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• In C, would !~b ever be faster than b == 0xff ?

  - by James Morris

  From a long time ago I have a memory which has stuck with me that says comparisons against zero are faster than any other value (ahem Z80). In some C code I'm writing I want to skip values which have all their bits set. Currently the type of these values is char but may change. I have two different alternatives to perform the test: if (!~b) /* skip */ and if (b == 0xff) /* skip */ Apart from the latter making the assumption that b is an 8bit char whereas the former does not, would the former ever be faster due to the old compare to zero optimization trick, or are the CPUs of today way beyond this kind of thing?

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• CPU Usage relative to number of users? - ASP.Net Application

  - by soldieraman

  My Asp.net application uses 25-30% of the CPU on a test server which has 600 MB Ram on it. I can see the asp_wb process taking that much percentage of CPU. This is when I am testing using one user. How many users can the server afford then without falling over? Is there a relationship between the CPU Usage and number of user aka if there are 2 users my application will sky rocket to 60% of memory usage? Or does/Should/How does the server handle this?

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• Render asp.net repeater as-and-when chunks of html is ready (streaming)

  - by sash

  The problem is to render huge reports. Basically we have lots of data that get rendered in html reports (mostly using repeater or gridview). As it so happens, the data started out small and now we have tons of it. There are lots of such reports already built so total rewrite is not an option. Heck, the business is not even letting us page the data. Now server memory is shooting up each time we try to render some reports. So the question is - is there some way we can bind data to repeater and have it stream html to browser as and when chunks are ready? That way we hope to not bring all that data into app server at once. I'm thinking we'll use a datareader or something to get parts of data and render it to browser. Any pointers, links, ideas?

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• Clojure closures and GC

  - by Ralph

  It is my understanding that the default ClassLoader used in Java (and thus, Clojure) holds on to pointers to any anonymous classes created, and thus, onto lambdas and closures. These are never garbage collected, and so represent a "memory leak". There is some investigation going on for Java 7 or 8 to adding an anonymous ClassLoader that will not retain references to these functions. In the mean time how are people dealing with writing long-running applications in languages like Clojure and Scala, that encourage the use of these constructs? Is there any possibility that Clojure could provide its own anonymous ClassLoader, extending the system one, but not holding onto created classes?

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• double fork using vfork

  - by Oren S

  HI I am writing a part of a server which should dispatch some other child processes. Because I want to wait on some of the processes, and dispatch others without waiting for completion, I use double fork for the second kind of processes (thus avoiding the zombie processes). Problem is, my server holds a lot of memory, so forking takes a long time (even the copy-on-write fork used in Linux which copies only the paging tables) I want to replace the fork() with vfork(), and it's easy for the second fork (as it only calls execve() in the child), but I couldn't find any way I can replace the first one. Does anyone know how I can do that? Thanks! The server is a linux (RH5U4), written in C++.

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• Why MSSQL keeps throwing me Exceptions?

  - by Augusto Càzares

  I have my project in .NET that uses a db in MSSQL Server,i'm using LINQ , sometimes when the projec throws me an exception (Constraint) in a part of the project this same error keeps showing in other part of the project when i do another thing with the db, like when i do an insertion and i had before an exception on delete the insertion throws me the delete exeption, and it remainds this way until i close and open again the project, my major problem is when this happen in my online project, this error in my project causes me problems in the project i'm testing online (i use the same db). I don't know if this exception is on the memory or something but its have been causing me a lot of headechs.

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• C++ initializing constants and inheritance

  - by pingvinus

  I want to initialize constant in child-class, instead of base class. And use it to get rid of dynamic memory allocation (I know array sizes already, and there will be a few child-classes with different constants). So I try: class A { public: const int x; A() : x(0) {} A(int x) : x(x) {} void f() { double y[this->x]; } }; class B : A { B() : A(2) {} }; Pretty simple, but compiler says: error C2057: expected constant expression How can I say to compiler, that it is really a constant?

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• just-in-time list

  - by intuited

  I'd like to know if there is a class available, either in the standard library or in pypi, that fits this description. The constructor would take an iterator. It would implement the container protocol (ie _getitem_, _len_, etc), so that slices, length, etc., would work. In doing so, it would iterate and retain just enough values from its constructor argument to provide whatever information was requested. So if jitlist[6] was requested, it would call self.source.next() 7 times, save those elements in its list, and return the last one. This would allow downstream code to use it as a list, but avoid unnecessarily instantiating a list for cases where list functionality was not needed, and avoid allocating memory for the entire list if only a few members ended up being requested. It seems like a pretty easy one to write, but it also seems useful enough that it's likely that someone would have already made it available in a module.

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• Direct video card access

  - by icemanind

  Guys, I am trying to write a class in C# that can be used as a direct replacement for the C# Bitmap class. What I want to do instead though is perform all graphic functions done on the bitmap using the power of the video card. From what I understand, functions such as DrawLine or DrawArc or DrawText are primitive functions that use simple cpu math algorithms to perform the job. I, instead, want to use the graphics card cpu and memory to do these and other advanced functions, such as skinning a bitmap (applying a texture) and true transparancy. My problem is, in C#, how do I access direct video functions? Is there a library or something I need?

