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• How to write a decent process filter?

  - by konr

  Hi there, I'm building a program that communicates with Emacs, and one of the challenges I'm facing is writing Emacs's process filter function. Its input string is a series of s-expressions to be evaluated. Here is a sample: (gimme-append-to-buffer "25 - William Christie dir, Les Arts Florissants - Scene 2. Prelude - Les Arts Florissants\n") (gimme-append-to-buffer "26 - William Christie dir, Les Arts Florissants - Cybele: 'Je Veux Joindre' - Les Arts Florissants\n") (gimme-append-to-buffer "27 - William Christie dir, Les Arts Florissants - Scene 3. Cybele: 'Tu T'Etonnes, Melisse' - Les Arts Florissants\n") (gimme-append-to-buffer "28 - William Christie dir, Les Arts Florissants - Cybele: 'Que Les Plus Doux Zephyrs'. Scene 4. - Les Arts Florissants\n") (gimme-append-to-buffer "29 - William Christie dir, Les Arts Florissants - Entree Des Nations - Les Arts Florissants\n") (gimme-append-to-buffer "30 - William Christie dir, Les Arts Florissants - Entree Des Zephyrs - Les Arts Florissants\n") (gimme-append-to-buffer "31 - William Christie dir, Les Arts Florissants - Choeur Des Nations' 'Que Devant Vous' - Les Arts Florissants\n") (gimme-append-to-buffer "32 - William Christie dir, Les Arts Florissants - Atys: 'Indigne Que Je Suis' - Les Arts Florissants\n") (gimme-append-to-buffer "33 - William Christie dir, Les Arts Florissants - Reprise Du Choeur Des Nations : 'Que Devant Nous' - Les Arts Florissants\n") (gimme-append-to-buffer "34 - William Christie dir, Les Arts Flor*emphasized text*issants - Reprise De L'Air Des Zephyrs - Les Arts Florissants\n") The first problem that I've faced is that the string is somehow not fully formed when the function is so called, so writing something like (mapcar 'eval (format "(%s)" input-string)) won't work. To deal with this first problem, I was using a loop. The full function I wrote is: (defun eval-all-sexps (s) (loop for x = (ignore-errors (read-from-string s)) then (ignore-errors (read-from-string (substring s position))) while x summing (or (cdr x) 0) into position doing (eval (car x)))) Now the second problem that showed up is that the function is called twice with a somewhat large input, first with valid but partial content, then with what looks like pieces of the remaining data. To solve this problem, I'm considering using a junk variable to hold up what remains from a loop and then concatenating it to the input of the next call, but I was wondering if you guys have any other suggestions on how to deal with such a problem more elegantly. Thanks!

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• C++ help with getline function with ifstream

  - by John

  So I am writing a program that deals with reading in and writing out to a file. I use the getline() function because some of the lines in the text file may contain multiple elements. I've never had a problem with getline until now. Here's what I got. The text file looks like this: John Smith // Client name 1234 Hollow Lane, Chicago, IL // Address 123-45-6789 // SSN Walmart // Employer 58000 // Income 2 // Number of accounts the client has 1111 // Account Number 2222 // Account Number ifstream inFile("ClientInfo.txt"); if(inFile.fail()) { cout << "Problem opening file."; } else { string name, address, ssn, employer; double income; int numOfAccount; getline(inFile, name); getline(inFile, address); // I'll stop here because I know this is where it fails. When I debugged this code, I found that name == "John", instead of name == "John Smith", and Address == "Smith" and so on. Am I doing something wrong. Any help would be much appreciated.

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• What file format can represent an uncompressed raster image at 48 or 64 bits per pixel?

