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• Function calls in virtual machine killing performance

  - by GenTiradentes

  I wrote a virtual machine in C, which has a call table populated by pointers to functions that provide the functionality of the VM's opcodes. When the virtual machine is run, it first interprets a program, creating an array of indexes corresponding to the appropriate function in the call table for the opcode provided. It then loops through the array, calling each function until it reaches the end. Each instruction is extremely small, typically one line. Perfect for inlining. The problem is that the compiler doesn't know when any of the virtual machine's instructions are going to be called, as it's decided at runtime, so it can't inline them. The overhead of function calls and argument passing is killing the performance of my VM. Any ideas on how to get around this?

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• Is it correct to refer to a performing programming assignments as a "computer labs"?

  - by Nick Rosencrantz

  Can we say that developing an algorithm is a "laboration"? Are these "labs"? At engineering performing an exercise or an assignement is refered to as "labs" but are those "labs" when in fact it is mainly software problem solving pretty much like numeric methods in math which are not "labs". When studying engineering such as electrical engineering or physics you might do a "laser lab" or a "chemical laboration" if you study chemical engineering for instance. How do you define "lab"? Just performing something experimental? This is sort of double meaning also the physical environment at universities which we call "computer labs" that in fact are just rooms with computers.

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• If I use locks, can my algorithm still be lock-free?

  - by Joe Pension

  A common definition of lock-free is that at least one process makes progress. 1 If I have a simple data structure such as a queue, protected by a lock, then one process can always make progress, as one process can acquire the lock, do what it wants, and release it. So does it meet the definition of lock-free? 1 See eg M. Herlihy, V. Luchangco, and M. Moir. Obstruction-free synchronization: Double-ended queues as an example. In Distributed Computing, 2003. "It is lock-free if it ensures only that some thread always makes progress".

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• Segmentation fault problem (C)

  - by user228938

  I have a struct named Game with an array of levels, defined like this: typedef struct { Level levels[x]; } Game; When I compile the code, if x is 1, 2 or 3, the program runs normally. If it's any other value (4, for instance), I get a segmentation fault. I'm not accessing the array anywhere. Main is something like this at the moment (commented everything except the initialization): int main (...) { Game g; return 0; } Any clue of what this might be? Thanks in advance.

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• Test-driven Development: Writing tests for private / protected variables

  - by Chetan

  I'm learning TDD, and I have a question about private / protected variables. My question is: If a function I want to test is operating on a private variable, how should I test it? Here is the example I'm working with: I have a class called Table that contains an instance variable called internalRepresentation that is a 2D array. I want to create a function called multiplyValuesByN that multiplies all the values in the 2D array by the argument n. So I write the test for it (in Python): def test_multiplyValuesByN (self): t = Table(3, 3) # 3x3 table, filled with 0's t.set(0, 0, 4) # Set value at position (0,0) to 4 t.multiplyValuesByN(3) assertEqual(t.internalRepresentation, [[12, 0, 0], [0, 0, 0], [0, 0, 0]]) Now, if I make internalRepresentation private or protected, this test will not work. How am I supposed to write the test so it doesn't depend on internalRepresentation but still tests that it looks correct after calling multiplyValuesByN?

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• Are these interview questions too difficult for entry-level C++ positions?

  - by Banana

  I recently had a few interviews for programming jobs within the financial industry. I am looking for entry-level positions as I specify in the cover letter. However I am usually asked questions such as: - all two-letters commands you know in unix - representation of float/double numbers (ieee standard) - segmentation fault memory dump, and related issues - all functions you know to convert string to integer (not just atoi) - how to avoid virtual tables - etc.. Is that the custom? Because I don't think this kind of questions make sense for someone willing to get an entry-level job. Is it totally crazy to think that they should ask more conceptual questions? This is beginning to driving me nuts, honestly. Thanks

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• Added a tableview in a viewcontroller. How do I load tableview cells

  - by user1509593

  I have a view controller In storyboard, added tableview to view controller. Created an IBOutlet for tableview to View controller's header file. The view controller's header file includes an resultsarray Changed the @interface to include delegates <\UITableViewDelegate, UITableViewDataSource View controller implementation file has mandatory tableview protocols (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath The view controller has search button in storyboard and IBAction in view controller header file. On click of search button, results are obtained. How do I load the array and redisplay tableview with results in search method. After I loaded the results in array, I tried [self viewdidload];, hoping the cells will be loaded. But didn't. I thought of calling [self.detailView cellForRowAtIndexPath:?indexpath], but dontknow what the value of index path is. Appreciate help from guru's to load the UItableviewcell Thanks

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• ampersand problem with wordpress categories

  - by InnateDev

  I have an array of categories, some with an & i.e. events & entertainment. My script imports these categories and gets the ID of each using its name. i.e.: $cat_id = array(get_cat_id($linearray[0]),get_cat_id($linearray[1]),get_cat_id($linearray[2]),get_cat_id($linearray[3])); My script then adds a post to wp using these category ID's. My problem is that categories from my import with the & are not imported. These same categories (when an email notice is sent) break the email at the &. Is there a simple workaround to this?

