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• Javascriptlibrary more efficient than Rickshaw for realtime visualizations

  - by dan kutz

  I want to visualize data as time-series graphs on mobile devices(tablets) and therefore stumbled upon rickshaw, which is based on D3. First I must say I was a little bit confused when I realized that realtime in web design is defined totally different to realtime in engineering which has fixed(and often very short) timeframes. Anyway my aim is to visualize the data as fast as possible, and on older tablets visualization with rickshaw is quite slow. Can anybody recommend another library, which may be more efficient in rendering? Or is there no way out and I have to go native? regards Dan.

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• Is this implementation truely tail-recursive?

  - by CFP

  Hello everyone! I've come up with the following code to compute in a tail-recursive way the result of an expression such as 3 4 * 1 + cos 8 * (aka 8*cos(1+(3*4))) The code is in OCaml. I'm using a list refto emulate a stack. type token = Num of float | Fun of (float->float) | Op of (float->float->float);; let pop l = let top = (List.hd !l) in l := List.tl (!l); top;; let push x l = l := (x::!l);; let empty l = (l = []);; let pile = ref [];; let eval data = let stack = ref data in let rec _eval cont = match (pop stack) with | Num(n) -> cont n; | Fun(f) -> _eval (fun x -> cont (f x)); | Op(op) -> _eval (fun x -> cont (op x (_eval (fun y->y)))); in _eval (fun x->x) ;; eval [Fun(fun x -> x**2.); Op(fun x y -> x+.y); Num(1.); Num(3.)];; I've used continuations to ensure tail-recursion, but since my stack implements some sort of a tree, and therefore provides quite a bad interface to what should be handled as a disjoint union type, the call to my function to evaluate the left branch with an identity continuation somehow irks a little. Yet it's working perfectly, but I have the feeling than in calling the _eval (fun y->y) bit, there must be something wrong happening, since it doesn't seem that this call can replace the previous one in the stack structure... Am I misunderstanding something here? I mean, I understand that with only the first call to _eval there wouldn't be any problem optimizing the calls, but here it seems to me that evaluation the _eval (fun y->y) will require to be stacked up, and therefore will fill the stack, possibly leading to an overflow... Thanks!

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• MySQL subqueries

  - by swamprunner7

  Can we do this query without subqueries? SELECT login, post_n, (SELECT SUM(vote) FROM votes WHERE votes.post_n=posts.post_n)AS votes, (SELECT COUNT(comments.post_n) FROM comments WHERE comments.post_n=posts.post_n)AS comments_count FROM users, posts WHERE posts.id=users.id AND (visibility=2 OR visibility=3) ORDER BY date DESC LIMIT 0, 15 tables: Users: id, login Posts: post_n, id, visibility Votes: post_n, vote id — it`s user id, Users the main table.

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• Optimizing Vector elements swaps using CUDA

  - by Orion Nebula

  Hi all, Since I am new to cuda .. I need your kind help I have this long vector, for each group of 24 elements, I need to do the following: for the first 12 elements, the even numbered elements are multiplied by -1, for the second 12 elements, the odd numbered elements are multiplied by -1 then the following swap takes place: Graph: because I don't yet have enough points, I couldn't post the image so here it is: http://www.freeimagehosting.net/image.php?e4b88fb666.png I have written this piece of code, and wonder if you could help me further optimize it to solve for divergence or bank conflicts .. //subvector is a multiple of 24, Mds and Nds are shared memory _shared_ double Mds[subVector]; _shared_ double Nds[subVector]; int tx = threadIdx.x; int tx_mod = tx ^ 0x0001; int basex = __umul24(blockDim.x, blockIdx.x); Mds[tx] = M.elements[basex + tx]; __syncthreads(); // flip the signs if (tx < (tx/24)*24 + 12) { //if < 12 and even if ((tx & 0x0001)==0) Mds[tx] = -Mds[tx]; } else if (tx < (tx/24)*24 + 24) { //if >12 and < 24 and odd if ((tx & 0x0001)==1) Mds[tx] = -Mds[tx]; } __syncthreads(); if (tx < (tx/24)*24 + 6) { //for the first 6 elements .. swap with last six in the 24elements group (see graph) Nds[tx] = Mds[tx_mod + 18]; Mds [tx_mod + 18] = Mds [tx]; Mds[tx] = Nds[tx]; } else if (tx < (tx/24)*24 + 12) { // for the second 6 elements .. swp with next adjacent group (see graph) Nds[tx] = Mds[tx_mod + 6]; Mds [tx_mod + 6] = Mds [tx]; Mds[tx] = Nds[tx]; } __syncthreads(); Thanks in advance ..

