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• Strategy for WCF server with .Net clients and Android clients?

  - by D.H.

  I am using WCF to write a server that should be able to communicate with .Net clients, Android clients and possibly other types of clients. The main type of client is a desktop application that will be written in .Net. This client will usually be on the same intranet as the server. It will make an initial call to the server to get the current state of the system and will then receive updates from the server whenever a value changes. These updates are frequent, perhaps once a second. The Android clients will connect over the Internet. This client is also interested in updates, but it is not as critical as for the desktop client so a (less frequent) polling scenario might be acceptable. All clients will have to login to use the services, and when connecting over the Internet the connection should be secure. I am familiar with WCF but I am not sure what bindings are most appropriate for the scenario and what security solution to use. Also, I have not used Android, but I would like to make it as simple as possible for the person implementing the Android client to consume my services. So, what is my strategy?

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• Rails: Multi-Step New User Signup Form (FSM?)

  - by neezer

  I've read the "Create Multi-Step Wizard" in Advanced Rails Recipes. I've also read and re-read the documentation for the updated FSM I'm using called Workflow, and looked here and here. The Advanced Rails Recipe focuses on records (quizzes) that already exist, and doesn't cover creating new ones. The Workflow docs don't cover any code for controllers or views, so I've no idea what to do with all this model magic, and the last two links barely touch on implementation either. From the aforementioned resources, I have a good understanding of what a FSM in Rails is and how to play with it in the console or IRB, but I've got very little direction or understanding how to implement one into my Rails app. What I would like is this: a simple, multi-step user signup process. Step 1: User enters in their critical details (with validations). Step 2: User enters in their search criteria, for their profile (with validations). Step 3: User agrees to the Terms of Service (with validations). Step 4: User is greeted by a confirmation page, including a link that takes them to their newly created account. I'd also like full navigation between the steps and full capture (saves to the database) with each transition. Can someone please give me a clear implementation of something similar to this? I would LOVE an example app that includes a multi-step signup process where I can look at the code (FULL source code--models AND controllers and views) under the hood, but I've been unable to find anything like that. Any guidance would be appreciated! EDIT: Please help make this a Railscast! Ryan B. (a.k.a. Superman), if you're reading this, we need you! http://feedback.railscasts.com/forums/77-episode-suggestions/suggestions/35553-multi-step-forms-and-wizards

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• How to publish internal data to the internet - as simple as possible

  - by mlarsen

  We have a .net 2-tier application where a desktop program is talking to a database. We support MS SQL Server 2000, 2005, 2008 and Oracle 9, 10 and 11. The application is sold, not as shrink-wrap, but pretty close. It is quite important for us that the installation and configuration is as easy as possible as installation instructions are usually supplied in written form to the customers internal IT-department. Our application is usually not seen as mission critical for the IT-department, so we need to keep their work down to a minimum. Now we are starting to get wishes for a web application build on top of the same data. The web application will be hosted by us and delivered as a SaaS application. Now the challenge is how to move data back and forth between the web application and the customers internal database. as I see it we have some requirements: We must be ready to handle the situation where the customers database is not accessible from the DMZ. I guess the easiest solution is that all communication is initiated from inside the customers lan. As little firewall configuration as possible. The best is if we can run without any special configuration as long as outgoing traffic from the customers lan are not blocked. If we need something changed in the firewall, we must be able to document that the change is secure. It doesn't have to be real time. Moving data in batches every ten minutes or so is OK. Data moves both ways, but not the same tables, so we don't have to support merges. It would be nice if we don't have to roll our own framework completely. Looking forward to hear your suggestions.

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• Mutex example / tutorial ?

  - by Nav

  I've noticed that asking questions for the sake of creating a reference list etc. is encouraged in SO. This is one such question, so that anyone Googling for a mutex tutorial will find a good one here. I'm new to multithreading, and was trying to understand how mutexes work. Did a lot of Googling and this is the only decent tutorial I found, but it still left some doubts of how it works because I created my own program and the locking didn't work. One absolutely non-intuitive syntax of the mutex is pthread_mutex_lock( &mutex1 );, where it looks like the mutex is being locked, when what I really want to lock is some other variable. Does this syntax mean that locking a mutex locks a region of code until the mutex is unlocked? Then how do threads know that the region is locked? And isn't such a phenomenon supposed to be called critical section? In short, could you please help with the simplest possible mutex example program and the simplest possible explanation on the logic of how it works? I'm sure this will help plenty of other newbies.

