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• Performance of std::pow - cache misses???

  - by Eamon Nerbonne

  I've been trying to optimize a numeric program of mine, and have run into something of a mystery. I'm looping over code that performs thousands of floating point operations, and just 1 call to pow nevertheless, that call takes 5% of the time... That's not necessarily a critical issue, but it is odd, so I'd like to understand what's happening. When I profiled for cache misses, VS.NET 2010RC's profiler reports that virtually all cache misses are occurring in std::pow... so... what's up with that? Is there a faster alternative? I tried powf, but that's only slightly faster; it's still responsible for an abnormal number of cache misses. Why would a basic function like pow cause cache-misses?

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• Efficient alternative to merge() when building dataframe from json files with R?

  - by Bryan

  I have written the following code which works, but is painfully slow once I start executing it over thousands of records: require("RJSONIO") people_data <- data.frame(person_id=numeric(0)) json_data <- fromJSON(json_file) n_people <- length(json_data) for(lender in 1:n_people) { person_dataframe <- as.data.frame(t(unlist(json_data[[person]]))) people_data <- merge(people_data, person_dataframe, all=TRUE) } output_file <- paste("people_data",".csv") write.csv(people_data, file=output_file) I am attempting to build a unified data table from a series of json-formated files. The fromJSON() function reads in the data as lists of lists. Each element of the list is a person, which then contains a list of the attributes for that person. For example: [[1]] person_id name gender hair_color [[2]] person_id name location gender height [[...]] structure(list(person_id = "Amy123", name = "Amy", gender = "F", hair_color = "brown"), .Names = c("person_id", "name", "gender", "hair_color")) structure(list(person_id = "matt53", name = "Matt", location = structure(c(47231, "IN"), .Names = c("zip_code", "state")), gender = "M", height = 172), .Names = c("person_id", "name", "location", "gender", "height")) The end result of the code above is matrix where the columns are every person-attribute that appears in the structure above, and the rows are the relevant values for each person. As you can see though, some data is missing for some of the people, so I need to ensure those show up as NA and make sure things end up in the right columns. Further, location itself is a vector with two components: state and zip_code, meaning it needs to be flattened to location.state and location.zip_code before it can be merged with another person record; this is what I use unlist() for. I then keep the running master table in people_data. The above code works, but do you know of a more efficient way to accomplish what I'm trying to do? It appears the merge() is slowing this to a crawl... I have hundreds of files with hundreds of people in each file. Thanks! Bryan

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• Hierarchical data in Linq - options and performance

  - by Anthony

  I have some hierarchical data - each entry has an id and a (nullable) parent entry id. I want to retrieve all entries in the tree under a given entry. This is in a SQL Server 2005 database. I am querying it with LINQ to SQL in C# 3.5. LINQ to SQL does not support Common Table Expressions directly. My choices are to assemble the data in code with several LINQ queries, or to make a view on the database that surfaces a CTE. Which option (or another option) do you think will perform better when data volumes get large? Is SQL Server 2008's HierarchyId type supported in Linq to SQL?

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• Loading animation Memory leak

  - by Ayaz Alavi

  Hi, I have written network class that is managing all network calls for my application. There are two methods showLoadingAnimationView and hideLoadingAnimationView that will show UIActivityIndicatorView in a view over my current viewcontroller with fade background. I am getting memory leaks somewhere on these two methods. Here is the code -(void)showLoadingAnimationView { textmeAppDelegate *textme = (textmeAppDelegate *)[[UIApplication sharedApplication] delegate]; [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES]; if(wrapperLoading != nil) { [wrapperLoading release]; } wrapperLoading = [[UIView alloc] initWithFrame:CGRectMake(0.0, 0.0, 320.0, 480.0)]; wrapperLoading.backgroundColor = [UIColor clearColor]; wrapperLoading.alpha = 0.8; UIView *_loadingBG = [[UIView alloc] initWithFrame:CGRectMake(0.0, 0.0, 320.0, 480.0)]; _loadingBG.backgroundColor = [UIColor blackColor]; _loadingBG.alpha = 0.4; circlingWheel = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge]; CGRect wheelFrame = circlingWheel.frame; circlingWheel.frame = CGRectMake(((320.0 - wheelFrame.size.width) / 2.0), ((480.0 - wheelFrame.size.height) / 2.0), wheelFrame.size.width, wheelFrame.size.height); [wrapperLoading addSubview:_loadingBG]; [wrapperLoading addSubview:circlingWheel]; [circlingWheel startAnimating]; [textme.window addSubview:wrapperLoading]; [_loadingBG release]; [circlingWheel release]; } -(void)hideLoadingAnimationView { [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO]; wrapperLoading.alpha = 0.0; [self.wrapperLoading removeFromSuperview]; //[NSTimer scheduledTimerWithTimeInterval:0.8 target:wrapperLoading selector:@selector(removeFromSuperview) userInfo:nil repeats:NO]; } Here is how I am calling these two methods [NSThread detachNewThreadSelector:@selector(showLoadingAnimationView) toTarget:self withObject:nil]; and then somewhere later in the code i am using following function call to hide animation. [self hideLoadingAnimationView]; I am getting memory leaks when I call showLoadingAnimationView function. Anything wrong in the code or is there any better technique to show loading animation when we do network calls?