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• How can I Query only __key__ on a Google Appengine PolyModel child?

  - by Gabriel

  So the situation is: I want to optimize my code some for doing counting of records. So I have a parent Model class Base, a PolyModel class Entry, and a child class of Entry Article: How would I query Article.key so I can reduce the query load but only get the Article count. My first thought was to use: q = db.GqlQuery("SELECT __key__ from Article where base = :1", i_base) but it turns out GqlQuery doesn't like that because articles are actually stored in a table called Entry. Would it be possible to Query the class attribute? something like: q = db.GqlQuery("select __key__ from Entry where base = :1 and :2 in class", i_base, 'Article') neither of which work. Turns out the answer is even easier. But I am going to finish this question because I looked everywhere for this. q = db.GqlQuery("select __key__ from Entry where base = :1 and class = :2", i_base, 'Article')

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• Delphi fast large bitmap creation (without clearing)

  - by Ritsaert Hornstra

  When using the TBitmap wrapper for a GDI bitmap from the unit Graphics I noticed it will always clear out the bitmap (using a PatBlt call) when setting up a bitmap with SetSize( w, h ). When I copy in the bits later on (see routine below) it seems ScanLine is the fastest possibility and not SetDIBits. function ToBitmap: TBitmap; var i, N, x: Integer; S, D: PAnsiChar; begin Result := TBitmap.Create(); Result.PixelFormat := pf32bit; Result.SetSize( width, height ); S := Src; D := Result.ScanLine[ 0 ]; x := Integer( Result.ScanLine[ 1 ] ) - Integer( D ); N := width * sizeof( longword ); for i := 0 to height - 1 do begin Move( S^, D^, N ); Inc( S, N ); Inc( D, x ); end; end; The bitmaps I need to work with are quite large (150MB of RGB memory). With these iomages it takes 150ms to simply create an empty bitmap and a further 140ms to overwrite it's contents. Is there a way of initializing a TBitmap with the correct size WITHOUT initializing the pixels itself and leaving the memory of the pixels uninitialized (eg dirty)? Or is there another way to do such a thing. I know we could work on the pixels in place but this still leaves the 150ms of unnessesary initializtion of the pixels.

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• Why is Javascript's Math.floor the slowest way to calculate floor in Javascript?

  - by z5h

  I'm generally not a fan of microbenchmarks. But this one has a very interesting result. http://ernestdelgado.com/archive/benchmark-on-the-floor/ It suggests that Math.floor is the SLOWEST way to calculate floor in Javascript. ~~n, n|n, n&n all being faster. This seems pretty shocking as I would expect that people implementing Javascript in today's modern browsers would be some pretty smart people. Does floor do something important that the other methods fail to do? Is there any reason to use it?

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• How to optimize an database suggestion engine

  - by Dimitar Vouldjeff

  Hi, I`m making an online engine for item-to-item recommending movies. I have made some researches and I think that the best way to implement that is using pearson correlation and make a table with item1, item2 and correlation fields, but the problem is that after each rate of item I have to regenerate the correlation for in the worst case N records (where N is the number of items). Another think that I read is the following article, but I haven`t thought a way to implement it. So what is your suggestion to optimize this process? Or any other suggestions? Thanks.

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• WPF: Improving Performance for Running on Older PCs

  - by Phil Sandler

  So, I'm building a WPF app and did a test deployment today, and found that it performed pretty poorly. I was surprised, as we are really not doing much in the way of visual effects or animations. I deployed on two machines: the fastest and the slowest that will need to run the application (the slowest PC has an Intel Celeron 1.80GHz with 2GB RAM). The application ran pretty well on the faster machine, but was choppy on the slower machine. And when I say "choppy", I mean the cursor jumped even just passing it over any open window of the app that had focus. I opened the Task Manager Performance window, and could see that the CPU usage jumped whenever the app had focus and the cursor was moving over it. If I gave focus to another (e.g. Excel), the CPU usage went back down after a second. This happened on both machines, but the choppiness was only noticeable on the slower machine. I had very limited time to tinker on the deployment machines, so didn't do a lot of detailed testing. The app runs fine on my development machine, but I also see the CPU spiking up to 10% there, just running the cursor over the window. I downloaded the WPF performance tool from MS and have been tinkering with it (on my dev machine). The docs say this about the "Frame Rate" metric in the Perforator tool: For applications without animation, this value should be near 0. The app is not doing any heavy animation, but the frame rate stays near 50 when the cursor is over any window. The screens I tested on have column headers in a grid that "highlight" and buttons that change color and appearance when scrolled over. Even moving the mouse on blank areas of the windows cause the same Frame rate and CPU usage (doesn't seem to be related to these minor animations). (Also, I am unable to figure out how to get anything but the two default tools--Perforator and Visual Profiler--installed into the WPF performance tool. That is probably a separate question). I also have Redgate's profiling tool, but I'm not sure if that can shed any light on rendering performance. So, I realize this is not an easy thing to troubleshoot without specifics or sample code (which I can't post). My questions are: What are some general things to look for (or avoid) in the code to improve performance? What steps can I take using the WPF performance tool to narrow down the problem? Is the PC spec listed above (Intel Celeron 1.80GHz with 2GB RAM) too slow to be running even vanilla WPF applications?

