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  • Why is System.arraycopy native in Java?

    - by James B
    I was surprised to see in the Java source that System.arraycopy is a native method. Of course the reason is because it's faster. But what native tricks is the code able to employ that make it faster? Why not just loop over the original array and copy each pointer to the new array - surely this isn't that slow and cumbersome? Thanks, -James

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  • Recommended textbook for machine-level programming?

    - by Norman Ramsey
    I'm looking at textbooks for an undergraduate course in machine-level programming. If the perfect book existed, this is what it would look like: Uses examples written in C or assembly language, or both. Covers machine-level operations such as two's-complement integer arithmetic, bitwise operations, and floating-point arithmetic. Explains how caches work and how they affect performance. Explains machine instructions or assembly instructions. Bonus if the example assembly language includes x86; triple bonus if it includes x86-64 (aka AMD64). Explains how C values and data structures are represented using hardware registers and memory. Explains how C control structures are translated into assembly language using conditional and unconditional branch instructions. Explains something about procedure calling conventions and how procedure calls are implemented at the machine level. Books I might be interested in would probably have the words "machine organization" or "computer architecture" in the title. Here are some books I'm considering but am not quite happy with: Computer Systems: A Programmer's Perspective by Randy Bryant and Dave O'Hallaron. This is quite a nice book, but it's a book for a broad, shallow course in systems programming, and it contains a great deal of material my students don't need. Also, it is just out in a second edition, which will make it expensive. Computer Organization and Design: The Hardware/Software Interface by Dave Patterson and John Hennessy. This is also a very nice book, but it contains way more information about how the hardware works than my students need. Also, the exercises look boring. Finally, it has a show-stopping bug: it is based very heavily on MIPS hardware and the use of a MIPS simulator. My students need to learn how to use DDD, and I can't see getting this to work on a simulator. Not to mention that I can't see them cross-compiling their code for the simulator, and so on and so forth. Another flaw is that the book mentions the x86 architecture only to sneer at it. I am entirely sympathetic to this point of view, but news flash! You guys lost! Write Great Code Vol I: Understanding the Machine by Randall Hyde. I haven't evaluated this book as thoroughly as the other two. It has a lot of what I need, but the translation from high-level language to assembler is deferred to Volume Two, which has mixed reviews. My students will be annoyed if I make them buy a two-volume series, even if the price of those two volumes is smaller than the price of other books. I would really welcome other suggestions of books that would help students in a class where they are to learn how C-language data structures and code are translated to machine-level data structures and code and where they learn how to think about performance, with an emphasis on the cache.

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  • How to convert records including 'include' associations to JSON.

    - by 99miles
    If I do something like: result = Appointment.find( :all, :include => :staff ) logger.debug { result.inspect } then it only prints out the Appointment data, and not the associated staff data. If I do result[0].staff.inpsect then I get the staff data of course. The problem is I want to return this to AJAX as JSON, including the staff rows. How do I force it to include the staff rows, or do I have to loop through and create something manually?

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  • logins with cURL

    - by steve
    I'm looking to use cURL to login to Blackboard, a course management system used a many universities. (For example, http://blackboard.unh.edu) How would I do this? Blackboard uses HTTPS certificates and cookies too I believe. Thanks!

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  • what's the way to determine if an Int a perfect square in Haskell?

    - by valya
    I need a simple function is_square :: Int -> Bool which determines if an Int N a perfect square (is there an integer x such that x*x = N). Of course I can just write something like is_square n = sq * sq == n where sq = floor $ sqrt $ (fromIntegral n::Double) but it looks terrible! Maybe there is a common simple way to implement such predicate?

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  • make textarea fullscreen jquery (for use as code editor)

    - by Jorre
    I have a text area in which users can type source code (html/css/js). I want to be able to let them click a "switch to fullscreen" link to make the editor fullscreen. Of course, this should work on any resolution and must also resize when a users resizes it's window. I found this plugin, http://plugins.jquery.com/project/fulltextarea, but it's not resizing when the browser windows is resized. Any tips or plugins for this one?

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  • Green Bars in Visual Studio 2010

    - by Braveyard
    I am wondering what these greens things are in Visual Studio 2010. What are they for? They look pretty random but of course they have to have some meaning. Can any one tell me? At first glance they don't mean any thing to me. Picture 1: Picture 2: Edit: They show saved changed content during the document open. Once you close the document they disappear.

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  • Using Python, what's the best way to create a set of files on disk for testing?

