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• Deterministic floating point and .NET

  - by code2code

  How can I guarantee that floating point calculations in a .NET application (say in C#) always produce the same bit-exact result? Especially when using different versions of .NET and running on different platforms (x86 vs x86_64). Inaccuracies of floating point operations do not matter. In Java I'd use strictfp. In C/C++ and other low level languages this problem is essentially solved by accessing the FPU / SSE control registers but that's probably not possible in .NET. Even with control of the FPU control register the JIT of .NET will generate different code on different platforms. Something like HotSpot would be even worse in this case... Why do I need it? I'm thinking about writing a real-time strategy (RTS) game which heavily depends on fast floating point math together with a lock stepped simulation. Essentially I will only transmit user input across the network. This also applies to other games which implement replays by storing the user input. Not an option are: decimals (too slow) fixed point values (too slow and cumbersome when using sqrt, sin, cos, tan, atan...) update state across the network like an FPS: Sending position information for hundreds or a few thousand units is not an option Any ideas?

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• REST design: what verb and resource name to use for a filtering service

  - by kabaros

  I am developing a cleanup/filtering service that has a method that receives a list of objects serialized in xml, and apply some filtering rules to return a subset of those objects. In a REST-ful service, what verb shall I use for such a method? I thought that GET is a natural choice, but I have to put the serialized XML in the body of the request which works but feels incorrect. The other verbs don't seem to fit semantically. What is a good way to define that Service interface? Naming the resource /Cleanup or /Filter seems weird mainly because in the examples I see online, it is always a name rather than a verb being used for resource name. Am I right to feel that REST services are better suited for CRUD operations and you start bending the rules in situations like this service? If yes, am I then making a wrong architectural choice. I've pushed to develop this service in REST-ful style (as opposed to SOAP) for simplicity, but such awkward cases happen a lot and make me feel like I am missing something. Either choosing REST where it shouldn't be used or may be over-thinking some stuff that doesn't really matter? In that case, what really matters?

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• Is locking on the requested object a bad idea?

  - by Quick Joe Smith

  Most advice on thread safety involves some variation of the following pattern: public class Thing { private static readonly object padlock = new object(); private string stuff, andNonsense; public string Stuff { get { lock (Thing.padlock) { if (this.stuff == null) this.stuff = "Threadsafe!"; } return this.stuff; } } public string AndNonsense { get { lock (Thing.padlock) { if (this.andNonsense == null) this.andNonsense = "Also threadsafe!"; } return this.andNonsense; } } // Rest of class... } In cases where the get operations are expensive and unrelated, a single locking object is unsuitable because a call to Stuff would block all calls to AndNonsense, degrading performance. And rather than create a lock object for each call, wouldn't it be better to acquire the lock on the member itself (assuming it is not something that implements SyncRoot or somesuch for that purpose? For example: public string Stuff { get { lock (this.stuff) { // Pretend that this is a very expensive operation. if (this.stuff == null) this.stuff = "Still threadsafe and good?"; } return this.stuff; } } Strangely, I have never seen this approach recommended or warned against. Am I missing something obvious?

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• Sphinx - delimiters

  - by yoda

  Hi, I would like to know if the Sphinx engine works with any delimiters (like commas and periods in normal MySQL). My question comes from the urge, not to use them at all, but to escape them or at least thay they don't enter in conflict when performing MATCH operations with FULLTEXT searches, since I have problems dealing with them in MySQL by default and I would prefer not to be forced to replace those delimiters by any other characters to provide a good set of results. Sorry if I'm saying something stupid, but I don't have experience with Sphinx or other complementary (?) search engines. To give you an example, if I perform a search with "Passat 2.0 TDI" MySQL by default would identify the period in this case as a delimiter and since the "2" and "0" are too short to be considered words by default, the results would be a bit messed up. Is it easy to handle with Sphinx (or other search engine)? I'm open to suggestions. This is for a large project, with probably more than 500.000 possible records (not trivial at all). Cheers!