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• How to rate a connect four game situation in java

  - by MrPink

  Hey, I am trying to write a simple AI for a "Get four" game. The basic game principles are done, so I can throw in coins of different color, and they stack on each other and fill a 2D Array and so on and so forth. until now this is what the method looks like: public int insert(int x, int color) //0 = empty, 1=player1 2=player2" X is the horizontal coordinate, as the y coordinate is determined by how many stones are in the array already, I think the idea is obvious. Now the problem is I have to rate specific game situations, so find how many new pairs, triplets and possible 4 in a row I can get in a specific situation to then give each situation a specific value. With these values I can setup a "Game tree" to then decide which move would be best next (later on implementing Alpha-Beta-Pruning). My current problem is that I can't think of an efficient way to implement a rating of the current game situation in a java method. Any ideas would be greatly appreciated! greetings from Germany Mr. Pink

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• Help with code optimization

  - by Ockonal

  Hello, I've written a little particle system for my 2d-application. Here is raining code: // HPP ----------------------------------- struct Data { float x, y, x_speed, y_speed; int timeout; Data(); }; std::vector<Data> mData; bool mFirstTime; void processDrops(float windPower, int i); // CPP ----------------------------------- Data::Data() : x(rand()%ScreenResolutionX), y(0) , x_speed(0), y_speed(0), timeout(rand()%130) { } void Rain::processDrops(float windPower, int i) { int posX = rand() % mWindowWidth; mData[i].x = posX; mData[i].x_speed = WindPower*0.1; // WindPower is float mData[i].y_speed = Gravity*0.1; // Gravity is 9.8 * 19.2 // If that is first time, process drops randomly with window height if (mFirstTime) { mData[i].timeout = 0; mData[i].y = rand() % mWindowHeight; } else { mData[i].timeout = rand() % 130; mData[i].y = 0; } } void update(float windPower, float elapsed) { // If this is first time - create array with new Data structure objects if (mFirstTime) { for (int i=0; i < mMaxObjects; ++i) { mData.push_back(Data()); processDrops(windPower, i); } mFirstTime = false; } for (int i=0; i < mMaxObjects; i++) { // Sleep until uptime > 0 (To make drops fall with randomly timeout) if (mData[i].timeout > 0) { mData[i].timeout--; } else { // Find new x/y positions mData[i].x += mData[i].x_speed * elapsed; mData[i].y += mData[i].y_speed * elapsed; // Find new speeds mData[i].x_speed += windPower * elapsed; mData[i].y_speed += Gravity * elapsed; // Drawing here ... // If drop has been falled out of the screen if (mData[i].y > mWindowHeight) processDrops(windPower, i); } } } So the main idea is: I have some structure which consist of drop position, speed. I have a function for processing drops at some index in the vector-array. Now if that's first time of running I'm making array with max size and process it in cycle. But this code works slower that all another I have. Please, help me to optimize it. I tried to replace all int with uint16_t but I think it doesn't matter.

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• Can I have fixed typed ArrayList in C#, just like C++?

  - by Kazoom

  I have an ArrayList which contains fixed type of objects. However everytime I need to extract an object a particular index, I need to typecast it to my user defined type from object type. Is there a way in C# to declare ArrayList of fixed types just like Java and C++, or is there a work around to avoid the typecasting everytime? Edit: I apologize I forgot mentioning that I require the datastructure to be thread-safe, which List is not. Otherwise I would have just used a normal Array. But I want to save myself from the effort of explicitly locking and unlocking while writing the array. So I thought of using ArrayList, synchronize it, but it requires typecasting every time.

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• document.getElementsByName returns elements more than expected

  - by Homer

  I have a RadioButtonList <asp:radiobuttonlist runat="server" id="rblList"> <asp:listitem>s1</asp:listitem> <asp:listitem>s2</asp:listitem> <asp:listitem>s3</asp:listitem> <asp:listitem>s4</asp:listitem> </asp:radiobuttonlist> In my client code I'm grabbing the array of radio buttons like this var elements = document.getElementsByName("rblList"); Why am I getting 5 items instead of 4? It makes elements like a 1 based array.

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• How do you ensure consistent experience across multiple graphics cards (or even driver versions)?