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• SVN checkout or export for production environment?

  - by Eran Galperin

  In a project I am working on, we have an ongoing discussion amongst the dev team - should the production environment be deployed as a checkout from the SVN repository or as an export? The development environment is obviously a checkout, since it is constantly updated. For the production, I'm personally for checking out the main trunk, since it makes future updates easier (just run svn update). However some of the devs are against it, as svn creates files with the group/owner and permissions of the svn process (this is on a linux OS, so those things matter), and also having the .svn directories on the production seem to them to be somewhat dirty. Also, if it is a checkout - how do you push individual features to the production without including in-development code? do you use tags or branch out for each feature? any alternatives? EDIT: I might not have been clear - one of the requirement is to be able to constantly be able to push fixes to the production environment. We want to avoid a complete build (which takes much longer than a simple update) just for pushing critical fixes.

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• Can threads safely read variables set by VCL events?

  - by Tom1952

  Is it safe for a thread to READ a variable set by a Delphi VCL event? When a user clicks on a VCL TCheckbox, the main thread sets a boolean to the checkbox's Checked state. CheckboxState := CheckBox1.Checked; At any time, a thread reads that variable if CheckBoxState then ... It doesn't matter if the thread "misses" a change to the boolean, because the thread checks the variable in a loop as it does other things. So it will see the state change eventually... Is this safe? Or do I need special code? Is surrounding the read and write of the variable (in the thread and main thread respectively) with critical code calls necessary and sufficient? As I said, it doesn't matter if the thread gets the "wrong" value, but I keep thinking that there might be a low-level problem if one thread tries to read a variable while the main thread is in the middle of writing it, or vice versa. My question is similar to this one: http://stackoverflow.com/questions/1353096/cross-thread-reading-of-a-variable. (Also related to my previous question: http://stackoverflow.com/questions/2449183/using-entercriticalsection-in-thread-to-update-vcl-label)

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• Representing complex scheduled reoccurance in a database

  - by David Pfeffer

  I have the interesting problem of representing complex schedule data in a database. As a guideline, I need to be able to represent the entirety of what the iCalendar -- ics -- format can represent, but in a database. I'm not actually implementing anything relating to ics, but it gives a good scope of the type of rules I need to be able to model. I need to allow allow representation of a single event or a reoccurring event based on multiple times per day, days of the week, week of a month, month, year, or some combination of those. For example, the third Thursday in November annually, or the 25th of December annually, or every two weeks starting November 2 and continuing until September 8 the following year. I don't care about insertion efficiency but query efficiency is critical. The operation I will be doing most often is providing either a single date/time or a date/time range, and trying to determine if the defined schedule matches any part of the date/time range. Other operations can be slower. For example, given January 15, 2010 at 10:00 AM through January 15, 2010 at 11:00 AM, find all schedules that match at least part of that time. (i.e. a schedule that covers 10:30 - 11:00 still matches.) Any suggestions? I looked at http://stackoverflow.com/questions/1016170/how-would-one-represent-scheduled-events-in-an-rdbms but it doesn't cover the scope of the type of reoccurance rules I'd like to model.

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• Animated transitions in WPF

  - by arconaut

  I can't figure out what I'm missing here. Here's the problem: Consider a (Control|Data)Template with a Trigger that switches visibility of some inner UI elements. E.g. show a TextBlock when IsReadOnly==true and show a TextBox when IsReadOnly==false. Everything is perfect if you do this without animation - one or two setters would do the job. But what if you want a fancy animation? Then you would specify which animations to start in EnterActions and ExitActions. But the problem is what exactly the animations should do? Modifying width/height seems really ugly, because fixed sizes in WPF are almost always a wrong way to go and also it's absolutely unflexible. So far, the best I've come up with is modifying MaxHeight/MaxWidth to some extent, this gives just a little more flexibility but still seems brutal. How do you tell WPF to animate Width/Height of an element from 0 to "as much as needed"? UPD: Currently I do animate Opacity and RenderTransform, and it works. It's just that sometimes I'd like to see animations where elements slide around without transformation. This is not a critical question, but a quite interesting one for me.