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• Memory mapping of files and system cache behavior in WinXP

  - by Canopus

  Our application is memory intensive and deals with reading a large number of disk files. The total load can be more than 3 GB. There is a custom memory manager that uses memory mapped files to achieve reading of such a huge data. The files are mapped into the process memory space only when needed and with this the process memory is well under control. But what is observed is, with memory mapping, the system cache keeps on increasing until it occupies the available physical memory. This leads to the slowing down of the entire system. My question is how to prevent system cache from hogging the physical memory? I attempted to remove the file buffering (by using FILE_FLAG_NO_BUFFERING ), but with this, the read operations take considerable amount of time and slows down the application performance. How to achieve the scalability without sacrificing much on performance. What are the common techniques used in such cases? I dont have a good understanding of the WinXP OS caching behavior. Any good links explaining the same would also be helpful.

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• Problem with Google Calendar API "getTimes()" method

  - by Raffo

  I'm trying to get several informations from google calendar's API in JAVA. While trying to access to informations about the time of an event I got a problem. I do the following: CalendarService myService = new CalendarService("project_name"); myService.setUserCredentials("user", "pwd"); URL feedUrl = new URL("http://www.google.com/calendar/feeds/default/private/full"); CalendarQuery q = new CalendarQuery(feedUrl); CalendarEventFeed resultFeed = myService.query(q, CalendarEventFeed.class); for (int i = 0; i < resultFeed.getEntries().size(); i++) { CalendarEventEntry g = resultFeed.getEntries().get(i); List<When> t = g.getTimes(); //other operations } The list t obtained with getTimes() on a CalendarEventEntry is always empty and I can't figure out why. This seems strange to me since for a calendar event it should always exist a description of when it should happen... what am I missing??

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• Exemplars of large document-centric applications with COM/XPCOM/.NET interfaces.

  - by Warren P

  I am looking for exemplars (design examples) showing the use of interfaces (aka 'protocols' for you smalltalkers) to design a document management architecture in a large Word Processor, Spreadsheet, vector graphic or publishing package, or office-productivity (non-database) application with support for as many of the following as possible: any open source project, will be ideal, and language of implementation is unimportant since I am looking for design examples, however an object oriented language with support for "interfaces" is a must. I know at least a dozen languages, and I'm willing to study any application's source. use of "interface" could loosely be applied to either XPCOM or COM interfaces, or .NET interfaces, or even the use of pure-virtual (virtual+abstract) base-classes for OOP languages that lack the ability to declare an interface distinct from a class. I am mostly looking for a robust, thorough and flexible implementation for a document, IDocument, various document views (IDocumentView), and whatever operations make sense in that case. I am particular interested in cases where the product in question is a real-world product. For example, if anybody familiar with OpenOffice can tell me if the code contains a good sample design. I am looking for design documentation that outlines the design of the interfaces for such an application. So for example, if the openoffice spreadsheet has such an interface design, then that might be the best case, because it is a widely used real-world design, with millions of users, rather than a textbook example, which is minimal, and contrived. I know that the Mozilla platform uses XPCOM, and its design is heavily "interface" oriented, but I am looking more for a "word processor" or "spreadsheet" type of document design, rather than a web-browser. I am particularly interested in the interfaces used to access to data and meta-data such as markup (attributes like bold, and italics, and font size), and the ability to search and look up named entities within a document.

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• Entity Framework 4 Entity with EntityState of Unchanged firing update

  - by Andy

  I am using EF 4, mapping all CUD operations for my entities using sprocs. I have two tables, ADDRESS and PERSON. A PERSON can have multiple ADDRESS associated with them. Here is the code I am running: Person person = (from p in context.People where p.PersonUID == 1 select p).FirstOrDefault(); Address address = (from a in context.Addresses where a.AddressUID == 51 select a).FirstOrDefault(); address.AddressLn2 = "Test"; context.SaveChanges(); The Address being updated is associated with the Person I am retrieveing - although they are not explicitly linked in any way in the code. When the context.SaveChanges() executes not only does the Update sproc for my Address entity get fired (like you would expect), but so does the Update sproc for the Person entity - even though you can see there was no change made to the Person entity. When I check the EntityState of both objects before the context.SaveChanges() call I see that my Address entity has an EntityState of "Modified" and my Person enity has an EntityState of "Unchanged". Why is the Update sproc being called for the Person entity? Is there a setting of some sort that I can set to prevent this from happening?

