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  • Cost of exception handlers in Python

    - by Thilo
    In another question, the accepted answer suggested replacing a (very cheap) if statement in Python code with a try/except block to improve performance. Coding style issues aside, and assuming that the exception is never triggered, how much difference does it make (performance-wise) to have an exception handler, versus not having one, versus having a compare-to-zero if-statement?

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  • Dynamics of the using keyword

    - by AngryHacker
    Consider the following code: // module level declaration Socket _client; void ProcessSocket() { _client = GetSocketFromSomewhere(); using (_client) { DoStuff(); // receive and send data Close(); } } void Close() { _client.Close(); _client = null; } Given that that the code calls the Close() method, which closes the _client socket and sets it to null, while still inside the `using' block, what exactly happens behind the scenes? Does the socket really get closed? Are there side effects? P.S. This is using C# 3.0 on the .NET MicroFramework, but I suppose the c#, the language, should function identically. The reason i am asking is that occasionally, very rarely, I run out of sockets (which is a very precious resource on a .NET MF devices).

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  • Compiler optimization of references

    - by Phineas
    I often use references to simplify the appearance of code: vec3f& vertex = _vertices[index]; // Calculate the vertex position vertex[0] = startx + col * colWidth; vertex[1] = starty + row * rowWidth; vertex[2] = 0.0f; Will compilers recognize and optimize this so it is essentially the following? _vertices[index][0] = startx + col * colWidth; _vertices[index][1] = starty + row * rowWidth; _vertices[index][2] = 0.0f;

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  • Query optimization (OR based)

    - by john194
    I have googled but I can't find answers for these questions. Your advice is appreciated. centOS on vps with 512MB RAM, nginx, php5 (fastcgi), mysql5 (myisam, not innodb). I need to optimize this app created by some ex-employee. This app is working, but it's slow. Table: t1(id[bigint(20)],c1[mediumtext],c2[mediumtext],c3[mediumtext],c4[mediumtext]) id is some random big number, and is PK Those mediumtext rows look like this: c1="|box-002877|" c2="|ct-2348|rd-11124854|hw-3949|wd-8872|hw-119037736|...etc.. " c3="|fg-2448|wd-11172|hw-1656|...etc.. " c4="|hg-2448|qd-16667|...etc." (some columns contain a lot of data, around 900 KiB, database around 300 MiB) Yes, mediumtext "is bad", and (20) is too big... but I didn't create this. Those codes can be found on any of those 4 mediumtext's... //he needs all the columns of the row containing $code, so he wrote this: function f1($code) { SELECT * FROM t1 WHERE c1 LIKE '%$code%' OR c2 LIKE '%$code%' OR c3 LIKE '%$code%' OR c4 LIKE '%$code%'; Questions: Q1. If $code is found on c1... mysql automatically stops checking and returns row=id+c1+c2+c3+c4? or it will continue (wasting time) checking c2, c3 and c4?... Q2. Mysql is working with this table on disk (not RAM) because of the mediumtext, right? is this the primary cause of slowness? Q3. That query can be cached by mysql (if using a big query_cache_size=128M value on the my.cnf)? or that's not cacheable due to the mediumtexts, or due to the "OR LIKE"...? Q4. Do you recommend rewriting this with mysql's INSTR() / LOCATE() / MATCH..AGAINST [FULLTEXT]?

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  • Speed of CSS

    - by Ólafur Waage
    This is just a question to help me understand CSS rendering better. Lets say we have a million lines of this. <div class="first"> <div class="second"> <span class="third">Hello World</span> </div> </div> Which would be the fastest way to change the font of Hello World to red? .third { color: red; } div.third { color: red; } div.second div.third { color: red; } div.first div.second div.third { color: red; } Also, what if there was at tag in the middle that had a unique id of "foo". Which one of the CSS methods above would be the fastest. I know why these methods are used etc, im just trying to grasp better the rendering technique of the browsers and i have no idea how to make a test that times it. UPDATE: Nice answer Gumbo. From the looks of it then it would be quicker in a regular site to do the full definition of a tag. Since it finds the parents and narrows the search for every parent found. That could be bad in the sense you'd have a pretty large CSS file though.

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  • SQL model optimization question

    - by supermogx
    I need to keep track of number of "hits" on a particular item in a DB. The thing is that the "hits" should stay unique with a user ID, so if a user hits the item 3 times, it should still count for a hit of 1. Also, I need to display the total number of hits for a particular item. Is there a better way than to store each hits for each items by each users in a separate table? Would keeping the user ID in a string separated by commas a better and efficient way?