  - by Grigory Javadyan

  So I was writing a simple 2D game with OpenGL and SDL and had this problem when there was awful tearing when running in windowed mode (even though I explicitly asked SDL_SetVideoMode to use double buffering). Didn't worry about it all too much because most of the time the game grabs the entire screen, windowed mode is just for debugging. Anyway, yesterday I updated my nVidia drivers and tearing disappeared, the game runs smooth and looks nice in windowed mode too. I can see how the problem may be in the graphics driver, but this leads to a question. Obviously, professional game developers have to deal with a lot of different hardware/software configurations. What are the techniques they use to make sure the game looks the roughly the same on different graphics cards or even the same model of graphics card, but with different driver versions?

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• Split text files Accross threads

  - by Kevin

  The problem: I have a few text files (10) with numbers in them on every line. I need to have them split across some threads I create using the pthread library. these threads that are created (worker threads) are to find the largest prime number that gets sent to them (and over all the largest prime from all of the text files). My current thoughts on solutions: I am thinking myself to have two arrays and all of the text files in one array and the other array will contain a binary file that I can read say 1000 lines and send the pointer to the index of that binary file in a struct that contains the id, file pointer, and file position and let it crank through that. a little bit of what I am talking about pthread_create(&threads[index],NULL,calc_sqrt,(void *)threadFields[index]);//Pass struct to each worker Struct: typedef struct threadFields{ int *id, *position; FILE *Fin; }tField; If anyone has any insight or a better solution it would be greatly appreciated Thanks

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• How can I compute the average cost for this solution of the element uniqueness problem?

  - by Alceu Costa

  In the book Introduction to the Design & Analysis of Algorithms, the following solution is proposed to the element uniqueness problem: ALGORITHM UniqueElements(A[0 .. n-1]) // Determines whether all the elements in a given array are distinct // Input: An array A[0 .. n-1] // Output: Returns "true" if all the elements in A are distinct // and false otherwise. for i := 0 to n - 2 do for j := i + 1 to n - 1 do if A[i] = A[j] return false return true How can I compute the average cost (i.e. number of comparisons for a given n) for this algorithm? What is a reasonable assumption about the input?

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• Adding an additional link button to a form (using form->create)

  - by cloudhead

  I have recently been assigned a CSS & design project that's in a CakePHP environment and would like to know if I can add an additional button to the form, for a "sign up" link. The form is currently: echo $form->create('User', array('action' => 'login')); echo $form->inputs(array( 'legend' => 'Please log in:', 'username', 'password')); echo $form->end('Login'); I would like to inject a button that goes to an action of 'register', preferably after the "Login" button, on the same line, like this: username: [ ] password: [ ] [Log In] [Register] I have everything but the 'register' button. Is this possible using the 'automagic' form creation? Thank you.

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• Python. Draw rectangle in basemap

  - by user2928318

  I need to add several rectangles in my basemap. I nee four rectangles with lat and log ranges as below. 1) llcrnrlon=-10, urcrnrlon=10, llcrnrlat=35,urcrnrlat=60 2) llcrnrlon=10.5, urcrnrlon=35, llcrnrlat=35,urcrnrlat=60 3) llcrnrlon=35.5, urcrnrlon=52, llcrnrlat=30,urcrnrlat=55 4) llcrnrlon=-20, urcrnrlon=35, llcrnrlat=20,urcrnrlat=34.5 My script is below. I found "polygon" packages to add lines but I do not exactly know how to do. Please help me!! Thanks a lot for your help in advance! from mpl_toolkits.basemap import Basemap m=basemaputpart.Basemap(llcrnrlon=-60, llcrnrlat=20, urcrnrlon=60, urcrnrlat=70, resolution='i', projection='cyl', lon_0=0, lat_0=45) lon1=np.array([[-180.+j*0.5 for j in range(721)] for i in range(181)]) lat1=np.array([[i*0.5 for j in range(721)] for i in range(181) ]) Nx1,Ny1=m(lon1,lat1,inverse=False) toplot=data[:,:] toplot[data==0]=np.nan toplot=np.ma.masked_invalid(toplot) plt.pcolor(Nx1,Ny1,np.log(toplot),vmin=0, vmax=5) cbar=plt.colorbar() m.drawcoastlines(zorder=2) m.drawcountries(zorder=2) plt.show()

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• UIsearch rearrange the indexpath.row

  - by abuyousif

  i have a problem that i have spend about a week trying to solve it, but no luke up to now. i have a uisearchbar implmented into my table view. and i also have two nsarray, one for tilte and one for discription. when i search through the array of the titles it returns the rights search, but when i click on a row that the search came with, i get "row 0" if i click on the first row. my question is how to make a connection between the two arrays so when the search rearrange the titles based on the user search the discription array correspond to the same row the title is at. i appreciate any help.

