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  • Speedup C++ code

    - by Werner
    Hi, I am writing a C++ number crunching application, where the bottleneck is a function that has to calculate for double: template<class T> inline T sqr(const T& x){return x*x;} and another one that calculates Base dist2(const Point& p) const { return sqr(x-p.x) + sqr(y-p.y) + sqr(z-p.z); } These operations take 80% of the computation time. I wonder if you can suggest approaches to make it faster, even if there is some sort of accuracy loss Thanks

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  • find all occurrences of comparison with == in visual studio

    - by Emiswelt
    Hi there I made the mistake of using == for comparing IP addresses instead of using the equals() method of the IPAddress class in C#, which will result in the comparison of references instead of values. Since the solution I am currently working on is very large for a one-man project ( 100.000 lines of source code), I am very sure that I still have some of these wrong statements in my code. Is there any possibility to tell Visual Studio to find all occurrences of == operations on a specific class for me, so that I can find and clean up the bugged comparisons? with best regards, emi

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  • How to integrate Python scripting in my Android App (like SL4A)

    - by Seraphim's host
    I need to add scripting layer to my android App. So I can remotely prepare a script that my app download form a web service and execute on the user device. I found a interesting project called Scripting Layer for Android (SL4A) here: http://code.google.com/p/android-scripting/ I'm not sure I can execute Python script without installing the PythonForAndroid_r4.apk first. I can't force my customer to install that application! So my question is, can the SL4A layer be integrated in my app without the need to install other apk? I need to execute actions like update data in the DB, create/read/delete a file on the sd card... Not so complex but I see SL4A can do a lot of things like these. Other scripting libraries? EDIT: Found also MVEL: http://mvel.codehaus.org/ but I think it needs to be integrated to execute complex operations like accessing a DB...

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  • Replace String pattern in Java

    - by Hirantha
    I have the following string "value=\"\\d{4}((((0[1-9])|(1[0-2]))((0[1-9])|([12]\\d)|(3[01]))?)?|(\\-(((0[1-9])|(1[0-2]))(\\-((0[1-9])|([12]\\d)|(3[01])))?)?)?)d{4}" There I want to replace all the occurrences of "{" with NCHAR(0x7B) "}" with NCHAR(0x7D). An the content in-between "{ }" should remain unchanged: Ex: \\d{4} after replacing -> NCHAR(0x7B) 4 NCHAR(0x7D). Is there a way to do this using Regular Expressions in Java?. Anyway, this can be done processing the whole string using string operations.

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  • How to safely remove a USB drive on Windows CE 5.0?

    - by Radu C
    Until today, I assumed that Windows CE was writing everything to disk and I wouldn't end up with a broken FAT16 when I removed the USB stick. Today, I was proven wrong. I use a USB stick to test things on a WinCE 5.0 device. I don't write anything from the app or WinCE to the stick. I just execute my app, and my app reads its settings and pictures from the stick. Today, just this order of operations broke my stick filesystem (and I have to fix it). Is there a way to tell WinCE 5.0 to unmount the stick before I remove it? It sees it as a "Hard Drive", and the tap-and-hold menu has nothing along the lines of "safely remove drive". I'm happy with both code to do this operation and some trick that I didn't find in Windows CE yet. Thank you.

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  • Shortest distance between points on a toroidally wrapped (x- and y- wrapping) map?

    - by mstksg
    I have a toroidal-ish Euclidean-ish map. That is the surface is a flat, Euclidean rectangle, but when a point moves to the right boundary, it will appear at the left boundary (at the same y value), given by x_new = x_old % width Basically, points are plotted based on: (x_new, y_new) = ( x_old % width, y_old % height) Think Pac Man -- walking off one edge of the screen will make you appear on the opposite edge. What's the best way to calculate the shortest distance between two points? The typical implementation suggests a large distance for points on opposite corners of the map, when in reality, the real wrapped distance is very close. The best way I can think of is calculating Classical Delta X and Wrapped Delta X, and Classical Delta Y and Wrapped Delta Y, and using the lower of each pair in the Sqrt(x^2+y^2) distance formula. But that would involve many checks, calculations, operations -- some that I feel might be unnecessary. Is there a better way?