    - by Chris R
    I'm looking for a way to create a tree of test files to unit test a packaging tool. Basically, I want to create some common file system structures -- directories, nested directories, symlinks within the selected tree, symlinks outside the tree, &c. Ideally I want to do this with as little boilerplate as possible. Of course, I could hand-write the set of files I want to see, but I'm thinking that somebody has to have automated this for a test suite somewhere. Any suggestions?

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  • What is the most efficient way to determine if a directed graph is singly connected?

    - by zebraman
    I am working on an assignment where one of the problems asks to derive an algorithm to check if a directed graph G=(V,E) is singly connected (there is at most one simple path from u to v for all distinct vertices u,v of V. Of course you can brute force check it, which is what I'm doing right now, but I want to know if there's a more efficient way. Could anyone point me in the right direction?

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  • Find Missing Records

    - by Lennie De Villiers
    Hi, My SQL is a bit bad. I got a query that when I run it I return for example 10 rows but there are 15 in my where clause, how do I identify those 5 that I can't find? Off course I can dump it in MS Excel but how do I use SQL?

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  • MVC validation error with strongly typed view

    - by Remnant
    I have a simple form that I would like to validate on form submission. Note I have stripped out the html for ease of viewing <%=Html.TextBox("LastName", "")%> //Lastname entry <%=Html.ValidationMessage("LastName")%> <%=Html.TextBox("FirstName", "")%>//Firstname entry <%=Html.ValidationMessage("FirstName")%> <%=Html.DropDownList("JobRole", Model.JobRoleList)%> //Dropdownlist of job roles <% foreach (var record in Model.Courses) // Checkboxes of different courses for user to select { %> <li><label><input type="checkbox" name="Courses" value="<%=record.CourseName%>" /><%= record.CourseName%></label></li> <% } %> On submission of this form I would like to check that both FirstName and LastName are populated (i.e. non-zero length). In my controller I have: public ActionResult Submit(string FirstName, string LastName) { if (FirstName.Trim().Length == 0) ModelState.AddModelError("FirstName", "You must enter a first name"); if (LastName.Trim().Length == 0) ModelState.AddModelError("LastName", "You must enter a first name"); if (ModelState.IsValid) { //Update database + redirect to action } return View(); //If ModelState not valid, return to View and show error messages } Unfortunately, this code logic produces an error that states that no objects are found for JobRole and Courses. If I remove the dropdownlist and checkboxes then all works fine. The issue appears to be that when I return the View the view is expecting objects for the dropwdownlist and checkboxes (which is sensible as that is what is in my View code) How can I overcome this problem? Things I have considered: In my controller I could create a JobRoleList object and Course object to pass to the View so that it has the objects to render. The issue with this is that it will overwrite any dropdownlist / checkbox selections that the user has already made. In the parameters of my controller method Submit I could aslo capture the JobRoleList object and Course object to pass back to the View. Again, not sure this would capture any items the user has already selected. I have done much googling and reading but I cannot find a good answer. When I look at examples in books or online (e.g. Nerddinner) all the validation examples involve simple forms with TextBox inputs and don't seems to show instances with multiple checkboxes and dropdownlists. Have I missed something obvious here? What would be best practice in this situation? Thanks

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  • Format number as I type Expand this post

    - by conorhiggins
    Hi I am working on an app at the moment that requires number input to be formatted as the textfield changes as well as perform a calculation. I have the text fields set up so that as the user types notifications are passed out and a calculation is performed. However what I need to do now is format the text to be in this style: €1,000,000 rather than 1000000. I have this working for the output of the calculation already but everytime I try to apply it to the input text the simulator seems to crash or at least freezes for a while. I'd imagine its a simple enough fix.

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  • Phonegap/Cordova orientation change Android 4

    - by user1477576
    I have a problem changing the orientation of the device (Android 4). In other versions it works fine. Versión of Cordova: cordova-1.8.0.js / cordova-1.8.1.js In Android 4 the app crash or show: "A network error occurred. (file:///android_asset/www/index.html)" I searched a lot about this and no answer solves the problem. In most cases users suggest adding: android:configChanges="orientation|keyboardHidden|screenSize" In other cases: super.setIntegerProperty("loadUrlTimeoutValue",60000); That not work for me :( My manifest activity: <activity android:name=".AppNameActivity" android:label="@string/app_name" android:configChanges="orientation|keyboardHidden|screenSize"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> The application should run on Android 2.2 to 4. Thank you very much for the help.

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  • Temporary PYTHONPATH in Windows

    - by Santa
    How do I set, temporarily, the PYTHONPATH environment variable just before executing a Python script? In *nix, I can do this: $ PYTHONPATH='.' python scripts/doit.py In Windows, this syntax does not work, of course. What is the equivalent, though?