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  • mysql index optimization for a table with multiple indexes that index some of the same columns

    - by Sean
    I have a table that stores some basic data about visitor sessions on third party web sites. This is its structure: id, site_id, unixtime, unixtime_last, ip_address, uid There are four indexes: id, site_id/unixtime, site_id/ip_address, and site_id/uid There are many different types of ways that we query this table, and all of them are specific to the site_id. The index with unixtime is used to display the list of visitors for a given date or time range. The other two are used to find all visits from an IP address or a "uid" (a unique cookie value created for each visitor), as well as determining if this is a new visitor or a returning visitor. Obviously storing site_id inside 3 indexes is inefficient for both write speed and storage, but I see no way around it, since I need to be able to quickly query this data for a given specific site_id. Any ideas on making this more efficient? I don't really understand B-trees besides some very basic stuff, but it's more efficient to have the left-most column of an index be the one with the least variance - correct? Because I considered having the site_id being the second column of the index for both ip_address and uid but I think that would make the index less efficient since the IP and UID are going to vary more than the site ID will, because we only have about 8000 unique sites per database server, but millions of unique visitors across all ~8000 sites on a daily basis. I've also considered removing site_id from the IP and UID indexes completely, since the chances of the same visitor going to multiple sites that share the same database server are quite small, but in cases where this does happen, I fear it could be quite slow to determine if this is a new visitor to this site_id or not. The query would be something like: select id from sessions where uid = 'value' and site_id = 123 limit 1 ... so if this visitor had visited this site before, it would only need to find one row with this site_id before it stopped. This wouldn't be super fast necessarily, but acceptably fast. But say we have a site that gets 500,000 visitors a day, and a particular visitor loves this site and goes there 10 times a day. Now they happen to hit another site on the same database server for the first time. The above query could take quite a long time to search through all of the potentially thousands of rows for this UID, scattered all over the disk, since it wouldn't be finding one for this site ID. Any insight on making this as efficient as possible would be appreciated :) Update - this is a MyISAM table with MySQL 5.0. My concerns are both with performance as well as storage space. This table is both read and write heavy. If I had to choose between performance and storage, my biggest concern is performance - but both are important. We use memcached heavily in all areas of our service, but that's not an excuse to not care about the database design. I want the database to be as efficient as possible.

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  • Any specifications/docs around optimization of Google Apps Script, to avoid timeouts and "hangs"

    - by BruceM
    From my experience so far, it seems that if you write a script that makes lots of expensive calls close together, the functionality just "hangs", or you get inconsistent responses, and have to refresh the browser because sheets stop updating etc. Are there any docs or specs that clarify this, as releasing an app fr real-world use is not possible if users can expect it to work most of the time, and produce random results every now and then...

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  • Function-Local Static Const variable Initialization semantics.

    - by Hassan Syed
    The questions are in bold, for those that cannot be bothered reading a question in depth. This is a followup to this question. It is to do with the initialization semantics of static variables in functions. Static variables should be initialized once, and their internal state might be altered later - as I (currently) do in the linked question. However, the code in question does not require the feature to change the state of the variable later. Let me clarrify my position, since I don't require the string object's internal state to change. The code is for a trait class for meta programming, and as such would would benifit from a const char * const ptr -- thus Ideally a local cost static const variable is needed. My educated guess is that in this case the string in question will be optimally placed in memory by the link-loader, and that the code is more secure and maps to the intended semantics. This leads to the semantics of such a variable "The C++ Programming language Third Edition -- Stroustrup" does not have anything (that I could find) to say about this matter. All that is said is that the variable is initialized once when the flow of control of the thread first reaches the code. This leads me to ponder if the following code would be sensible, and if not what are the intended semantics ?. #include <iostream> const char * const GetString(const char * x_in) { static const char * const x = x_in; return x; } int main() { const char * const temp = GetString("yahoo"); std::cout << temp << std::endl; const char * const temp2 = GetString("yahoo2"); std::cout << temp2 << std::endl; } The following compiles on GCC and prints "yahoo" twice. Which is what I want -- However it might not be standards compliant (which is why I post this question). It might be more elegant to have two functions, "SetString" and "String" where the latter forwards to the first. If it is standards compliant does someone know of a templates implementation in boost (or elsewhere) ?

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  • SSE SIMD Optimization For Loop

    - by Projectile Fish
    I have some code in a loop for(int i = 0; i < n; i++) { u[i] = c * u[i] + s * b[i]; } So, u and b are vectors of the same length, and c and s are scalars. Is this code a good candidate for vectorization for use with SSE in order to get a speedup?