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• C++ - Print Out Objects From Set

  - by John Smith

  If I have a C++ set, declaration set personList; with iterator, set::const_iterator location; how can I print out the contents of the set? They are all person objects, and I have overridden the operator<< for Person. The line that errors is: cout << location and it's in a basic for loop. Netbeans gives the following error: proj.cpp:78: error: no match for ‘operator<<’ in ‘std::cout << location’ so it looks like it wants an override for the iterator's <<. Basically, I am taking objects that used to be stored in an array format, but are now in a set. What is the equivalent to cout << array[i] for sets?

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• Collision Detection within Player/Enemy Class

  - by user1264811

  I'm making a 2D platform game. Right now I'm just working on making a very generic Player class. I'm wondering if it would be more efficient/better practice to have an ActionListener within the Player class to detect collisions with Enemy objects (also have an ActionListener) or to handle all the collisions in the main world. Furthermore, I'm thinking ahead about how I will handle collisions with the platforms themselves. I've looked into the double boolean arrays to see which tiles players can go to and which they can't. I don't understand how to use this class and the player class at the same time. Thank you.

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• odd behavior setting timeouts inside a function with global references in javascript

  - by Pablo

  Here is the the function and the globals: $note_instance = Array(); $note_count = 0; function create(text){ count = $note_count++; time = 5000; $note_instance[count] = $notifications.notify("create", text); setTimeout(function(){ $note_instance[count].close() }, time); } The function simply opens a notification, a sets a timeout to close it in 5 seconds. so if i call this create("Good Note 1"); create("Good Note 2"); create("Good Note 3"); Ecah note should close 5 seconds from their creation, however always and only the last note closes, in this case "Good Note 3". Each note object has its own entry in the the $note_instance global array so the timeouts should no be overwriting themselves. What am i missing here folks? Thanks in advance

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• PHP's preg_split question

  - by WekiLol

  I want to split text by the letter-followed-by-period rule. So I do this: $text = 'One two. Three test. And yet another one'; $splitted_text = preg_split("/\w\./", $text); print_r($splitted_text); Then I get this: Array ( [0] => One tw [1] => Three tes [2] => And yet another one ) But I do need it to be like this: Array ( [0] => One two [1] => Three test [2] => And yet another one ) How to settle the matter?

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• How do you get the ID of a control in ASP.NET

  - by James

  I am attempting to loop through an array of numbers, match them to the checkbox they they are associated with, and checkmark that box. My checkbox is set up like: <input type="checkbox" runat="server" id="someID" name="somename" value="1234" /> My code when the page loads currently looks like: foreach (string interest in interests_Var){ foreach (var c in Page.Controls) { } } interests_Var is my array containing different numbers. We'll assume one of them is 1234. While looping through the page controls, I want to compare the value of the control to my number. If it equals my number, I want to then apply the attribute checked="checked". I'm assuming I have to find the ID of the control I am using, then use that ID to add a new attribute. Or is there a way I can add the attribute using the c variable? I'm not dead set on this setup, so if you know a better way, I'm all ears. Thanks for any help and suggestions.

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• Joomla forwarding code to the View...is this the correct way to do it?

  - by jax

  Here are some sample methods from my Controller class. Now when the user clicks the New button $task=add is sent to the Controller and the add() method is called. As you can see it does not really do anything, it just creates a url and forwards it off to the correct view. Is this the correct way of doing things in the MVC pattern? /** * New button was pressed */ function add() { $link = JRoute::_('index.php?option=com_myapp&c=apps&view=editapp&cid[]=', false); $this->setRedirect($link); } /** * Edit button was pressed - just use the first selection for editing */ function edit() { $cid = JRequest::getVar( 'cid', array(0), '', 'array' ); $id = $cid[0]; $link = JRoute::_("index.php?option=com_myapp&c=apps&view=editapp&cid[]=$id", false); $this->setRedirect($link); }

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• What exactly does an installer do and why might I need one?

  - by Jan

  this is probably the noob-question of the day: So I've written this game. Now there's the .exe file that does the work, a folder with my beautiful, beautiful assets and a bunch of .dll files and other stuff that I probably shouldn't touch. To run the game, I copy the whole lot to the desired computer, double-click the .exe file and start shooting some dudes. Yay! But what exactly is the difference between that and using an installer? What else does an installer do besides copying files and looking more professional than a .zip-file? Is there generally a lot of patching/configuring involved when trying to make a game run on a different computer? I tested my game on all windows computers I could get my greedy fingers on and it works great. Thanks for your time.

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