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• F# performance question: what is the compiler doing?

  - by Stephen Swensen

  Referencing this code: http://stackoverflow.com/questions/2840714/f-static-member-type-constraints/2842037#2842037 Why is, for example, [1L..100000L] |> List.map (fun n -> factorize gL n) significantly slower than [1L..100000L] |> List.map (fun n -> factorize (G_of 1L) n) By looking at Reflector, I can see that the compiler is treating each of these in very different ways, but there is too much going on for me to decipher the essential difference. Naively I assumed the former would perform better than the later because gL is precomputed whereas G_of 1L has to be computed 100,000 times (at least it appears that way).

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• Practical refactoring using unit tests

  - by awhite

  Having just read the first four chapters of Refactoring: Improving the Design of Existing Code, I embarked on my first refactoring and almost immediately came to a roadblock. It stems from the requirement that before you begin refactoring, you should put unit tests around the legacy code. That allows you to be sure your refactoring didn't change what the original code did (only how it did it). So my first question is this: how do I unit-test a method in legacy code? How can I put a unit test around a 500 line (if I'm lucky) method that doesn't do just one task? It seems to me that I would have to refactor my legacy code just to make it unit-testable. Does anyone have any experience refactoring using unit tests? And, if so, do you have any practical examples you can share with me? My second question is somewhat hard to explain. Here's an example: I want to refactor a legacy method that populates an object from a database record. Wouldn't I have to write a unit test that compares an object retrieved using the old method, with an object retrieved using my refactored method? Otherwise, how would I know that my refactored method produces the same results as the old method? If that is true, then how long do I leave the old deprecated method in the source code? Do I just whack it after I test a few different records? Or, do I need to keep it around for a while in case I encounter a bug in my refactored code? Lastly, since a couple people have asked...the legacy code was originally written in VB6 and then ported to VB.NET with minimal architecture changes.