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• Speed comparison - Template specialization vs. Virtual Function vs. If-Statement

  - by Person

  Just to get it out of the way... Premature optimization is the root of all evil Make use of OOP etc. I understand. Just looking for some advice regarding the speed of certain operations that I can store in my grey matter for future reference. Say you have an Animation class. An animation can be looped (plays over and over) or not looped (plays once), it may have unique frame times or not, etc. Let's say there are 3 of these "either or" attributes. Note that any method of the Animation class will at most check for one of these (i.e. this isn't a case of a giant branch of if-elseif). Here are some options. 1) Give it boolean members for the attributes given above, and use an if statement to check against them when playing the animation to perform the appropriate action. Problem: Conditional checked every single time the animation is played. 2) Make a base animation class, and derive other animations classes such as LoopedAnimation and AnimationUniqueFrames, etc. Problem: Vtable check upon every call to play the animation given that you have something like a vector<Animation>. Also, making a separate class for all of the possible combinations seems code bloaty. 3) Use template specialization, and specialize those functions that depend on those attributes. Like template<bool looped, bool uniqueFrameTimes> class Animation. Problem: The problem with this is that you couldn't just have a vector<Animation> for something's animations. Could also be bloaty. I'm wondering what kind of speed each of these options offer? I'm particularly interested in the 1st and 2nd option because the 3rd doesn't allow one to iterate through a general container of Animations. In short, what is faster - a vtable fetch or a conditional?

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• What C# container is most resource-efficient for existence for only one operation?

  - by ccornet

  I find myself often with a situation where I need to perform an operation on a set of properties. The operation can be anything from checking if a particular property matches anything in the set to a single iteration of actions. Sometimes the set is dynamically generated when the function is called, some built with a simple LINQ statement, other times it is a hard-coded set that will always remain the same. But one constant always exists: the set only exists for one single operation and has no use before or after it. My problem is, I have so many points in my application where this is necessary, but I appear to be very, very inconsistent in how I store these sets. Some of them are arrays, some are lists, and just now I've found a couple linked lists. Now, none of the operations I'm specifically concerned about have to care about indices, container size, order, or any other functionality that is bestowed by any of the individual container types. I picked resource efficiency because it's a better idea than flipping coins. I figured, since array size is configured and it's a very elementary container, that might be my best choice, but I figure it is a better idea to ask around. Alternatively, if there's a better choice not out of resource-efficiency but strictly as being a better choice for this kind of situation, that would be nice as well.

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• Tree iterator, can you optimize this any further?

  - by Ron

  As a follow up to my original question about a small piece of this code I decided to ask a follow up to see if you can do better then what we came up with so far. The code below iterates over a binary tree (left/right = child/next ). I do believe there is room for one less conditional in here (the down boolean). The fastest answer wins! The cnt statement can be multiple statements so lets make sure this appears only once The child() and next() member functions are about 30x as slow as the hasChild() and hasNext() operations. Keep it iterative <-- dropped this requirement as the recursive solution presented was faster. This is C++ code visit order of the nodes must stay as they are in the example below. ( hit parents first then the children then the 'next' nodes). BaseNodePtr is a boost::shared_ptr as thus assignments are slow, avoid any temporary BaseNodePtr variables. Currently this code takes 5897ms to visit 62200000 nodes in a test tree, calling this function 200,000 times. void processTree (BaseNodePtr current, unsigned int & cnt ) { bool down = true; while ( true ) { if ( down ) { while (true) { cnt++; // this can/will be multiple statesments if (!current->hasChild()) break; current = current->child(); } } if ( current->hasNext() ) { down = true; current = current->next(); } else { down = false; current = current->parent(); if (!current) return; // done. } } }