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• How to store static content across branches in a single location in version control

  - by Shravan

  [Just a random thought] I have a pdf doc that is downloaded when the user clicks on 'help' on my website. Now, this is a pretty huge document and is saved in version control (SVN) and is thus copied for all branches that exist in SVN. This is static content and something that developers are not working on, and does not change often. Is there a more efficient way to store it (that would not hamper local deployments) that would make SVN checkouts and updates relatively faster. I know the benefit we get is not huge, this is something that came to my head none the less.

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• Nodes set of the same type with if-test. Make it less.

  - by Kalinin

  How to make the code more beautiful (compact)? <xsl:template match="part"> <table class="part"> <xsl:if test="name != ''"> <tr> <td>????????</td><td><xsl:value-of select="name"/></td> </tr> </xsl:if> <xsl:if test="model != ''"> <tr> <td>??????</td><td><xsl:value-of select="model"/></td> </tr> </xsl:if> <xsl:if test="year != ''"> <tr> <td>???</td><td><xsl:value-of select="year"/></td> </tr> </xsl:if> <xsl:if test="glass_type != ''"> <tr> <td>???</td><td><xsl:value-of select="glass_type"/></td> </tr> </xsl:if> <xsl:if test="scancode != ''"> <tr> <td>???????</td><td><xsl:value-of select="scancode"/></td> </tr> </xsl:if> <xsl:if test="eurocode != ''"> <tr> <td>???????</td><td><xsl:value-of select="eurocode"/></td> </tr> </xsl:if> <xsl:if test="coment != ''"> <tr> <td>???????????</td><td><xsl:value-of select="coment"/></td> </tr> </xsl:if> <xsl:if test="glass_size != ''"> <tr> <td>??????</td><td><xsl:value-of select="glass_size"/></td> </tr> </xsl:if> <xsl:if test="vendor != ''"> <tr> <td>?????????????</td><td><xsl:value-of select="vendor"/></td> </tr> </xsl:if> <xsl:if test="trademark != ''"> <tr> <td>???????? ?????</td><td><xsl:value-of select="trademark"/></td> </tr> </xsl:if> <xsl:if test="fprice != ''"> <tr> <td>????</td><td><xsl:value-of select="fprice"/></td> </tr> </xsl:if> </table> </xsl:template> Update: i wrote: <my:translations xmlns:my="my:my"> <w e="name" r="????????"/> <w e="model" r="??????"/> <w e="year" r="???"/> <w e="glass_type" r="???"/> <w e="scancode" r="???????"/> <w e="eurocode" r="???????"/> <w e="comment" r="???????????"/> <w e="glass_size" r="??????"/> <w e="vendor" r="?????????????"/> <w e="trademark" r="???????? ?????"/> <w e="fprice" r="????"/> </my:translations> <xsl:value-of select="//w/@r"/> And have no result from this code. Is it normal? And how can i get new element w?

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• Vector [] vs copying

  - by sak

  What is faster and/or generally better? vector<myType> myVec; int i; myType current; for( i = 0; i < 1000000; i ++ ) { current = myVec[ i ]; doSomethingWith( current ); doAlotMoreWith( current ); messAroundWith( current ); checkSomeValuesOf( current ); } or vector<myType> myVec; int i; for( i = 0; i < 1000000; i ++ ) { doSomethingWith( myVec[ i ] ); doAlotMoreWith( myVec[ i ] ); messAroundWith( myVec[ i ] ); checkSomeValuesOf( myVec[ i ] ); } I'm currently using the first solution. There are really millions of calls per second and every single bit comparison/move is performance-problematic.