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• ListView slow performance

  - by Mohamed Hemdan

  I've created a list of recipes using Listview/customcursoradapter. A custom layout includes a photo for the recipe , Now I've some problems with the performance of viewing and scrolling the Listview although it has only 10 records (Target is 150). sometimes i get this error java.lang.OutOfMemoryError: bitmap size exceeds VM budget , I've tried to implement the Async task but i failed to do it. Is there any way i can overcome this problem? Your help is highly appreciated !! Here is my GetView method public View getView(int position, View convertView, ViewGroup parent) { View row = super.getView(position, convertView, parent); Cursor cursbbn = getCursor(); if (row == null) { LayoutInflater inflater = (LayoutInflater) localContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE); row = inflater.inflate(R.layout.listtype, null); } String Title = cursbbn.getString(2); String SandID=cursbbn.getString(1); String Readyin = cursbbn.getString(4); String Faovoites=cursbbn.getString(8); TextView titler=(TextView)row.findViewById(R.id.listmaintitle); TextView readyinr=(TextView)row.findViewById(R.id.listreadyin); int colorPos = position % colors.length; row.setBackgroundColor(colors[colorPos]); titler.setText(Title); readyinr.setText(Readyin); ImageView picture = (ImageView) row.findViewById(R.id.imageView1); Bitmap bitImg1 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0001); Bitmap bitImg2 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0002); Bitmap bitImg3 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0003); Bitmap bitImg4 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0004); Bitmap bitImg5 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0005); Bitmap bitImg6 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0006); Bitmap bitImg7 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0007); Bitmap bitImg8 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0008); Bitmap bitImg9 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0009); Bitmap bitImg10 = BitmapFactory.decodeResource(localContext.getResources(), R.drawable.rec0010); if(SandID.contentEquals("0001")) picture.setImageBitmap(getRoundedCornerImage(bitImg1)); if(SandID.contentEquals("0002")) picture.setImageBitmap(getRoundedCornerImage(bitImg2)); if(SandID.contentEquals("0003")) picture.setImageBitmap(getRoundedCornerImage(bitImg3)); if(SandID.contentEquals("0004")) picture.setImageBitmap(getRoundedCornerImage(bitImg4)); if(SandID.contentEquals("0005")) picture.setImageBitmap(getRoundedCornerImage(bitImg5)); if(SandID.contentEquals("0006")) picture.setImageBitmap(getRoundedCornerImage(bitImg6)); if(SandID.contentEquals("0007")) picture.setImageBitmap(getRoundedCornerImage(bitImg7)); if(SandID.contentEquals("0008")) picture.setImageBitmap(getRoundedCornerImage(bitImg8)); if(SandID.contentEquals("0009")) picture.setImageBitmap(getRoundedCornerImage(bitImg9)); if(SandID.contentEquals("0010")) picture.setImageBitmap(getRoundedCornerImage(bitImg10)); return row; } And This is the error : 05-02 03:11:55.898: E/AndroidRuntime(376): FATAL EXCEPTION: main 05-02 03:11:55.898: E/AndroidRuntime(376): java.lang.OutOfMemoryError: bitmap size exceeds VM budget 05-02 03:11:55.898: E/AndroidRuntime(376): at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:460) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.graphics.BitmapFactory.decodeResourceStream(BitmapFactory.java:336) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.graphics.BitmapFactory.decodeResource(BitmapFactory.java:359) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.graphics.BitmapFactory.decodeResource(BitmapFactory.java:385) 05-02 03:11:55.898: E/AndroidRuntime(376): at master.chef.mediamaster.AlternateRowCursorAdapter.getView(AlternateRowCursorAdapter.java:83) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.AbsListView.obtainView(AbsListView.java:1409) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.ListView.makeAndAddView(ListView.java:1745) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.ListView.fillUp(ListView.java:700) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.ListView.fillGap(ListView.java:646) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.AbsListView.trackMotionScroll(AbsListView.java:3399) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.AbsListView.onTouchEvent(AbsListView.java:2233) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.widget.ListView.onTouchEvent(ListView.java:3446) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.View.dispatchTouchEvent(View.java:3885) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:903) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:942) 05-02 03:11:55.898: E/AndroidRuntime(376): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1691) 05-02 03:11:55.898: E/AndroidRuntime(376): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1125) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.app.Activity.dispatchTouchEvent(Activity.java:2096) 05-02 03:11:55.898: E/AndroidRuntime(376): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1675) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewRoot.deliverPointerEvent(ViewRoot.java:2194) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.view.ViewRoot.handleMessage(ViewRoot.java:1878) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.os.Handler.dispatchMessage(Handler.java:99) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.os.Looper.loop(Looper.java:123) 05-02 03:11:55.898: E/AndroidRuntime(376): at android.app.ActivityThread.main(ActivityThread.java:3683) 05-02 03:11:55.898: E/AndroidRuntime(376): at java.lang.reflect.Method.invokeNative(Native Method) 05-02 03:11:55.898: E/AndroidRuntime(376): at java.lang.reflect.Method.invoke(Method.java:507) 05-02 03:11:55.898: E/AndroidRuntime(376): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 05-02 03:11:55.898: E/AndroidRuntime(376): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 05-02 03:11:55.898: E/AndroidRuntime(376): at dalvik.system.NativeStart.main(Native Method)

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• Newbie question: When to use extern "C" { //code } ?

  - by Russel

  Hello, Maybe I'm not understanding the differences between C and C++, but when and why do we need to use: extern "C" { ? Apparently its a "linkage convention"? I read about it briefly and noticed that all the .h header files included with MSVS surround their code with it. What type of code exactly is "C code" and NOT "C++ code"? I thought C++ included all C code? I'm guessing that this is not the case and that C++ is different and that standard features/functions exist in one or the other but not both (ie: printf is C and cout is C++), but that C++ is backwards compatible though the extern "C" declaration. Is this correct? My next question depends on the answer to the first, but I'll ask it here anyway: Since MSVS header files that are written in C are surrounded by extern "C" { ... }, when would you ever need to use this yourself in your own code? If your code is C code and you are trying to compile it in a C++ compiler, shouldn't it work without problem because all the standard h files you include will already have the extern "C" thing in them with the C++ compiler? Do you have to use this when compiling in C++ but linking to alteady built C libraries or something? Please help clarify this for me... Thanks! --Keith

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• What limits scaling in this simple OpenMP program?