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• Flash Player, security: If a URL starts with "http://" will the SWF always be loaded into REMOTE san

  - by Pavel

  Seems to be a question for a Flash security guru. Suppose we are loading an external SWF movie with MovieClipLoader.loadMovie(url:String) Is it safe to assume that if url starts with "http://", the movie will be loaded in REMOTE sandbox? We need to tell local SWFs from remote ones to close a security hole. If you need the context read on. We have developed a Projector, written in C++ embedding Flash Player ActiveX. Our Flash application runs inside the Projector. Soon we want to give our users a way to create plugins for the application. The plugins are obviously will be SWF movies. The case I'm afraid of is the following. A bad person creates a malicious evil.swf pretending it to be nice plugin for our app. In case evil.swf is loaded from the local file system it is granted an access to the whole MovieClip tree and Projector API, opening C++ file access operations. On the other hand if evil.swf is loaded from the internet, remotely, it will be locked in REMOTE sandbox by Flash security model. Because of this, we need a reliable way to tell local SWF from remote one before loading it. And we must not make a mistake. So again, is it safe to assume that if url begins with "http://", the clip will be loaded inside REMOTE sandbox?

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• How to get JTree expanded?

  - by Dzmitry Zhaleznichenka

  I have a wizard with several screens where user has to fill his/her details for further processing. At the second screen I have a radio group with three radio buttons that enable additional elements. To proceed, user has to choose one of them. When user selects third button, single-selection JTree filled in with data enables and user has to select an option from it. Then user has to press "Next" to get to next screen. The option he\she had selected is stored as a TreePath. So far so good. My problem is the following. If the user wants to come back from the following screen to the screen with a JTree, I want to provide him\her with the JTree expanded to the option that had been selected and to highlight the option. However, whatsoever I try to do for that (any combinations of expandPath, scrollPathToVisible, addSelectionPath, makeVisible) always provides me with a collapsed tree. I try to expand both leaves and nodes. My code looks like this: rbProcessJTree.setSelected(isProcessJTree()); if (null != getSelectedTablePath()){ trTables.addSelectionPath(getSelectedTablePath()); trTables.expandPath(getSelectedTablePath()); trTables.scrollPathToVisible(getSelectedTablePath()); } When setSelected() is called, state change listener is invoked that enables JTree. The model is loaded during the form initialization. Each time I switch between screens, I save the input data from previous screen and dispose it. Then, when I need to open previous screen back, I save data from the following screen, dispose it, load data to this screen and show it. So each time the screen is generating from scratch. Could you please explain, what sequence of operations has to be done to get JTree expanded in a newly created form,with data model loaded and selection path provided?

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• LINQ to SQL - database relationships won't update after submit

  - by Quantic Programming

  I have a Database with the tables Users and Uploads. The important columns are: Users -> UserID Uploads -> UploadID, UserID The primary key in the relationship is Users -> UserID and the foreign key is Uploads -> UserID. In LINQ to SQL, I do the following operations: Retrieve files var upload = new Upload(); upload.UserID = user.UserID; upload.UploadID = XXX; db.Uploads.InsertOnSubmit(upload) db.SubmitChanges(); If I do that and rerun the application (and the db object is re-built, of course) - if do something like this: foreach(var upload in user.Uploads) I get all the uploads with that user's ID. (like added in the previous example) The problem is, that my application, after adding an upload an submitting changes, doesn't update the user.Uploads collection. i.e - I don't get the newly added uploads. The user object is stored in the Session object. At first, I though that the LINQ to SQL Framework doesn't update the reference of the object, therefore I should simply "reset" the user object from a new SQL request. I mean this: Session["user"] = db.Users.Where(u => u.UserID == user.UserID).SingleOrDefault(); (Where user is the previous user) But it didn't help. Please note: After rerunning the application, user.Uploads does have the new upload! Did anyone experience this type of problem, or is it normal behavior? I am a newbie to this framework. I would gladly take any advice. Thank you!