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  • Commercial use of Google API

    - by Mac
    This question maybe a better fit on The Business of Software forum but despite my post on there, I'm still unable to determine the following: Can I use the Google API to build commercial software? If not how can the people behind Byline charge for their app? Update: I'm specifically interested in Google's Picasa & Reader APIs

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  • C#, weird optimization

    - by Snake
    Hi, I'm trying to read my compiled C# code. this is my code: using(OleDbCommand insertCommand = new OleDbCommand("...", connection)) { // do super stuff } But! We all know that a using gets translated to this: { OleDbCommand insertCommand = new OleDbCommand("...", connection) try { //do super stuff } finally { if(insertCommand != null) ((IDisposable)insertCommand).Dispose(); } } (since OleDbCommand is a reference type). But when I decompile my assembly (compiled with .NET 2.0) I get this in Resharper: try { insertCommand = new OleDbCommand("", connection); Label_0017: try { //do super stuff } finally { Label_0111: if ((insertCommand == null) != null) { goto Label_0122; } insertCommand.Dispose(); Label_0122:; } I'm talking about this line: if ((insertCommand == null) != null). True is not null, it never is, nor is false. So how is my object disposed properly? WTF? Thanks! -Kristof

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  • What languages should a microISV use to write commercial software?

    - by Wal
    I've been writing software in Java for many years now, but it was always for internal applications that would be deployed to a server. I'd like to get into writing desktop applications now but I don't know where to start. I've written a few Java/Swing applications but again they were for internal use. My understanding is that Java and other semi-compiled and interpreted languages are too easy to reverse engineer, making them unsuitable for commercial software. I am aware that there are compilers for Java and some other interpreted language, but I've also heard that they are pricey and/or unreliable. Assuming I start a microISV and wish to develop and sell applications to a broad audience, what's my best bet? I would prefer something that can be written close to once, and compiled for different operating systems but I am not opposed to .NET and a Windows-only audience if other languages would compromise the experience (installation ease & user experience) in Windows. My only issue there is that I don't have a large starting budget and paying out the wazoo for the required development tools is not really in the cards.

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  • Display a ranking grid for game : optimization of left outer join and find a player

    - by Jerome C.
    Hello, I want to do a ranking grid. I have a table with different values indexed by a key: Table SimpleValue : key varchar, value int, playerId int I have a player which have several SimpleValue. Table Player: id int, nickname varchar Now imagine these records: SimpleValue: Key value playerId for 1 1 int 2 1 agi 2 1 lvl 5 1 for 6 2 int 3 2 agi 1 2 lvl 4 2 Player: id nickname 1 Bob 2 John I want to display a rank of these players on various SimpleValue. Something like: nickname for lvl Bob 1 5 John 6 4 For the moment I generate an sql query based on which SimpleValue key you want to display and on which SimpleValue key you want to order players. eg: I want to display 'lvl' and 'for' of each player and order them on the 'lvl' The generated query is: SELECT p.nickname as nickname, v1.value as lvl, v2.value as for FROM Player p LEFT OUTER JOIN SimpleValue v1 ON p.id=v1.playerId and v1.key = 'lvl' LEFT OUTER JOIN SimpleValue v2 ON p.id=v2.playerId and v2.key = 'for' ORDER BY v1.value This query runs perfectly. BUT if I want to display 10 different values, it generates 10 'left outer join'. Is there a way to simplify this query ? I've got a second question: Is there a way to display a portion of this ranking. Imagine I've 1000 players and I want to display TOP 10, I use the LIMIT keyword. Now I want to display the rank of the player Bob which is 326/1000 and I want to display 5 rank player above and below (so from 321 to 331 position). How can I achieve it ? thanks.

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  • Simple neon optimization in Android

    - by Peter
    In my Android application, I use a bunch of open source libraries such as libyuv, libvpx, libcrypto, libssl, etc. Some of them come with Android.mk. For others, I hand-crafted Android.mk. The code is built only for arm for now. Here is my Application.mk: APP_ABI := armeabi-v7a APP_OPTIM := release APP_STL := gnustl_static APP_CPPFLAGS := -frtti I am looking for way to generate binaries that are optimized for neon. Browsing the net, I found the following setting that someone is using in his Android.mk: LOCAL_CFLAGS += -mfloat-abi=softfp -mfpu=neon -march=armv7 I wonder if I simply put this setting in Application.mk, will it automatically get applied across all the libraries? A step before each library is built is the following: include $(CLEAR_VARS) Is it better to include LOCAL_CFLAGS directive after this line (instead of including it in Application.mk)? Finally, why doesn't ndk-build automatically optimize for neon when it sees armabi in Application.mk? Regards.