  - by Douglas B. Staple

  I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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• Difference in linq-to-sql query performance using GenericRespositry

  - by Neil

  Given i have a class like so in my Data Layer public class GenericRepository<TEntity> where TEntity : class { [System.ComponentModel.DataObjectMethod(System.ComponentModel.DataObjectMethodType.Select)] public IQueryable<TEntity> SelectAll() { return DataContext.GetTable<TEntity>(); } } I would be able to query a table in my database like so from a higher layer using (GenericRepositry<MyTable> mytable = new GenericRepositry<MyTable>()) { var myresult = from m in mytable.SelectAll() where m.IsActive select m; } is this considerably slower than using the usual code in my Data Layer using (MyDataContext ctx = new MyDataContext()) { var myresult = from m in ctx.MyTable where m.IsActive select m; } Eliminating the need to write simple single table selects in the Data layer saves a lot of time, but will i regret it?

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• Vb.exe performance time

  - by vinodacharyabva

  Hi I am running a vb.exe through automation. In exe I have return a code which takes a data from database and saves that data into file. I ran that .exe for the first time. It took 1 mins. For testing baseline I called same .exe 5 times one after the other. But it took nearly 10 mins to generate. My question is if it takes 1 min for 1 report to generate then it should take 5 mins to generate 5 report but why it is taking 10 mins (more than the double). Is there any problem while calling a exe one after the other?

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• ~1 second TcpListener Pending()/AcceptTcpClient() lag

  - by cpf

  Probably just watch this video: http://screencast.com/t/OWE1OWVkO As you see, the delay between a connection being initiated (via telnet or firefox) and my program first getting word of it. Here's the code that waits for the connection public IDLServer(System.Net.IPAddress addr,int port) { Listener = new TcpListener(addr, port); Listener.Server.NoDelay = true;//I added this just for testing, it has no impact Listener.Start(); ConnectionThread = new Thread(ConnectionListener); ConnectionThread.Start(); } private void ConnectionListener() { while (Running) { while (Listener.Pending() == false) { System.Threading.Thread.Sleep(1); }//this is the part with the lag Console.WriteLine("Client available");//from this point on everything runs perfectly fast TcpClient cl = Listener.AcceptTcpClient(); Thread proct = new Thread(new ParameterizedThreadStart(InstanceHandler)); proct.Start(cl); } } (I was having some trouble getting the code into a code block) I've tried a couple different things, could it be I'm using TcpClient/Listener instead of a raw Socket object? It's not a mandatory TCP overhead I know, and I've tried running everything in the same thread, etc.

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• Why are compilers so stupid?

  - by martinus

  I always wonder why compilers can't figure out simple things that are obvious to the human eye. They do lots of simple optimizations, but never something even a little bit complex. For example, this code takes about 6 seconds on my computer to print the value zero (using java 1.6): int x = 0; for (int i = 0; i < 100 * 1000 * 1000 * 1000; ++i) { x += x + x + x + x + x; } System.out.println(x); It is totally obvious that x is never changed so no matter how often you add 0 to itself it stays zero. So the compiler could in theory replace this with System.out.println(0). Or even better, this takes 23 seconds: public int slow() { String s = "x"; for (int i = 0; i < 100000; ++i) { s += "x"; } return 10; } First the compiler could notice that I am actually creating a string s of 100000 "x" so it could automatically use s StringBuilder instead, or even better directly replace it with the resulting string as it is always the same. Second, It does not recognize that I do not actually use the string at all, so the whole loop could be discarded! Why, after so much manpower is going into fast compilers, are they still so relatively dumb? EDIT: Of course these are stupid examples that should never be used anywhere. But whenever I have to rewrite a beautiful and very readable code into something unreadable so that the compiler is happy and produces fast code, I wonder why compilers or some other automated tool can't do this work for me.

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• What is your personal approach/take on commenting?

