WoWInterface - Efficient LUA code?

Page 2 of 3

Show 60 post(s) from this thread on one page

WoWInterface (https://www.wowinterface.com/forums/index.php)

- Lua/XML Help (https://www.wowinterface.com/forums/forumdisplay.php?f=16)

- - Efficient LUA code? (https://www.wowinterface.com/forums/showthread.php?t=21444)

Foxlit

03-31-09 02:03 AM

Quote:

Originally Posted by watchout (Post 123219)

O(1) (for lookup) is only average case for your typical hash table implementation, and that only if the key-hashes follow the perfect distribution that the hash-function designer thought to be universal.

You might have a point if you can show that hash collisions occur more frequently in the global environment than they would in your small table, taking into account the difference in the amount of allocated hash buckets. Personally, I don't think that's the case.

Quote:

Worst case is O(n). Reality will be somewhere in between, especially since best case O(1) = average case O(1) should give you a hint on why the O-notation is not always the perfect method to judge the performance of an algorithm.

I don't see a problem with the O-notation here.

Quote:

This however... is wrong. In the specific way that you did not correctly guess what performance difference I observed. [...] I reran my bench when writing this post and found that the performance of the global table has significantly improved (it's still not completely the same as an empty table though, about 2-5% off *cough*), I apologize for this. I just should have rerun the bench when writing my previous post.

Unfortunately, I can only guess at what testing you're doing without looking at the code. A 2-5% difference seems small enough to be caused by some form of noise.

Quote:

It [the number of entries in the global environment] used to be much bigger - so big actually that my client locked up and disconnected before finishing counting.

Iterating over a table with one million string keys and incrementing a counter each iteration takes slightly over 0.3s using lua on my laptop. It's possible that WoW's Lua implementation, or your PC (or both) are slower than what I'm testing against; on the other hand, I doubt the difference is much greater than 1:10. Extrapolating on that, it'd take at least several million entries to freeze your client long enough to force a disconnect. The most obvious conclusion is that your counting code did something other than just count entries.

Aezay

03-31-09 06:14 AM

Now that we are already talking about "efficient" Lua code, I have a few things I've been wondering about lately.
String concats, I know they are bad to do many times as it will create a new sting each time, but I was curious which one of these lines would be the best to use? Does a concat of an empty string mean much?

Code:

label:SetText(FormatTime(timeLeft)..(showTotalTime and " / "..duration or ""));

label:SetText(showTotalTime and FormatTime(timeLeft).." / "..duration or FormatTime(timeLeft));

Is there any performance benefits in assigning multiple variables at the same times compared to one per line?

Code:

tbl.name, tbl.value, tbl.color = name, value, color;



tbl.name = name;

tbl.value = value;

tbl.color = color;

Also, what is this O-notation you're talking about?

watchout
Doh, you're right, ah well, not like it really means anything :rolleyes:

Slakah

03-31-09 08:49 AM

Quote:

Originally Posted by Aezay (Post 123264)

Is there any performance benefits in assigning multiple variables at the same times compared to one per line?

Code:

tbl.name, tbl.value, tbl.color = name, value, color;



tbl.name = name;

tbl.value = value;

tbl.color = color;

Code:

local clock = os.clock

local insert, sort = table.insert, table.sort



local orderednames = {}

local names = setmetatable({}, {__newindex = function(t, k, v)

    insert(orderednames, k)

    rawset(t, k, v)

end})



local function bench(name, func, ...)

    local start = clock()

    for i = 1, 1e7 do

        func(...)

    end

    names[name] = clock() - start

end



local function printresults()

    sort(orderednames, function(a, b)

        return names[a] < names[b]

    end)



    for i, v in pairs(orderednames) do

        print(string.format("%d  %s took %.5f secs", i, v, names[v]))

    end

end



local tbl = {}

tbl.cat, tbl.dog, tbl.cow, tbl.pig = "Meow", "Woof", "Moo", "Oink"





bench("1 line assign", function()

    tbl.cat, tbl.dog, tbl.cow, tbl.pig = "Meow", "Woof", "Moo", "Oink"

end)



bench("multi line assign", function()

    tbl.cat = "Meow"

    tbl.dog = "Woof"

    tbl.cow = "Moo"

    tbl.pig = "Oink"

end)



printresults()

I'm consistently getting these results

Code:

1  multi line assign took 11.77000 secs

2  1 line assign took 12.55000 secs

I can't explain it.