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• Is it better to echo javascript in raw format with php, or echo a script include that has been minif

  - by Scarface

  Hey guys quick question, I am currently echoing a lot of javascript that is based conditionally on login status and other variables. I was wondering if it would be better to simply echo the script include like <script type="text/javascript" src="javascript/openlogin.js"></script> that has been run through a minifying program and been gzipped or to echo the full script in raw format. The latter suggestion is messier to me but it reduces http requests while the latter would probably be smaller but take more cpu? Just wondering what some other people think. Thanks in advance for any advice.

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• NHibernate, each property is filled with a different select statement

  - by Eitan

  I'm retrieving a list of nhibernate entites which have relationships to other tables/entities. I've noticed instead of NHibernate performing JOINS and populating the properties, it retrieves the entity and then calls a select for each property. For example if a user can have many roles and I retrieve a user from the DB, Nhibernate retrieves the user and then populates the roles with another select statement. The problem is that I want to retrieve oh let's say a list of products which have various many-to-many relationships and relationships to items which have their own relationships. In the end I'm left with over a thousand DB calls to retrieve a list of 30 products. Thanks. I've also set default lazy loading to false because whenever I save the list of entities to a session, I get an error when trying to retrieve it on another page: LazyInitializationException: could not initialize proxy If anybody could shed any light I would truly appreciate it. Thanks. Eitan

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• SEO Google - Navigation Title vs. Page Heading

  - by louism

  Hi, i was wondering if anyone knows if theres a connection between what a navigation item is named and the page heading it goes to - does this have an impact on SEO? so for example, if i had in my navigation menu an item called About Us, but when you click it you come to a page with the heading Learn Who We Are (i.e. wrapped in [h1] heading tags) because there isnt an exact one-to-one match, is that a bad thing in terms of SEO? thanks

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• Does the order of columns in a query matter?

  - by James Simpson

  When selecting columns from a MySQL table, is performance affected by the order that you select the columns as compared to their order in the table (not considering indexes that may cover the columns)? For example, you have a table with rows uid, name, bday, and you have the following query. SELECT uid, name, bday FROM table Does MySQL see the following query any differently and thus cause any sort of performance hit? SELECT uid, bday, name FROM table

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• In PHP is faster to get a value from an if statement or from an array?

  - by Vittorio Vittori

  Maybe this is a stupid question but what is faster? <?php function getCss1 ($id = 0) { if ($id == 1) { return 'red'; } else if ($id == 2) { return 'yellow'; } else if ($id == 3) { return 'green'; } else if ($id == 4) { return 'blue'; } else if ($id == 5) { return 'orange'; } else { return 'grey'; } } function getCss2 ($id = 0) { $css[] = 'grey'; $css[] = 'red'; $css[] = 'yellow'; $css[] = 'green'; $css[] = 'blue'; $css[] = 'orange'; return $css[$id]; } echo getCss1(3); echo getCss2(3); ?> I suspect is faster the if statement but I prefere to ask!

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• What is the minimal set of coins you should carry to always make exact change?

  - by ??iu

  US coin values: .01, .05, .10, .25 (*) What configuration(s) of US coins can be used to match every value from .01-.99 using the fewest coins possible? How can you find an answer? * note: there is actually a .50 coin but it is very rarely seen

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• The explain tells that the query is awful (it doesn't use a single key) but I'm using LIMIT 1. Is th

  - by Ricardo

  The explain command with the query: explain SELECT * FROM leituras WHERE categorias_id=75 AND textos_id=190304 AND cookie='3f203349ce5ad3c67770ebc882927646' AND endereco_ip='127.0.0.1' LIMIT 1 The result: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE leituras ALL (null) (null) (null) (null) 1022597 Using where Will it make any difference adding some keys on the table? Even that the query will always return only one row.

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• Completely remove ViewState for specific pages

  - by Kerido

  Hi everybody, I have a site that features some pages which do not require any post-back functionality. They simply display static HTML and don't even have any associated code. However, since the Master Page has a <form runat="server"> tag which wraps all ContentPlaceHolders, the resulting HTML always contains the ViewState field, i.e: <input type="hidden" id="__VIEWSTATE" value="/wEPDwUKMjEwNDQyMTMxM2Rk0XhpfvawD3g+fsmZqmeRoPnb9kI=" /> I realize, that when decrypted, this string corresponds to the <form> tag which I cannot remove. However, I would still like to remove the ViewState field for pages that only display static HTML. Is it possible?