  - by Trae

  Duplicate What are your hard rules about commenting? A Developer I work with had some things to say about commenting that were interesting to me (see below). What is your personal approach/take on commenting? "I don't add comments to code unless its a simple heading or there's a platform-bug or a necessary work-around that isn't obvious. Code can change and comments may become misleading. Code should be self-documenting in its use of descriptive names and its logical organization - and its solutions should be the cleanest/simplest way to perform a given task. If a programmer can't tell what a program does by only reading the code, then he's not ready to alter it. Commenting tends to be a crutch for writing something complex or non-obvious - my goal is to always write clean and simple code." "I think there a few camps when it comes to commenting, the enterprisey-type who think they're writing an API and some grand code-library that will be used for generations to come, the craftsman-like programmer that thinks code says what it does clearer than a comment could, and novices that write verbose/unclear code so as to need to leave notes to themselves as to why they did something."

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• Quickest way to compare a bunch of array or list of values.

  - by zapping

  Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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• avoiding code duplication in Rails 3 models

  - by Dustin Frazier

  I'm working on a Rails 3.1 application where there are a number of different enum-like models that are stored in the database. There is a lot of identical code in these models, as well as in the associated controllers and views. I've solved the code duplication for the controllers and views via a shared parent controller class and the new view/layout inheritance that's part of Rails 3. Now I'm trying to solve the code duplication in the models, and I'm stuck. An example of one of my enum models is as follows: class Format < ActiveRecord::Base has_and_belongs_to_many :videos attr_accessible :name validates :name, presence: true, length: { maximum: 20 } before_destroy :verify_no_linked_videos def verify_no_linked_videos unless self.videos.empty? self.errors[:base] << "Couldn't delete format with associated videos." raise ActiveRecord::RecordInvalid.new self end end end I have four or five other classes with nearly identical code (the association declaration being the only difference). I've tried creating a module with the shared code that they all include (which seems like the Ruby Way), but much of the duplicate code relies on ActiveRecord, so the methods I'm trying to use in the module (validate, attr_accessible, etc.) aren't available. I know about ActiveModel, but that doesn't get me all the way there. I've also tried creating a common, non-persistent parent class that subclasses ActiveRecord::Base, but all of the code I've seen to accomplish this assumes that you won't have subclasses of your non-persistent class that do persist. Any suggestions for how best to avoid duplicating these identical lines of code across many different enum models?

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• Inline function v. Macro in C -- What's the Overhead (Memory/Speed)?

  - by Jason R. Mick

  I searched Stack Overflow for the pros/cons of function-like macros v. inline functions. I found the following discussion: Pros and Cons of Different macro function / inline methods in C ...but it didn't answer my primary burning question. Namely, what is the overhead in c of using a macro function (with variables, possibly other function calls) v. an inline function, in terms of memory usage and execution speed? Are there any compiler-dependent differences in overhead? I have both icc and gcc at my disposal. My code snippet I'm modularizing is: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = AttractiveTerm * AttractiveTerm; EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); My reason for turning it into an inline function/macro is so I can drop it into a c file and then conditionally compile other similar, but slightly different functions/macros. e.g.: double AttractiveTerm = pow(SigmaSquared/RadialDistanceSquared,3); double RepulsiveTerm = pow(SigmaSquared/RadialDistanceSquared,9); EnergyContribution += 4 * Epsilon * (RepulsiveTerm - AttractiveTerm); (note the difference in the second line...) This function is a central one to my code and gets called thousands of times per step in my program and my program performs millions of steps. Thus I want to have the LEAST overhead possible, hence why I'm wasting time worrying about the overhead of inlining v. transforming the code into a macro. Based on the prior discussion I already realize other pros/cons (type independence and resulting errors from that) of macros... but what I want to know most, and don't currently know is the PERFORMANCE. I know some of you C veterans will have some great insight for me!!

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• Displaying code with <pre> tags.

  - by iMaster

  Currently I'm using <pre><code> code here </code><pre> to display code. I'm pulling this information from a DB for a blog. The problem I'm having is that some of the code isn't showing. For example, in the source code I have this: <pre><code><br /> echo '<ul class="mylist"><li><ul class="left">'; foreach($nameArray as $name) { if($countervar == $half) { echo '</ul></li>'; echo'<li><ul class="right">'; } echo '<li>$name</li>'; ++$i; } echo '</ul></li>'; echo '</ul>'; ?> But all that shows up is this: echo ''; foreach($nameArray as $name) { if($countervar == $half) { echo ''; echo''; } echo '$name'; ++$i; } echo ' An there's some really weird formatting/spacing issues as well. Any ideas as to what is causing this? I should also mention that some of the other sets of code show up just fine.