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• Image processing on bifurcation diagram to get small eps size

  - by yCalleecharan

  Hello, I'm producing bifurcation diagrams (which are normally used in nonlinear dynamics). These diagrams identify abrupt changes in topologies due to stability changes. These abrupt changes occur as one or more parameters pass through some critical value(s). An example is here: http://en.wikipedia.org/wiki/File:LogisticMap_BifurcationDiagram.png On the above figure, some image processing has been done so as to make the plot more visually pleasant. A bifurcation diagram usually contains hundreds of thousands of points and the resulting eps file can become very big. Journal submission in the LaTeX format require that figures are to be submitted in the eps format. In my case one of such figures can result in about 6 MB in Matlab and even much more in Gnuplot. For the example in the above figure, 100,000 x values are calculated for each r and one can imagine that the resulting eps file would be huge. The site however explains some image processing that makes the plot more visually pleasing. Can anyone explain to me stepwise how go about? I can't understand the explanation provided in the "summary" section. Will the resulting image processing also reduce the figure size? Furthermore, any tips on reducing the file size of such a huge eps figure? Thanks a lot...

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• Cross compiling from MinGW on Fedora 12 to Windows - console window?

  - by elcuco

  After reading this article http://lukast.mediablog.sk/log/?p=155 I decided to use mingw on linux to compile windows applications. This means I can compile, test, debug and release directly from Linux. I hacked this build script which will cross compile the application and even package it in a ZIP file. Note that I am using out of source builds for QMake (did you even know this is supported? wow...). Also note that the script will pull the needed DLLs automagically. Here is the script for you all internets to use and abuse: #! /bin/sh set -x set -e VERSION=0.1 PRO_FILE=blabla.pro BUILD_DIR=mingw_build DIST_DIR=blabla-$VERSION-win32 # clean up old shite rm -fr $BUILD_DIR mkdir $BUILD_DIR cd $BUILD_DIR # start building QMAKESPEC=fedora-win32-cross qmake-qt4 QT_LIBINFIX=4 config=\"release\ quiet\" ../$PRO_FILE #qmake-qt4 -spec fedora-win32-cross make DLLS=`i686-pc-mingw32-objdump -p release/*.exe | grep dll | awk '{print $3}'` for i in $DLLS mingwm10.dll ; do f=/usr/i686-pc-mingw32/sys-root/mingw/bin/$i if [ ! -f $f ]; then continue; fi cp -av $f release done mkdir -p $DIST_DIR mv release/*.exe $DIST_DIR mv release/*.dll $DIST_DIR zip -r ../$DIST_DIR.zip $DIST_DIR The compiled binary works on the Windows7 machine I tested. Now to the questions: When I execute the application on Windows, the theme is not the Windows7 theme. I assume I am missing a style module, I am not really sure yet. The application gets a console window for some reason. The second point (the console window) is critical. How can I remove this background window? Please note that the extra config lines are not working for me, what am I missing there?

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• javascript toolkit for offline webapps

  - by anjanb

  hi all, we're building an survey webapp which will let the user to add new records to the survey when offline and will upload when the browser reconnects with the server. We've identified that this will need offline storage and hence google gears seems to be an obvious choice (we understand that adobe Flash has Offline Storage but not sure if that is the best way). I am aware of Dojo offline javascript toolkit which uses google gears for the underlying functionality. However, dojo offline is not part of the dojo toolkit after version 1.3. (currently dojo is 1.4.2). Google gears toolkit is currently frozen except for critical vulnerability fixes (it has not been updated almost for the last 1 yr) because they think that HTML 5 is the way to go ahead. Hence, we're looking for a higher abstraction on top of Google Gears engine TODAY, AND which will (in the future) switch the underlying engine to HTML5 if the browser supports HTML5 standards. We'd love to use Dojo but they have discontinued Dojo offline -- we'd prefer something that will be maintained for some time. Which are possible good strategies, JS toolkits/libraries to use for building this webapp ? Pls. advise.