Aezay

03-31-09 10:42 AM

I completely forgot I had a lua5.1.exe lying around, so I just ran your code and come up with this, same results really, just faster. What did you use to run the code in?

Code:

1  multi line assign took 2.01600 secs

2  1 line assign took 2.54600 secs

Using your benchmark code, I tried running this to see which was fastest. It is more or less a copy/paste from one of my addons, from an OnUpdate script on a timer.

Code:

local text;

local showTotalTime = false;

local timeLeft, endTime;

local duration = 60;



local function FormatTime(sec)

        if (abs(sec) <= 60) then

                return string.format("%.1f",sec);

        else

                return string.format("%d:%.2d",sec / 60,abs(sec) % 60);

        end

end



endTime = clock() + duration;

bench("empty string concat",function()

        timeLeft = (endTime - clock());

        text = FormatTime(timeLeft)..(showTotalTime and " / "..duration or "");

end);



endTime = clock() + duration;

bench("no concat",function()

        timeLeft = (endTime - clock());

        text = showTotalTime and FormatTime(timeLeft).." / "..duration or FormatTime(timeLeft);

end);

To my surprise it didn't really matter which way it's done, I guess that is because the concat of an empty string is on the same line as the FormatTime call, and thus is done in the same go, meaning it wont actually create a new Lua string.

Code:

1  no concat took 13.15700 secs

2  empty string concat took 13.21800 secs

Setting the showTotalTime to true produces these results, which again is pretty much the same.

Code:

1  no concat took 23.56300 secs

2  empty string concat took 24.56200 secs

Slakah

03-31-09 11:23 AM

Quote:

Originally Posted by Aezay (Post 123290)

What did you use to run the code in?

I'm on my netbook, so that's to be expected :).

Aezay

03-31-09 11:26 AM

Just updated my post above, while you posted, with some tests about string concats.

What about meant with where you ran your code, was which program, was it also lua5.1.exe?

Slakah

03-31-09 11:49 AM

Yeah I'm using lua 5.1 on Fedora Core 10, on an Asus Aspire One.

Quote:

Also, what is this O-notation you're talking about?

I was also interested so I found this http://www.perlmonks.org/?node_id=227909.

So if my understanding is correct, if a table lookup is O(1) then the size of the table doesn't affect the speed of the lookup?

IBLJerry

03-31-09 01:00 PM

O(1) means that the time taken to perform an algorithm is a constant, whatever the input size. O(n) means that the time is a multiple of the input size (plus a possible constant).

Algorithm complexity is interesting as a tool to compare how algorithm scale with the input size. But what this tool doesn't tell you, is which algorithm is the fastest. An O(1) algorithm that takes one hour to complete is worthless compared to an O(n) algorithm that takes seconds to do the same for reasonable input sizes.

Aezay

03-31-09 01:32 PM

Thanks for the explanation IBLJerry.

I'm a little curious though, can anyone give an example of an algorithm that doesn't scale with the data?

Zergreth

03-31-09 01:47 PM

"Determining if a number is even or odd; using a constant-size lookup table or hash table" is the example delivered by Wikipedia.

Shadowed

03-31-09 04:46 PM

You guys are vastly over-complicating this, from a fun abstract random curiosity type of question sure, but for practical applications, all you really need to ask yourself is "Am I doing something really stupid?" The majority of the mistakes I see new people make are they create a static table every time a function is loaded instead of once on file load like you see below. Creating options tables only when needed instead of all the time as Slakah mentioned as well.