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• Suggestions for performance improvement surrounding sending email notifications?

  - by jcmoney

  It takes around a couple of seconds for my app to execute the code to send an email right now on a test server with nothing much else running. Not sure if this is typical/expected. I'm also using the php framework Kohana's email helper and not php's mail directly out of convenience if that matters. Is it always just better to schedule a cron job to send emails every 5 min or so? Or should I be able to send emails immediately and I'm just not doing something right? What the script does is insert a row into the db and notifies the relevant group that the row was created. The groups are usually < 20 people so I just do a loop calling Kohana's email helper each time for each member of the group.

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• Quickest way to compare a buch of array or list of values.

  - by zapping

  Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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• C++ performance, optimizing compiler, empty function in .cpp

  - by Dodo

  I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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• C++ assignment - stylish or performance?

  - by joejax

  Having been writing Java code for many years, I was amazed when I see this C++ statement: int a,b; int c = (a=1, b=a+2, b*3); My question is: Is this a choice of coding style, or it has real benefit? (looking for a practicle use case) I think the compiler will see it the same as following: int a=1, b=a+2; int c = b*3; (What's the offical name for this? I assume it's a standard C/C++ syntax.)

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• Eclipse plugin to measure programmer performance/stats

  - by trenki

  Does anyone know of an Eclipse plugin that can give me some stats about my behavior/usage of the Eclipse IDE? There are quite a few things I would like to know: How often/when do I invoke the "Build All" command (through Ctrl+B) How often does compilation fail/succeed (+ number of errors/warnings) How often do I hit Backspace? (I do that way to often; If pressing that key would give a nasty sound I would in time learn to type correctly in the first place) How many characters/lines of code that I typed do I delete (possibly quite immediately) How (effective/efficient/...) is my Mouse/Keyboard/IDE usage? (Kinda like measuring APM in StarCraft; this could be fun) If there is no such Eclipse plugin around, how complex and time consuming would It be to write a plugin that can accomplish the above?

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• F# why my recursion is faster than Seq.exists?

  - by user38397

  I am pretty new to F#. I'm trying to understand how I can get a fast code in F#. For this, I tried to write two methods (IsPrime1 and IsPrime2) for benchmarking. My code is: // Learn more about F# at http://fsharp.net open System open System.Diagnostics #light let isDivisible n d = n % d = 0 let IsPrime1 n = Array.init (n-2) ((+) 2) |> Array.exists (isDivisible n) |> not let rec hasDivisor n d = match d with | x when x < n -> (n % x = 0) || (hasDivisor n (d+1)) | _ -> false let IsPrime2 n = hasDivisor n 2 |> not let SumOfPrimes max = [|2..max|] |> Array.filter IsPrime1 |> Array.sum let maxVal = 20000 let s = new Stopwatch() s.Start() let valOfSum = SumOfPrimes maxVal s.Stop() Console.WriteLine valOfSum Console.WriteLine("IsPrime1: {0}", s.ElapsedMilliseconds) ////////////////////////////////// s.Reset() s.Start() let SumOfPrimes2 max = [|2..max|] |> Array.filter IsPrime2 |> Array.sum let valOfSum2 = SumOfPrimes2 maxVal s.Stop() Console.WriteLine valOfSum2 Console.WriteLine("IsPrime2: {0}", s.ElapsedMilliseconds) Console.ReadKey() IsPrime1 takes 760 ms while IsPrime2 takes 260ms for the same result. What's going on here and how I can make my code even faster?