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• Problem consuming a dataset via a .NET web service from Flex-ActionScript

  - by DEH

  Hi, I am returning a .NET dataset to Flex Actionscript via a web service. Actionscript snippet as follows: var websvc:WebService = new WebService(); websvc.useProxy=false; websvc.wsdl = "http://localhost:13229/test/mysvc.asmx?WSDL"; websvc.loadWSDL(); var operation:Operation = new Operation(null, "GetData"); operation.arguments.command="xx_gethierdata_"+mode+"_"+identifier; operation.addEventListener(ResultEvent.RESULT, onResultHandler, false, 0, true); operation.addEventListener(FaultEvent.FAULT, onFaultHandler, false, 0, true); operation.resultFormat="object"; websvc.operations = [operation]; operation.send(); Once in the onResultHandler function I have access to the datatable - I then want to grab the column names. The following code outputs my column names: for each (var tcolumn:Object in datatable.Columns){trace('Column:'+tcolumn);} This works ok, but the column names are encoded, so a column name that is actually "1-9" is output as "_x005B_1-9_x005D_" Anyone know the best way to decode the column name? I could replace all the encoding strings, but surely there is a better way? Thanks

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• GUI for server-client program

  - by sksingh73

  I am making a server-client application in c++. In this i am also using shared memory & file read-write operations. my program is completely ready & i now wants to make a gui for it. someone suggested me to go for QT4, but when i tried it, i found i have to re-write 80% of the code because QT has got its own classes & variable. i don't want to do it. i want suggestions from you on this regard. my requirements for gui are very simple i.e there will be a main form, which will have two text boxes in which all messages being sent & received by client & server should be shown. there should be another lineedit box, through which i can send the messages to the other end server. I don't know how to make this gui. someone suggested tcl/tk, other suggested me use php/swig. i am not sure how to go about this. my only requirement is that i want to make this simple gui with minimum of changes in my code. THANX

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• Creating simple calculator with bison & flex in C++ (not C)

  - by ak91

  Hey, I would like to create simple C++ calculator using bison and flex. Please note I'm new to the creating parsers. I already found few examples in bison/flex but they were all written in C. My goal is to create C++ code, where classes would contain nodes of values, operations, funcs - to create AST (evaluation would be done just after creating whole AST - starting from the root and going forward). For example: my_var = sqrt(9 ** 2 - 32) + 4 - 20 / 5 my_var * 3 Would be parsed as: = / \ my_var + / \ sqrt - | / \ - 4 / / \ / \ ** 32 20 5 / \ 9 2 and the second AST would look like: * / \ my_var 3 Then following pseudocode reflects AST: ast_root = create_node('=', new_variable("my_var"), exp) where exp is: exp = create_node(OPERATOR, val1, val2) but NOT like this: $$ = $1 OPERATOR $3 because this way I directly get value of operation instead of creation the Node. I believe the Node should contain type (of operation), val1 (Node), val2 (Node). In some cases val2 would be NULL, like above mentioned sqrt which takes in the end one argument. Right? It will be nice if you can propose me C++ skeleton (without evaluation) for above described problem (including *.y file creating AST) to help me understand the way of creating/holding Nodes in AST. Code can be snipped, just to let me get the idea. I'll also be grateful if you point me to an existing (possibly simple) example if you know any. Thank you all for your time and assistance!

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• Is this a safe way to release resources in Java?