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• Cross-Platform Camera API

  - by Karim

  Hi, I'm now building a video transforming filter that have to transform video frames in real-time. One of the key requirements of the filter is to have high performance to minimize the number of dropped frames during the transform. Another requirement that is of lower priority but also nice to have is to make it cross-platform (both PC's and Mobile devices). The application is built in C++. Now my question is: is there any API that is more portable and has a similar or better performance characteristics than DirectShow? as DirectShow's portability is only limited to Windows-based devices (PCs and Windows Mobile&CE platforms). Also I've notices that for example using HTC's custom camera API has far better performance than what DirectShow offers. If you want to check this, try to build a filter in DirectShow that will multiply each color by 2 and render that in real-time from camera on the screen. Then do the same with HTC's API. There is almost 4-5x performance boost with vendor's specific API. So it'd be very nice if the library used the device-specific implementation of the driver, as performance is critical when doing this transforms on a mobile device (which is about ~500 MHz).

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• Problems with Json Serialize Dictionary<Enum, Int32>

  - by dbemerlin

  Hi, whenever i try to serialize the dictionary i get the exception: System.ArgumentException: Type 'System.Collections.Generic.Dictionary`2[[Foo.DictionarySerializationTest+TestEnum, Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' is not supported for serialization/deserialization of a dictionary, keys must be strings or object My Testcase is: public class DictionarySerializationTest { private enum TestEnum { A, B, C } public void SerializationTest() { Dictionary<TestEnum, Int32> data = new Dictionary<TestEnum, Int32>(); data.Add(TestEnum.A, 1); data.Add(TestEnum.B, 2); data.Add(TestEnum.C, 3); JavaScriptSerializer serializer = new JavaScriptSerializer(); String result = serializer.Serialize(data); // Throws } public void SerializationStringTest() { Dictionary<String, Int32> data = new Dictionary<String, Int32>(); data.Add(TestEnum.A.ToString(), 1); data.Add(TestEnum.B.ToString(), 2); data.Add(TestEnum.C.ToString(), 3); JavaScriptSerializer serializer = new JavaScriptSerializer(); String result = serializer.Serialize(data); // Succeeds } } Of course i could use .ToString() whenever i enter something into the Dictionary but since it's used quite often in performance relevant methods i would prefer using the enum. My only solution is using .ToString() and converting before entering the performance critical regions but that is clumsy and i would have to change my code structure just to be able to serialize the data. Does anyone have an idea how i could serialize the dictionary as <Enum, Int32>? I use the System.Web.Script.Serialization.JavaScriptSerializer for serialization.

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• Blocking error in celery

  - by dmitry

  I have no idea what's this. Python 2.7 + django-1.5.1 + httpd + rabbitmq + django-celery==3.0.17 Tasks are not executed because of some error. Below is celery's log. Maybe someone has faced it before. [2013-06-24 17:10:03,792: CRITICAL/MainProcess] Can't decode message body: AttributeError("'JoinInfo' object has no attribute '__dict__'",) (type:u'application/x-python-serialize' encoding:u'binary' raw:'\'\\x80\\x02}q\\x01(U\\x07expiresq\\x02NU\\x03utcq\\x03\\x88U\\x04argsq\\x04cdjango.contrib.auth.models\\nUser\\nq\\x05)\\x81q\\x06}q\\x07(U\\x08usernameq\\x08X\\x19\\x00\\x00\\[email protected]\\nfirst_nameq\\tX\\x05\\x00\\x00\\x00BibbyU\\tlast_nameq\\nX\\x08\\x00\\x00\\x00OffshoreU\\r_client_cacheq\\x0bccopy_reg\\n_reconstructor\\nq\\x0ccbongoregistration.models\\nClient\\nq\\rc__builtin__\\nobject\\nq\\x0eN\\x87Rq\\x0f}q\\x10(h\\nX\\x08\\x00\\x00\\x00OffshoreU\\x1bpurchase_confirmation_emailq\\x11X\\x1f\\x00\\x00\\[email protected]\\x1dpurchase_confirmation_email_1q\\x12X!\\x00\\x00\\[email protected]\\x06_stateq\\x13cdjango.db.models.base\\nModelState\\nq\\x14)\\x81q\\x15}q\\x16(U\\x06addingq\\x17\\x89U\\x02dbq\\x18U\\x07defaultq\\x19ubU\\x0buser_ptr_idq\\x1aJ\\xb4\\xa2\\x03\\x00U\\x08is_staffq\\x1b\\x89U\\x08postcodeq\\x1cX\\x08\\x00\\x00\\x00AB11 5BSU\\x0cdegree_limitq\\x1dK\\x06U\\x07messageq\\x1eX\\xd1E\\x00\\x00<table id="container" style="margin: 0px; padding: 0px; width: 100%; background-color: #ffffff;" cellspacing="0" cellpadding="0"... (22911b)'') Traceback (most recent call last): File "/opt/www/MyProject-main/eggs/kombu-2.5.10-py2.7.egg/kombu/messaging.py", line 556, in _receive_callback decoded = None if on_m else message.decode() File "/opt/www/MyProject-main/eggs/kombu-2.5.10-py2.7.egg/kombu/transport/base.py", line 147, in decode self.content_encoding, accept=self.accept) File "/opt/www/MyProject-main/eggs/kombu-2.5.10-py2.7.egg/kombu/serialization.py", line 187, in decode return decode(data) File "/opt/www/MyProject-main/eggs/kombu-2.5.10-py2.7.egg/kombu/serialization.py", line 74, in pickle_loads return load(BytesIO(s)) AttributeError: 'JoinInfo' object has no attribute '__dict__'