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• Can't view order in magento

  - by koko

  Hi, I've been setting up a fresh magento 1.4.0.1 install, working great so far. I did some test orders just to see. Everything works fine, but when I click on "view order" under "my orders", I get a bunch of error messages: There has been an error processing your request Notice: iconv_substr() [function.iconv-substr]: Unknown error (0) in /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Helper/String.php on line 98 Trace: #0 [internal function]: mageCoreErrorHandler(8, 'iconv_substr() ...', '/data/web/A1423...', 98, Array) #1 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Helper/String.php(98): iconv_substr('1', 0, 50, 'UTF-8') #2 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Helper/String.php(173): Mage_Core_Helper_String-substr('1', 0, 50) #3 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Helper/String.php(112): Mage_Core_Helper_String-str_split('1', 50) #4 /data/web/A14237/htdocs/magento/app/design/frontend/base/default/template/sales/order/items/renderer/default.phtml(58): Mage_Core_Helper_String-splitInjection('1') #5 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(189): include('/data/web/A1423...') #6 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(225): Mage_Core_Block_Template-fetchView('frontend/base/d...') #7 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(242): Mage_Core_Block_Template-renderView() #8 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(674): Mage_Core_Block_Template-_toHtml() #9 /data/web/A14237/htdocs/magento/app/code/core/Mage/Sales/Block/Items/Abstract.php(137): Mage_Core_Block_Abstract-toHtml() #10 /data/web/A14237/htdocs/magento/app/design/frontend/base/default/template/sales/order/items.phtml(52): Mage_Sales_Block_Items_Abstract-getItemHtml(Object(Mage_Sales_Model_Order_Item)) #11 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(189): include('/data/web/A1423...') #12 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(225): Mage_Core_Block_Template-fetchView('frontend/base/d...') #13 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(242): Mage_Core_Block_Template-renderView() #14 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(674): Mage_Core_Block_Template-_toHtml() #15 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(516): Mage_Core_Block_Abstract-toHtml() #16 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(467): Mage_Core_Block_Abstract-_getChildHtml('order_items', true) #17 /data/web/A14237/htdocs/magento/app/design/frontend/base/default/template/sales/order/view.phtml(64): Mage_Core_Block_Abstract-getChildHtml('order_items') #18 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(189): include('/data/web/A1423...') #19 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(225): Mage_Core_Block_Template-fetchView('frontend/base/d...') #20 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(242): Mage_Core_Block_Template-renderView() #21 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(674): Mage_Core_Block_Template-_toHtml() #22 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(516): Mage_Core_Block_Abstract-toHtml() #23 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(463): Mage_Core_Block_Abstract-_getChildHtml('sales.order.vie...', true) #24 /data/web/A14237/htdocs/magento/app/code/core/Mage/Page/Block/Html/Wrapper.php(52): Mage_Core_Block_Abstract-getChildHtml('', true, true) #25 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(674): Mage_Page_Block_Html_Wrapper-_toHtml() #26 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Text/List.php(43): Mage_Core_Block_Abstract-toHtml() #27 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(674): Mage_Core_Block_Text_List-_toHtml() #28 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(516): Mage_Core_Block_Abstract-toHtml() #29 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(467): Mage_Core_Block_Abstract-_getChildHtml('content', true) #30 /data/web/A14237/htdocs/magento/app/design/frontend/base/default/template/page/2columns-left.phtml(48): Mage_Core_Block_Abstract-getChildHtml('content') #31 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(189): include('/data/web/A1423...') #32 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(225): Mage_Core_Block_Template-fetchView('frontend/base/d...') #33 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Template.php(242): Mage_Core_Block_Template-renderView() #34 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Block/Abstract.php(674): Mage_Core_Block_Template-_toHtml() #35 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Model/Layout.php(536): Mage_Core_Block_Abstract-toHtml() #36 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Controller/Varien/Action.php(389): Mage_Core_Model_Layout-getOutput() #37 /data/web/A14237/htdocs/magento/app/code/core/Mage/Sales/controllers/OrderController.php(100): Mage_Core_Controller_Varien_Action-renderLayout() #38 /data/web/A14237/htdocs/magento/app/code/core/Mage/Sales/controllers/OrderController.php(136): Mage_Sales_OrderController-_viewAction() #39 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Sales_OrderController-viewAction() #40 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action-dispatch('view') #41 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Controller/Varien/Front.php(177): Mage_Core_Controller_Varien_Router_Standard-match(Object(Mage_Core_Controller_Request_Http)) #42 /data/web/A14237/htdocs/magento/app/code/core/Mage/Core/Model/App.php(304): Mage_Core_Controller_Varien_Front-dispatch() #43 /data/web/A14237/htdocs/magento/app/Mage.php(596): Mage_Core_Model_App-run(Array) #44 /data/web/A14237/htdocs/magento/index.php(78): Mage::run('', 'store') #45 {main} gtx, koko

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