  - by palto

  Usually when code needs some resource that needs to be released I see it done like this: InputStream in = null; try{ in = new FileInputStream("myfile.txt"); doSomethingWithStream(in); }finally{ if(in != null){ in.close(); } } What I don't like is that you have to initialize the variable to null and after that set it to another value and in the finally block check if the resource was initialized by checking if it is null. If it is not null, it needs to be released. I know I'm nitpicking, but I feel like this could be done cleaner. What I would like to do is this: InputStream in = new FileInputStream("myfile.txt"); try{ doSomethingWithStream(in); }finally{ in.close(); } To my eyes this looks almost as safe as the previous one. If resource initialization fails and it throws an exception, there's nothing to be done(since I didn't get the resource) so it doesn't have to be inside the try block. The only thing I'm worried is if there is some way(I'm not Java certified) that an exception or error can be thrown between operations? Even simpler example: Inputstream in = new FileInputStream("myfile.txt"); in.close(); Is there any way the stream would be left open that a try-finally block would prevent?

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• Is it possible to load an entire SQL Server CE database into RAM?

  - by DanM

  I'm using LinqToSql to query a small SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table via a foreign key, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of the appeal of LinqToSql. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view.

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• Locking database edit by key name

  - by Will Glass

  I need to prevent simultaneous edits to a database field. Users are executing a push operation on a structured data field, so I want to sequence the operations, not simply ignore one edit and take the second. Essentially I want to do synchronized(key name) { push value onto the database field } and set up the synchronized item so that only one operation on "key name" will occur at a time. (note: I'm simplifying, it's not always a simple push). A crude way to do this would be a global synchronization, but that bottlenecks the entire app. All I need to do is sequence two simultaneous writes with the same key, which is rare but annoying occurrence. This is a web-based java app, written with Spring (and using JPA/MySQL). The operation is triggered by a user web service call. (the root cause is when a user sends two simultaneous http requests with the same key). I've glanced through the Doug Lea/Josh Bloch/et al Concurrency in Action, but don't see an obvious solution. Still, this seems simple enough I feel there must be an elegant way to do this.

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• PHP Access property of a class from within a class instantiated in the original class.

  - by Iain

  I'm not certain how to explain this with the correct terms so maybe an example is the best method... $master = new MasterClass(); $master->doStuff(); class MasterClass { var $a; var $b; var $c; var $eventProccer; function MasterClass() { $this->a = 1; $this->eventProccer = new EventProcess(); } function printCurrent() { echo '<br>'.$this->a.'<br>'; } function doStuff() { $this->printCurrent(); $this->eventProccer->DoSomething(); $this->printCurrent(); } } class EventProcess { function EventProcess() {} function DoSomething() { // trying to access and change the parent class' a,b,c properties } } My problem is i'm not certain how to access the properties of the MasterClass from within the EventProcess-DoSomething() method? I would need to access, perform operations on and update the properties. The a,b,c properties will be quite large arrays and the DoSomething() method would be called many times during the execuction of the script. Any help or pointers would be much appreciated :)

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• The sign of zero with float2

  - by JackOLantern

  Consider the following code performing operations on complex numbers with C/C++'s float: float real_part = log(3.f); float imag_part = 0.f; float real_part2 = (imag_part)*(imag_part)-(real_part*real_part); float imag_part2 = (imag_part)*(real_part)+(real_part*imag_part); The result will be real_part2= -1.20695 imag_part2= 0 angle= 3.14159 where angle is the phase of the complex number and, in this case, is pi. Now consider the following code: float real_part = log(3.f); float imag_part = 0.f; float real_part2 = (-imag_part)*(-imag_part)-(real_part)*(real_part); float imag_part2 = (-imag_part)*(real_part)+(real_part)*(-imag_part); The result will be real_part2= -1.20695 imag_part2= 0 angle= -3.14159 The imaginary part of the result is -0 which makes the phase of the result be -pi. Although still accomplishing with the principal argument of a complex number and with the signed property of floating point's 0, this changes is a problem when one is defining functions of complex numbers. For example, if one is defining sqrt of a complex number by the de Moivre formula, this will change the sign of the imaginary part of the result to a wrong value. How to deal with this effect?

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• Is Domain Anaemia appropriate in a Service Oriented Architecture?