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• Alternative or succesor to GDBM

  - by Anon Guy

  We a have a GDBM key-value database as the backend to a load-balanced web-facing application that is in implemented in C++. The data served by the application has grown very large, so our admins have moved the GDBM files from "local" storage (on the webservers, or very close by) to a large, shared, remote, NFS-mounted filesystem. This has affected performance. Our performance tests (in a test environment) show page load times jumping from hundreds of milliseconds (for local disk) to several seconds (over NFS, local network), and sometimes getting as high as 30 seconds. I believe a large part of the problem is that the application makes lots of random reads from the GDBM files, and that these are slow over NFS, and this will be even worse in production (where the front-end and back-end have even more network hardware between them) and as our database gets even bigger. While this is not a critical application, I would like to improve performance, and have some resources available, including the application developer time and Unix admins. My main constraint is time only have the resources for a few weeks. As I see it, my options are: Improve NFS performance by tuning parameters. My instinct is we wont get much out of this, but I have been wrong before, and I don't really know very much about NFS tuning. Move to a different key-value database, such as memcachedb or Tokyo Cabinet. Replace NFS with some other protocol (iSCSI has been mentioned, but i am not familiar with it). How should I approach this problem?

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• Some optimization about the code (computing ranks of a vector)?

  - by user1748356

  The following code is a function (performance-critical) to compute tied ranks of a vector: mergeSort(x,inds,ci); //a sort function to sort vector x of length ci, also returns keys (inds) of x. int tj=0; double xi=x[0]; for (int j = 1; j < ci; ++j) { if (x[j] > xi) { double rankvalue = 0.5 * (j - 1 + tj); for (int k = tj; k < j; ++k) { ranks[inds[k]]=rankvalue; }; tj = j; xi = x[j]; }; }; double rankvalue = 0.5 * (ci - 1 + tj); for (int k = tj; k < ci; ++k) { ranks[inds[k]]=rankvalue; }; The problem is, the supposed performance bottleneck mergeSort(), which is O(NlogN) is several times faster than the other part of codes (which is O(N)), which suggests there is room for huge improvment with the other part of the codes, any advices?

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• How to get the most out of a 3 month intern?

  - by firoso

  We've got a software engineering intern coming in who's fairly competent and shows promise. There's one catch: we have him for 3 months full time and can't count on anything past that. He still has a year of school left, which is why we can't say for sure that we have him past 3 months. We have a specific project we're putting him on. How can we maximize his productivity while still giving him a positive learning experience? He wants to learn about development cycles and real-world software engineering. Anything that you think would be critical that you wish you had learned earlier? Nearly six months later: He's preformed admirably and even I have learned a lot from him. Thank you all for the input. Now I want to provide feedback to YOU! He has benefited most from sitting down and writing code. However, he has had a nasty history of bad software engineering practices which I'm trying to replace with good habits (properly finishing a method before moving on, not hacking code together, proper error channeling, etc). He has also really gained a lot by feeling involved in design decisions, even if most of the time they're related to my own design plans.