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  • MongoDB vs CouchDB (Speed optimization)

    - by Edward83
    Hi! I made some tests of speed to compare MongoDB and CouchDB. Only inserts were while testing. I got MongoDB 15x faster than CouchDB. I know that it is because of sockets vs http. But, it is very interesting for me how can I optimize inserts in CouchDB? Test platform: Windows XP SP3 32 bit. I used last versions of MongoDB, MongoDB C# Driver and last version of installation package of CouchDB for Windows. Thanks!

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  • url optimization in rails?

    - by piemesons
    Hello I want to create seo optimize url in rails.Same like done in stackoverflow. Right now this is my url http://localhost:3000/questions/56 I want to make it something like this:- http://localhost:3000/questions/56/this-is-my-optimized-url i am using restful approach. is there any plug-in available for this.

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  • Stored procedure optimization

    - by George Zacharia
    Hi, i have a stored procedure which takes lot of time to execure .Can any one suggest a better approch so that the same result set is achived. ALTER PROCEDURE [dbo].[spFavoriteRecipesGET] @USERID INT, @PAGENUMBER INT, @PAGESIZE INT, @SORTDIRECTION VARCHAR(4), @SORTORDER VARCHAR(4),@FILTERBY INT AS BEGIN DECLARE @ROW_START INT DECLARE @ROW_END INT SET @ROW_START = (@PageNumber-1)* @PageSize+1 SET @ROW_END = @PageNumber*@PageSize DECLARE @RecipeCount INT DECLARE @RESULT_SET_TABLE TABLE ( Id INT NOT NULL IDENTITY(1,1), FavoriteRecipeId INT, RecipeId INT, DateAdded DATETIME, Title NVARCHAR(255), UrlFriendlyTitle NVARCHAR(250), [Description] NVARCHAR(MAX), AverageRatingId FLOAT, SubmittedById INT, SubmittedBy VARCHAR(250), RecipeStateId INT, RecipeRatingId INT, ReviewCount INT, TweaksCount INT, PhotoCount INT, ImageName NVARCHAR(50) ) INSERT INTO @RESULT_SET_TABLE SELECT FavoriteRecipes.FavoriteRecipeId, Recipes.RecipeId, FavoriteRecipes.DateAdded, Recipes.Title, Recipes.UrlFriendlyTitle, Recipes.[Description], Recipes.AverageRatingId, Recipes.SubmittedById, COALESCE(users.DisplayName,users.UserName,Recipes.SubmittedBy) As SubmittedBy, Recipes.RecipeStateId, RecipeReviews.RecipeRatingId, COUNT(RecipeReviews.Review), COUNT(RecipeTweaks.Tweak), COUNT(Photos.PhotoId), dbo.udfGetRecipePhoto(Recipes.RecipeId) AS ImageName FROM FavoriteRecipes INNER JOIN Recipes ON FavoriteRecipes.RecipeId=Recipes.RecipeId AND Recipes.RecipeStateId <> 3 LEFT OUTER JOIN RecipeReviews ON RecipeReviews.RecipeId=Recipes.RecipeId AND RecipeReviews.ReviewedById=@UserId AND RecipeReviews.RecipeRatingId= ( SELECT MAX(RecipeReviews.RecipeRatingId) FROM RecipeReviews WHERE RecipeReviews.ReviewedById=@UserId AND RecipeReviews.RecipeId=FavoriteRecipes.RecipeId ) OR RecipeReviews.RecipeRatingId IS NULL LEFT OUTER JOIN RecipeTweaks ON RecipeTweaks.RecipeId = Recipes.RecipeId AND RecipeTweaks.TweakedById= @UserId LEFT OUTER JOIN Photos ON Photos.RecipeId = Recipes.RecipeId AND Photos.UploadedById = @UserId AND Photos.RecipeId = FavoriteRecipes.RecipeId AND Photos.PhotoTypeId = 1 LEFT OUTER JOIN users ON Recipes.SubmittedById = users.UserId WHERE FavoriteRecipes.UserId=@UserId GROUP BY FavoriteRecipes.FavoriteRecipeId, Recipes.RecipeId, FavoriteRecipes.DateAdded, Recipes.Title, Recipes.UrlFriendlyTitle, Recipes.[Description], Recipes.AverageRatingId, Recipes.SubmittedById, Recipes.SubmittedBy, Recipes.RecipeStateId, RecipeReviews.RecipeRatingId, users.DisplayName, users.UserName, Recipes.SubmittedBy; WITH SortResults AS ( SELECT ROW_NUMBER() OVER ( ORDER BY CASE WHEN @SORTDIRECTION = 't' AND @SORTORDER='a' THEN TITLE END ASC, CASE WHEN @SORTDIRECTION = 't' AND @SORTORDER='d' THEN TITLE END DESC, CASE WHEN @SORTDIRECTION = 'r' AND @SORTORDER='a' THEN AverageRatingId END ASC, CASE WHEN @SORTDIRECTION = 'r' AND @SORTORDER='d' THEN AverageRatingId END DESC, CASE WHEN @SORTDIRECTION = 'mr' AND @SORTORDER='a' THEN RecipeRatingId END ASC, CASE WHEN @SORTDIRECTION = 'mr' AND @SORTORDER='d' THEN RecipeRatingId END DESC, CASE WHEN @SORTDIRECTION = 'd' AND @SORTORDER='a' THEN DateAdded END ASC, CASE WHEN @SORTDIRECTION = 'd' AND @SORTORDER='d' THEN DateAdded END DESC ) RowNumber, FavoriteRecipeId, RecipeId, DateAdded, Title, UrlFriendlyTitle, [Description], AverageRatingId, SubmittedById, SubmittedBy, RecipeStateId, RecipeRatingId, ReviewCount, TweaksCount, PhotoCount, ImageName FROM @RESULT_SET_TABLE WHERE ((@FILTERBY = 1 AND SubmittedById= @USERID) OR ( @FILTERBY = 2 AND (SubmittedById <> @USERID OR SubmittedById IS NULL)) OR ( @FILTERBY <> 1 AND @FILTERBY <> 2)) ) SELECT RowNumber, FavoriteRecipeId, RecipeId, DateAdded, Title, UrlFriendlyTitle, [Description], AverageRatingId, SubmittedById, SubmittedBy, RecipeStateId, RecipeRatingId, ReviewCount, TweaksCount, PhotoCount, ImageName FROM SortResults WHERE RowNumber BETWEEN @ROW_START AND @ROW_END print @ROW_START print @ROW_END SELECT @RecipeCount=dbo.udfGetFavRecipesCount(@UserId) SELECT @RecipeCount AS RecipeCount SELECT COUNT(Id) as FilterCount FROM @RESULT_SET_TABLE WHERE ((@FILTERBY = 1 AND SubmittedById= @USERID) OR (@FILTERBY = 2 AND (SubmittedById <> @USERID OR SubmittedById IS NULL)) OR (@FILTERBY <> 1 AND @FILTERBY <> 2)) END