  - by Stimul8d

  I want to be clear on this. When I say domain anaemia, I mean intentional domain anaemia, not accidental. In a world where most of our business logic is hidden away behind a bunch of services, is a full domain model really necessary? This is the question I've had to ask myself recently since working on a project where the "domain" model is in reality a persistence model; none of the domain objects contain any methods and this is a very intentional decision. Initially, I shuddered when I saw a library full of what are essentially type-safe data containers but after some thought it struck me that this particular system doesn't do much but basic CRUD operations, so maybe in this case this is a good choice. My problem I guess is that my experience so far has been very much focussed on a rich domain model so it threw me a little. The remainder of the domain logic is hidden away in a group of helpers, facades and factories which live in a separate assembly. I'm keen to hear what people's thoughts are on this. Obviously, the considerations for reuse of these classes are much simpler but is really that great a benefit?

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• RIA Service/oData ... "Requests that attempt to access a single element using key values from a resu

  - by user327911

  I've recently started working up a sample project to play with an oData feed coming from a RIA service. I am able to view the feed and the metadata via any web browser, however, if I try to perform certain query operations on the feed I receive "unsupported" exceptions. Sample oData feed: ProductSet http://localhost:50880/Services/Rebirth-Web-Services-ProductService.svc/OData/ProductSet/ 2010-04-28T14:02:10Z http://localhost:50880/Services/Rebirth-Web-Services-ProductService.svc/OData/ProductSet(guid'b0a2b170-c6df-441f-ae2a-74dd19901128') 2010-04-28T14:02:10Z b0a2b170-c6df-441f-ae2a-74dd19901128 Product 0 Type 1 Active Sample web.config entry: Sample service: [EnableClientAccess()] public class ProductService : DomainService { [Query(IsDefault = true)] public IQueryable GetProducts() { IList products = new List(); for (int i = 0; i < 90; i++) { Product product = new Product { Id = Guid.NewGuid(), Name = "Product " + i.ToString(), ProductType = i < 30 ? "Type 1" : ((i > 30 && i < 60) ? "Type 2" : "Type 3"), Status = i % 2 == 0 ? "Active" : "NotActive" }; products.Add(product); } return products.AsQueryable(); } } If I provide the url "http://localhost:50880/Services/Rebirth-Web-Services-ProductService.svc/OData/ProductSet(guid'b0a2b170-c6df-441f-ae2a-74dd19901128')" to my web browser I receive the following xml: Requests that attempt to access a single element using key values from a result set are not supported. I'm new to RIA and oData. Could this be something as simple as my web browsers not supporting this type of querying on the result set or something else? Thanks ahead! Corey

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• How should I lock the table in this VB6 / Access application?

  - by Brian Hooper

  I'm working on a VB6 application using an Access database. The application writes messages to a log table from time to time. Several instances of the application may be running simultaneously and to distinguish them they each have their own run number. The run number is deduced from the log table thus... Set record_set = New ADODB.Recordset query_string = "SELECT MAX(RUN_NUMBER) + 1 AS NEW_RUN_NUMBER FROM ERROR_LOG" record_set.CursorLocation = adUseClient record_set.Open query_string, database_connection, adOpenStatic, , adCmdText record_set.MoveLast If IsNull(record_set.Fields("NEW_RUN_NUMBER")) Then run_number = 0 Else run_number = record_set.Fields("NEW_RUN_NUMBER") End If command_string = "INSERT INTO ERROR_LOG (RUN_NUMBER, SEVERITY, MESSAGE) " & _ " VALUES (" & Str$(run_number) & ", " & _ " " & Str$(SEVERITY_INFORMATION) & ", " & _ " 'Run Started'); " database_connection.Execute command_string Obviously there is a small gap between the calculation of the run number and the appearance of the new row in the database, and to prevent another instance getting access between the two operations I'd like to lock the table; something along the lines of SET TRANSACTION READ WRITE RESERVING ERROR_LOG FOR PROTECTED WRITE; How should I go about doing this? Would locking the recordset do any good (the row in the record set doesn't match any particular row in the database)?

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