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  • Checking For Word Wrap In Table Column

    - by Sparafusile
    I'm writing part of a web page that allows a user to build a table and fill it with information. In the course of building the table, the user will be adding additional columns with headers. I'd like to code it so when the combined width of all the headers causes one of them to wrap that the table columns switch to using vertical text (writing-mode: tb-rl). Is there any way, using JavaScript, to determine if the contents of a specific cell have wrapped? Thanks, Spara

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  • Eclipse + Django: How to get bytecode output when python source files change?

    - by Sean Ochoa
    Whenever I change my python source files in my Django project, the .pyc files become out of date. Of course that's because I need to recompile them in order to test them through my local Apache web server. I would like to get around this manual process by employing some automatic means of compiling them on save, or on build through Eclipse, or something like that. What's the best and proper way to do this?

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  • SQL Server: How to call a UDF, if available?

    - by Ian Boyd
    Most systems will have a user-defined function (UDF) available. Some will not. i want to use the UDF if it's there: SELECT Users.*, dbo.UserGroupMembershipNames(Users.UserID) AS MemberOfGroupNames FROM Users Otherwise fallback to the acceptable alternative SELECT Users.*, (SELECT TOP 1 thing FROM Something WHERE Something.ID = Users.UserID) AS MemberGroupNames FROM Users How do? My first attempt, using the obvious solution, of course failed: SELECT Users.*, CASE WHEN (OBJECT_ID('dbo.UserGroupMembershipNames') IS NOT NULL) THEN dbo.UserGroupMembershipNames(Users.UserID) ELSE (SELECT TOP 1 thing FROM Something WHERE Something.ID = Users.UserID) END AS MemberOfGroupNames FROM Users for reasons beyond me

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  • How do I use Django to insert a Geometry Field into the database?

    - by alex
    class LocationLog(models.Model): user = models.ForeignKey(User) utm = models.GeometryField(spatial_index=True) This is my database model. I would like to insert a row. I want to insert a circle at point -55, 333. With a radius of 10. How can I put this circle into the geometry field? Of course, then I would want to check which circles overlap a given circle. (my select statement)

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  • how can i set the key 'blob-key' about BlobStore?

    - by pyleaf
    I use the jquery plugin "uploadify" to upload multiple files to My App(GAE), and then save them with blobstore, but it failed. I debug the code into get_uploads, it seems field.type_options is empty and of course has 'blob-key'. Q: where does the key 'blob-key' come from? thank you!

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  • ADB crashes when device attached with eclipse

    - by user559592
    I am trying to get a development environment setup and having some problems with adb. I have eclipse installed and can create android projects and run/debug them in the emulator. But if I attached my device (HTC Evo) and try running on it, adb crashes. My device shows up so adb sees it. Everything is updated to the latest version. I even went and reinstalled my system so I had a clean start. It would still crash when I connect to the device. I restart adb but it just shuts right back down. Anyone have any suggestions on what I can do to fix this? Running on Windows 7.

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  • run wxHaskell on other machine

    - by snorlaks
    Hello, I've compiled haskell program which uses wxHaskell library, now I would like to know how to make it run on other machines which doesn't have wxHaskell installed. Of course I can see errors and I can copy dlls written in output and copy them to that machine but what is professioal sollution, can I write any installer or something like that? thanks for help

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  • using ruby-debug with jruby-1.5.0

    - by brad
    Release notes say that ruby-debug is installed by default. I'm using rvm. In my rails app I figured something as simple as script/server --debugger would suffice, but it complains that the ruby-debug gem isn't installed, suggests using gem install ruby-debug, which of course doesn't work (building native extensions) and is contrary to the docs anyway. Just wondering if anyone's had any luck using the built in ruby-debug in jruby 1.5 and what one needs to do in order run jruby in debug mode

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  • SQL join produces one result only

    - by Rami
    Can anyone please tell me why this result is generation only one results? taking in mind that everything is set right and the three tables are populated correctly, i took out the group_concat and it worked but of course with a php undefined index error! SELECT `songs`.`song_name`, `songs`.`add_date`, `songs`.`song_id`, `songs`.`song_picture`, group_concat(DISTINCT artists.artist_name) as artist_name FROM (`songs`) JOIN `mtm_songs_artists` ON `songs`.`song_id` = `mtm_songs_artists`.`song_id` JOIN `artists` ON `artists`.`artist_id` = `mtm_songs_artists`.`artist_id` ORDER BY `songs`.`song_id` DESC LIMIT 10 so i'm guessing it's something related to group_concat. best regards, Rami

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