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  • How efficient is an if statement compared to a test that doesn't use an if? (C++)

    - by Keand64
    I need a program to get the smaller of two numbers, and I'm wondering if using a standard "if x is less than y" int a, b, low; if (a < b) low = a; else low = a; is more or less efficient than this: int a, b, low; low = b + ((a - b) & ((a - b) >> 31)); (or the variation of putting int delta = a - b at the top and rerplacing instances of a - b with that). I'm just wondering which one of these would be more efficient (or if the difference is to miniscule to be relevant), and the efficiency of if-else statements versus alternatives in general.

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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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  • ControlCollection extension method optimization

    - by Johan Leino
    Hi, got question regarding an extension method that I have written that looks like this: public static IEnumerable<T> FindControlsOfType<T>(this ControlCollection instance) where T : class { T control; foreach (Control ctrl in instance) { if ((control = ctrl as T) != null) { yield return control; } foreach (T child in FindControlsOfType<T>(ctrl.Controls)) { yield return child; } } } public static IEnumerable<T> FindControlsOfType<T>(this ControlCollection instance, Func<T, bool> match) where T : class { return FindControlsOfType<T>(instance).Where(match); } The idea here is to find all controls that match a specifc criteria (hence the Func<..) in the controls collection. My question is: Does the second method (that has the Func) first call the first method to find all the controls of type T and then performs the where condition or does the "runtime" optimize the call to perform the where condition on the "whole" enumeration (if you get what I mean). secondly, are there any other optimizations that I can do to the code to perform better. An example can look like this: var checkbox = this.Controls.FindControlsOfType<MyCustomCheckBox>( ctrl => ctrl.CustomProperty == "Test" ) .FirstOrDefault();

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  • Database maintenance, big binary table optimization

    - by jgemedina
    Hi i have a huge database, around 1 TB in size, most of the space is consumed by a table which stores images, the tables has right now almost 800k rows. server response time has increased, i would like to know which techniques should i use or you recomend, partitioning? o how to reorganize the table every row is accessed by the image id column, and it has its clustered index by that column, and every two days i reorganize the index and every 7 days i rebuild it, but it seems not to be working any suggestions?

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