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• Is the REST support in Spring 3's MVC Framework production quality yet?

  - by glenjohnson

  Hi all, Since Spring 3 was released in December last year, I have been trying out the new REST features in the MVC framework for a small commercial project involving implementing a few RESTful Web Services which consume XML and return XML views using JiBX. I plan to use either Hibernate or JDBC Templates for the data persistence. As a Spring 2.0 developer, I have found Spring 3's (and 2.5's) new annotations way of doing things quite a paradigm shift and have personally found some of the new MVC annotation features difficult to get up to speed with for non-trivial applications - as such, I am often having to dig for information in forums and blogs that is not apparent from going through the reference guide or from the various Spring 3 REST examples on the web. For deadline-driven production quality and mission critical applications implementing a RESTful architecture, should I be holding off from Spring 3 and rather be using mature JSR 311 (JAX-RS) compliant frameworks like RESTlet or Jersey for the REST layer of my code (together with Spring 2 / 2.5 to tie things together)? I had no problems using RESTlet 1.x in a previous project and it was quite easy to get up to speed with (no magic tricks behind the scenes), but when starting my current project it initially looked like the new REST stuff in Spring 3's MVC Framework would make life easier. Do any of you out there have any advice to give on this? Does anyone know of any commercial / production-quality projects using, or having successfully delivered with, the new REST stuff in Spring 3's MVC Framework. Many thanks Glen

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• Is there a way to increase the efficiency of shared_ptr by storing the reference count inside the co

  - by BillyONeal

  Hello everyone :) This is becoming a common pattern in my code, for when I need to manage an object that needs to be noncopyable because either A. it is "heavy" or B. it is an operating system resource, such as a critical section: class Resource; class Implementation : public boost::noncopyable { friend class Resource; HANDLE someData; Implementation(HANDLE input) : someData(input) {}; void SomeMethodThatActsOnHandle() { //Do stuff }; public: ~Implementation() { FreeHandle(someData) }; }; class Resource { boost::shared_ptr<Implementation> impl; public: Resource(int argA) explicit { HANDLE handle = SomeLegacyCApiThatMakesSomething(argA); if (handle == INVALID_HANDLE_VALUE) throw SomeTypeOfException(); impl.reset(new Implementation(handle)); }; void SomeMethodThatActsOnTheResource() { impl->SomeMethodThatActsOnTheHandle(); }; }; This way, shared_ptr takes care of the reference counting headaches, allowing Resource to be copyable, even though the underlying handle should only be closed once all references to it are destroyed. However, it seems like we could save the overhead of allocating shared_ptr's reference counts and such separately if we could move that data inside Implementation somehow, like boost's intrusive containers do. If this is making the premature optimization hackles nag some people, I actually agree that I don't need this for my current project. But I'm curious if it is possible.

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• How to insert zeros between bits in a bitmap?

  - by anatolyg

  I have some performance-heavy code that performs bit manipulations. It can be reduced to the following well-defined problem: Given a 13-bit bitmap, construct a 26-bit bitmap that contains the original bits spaced at even positions. To illustrate: 0000000000000000000abcdefghijklm (input, 32 bits) 0000000a0b0c0d0e0f0g0h0i0j0k0l0m (output, 32 bits) I currently have it implemented in the following way in C: if (input & (1 << 12)) output |= 1 << 24; if (input & (1 << 11)) output |= 1 << 22; if (input & (1 << 10)) output |= 1 << 20; ... My compiler (MS Visual Studio) turned this into the following: test eax,1000h jne 0064F5EC or edx,1000000h ... (repeated 13 times with minor differences in constants) I wonder whether i can make it any faster. I would like to have my code written in C, but switching to assembly language is possible. Can i use some MMX/SSE instructions to process all bits at once? Maybe i can use multiplication? (multiply by 0x11111111 or some other magical constant) Would it be better to use condition-set instruction (SETcc) instead of conditional-jump instruction? If yes, how can i make the compiler produce such code for me? Any other idea how to make it faster? Any idea how to do the inverse bitmap transformation (i have to implement it too, bit it's less critical)?