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  • Can I find out what WCF methods are supported on the endpoint before calling it?

    - by alord1689
    I have a versioning issue with a WCF service contract in which one of the many endpoints which are called for the operation is missing one method from the contract. My question is, how can I make sure the command is available on the client before attempting to call it? I tried: foreach (var od in proxy.Endpoint.Contract.Operations) { if (od.Name == "MyMethodName") { hasMethod = true; break; } } Unfortunately, this is using the contract from the calling app and does not actually describe the implementations on the endpoint itself. As a result, it returns true even though the endpoint has failed to implement the command.

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  • Rails modeling for a user

    - by Trevor Hartman
    When building a rails app that allows a User to login and create data, is it best to setup a belongs_to :user association on every single model? For example, let's say a user can create Favorites, Colors and Tags. And let's say Favorites has_many :tags and Colors also has_many :tags. Is it still important for Tags to belong_to :user assuming the User is the only person who has authority to edit those tags? And a similar question along the same lines: When updating data in FavoritesController, I've come to the conclusion that you perform CRUD operations by always doing something like User.favorites.find(params[:id].update_attributes(param[:favorite]) so that they can definitely only update models that belong to them. Right?

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  • Controlled hyperlink hijaxing

    - by Izmoto
    I am working on a web application. I have a data grid with a 'commands' column that has hyperlinks for some common CRUD operations (Edit, Delete, etc). When a user clicks on say the Edit hyperlink, I retrieve the unique identifier for the data grid row and load a modal form dialog (i am using jQuery UI) so the user is able to edit the row data and subsequently close the modal form dialog at which point I refresh the page. Now, before the page is done refreshing, there's a chance that a user might click on the edit link again, and whenever that happens, 'hijaxing' fails. My question is how can i check that if a user clicks on a hyperlink and the page is refreshing, i delay until it is done refreshing, then i allow the 'hijax' to kick in.

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  • Detecting metadata-only read requests in windows filesystem

    - by HyLian
    Hello, I'm developing a kind of filesystem driver. All of read requests that windows makes to my filesystem goes by the driver implementation. I would like to distinguish between "normal" read requests and those who want to get only the metadata from the file. ( Windows reads first 4K of the file and then stop reading ). Does Windows mark this metadata reads in some way? It would be very useful in order to treat that two kind of operations in a different way. In a typical CreateFile call, we have AccessMode, ShareMode, CreationDisposition and FlagsAndAttributes parameters ( being DWORD ), i'm not sure if it's possible to extract some clue of the operation requested. Thanks for reading :)

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  • func_get_args detect context

    - by Steve
    I have a script where it accepts a varying number of arguments. I want to use func_get_args to perform operations on said arguments. If I have one function like this: function Something() { foreach(func_get_args($this) as $functions) { // Do something } // Return.. } I want to be able to call this function in, for example, another function to add/save entries. The add/save function would have arguments 'title', 'description' etc.. I basically want to know if there is a way to detect the context of a function call. Can I pass something to func_get_args that will let it know that its called in a certain function? So if I do: function Save($title, $desc) { $vars = $this->Something(); } I want $vars to contain $title and $desc after modifying them.

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  • Sql Server 2000 Stored Procedure Prevents Parallelism or something?

    - by user187305
    I have a huge disgusting stored procedure that wasn't slow a couple months ago, but now is. I barely know what this thing does and I am in no way interested in rewriting it. I do know that if I take the body of the stored procedure and then declare/set the values of the parameters and run it in query analyzer that it runs more than 20x faster. From the internet, I've read that this is probably due to a bad cached query plan. So, I've tried running the sp with "WITH RECOMPILE" after the EXEC and I've also tried putting the "WITH RECOMPLE" inside the sp, but neither of those helped even a little bit. When I look at the execution plan of the sp vs the query, the biggest difference is that the sp has "Parallelism" operations all over the place and the query doesn't have any. Can this be the cause of the difference in speeds? Thank you, any ideas would be great... I'm stuck.

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  • sortable + draggable demo - how to get access to dropped item?