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• Parsing a text file with a fixed format in Java

  - by EugeneP

  Suppose I know a text file format, say, each line contains 4 fields like this: firstword secondword thirdword fourthword firstword2 secondword2 thirdword2 fourthword2 ... and I need to read it fully into memory I can use this approach: open a text file while not EOF read line by line split each line by a space create a new object with four fields extracted from each line add this object to a Set Ok, but is there anything better, a special 3-rd party Java library? So that we could define the structure of each text line beforehand and parse the file with some function thirdpartylib.setInputTextFileFormat("format.xml"); thirdpartylib.parse(Set, "pathToFile") ?

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• Which Ipod touch generation should I buy? 2nd or 3rd?

  - by kukabunga

  I want to create games for Iphone/Ipod touch. Unfortunately I don't have a lot of money so I can buy only one device. Ipod is cheaper than Iphone, so I decided to bought Ipod touch. But I am afraid of buying 3rd generation - because it has more memory, more faster CPU, etc. And I think if I post my app on appstore - people with 2nd generation Ipod might have trouble with my app (because I was testing it on 3rd generation). But on the other hand - I am planning to create 3d/cpu demanding game - and it would be easy for me to implement it on device with more calculation power... What should I do in this situation? Any advice is appreciate.

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• Entity Framework ObjectContext Life-cycle

  - by Leonardo

  Hello, I'm developing a web application using asp.net 4.0 with Entity Framework. In my apllication I have a page DataEntry.aspx wich has 3 web user control.Each user control manage an entity and use a repository class to access data. The final user before save all the changes can add or remove entity in memory. My question is: how can i share the ObjectContext between the repositories? Basically I need a ObjectContext for the entire session working of DataEntry.aspx. How can I achive this? Thank you

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• Cilk or Cilk++ or OpenMP

  - by Aman Deep Gautam

  I'm creating a multi-threaded application in Linux. here is the scenario: Suppose I am having x instance of a class BloomFilter and I have some y GB of data(greater than memory available). I need to test membership for this y GB of data in each of the bloom filter instance. It is pretty much clear that parallel programming will help to speed up the task moreover since I am only reading the data so it can be shared across all processes or threads. Now I am confused about which one to use Cilk, Cilk++ or OpenMP(which one is better). Also I am confused about which one to go for Multithreading or Multiprocessing

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• Storing CLLocationCoordinates2D in NSMutableArray

  - by Amarsh

  After some searching, I got the following solution : ref: http://stackoverflow.com/questions/1392909/nsmutablearray-addobject-with-mallocd-struct CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D)); new_coordinate->latitude = latitude; new_coordinate->longitude = longitude; [points addObject:[NSData dataWithBytes:(void *)new_coordinate length:sizeof(CLLocationCoordinate2D)]]; free(new_coordinate); And access it as: CLLocationCoordinate2D* c = (CLLocationCoordinate2D*) [[points objectAtIndex:0] bytes]; However, someone claims that there is a memory leak here? Can anyone suggest me where is the leak and how to fix it. Further, is there a better way of storing a list of CLLocationCoordinate2D in NSMutableArray? Please give sample code since I am an Objective C newbie.

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• Splitting a string into new rows in R

  - by user3703195

  I have a data set like below: Country Region Molecule Item Code IND NA PB102 FR206985511 THAI AP PB103 BA-107603 / F000113361 / 107603 LUXE NA PB105 1012701 / SGP-1012701 / F041701000 IND AP PB106 AU206985211 / CA-F206985211 THAI HP PB107 F034702000 / 1010701 / SGP-1010701 BANG NA PB108 F000007970/25781/20009021 I want to split based the string values in ITEMCODE column on / and create a new row for each entry. For instance, the desired output will be: Country Region Molecule Item Code New row IND NA PB102 FR206985511 FR206985511 THAI AP PB103 BA-107603 / F000113361 / 107603 F000113361 107603 BA-107603 LUXE NA PB105 1012701 / SP-1012701 / F041701000 1012701 SP-1012701 F041701000 IND AP PB106 AU206985211 / CA-F206985211 AU206985211 CA-F206985211 THAI HP PB107 F034702000 / 1010701 / SP-1010701 F034702000 1010701 SP-1010701 BANG NA PB108 F000007970/25781/20009021 F000007970 25781 20009021 I tried the below code library(splitstackshape) df2=concat.split.multiple(df1,"Plant.Item.Code","/", direction="long") but got the Error "Error: memory exhausted (limit reached?)" When i tried strsplit() i got the below error message. Error in strsplit(df1$Plant.Item.Code, "/") : non-character argument Any help from you will be appreciated.

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• Why is 'volatile' parasitic in C++?