Code:

function foo()

    local staticColor = { r = 1.0, g = 1.0, b = 1.0 };

end

Where you can shift it up so it becomes

Code:

local staticColor = { r = 1.0, g = 1.0, b = 1.0 };

function foo()

end

So you only create one table instead of the same table every time the function is called.

Eggi touched on this, but always ask yourself what the function is doing. If you're writing a mod for checking if the player has a buff and warning them, efficiency is a good goal but you shouldn't worry about it; on the other hand, if you're writing a mod to monitor the auras of 25 people in a raid during combat, then efficiency should be something you care more about. If you it requires user interface (GUIs, and that kind of thing) or they can't do it in combat then efficiency should be a lot lower on your list.

watchout

03-31-09 07:31 PM

More tips:

Turn off what you don't need. Think about whether you really always need those 1000 lines of OnEvent/OnUpdate function. Maybe you can split it into smaller functions that you switch on rare events? (like entering/leaving combat or switching gear, etc.)
reuse your frames
maybe split multiple events on multiple frames so that C-code handles the distribution and you don't have to manually check if it's actually the right event when the handler is called
Strings generate their hashes when created - that's pretty fast but it can't hurt to keep string generations at a minimum.
Use numbers over strings where possible.
Don't create functions that are called only directly (that means not through some table like I did in my example above) and in one place.
Memory usually comes cheap, while processor time is expensive.

@Aezay: of course, I just saw it and... just... had to say it... aaah the dark side of the force is beckoning!

Aezay

04-02-09 03:05 PM

If I want to store a list of strings, let's say for some kind of filter, what is the fastest way to do it, store them as keys, or as values?
Storing them as keys looks better code wise, but that doesn't mean it is faster. But based on the previous talk in this thread, I assume that keys is just as fast, if not faster?

Code:

if (tableFilter[name]) then

        frame:Show();

end

Code:

for index, entry in ipairs(tableFilter) do

        if (name == entry) then

                frame:Show();

                break;

        end

end

Tekkub

04-02-09 03:09 PM

Keys are always faster for that sort of thing. Iterating over the table makes a bunch of function calls.

IBLJerry

04-03-09 03:24 AM

Quote:

Originally Posted by Tekkub (Post 123811)

Keys are always faster for that sort of thing.

Unless you want to sort the keys :-)

Tekkub

04-03-09 03:56 AM

Which wouldn't be "that sort of thing" (finding out if the value is in the talbe)

Aezay

04-04-09 03:39 PM

To save a function call, many uses next() as the iterater in a for loop, why not do the same for ipairs(), should be easily obtainable using this code. Or is there an iterator function already available for array type tables, like next?
This would probably be quite silly normally, unless it's code run often like in an OnUpdate script.

Code:

local iterator = ipairs(_G);

Tekkub

04-04-09 03:46 PM

You'd only save one function call out of all the ones made while looping. It'd be better to optimize so that you don't need to iter at all.

Shadowed

04-04-09 03:46 PM

Quote:

Originally Posted by Aezay (Post 124195)

Code:

local iterator = ipairs(_G);

I think I've seen maybe one or two people use next, I'm not sure I would call it common at all. This gets into premature/unnecessary optimization

shiin

04-14-09 07:27 AM

Regarding events, I was always wondering would be the better coding style:
a) Catching all events of one type (i.e. UNIT_BUFF) in one central location and distributing them to the relevant frames (i.e. RaidFrameNumberXY),
b) Having decentralised event handlers for each frame, each listening for all relevant events.

Evidently, variant b) uses more CPU time, since each event would have to be analysed once for each frame, but having frames as independent building blocks seems to be more manageable and extendable.

All times are GMT -6. The time now is 12:01 PM.

Page 2 of 3

Show 60 post(s) from this thread on one page