    - by user246114
    Hi, I have a sortable list. When a new item is dropped into the list (from a draggable), I'd like to get access to it to perform some operations on it. This is what I have: $("#mySortableList").sortable({ receive: function(event, ui) { alert("this is the dropped item: " + ui.item.toString()); } }).disableSelection(); so "ui.item" is the element that was dropped, but it's not the duplicated item that will now be part of my list. How do I get access to the new item that was dropped? I am using the exact demo from the jquery-ui site here: http://jqueryui.com/demos/draggable/#sortable Thanks

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  • What exactly is a variable in C++?

    - by FredOverflow
    The standard says A variable is introduced by the declaration of an object. The variable's name denotes the object. But what does this definition actually mean? Does a variable give a name to an object, i.e. are variables just a naming mechanism for otherwise anonymous objects? Or is a variable the name itself? Or is a variable a named object in the sense that every variable is also an object? Or is a variable just a "proxy" with a name that "delegates" all operations to the real object? To confuse things further, many C++ books seem to treat variables and objects as synonyms. What is your take on this?

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  • When is a program limited by the memory bandwidth?

    - by hanno
    I want to know if a program that I am using and which requires a lot of memory is limited by the memory bandwidth. When do you expect this to happen? Did it ever happen to you in a real life scenario? I found several articles discussing this issue, including http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node12.html http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node13.html http://ispass.org/ucas5/session2_3_ibm.pdf The first link is a bit old, but suggests that you need to perform less than about 1-40 floating point operations per floating point variable in order to see this effect (correct me if I'm wrong). How can I measure the memory bandwidth that a given program is using and how do I measure the (peak) bandwidth that my system can offer? I don't want to discuss any complicated cache issues here. I'm only interested in the communication between the CPU and the memory.

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  • Which NoSQL db to use with C?

    - by systemsfault
    Hello all, I'm working on an application that I'm going to write with C and i am considering to use a nosql db for storing timeseries data with at most 8 or 9 fields. But in every 5 minutes there will huge write operations such as 2-10 million rows and then there will be reads(but performance is not as crucial in read as in the write operation). I'm considering to use a NoSQL db here in order to store the data but couldn't decide on which one to use. Couchdb seems to have a stable driver called pillowtalk for C; but Mongo's driver doesn't look as promising as pillowtalk. I'm also open to other suggestions. What is your recommendation?

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  • Speed of interpolation algorithms, C# and C++ working together.

    - by Kaminari
    Hello. I need fast implementation of popular interpolation algorithms. I figured it out that C# in such simple algorithms will be much slower than C++ so i think of writing some native code and using it in my C# GUI. First of all i run some tests and few operations on 1024x1024x3 matrix took 32ms in C# and 4ms in C++ and that's what i basicly need. Interpolation however is not a good word because i need them only for downscaling. But the question is: Will it be faster than C# methods in Drawing2D Image outputImage = new Bitmap(destWidth, destHeight, PixelFormat.Format24bppRgb); Graphics grPhoto = Graphics.FromImage(outputImage); grPhoto.InterpolationMode = InterpolationMode.*; //all of them grPhoto.DrawImage(bmp, new Rectangle(0, 0, destWidth, destHeight), Rectangle(0, 0, sourceWidth, sourceHeight), GraphicsUnit.Pixel); grPhoto.Dispose(); Some of these method run in 20ms and some in 80. Is there a way to do it faster?

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  • What types of conditions can be used for conditional compilation in C++?

    - by user1002288
    This is an exam question for C++: Which of the following statements accurately describe the condition that can be used for conditional compilation in C++? A. The condition can depend on the value of environment variables. B. The condition can depend on the value of any const variables. C. The condition can depend on the value of program variables. D. The condition can use the sizeof() operator to make decision about compiler-dependent operations based on the size of standard data type. E. The condition must evaluate to either a 0 or 1 during preprocessing. I think the answer is E. Is this correct?

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  • How to group rows into two groups in sql?

    - by user1055638
    Lets say I have such a table: id|time|operation 1 2 read 2 5 write 3 3 read 4 7 read 5 2 save 6 1 open and now I would like to do two things: Divide all these records into two groups: 1) all rows where operation equals to "read" 2) all other rows. Sum the time in each group. So that my query would result only into two rows. What I got so far is: select sum(time) as total_time, operation group by operation ; Although that gives me many groups, depending on the number of distinct operations. How I could group them only into two categories? Cheers!