  - by Steve

  Consider the following code: int main() { int i; volatile int* p = &i; int *v = p; return 0; } This gives an error in g++: $ g++ -o volatile volatile.cpp volatile.cpp: In function ‘int main()’: volatile.cpp:6: error: invalid conversion from ‘volatile int*’ to ‘int*’ My intention was that I want to make p volatile. However, once I've read the value of p, I don't care if accessing v is volatile. Why is it required that v be declared volatile? This is hypothetical code of course. In a real situation you could imagine that p points to a memory location, but is modified externally and I want v to point to the location that p pointed to at the time of v = p, even if later p is externally modified. Therefore p is volatile, but v is not. By the way I am interested in the behaviour both when this is considered C and C++, but in C this only generates a warning, not an error.

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• What's your favorite programmable calculator?

  - by Pat Notz

  The HP-32S still holds a soft spot in my heart, even though it only had 4 registers. I have fond memories of writing a nonlinear solver for finding an azeotrope curve during a Thermodynamics final. Despite the increase in power, memory, pixels and features the HP-32G that followed never could steal my heart away. Here's to you, HP-32S. Let's hear it, what's your favorite programmable calculator? As with all poll type questions, do NOT submit a new answer unless your answer is not represented. Vote up your answer instead of adding yet another TI-85 or HP-49 to the list, and add comments to that answer if you want to relate specifics. EDIT: I moved my photo into an answer for polling.

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• efficient way to detect if an image is empty

  - by Jos

  Hi, I need a very fast method to detect if an image is empty. Im my case then all pixels are white and transparant. The images are png's. My current method is to load them in a memory bitmap and check each pixel value, but this is way to slow. Is there a more efficient way? This is my current code: 'Lock the bitmap bits. Dim bmpData As System.Drawing.Imaging.BitmapData = bmp.LockBits(rectBmp, _ Drawing.Imaging.ImageLockMode.ReadOnly, bmp.PixelFormat) Try Dim x As Integer Dim y As Integer For y = 0 To bmpData.Height - 1 For x = 0 To bmpData.Width - 1 If System.Runtime.InteropServices.Marshal.ReadByte(bmpData.Scan0, (bmpData.Stride * y) + (4 * x) + 3) <> 0 Then Return True Exit For End If Next Next Finally bmp.UnlockBits(bmpData) End Try

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• How can I access and modify objects inside frames with AS3 in a permanent way?

  - by curro

  I have a MovieClip symbol created with flash in a fla file library. There is a textfield in frame one of this movieclip's timeline . There is another frame in the movieclip timeline. There is a custon class definition for this symbol. It is a flipping card in a memory game. I access the textfield by going to frame 2 (gotoAndStop(2)) and setting the textfield's text property ( this.field.text = "hello" ). However if I go to frame 1 and then return to frame 2, the text becomes the original one in the library's symbol. I have to modify the text propery again in a showFace method I've written. Besides, I cannot pass parameters in the constructor because it is a symbol in the library and that would give errors. I find this behaviour of flash extremely weird. Is there a way I can set properties inside frames permanently? Thank you

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• Treat a void function as a value

  - by Brendan Long

  I'm writing some terrible, terrible code, and I need a way to put a free() in the middle of a statement. The actual code is: int main(){ return printf("%s", isPalindrome(fgets(malloc(1000), 1000, stdin))?"Yes!\n":"No!\n") >= 0; // leak 1000 bytes of memory } I was using alloca(), but I can't be sure that will actually work on my target computer. My problem is that free returns void, so my code has this error message: error: void value not ignored as it ought to be The obvious idea I had was: int myfree(char *p){ free(p); return 0; } Which is nice in that it makes the code even more unreadable, but I'd prefer not to add another function. I also briefly tried treating free() as a function pointer, but I don't know if that would work, and I don't know enough about C to do it properly. Note: I know this is a terrible idea. Don't try this at home kids.

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• How might one develop a program like FRAPS?

  - by blood

  I would like to make a program to capture video. What is the best way to capture video? I know C++ and I'm learning assembly. I found in my assembly book that I can get data from the video card. Would that be the best way? I know FRAPS hooks into programs, but I would like my program to take video of the entire screen. I would like something something fast, with low memory usage if possible. A requirement is that the program must be usable on other computers, despite dissimilar hardware.

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• Can't inherit from auto_str without problems

  - by fret

  What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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• Can't inherit from auto_ptr without problems

  - by fret

  What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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• Creating additional Window by a thread - C

  - by Jamie Keeling

  Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a separate thread so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate thread 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I hope it makes sense. Thanks!

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• [FreeBSD kernel ]How to maintain a linked list on kernel lever?

  - by Andy Leman

  The situation is: I will implement sets of new system calls. Each of them need to access (read or write) a linked list. So, that means I will have several C programs. So, how can I maintain a linked list in memory and let several programs access it? Or,this is wrong....I should save it as a file? (but I hardly think this is a good idea).. A lot of confused questions here...Need help. Thank you indeed!

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