (false): {};
	case (true) : {};
	case (false): {};
	case (false): {};
};							// 0.0047 ms

Template:colorball for

The for..from..to..do is twice as fast as its alternative syntax, for..do.

for "_i" from 0 to 10 do { /* forCode */ };										// 0.015 ms
for [{_i = 0}, {_i < 100}, {_i = _i + 1}] do { /* forCode */ };					// 0.030 ms

Template:colorball forEach vs count vs findIf

Both forEach and count commands will step through all the array elements and both commands will contain reference to current element with the _x variable. However, count loop is a little faster than forEach loop, but it does not benefit from the _forEachIndex variable.
Also, there is a limitation as the code inside count expects Boolean or Nothing while the command itself returns Number. This limitation is very important if you try to replace your forEach by count. If you have to add a extra true/false/nil at the end to make count work, it will be slower than the forEach equivalent.

{ diag_log _x } count   [1,2,3,4,5];											// 0.082 ms
{ diag_log _x } forEach [1,2,3,4,5];											// 0.083 ms

// with an empty array
_someoneIsNear = (allUnits findIf { _x  distance [0,0,0] < 1000 }) != -1;		// 0.0046 ms
_someoneIsNear = { _x distance [0,0,0] < 1000 } count allUnits > 0;				// 0.0047 ms
_someoneIsNear = {
	if (_x distance [0,0,0] < 1000) exitWith { true };
	false
} forEach allUnits;																// 0.0060 ms

// with a 30 items array
_someoneIsNear = (allUnits findIf { _x  distance [0,0,0] < 1000 }) != -1;		// 0.0275 ms
_someoneIsNear = { _x distance [0,0,0] < 1000 } count allUnits > 0;				// 0.0645 ms
_someoneIsNear = {
	if (_x distance [0,0,0] < 1000) exitWith { true };
	false
} forEach allUnits;																// 0.0390 ms

Template:colorball findIf 1.82 stops array iteration as soon as the condition is met.

[0,1,2,3,4,5,6,7,8,9] findIf { _x == 2 };										// 0.0050 ms
{ if (_x == 2) exitWith { _forEachIndex; }; } forEach [0,1,2,3,4,5,6,7,8,9];	// 0.0078 ms
_quantity = { _x == 2 } count [0,1,2,3,4,5,6,7,8,9];							// 0.0114 ms

Template:colorball + and format

When concatenating more than two strings, format is faster than +.

format ["%1%2%3%4%5", "string1", "string2", "string3", "string4", "string5"];	// 0.0019 ms
"string1" + "string2" + "string3" + "string4" + "string5";						// 0.0021 ms

Template:colorball format and str

str 33;				// 0.0016 ms
format ["%1", 33];	// 0.0022 ms

Template:colorball private

Direct declaration (private _var = value, since 1.53) is faster than declaring then assigning the variable.

private _a = 1;
private _b = 2;
private _c = 3;
private _d = 4;
// 0.0023 ms

private ["_a", "_b", "_c", "_d"];
_a = 1;
_b = 2;
_c = 3;
_d = 4;
// 0.0040 ms

However, if you have to reuse the same variable in a loop, external declaration is faster.
The reason behind this is that a declaration in the loop will create, assign and delete the variable in each loop.
An external declaration creates the variable only once and the loop only assigns the value.

private ["_a", "_b", "_c", "_d"];
for "_i" from 1 to 10 do
{
	_a = 1; _b = 2; _c = 3; _d = 4;
};
// 0.0195 ms

for "_i" from 1 to 10 do
{
	private _a = 1; private _b = 2; private _c = 3; private _d = 4;
};
// 0.0235 ms

Template:colorball isNil

isNil "varName";					// 0.0007 ms
isNil {varName};					// 0.0012 ms

Template:colorball isEqualType and typeName

isEqualType is much faster than typeName

"string" isEqualType 33;			// 0.0006 ms
typeName "string" == typeName 33;	// 0.0018 ms

Template:colorball isEqualTo and count

// with a items array
allUnits isEqualTo [];				// 0.0040 ms
count allUnits == 0;				// 0.0043 ms

Template:colorball select and param

 [1,2,3] select 0;					// 0.0008 ms
 [1,2,3] param [0];					// 0.0011 ms

Template:colorball objectParent and vehicle

isNull objectParent player;			// 0.0013 ms
vehicle player == player;			// 0.0022 ms

Template:colorball nearEntities and nearestObjects

nearEntities is much faster than nearestObjects given on range and amount of objects within the given range. If range is over 100 meters it is highly recommended to use nearEntities over nearestObjects.

NOTE: nearEntities only searches for alive objects. Killed units, destroyed vehicles, static objects and buildings will be ignored by the nearEntities command.

Template:colorball Global variables vs. local variables

If you need to call global variable repeatedly in a loop, copy its value to local variable and use local variable instead:

//-- 0.13ms SomeGlobalVariable = [123]; for "_i" from 1 to 100 do { SomeGlobalVariable select 0; };

is noticeably slower than

//-- 0.08ms SomeGlobalVariable = [123]; private _var = SomeGlobalVariable; for "_i" from 1 to 100 do { _var select 0; };

Template:colorball Config path delimiter

>> is slightly faster than / when used in config path with configFile or missionConfigFile.

configFile >> "CfgVehicles";		// 0.0019 ms
configFile  / "CfgVehicles";		// 0.0023 ms