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  • Event(s) for opening the workbook AND worksheets

    - by KeyMs92
    I'm looking for an elegant solution to trigger an event for opening the workbook as well as opening different worksheets. I don't need seperate operations for each worksheet: they all trigger the same method. I know I can use the events Workbook_Activate / Workbook_Open and Workbook_SheetActivate at the same time but I don't know if this is 'the official way' to do it. Perhaps there's a way to do this with one event. I was also wondering if it is relevant in this matter where I put the code. I now have all the code inside "ThisWorkbook" and not in a "Module"...

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  • finding character in string C language

    - by iSight
    Hi, I am searching a character at first occurence in string using the following code. But, it is taking some time when the character is too long or the character that i am searching is at far extend, which makes delay in other operations. How could i tackle with this problem. The code is below here. Note: attrPtr is a char* which holds a reference to a string containing '"' character at far extend. int position = 0; char qolon = '"';//character to search while (*(attrPtr + position++) != qolon); char* attrValue = NULL; attrValue = (char*)malloc(position * sizeof(char)); strncpy(attrValue, attrPtr, position-1);

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  • Special simple random number generator

    - by psihodelia
    How to create a function, which on every call generates a random integer number? This number must be most random as possible (according to uniform distribution). It is only allowed to use one static variable and at most 3 elementary steps, where each step consists of only one basic arithmetic operation of arity 1 or 2. Example: int myrandom(void){ static int x; x = some_step1; x = some_step2; x = some_step3; return x; } Basic arithmetic operations are +,-,%,and, not, xor, or, left shift, right shift, multiplication and division. Of course, no rand(), random() or similar staff is allowed.

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  • Low-overhead way to access the memory space of a traced process?

    - by vovick
    Hello all. I'm looking for an efficient way to access(for both read and write operations) the memory space of my ptraced child process. The size of blocks being accessed may vary from several bytes up to several megabytes in size, so using the ptrace call with PTRACE_PEEKDATA and PTRACE_POKEDATA which read only one word at a time and switch context every time they're called seems like a pointless waste of resources. The only one alternative solution I could find, though, was the /proc/<pid>/mem file, but it has long since been made read only. Is there any other (relatively simple) way to do that job? The ideal solution would be to somehow share the address space of my child process with its parent and then use the simple memcpy call to copy data I need in both directions, but I have no clues how to do it and where to begin. Any ideas?

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  • How online-game clients are able to exchange data through internet so fast?

    - by Kirzilla
    Hello, Let's imagine really simple game... We have a labirinth and two players trying to find out exit in real time through internet. On every move game client should send player's coordinates to server and accept current coordinates of another client. How is it possible to make this exchange so fast (as all modern games do). Ok, we can use memcache or similar technology to reduce data mining operations on server side. We can also use fastest webserver etc., but we still will have problems with timings. So, the questions are... What protocol game clients are usually using for exchanging information with server? What server technologies are coming to solve this problem? What algorithms are applied for fighting with delays during game etc. PS: Sorry for my English and I hope that my question is clear. Thank you.

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  • Add 64 bit offset to a pointer

    - by Novox
    In F#, there's the NativePtr module, but it seems to only support 32 bit offsets for its’ add/get/set functions, just like System.IntPtr does. Is there a way to add a 64 bit offset to a native pointer (nativeptr<'a) in F#? Of course I could convert all addresses to 64 bit integers, do normal integer operations and then convert the result again to nativeptr<'a, but this would cost additional add and imul instructions. I really want the AGUs to perform the address calculations. For instance, using unsafe in C# you could do something like void* ptr = Marshal.AllocHGlobal(...).ToPointer(); int64 offset = ...; T* newAddr = (T*)ptr + offset; // T has to be an unmanaged type Well actually you can't, because there is no "unmanaged" constraint for type parameters, but at least you can do general pointer arithmetic in a non-generic way. In F# we finally got the unmanaged constraint; but how do I do the pointer arithmetic?

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