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• Is learning C++ a good idea?

  - by chang

  The more I hear and read about C++ (e.g. this: http://lwn.net/Articles/249460/), I get the impression, that I'd waste my time learning C++. I some wrote network routing algorithm in C++ for a simulator, and it was a pain (as expected, especially coming from a perl/python/Java background ...). I'm never happy about giving up on some technology, but I would be happy, if I could limit my knowledge of C-family languages to just C, C# and Objective-C (even OS Xs Cocoa, which is huge and takes a lot of time to learn looks like joy compared to C++ ...). Do I need to consider myself dumb or unwilling, just because I'm not partial to the pain involved learning this stuff? Technologies advance and there will be options other than C++, when deciding on implementation languages, or not? And for speed: If speed were that critical, I'd go for a plain C implementation instead, or write C extensions for much more productive languages like ruby or python ... The one-line version of the above: Will C++ stay such a relevant language that every committed programmer should be familiar with it? [ edit / thank you very much for your interesting and useful answers so far .. ] [ edit / .. i am accepting the top-rated answer; thanks again for all answers! ]

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• Why have or haven't you moved to ASP.NET MVC yet?

  - by Jason

  I find myself on the edge of trying out ASP.NET MVC but there is still "something" holding me back. Are you still waiting to try it, and if so, why? If you finally decided to use it, what helped you get over your hesitation? I'm not worried about it from a technical point of view; I know the pros and cons of web forms vs MVC. My concerns are more on the practical side. Will Microsoft continue to support ASP.NET MVC if they don't reach some critical threshold of developers/customers using it? Are customers willing to try ASP.NET MVC? Have you had to convince a customer to use it? How did that go? Are there major sites using ASP.NET MVC (besides SO)? Could you provide links if you have them? Did you try ASP.NET MVC and found yourself regretting it? If so, what do you regret? If you have any other concerns preventing you from using MVC.NET, what are they? If you had concerns but felt they were addressed and now use MVC.NET, could you list them as well? Thanks

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• Which is faster for large "for" loop: function call or inline coding?

  - by zaplec

  Hi, I have programmed an embedded software (using C of course) and now I'm considering ways to improve the running time of the system. The most important single module in my system is one very large nested for loop module. That module consists of two nested for loops that loops max 122500 times. That's not very much yet, but the problem is that inside that nested for loop I have a function call to a function that is in another source file. That specific function consists mostly of two another nested for loops which loops always 22500 times. So now I have to make a function call 122500 times. I have made that function that is to be called a lot lighter and shorter (yet still works as it should) and now I started to think that would it be faster to rip off that function call and write that process directly inside those first two for loops? The processor in that system is ARM7TDMI and its frequency is 55MHz. The system itself isn't very time critical so it doesn't have to be real time capable. However the faster it can process its duties the better. Also would it be also faster to use while loops instead of fors? And any piece of advice about how to improve the running time is appreciated. -zaplec

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• how to Solve the "Digg" problem in MongoDB

  - by user193116

  A while back,a Digg developer had posted this blog ,"http://about.digg.com/blog/looking-future-cassandra", where the he described one of the issues that were not optimally solved in MySQL. This was cited as one of the reasons for their move to Cassandra. I have been playing with MongoDB and I would like to understand how to implement the MongoDB collections for this problem From the article, the schema for this information in MySQL : CREATE TABLE Diggs ( id INT(11), itemid INT(11), userid INT(11), digdate DATETIME, PRIMARY KEY (id), KEY user (userid), KEY item (itemid) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; CREATE TABLE Friends ( id INT(10) AUTO_INCREMENT, userid INT(10), username VARCHAR(15), friendid INT(10), friendname VARCHAR(15), mutual TINYINT(1), date_created DATETIME, PRIMARY KEY (id), UNIQUE KEY Friend_unique (userid,friendid), KEY Friend_friend (friendid) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; This problem is ubiquitous in social networking scenario implementation. People befriend a lot of people and they in turn digg a lot of things. Quickly showing a user what his/her friends are up to is very critical. I understand that several blogs have since then provided a pure RDBMs solution with indexes for this issue; however I am curious as to how this could be solved in MongoDB.

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