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• Script Speed vs Memory Usage

  - by Doug Neiner

  I am working on an image generation script in PHP and have gotten it working two ways. One way is slow but uses a limited amount of memory, the second is much faster, but uses 6x the memory . There is no leakage in either script (as far as I can tell). In a limited benchmark, here is how they performed: -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 65.626 | 540,036 | 200 Two | 20.207 | 3,269,600 | 200 -------------------------------------------- And here is the average of the previous numbers (if you don't want to do your own math): -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 0.328 | 540,036 | 1 Two | 0.101 | 3,269,600 | 1 -------------------------------------------- Which method should I use and why? I anticipate this being used by a high volume of users, with each user making 10-20 requests to this script during a normal visit. I am leaning toward the faster method because though it uses more memory, it is for a 1/3 of the time and would reduce the number of concurrent requests.

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• MySQL Paritioning performance

  - by Imran Pathan

  Measured performance on key partitioned tables and normal tables separately. But we couldn't find any performance improvement with partitioning. Queries are pruned. Using MySQL 5.1.47 on RHEL 4. Table details: UserUsage - Will have entries for user mobile number and data usage for each date. Mobile number and Date as PRI KEY. UserProfile - Queries prev table and stores summary for each mobile number. Mobile number PRI KEY. CREATE TABLE `UserUsage` ( `Msisdn` decimal(20,0) NOT NULL, `Date` date NOT NULL, . . PRIMARY KEY USING BTREE (`Msisdn`,`Date`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; CREATE TABLE `UserProfile` ( `Msisdn` decimal(20,0) NOT NULL, . . PRIMARY KEY (`Msisdn`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; Second table is updated by query select and order by date in first table in a perl program, query is select * from UserUsage where Msisdn=number order by Date desc limit 7 [Process data in perl] update UserProfile values(....) where Msisdn=number explain partition for select, shows row being scanned in a particular partition only. Is something wrong with partition design or queries as partitioning is taking almost same or more time compared to normal tables?

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• Is "for(;;)" faster than "while (TRUE)"? If not, why do people use it?

  - by Chris Cooper

  for (;;) { //Something to be done repeatedly } I have seen this sort of thing used a lot, but I think it is rather strange... Wouldn't it be much clearer to say while (TRUE), or something along those lines? I'm guessing that (as is the reason for many-a-programmer to resort to cryptic code) this is a tiny margin faster? Why, and is it REALLY worth it? If so, why not just define it this way: #DEFINE while(TRUE) for(;;)

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• Which fieldtype is best for storing PRICE values?

  - by BerggreenDK

  Hi there I am wondering whats the best "price field" in MSSQL for a shoplike structure? Looking at this overview: http://www.teratrax.com/sql_guide/data_types/sql_server_data_types.html We have datatypes called money, smallmoney, then we have decimal/numeric and lastly float and real Name, memory/disk-usage and value ranges: Money: 8 bytes (values: -922,337,203,685,477.5808 to +922,337,203,685,477.5807) Smallmoney: 4 bytes (values: -214,748.3648 to +214,748.3647) Decimal: 9 [default, min. 5] bytes (values: -10^38 +1 to 10^38 -1 ) Float: 8 bytes (values: -1.79E+308 to 1.79E+308 ) Real: 4 bytes (values: -3.40E+38 to 3.40E+38 ) My question is: is it really wise to store pricevalues in those types? what about eg. INT? Int: 4 bytes (values: -2,147,483,648 to 2,147,483,647) Lets say a shop uses dollars, they have cents, but I dont see prices being $49.2142342 so the use of a lot of decimals showing cents seems waste of SQL bandwidth. Secondly, most shops wouldn't show any prices near 200.000.000 (not in normal webshops at least... unless someone is trying to sell me a famous tower in Paris) So why not go for an int? An int is fast, its only 4 bytes and you can easily make decimals, by saving values in cents instead of dollars and then divide when you present the values. The other approach would be to use smallmoney which is 4 bytes too, but this will require the math part of the CPU to do the calc, where as Int is integer power... on the downside you will need to divide every single outcome. Are there any "currency" related problems with regionalsettings when using smallmoney/money fields? what will these transfer too in C#/.NET ? Any pros/cons? Go for integer prices or smallmoney or some other? Whats does your experience tell?

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• Verifying compiler optimizations in gcc/g++ by analyzing assembly listings

  - by Victor Liu

  I just asked a question related to how the compiler optimizes certain C++ code, and I was looking around SO for any questions about how to verify that the compiler has performed certain optimizations. I was trying to look at the assembly listing generated with g++ (g++ -c -g -O2 -Wa,-ahl=file.s file.c) to possibly see what is going on under the hood, but the output is too cryptic to me. What techniques do people use to tackle this problem, and are there any good references on how to interpret the assembly listings of optimized code or articles specific to the GCC toolchain that talk about this problem?

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