  - by finnw

  I am creating screenshots under Windows and using the LockBits function from GDI+ to extract the pixel data, which will then be written to a file. To maximise performance I am also: Using the same PixelFormat as the source bitmap, to avoid format conversion Using the ImageLockModeUserInputBuf flag to extract the pixel data into a pre-allocated buffer This pre-allocated buffer (pointed to by BitmapData::Scan0) is part of a memory-mapped file (to avoid copying the pixel data again.) I will also be writing the code that reads the file, so I can use (or invent) any format I wish. However I would prefer to use a well-known format that existing programs (ideally web browsers) are able to read, because that means I can visually confirm that the images are correct before writing the code for the other program (that reads the image.) I have implemented this successfully for the PixelFormat32bppRGB format, which matches the format of a 32bpp BMP file, so if I extract the pixel data directly into the memory-mapped BMP file and prefix it with a BMP header I get a valid BMP image file that can be opened in Paint and most browsers. Unfortunately one of the machines I am testing on returns pixels in PixelFormat64bppPARGB format (presumably this is influenced by the video adapter driver) and there is no corresponding BMP pixel format for this. Converting to a 16, 24 or 32bpp BMP format slows the program down considerably (as well as being lossy) so I am looking for a file format that can use this pixel format without conversion, so I can extract directly into the memory-mapped file as I have done with the 32bpp format. What raster image file formats support 48bpp and/or 64bpp?

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• How can I write classes that don't rely on "global" variables?

  - by Joel

  When I took my first programming course in university, we were taught that global variables were evil & should be avoided at all cost (since you can quickly develop confusing and unmaintainable code). The following year, we were taught object oriented programming, and how to create modular code using classes. I find that whenever I work with OOP, I use my classes' private variables as global variables, i.e., they can be (and are) read and modified by any function within the class. This isn't really sitting right with me, as it seems to introduce the same problems global variables had in languages like C. So I guess my question is, how do I stop writing classes with "global" variables? Would it make more sense to pretend I'm writing in a functional language? By this I mean having all functions take parameters & return values instead of directly modifying class variables. If I need to set any fields, I can just take the output of the function and assign it instead of having the function do it directly. This seems like it might make more maintainable code, at least for larger classes. What's common practice? Thanks!

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• How can I effectively test against the Windows API?

  - by Billy ONeal

  I'm still having issues justifying TDD to myself. As I have mentioned in other questions, 90% of the code I write does absolutely nothing but Call some Windows API functions and Print out the data returned from said functions. The time spent coming up with the fake data that the code needs to process under TDD is incredible -- I literally spend 5 times as much time coming up with the example data as I would spend just writing application code. Part of this problem is that often I'm programming against APIs with which I have little experience, which forces me to write small applications that show me how the real API behaves so that I can write effective fakes/mocks on top of that API. Writing implementation first is the opposite of TDD, but in this case it is unavoidable: I do not know how the real API behaves, so how on earth am I going to be able to create a fake implementation of the API without playing with it? I have read several books on the subject, including Kent Beck's Test Driven Development, By Example, and Michael Feathers' Working Effectively with Legacy Code, which seem to be gospel for TDD fanatics. Feathers' book comes close in the way it describes breaking out dependencies, but even then, the examples provided have one thing in common: The program under test obtains input from other parts of the program under test. My programs do not follow that pattern. Instead, the only input to the program itself is the system upon which it runs. How can one effectively employ TDD on such a project?

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• BDD on Rails - Is the community more behind Shoulda or RSpec?

  - by Wayne M

  For a new application I want to start dabbling in BDD and I'm trying to decide between using RSpec or Thoughtbot's Shoulda. I like the macros that Shoulda uses, and the fact that it doesn't seem to reinvent the way Ruby/Rails does testing, but simply provides an add-on. On the other hand, the macros seem like a bit too much "magic" instead of being explicit about what you're testing (however I know from dabbling that it's annoying to write a dozen "should be invalid without xxx" two-liners on a model). To be honest I find writing specifications/tests for models to be trivially and almost boringly easy, but I find writing them for controllers to be insanely difficult because I'm never sure exactly what I should be testing or how to write it. I'm iffy on the subject of mocking and stubbing since I think they give you false assumptions (since you can just tell it to think it has whatever data you need or to pretend that Method X was called) and I know that RSpec makes heavy use of both of them. I like the documentation that RSPec produces but I'm creating an application for sale, not to give to a client so the pretty documentation isn't that useful. I like Cucumber but it seems like overkill (and yes I know it can be used with Shoulda). At this point is the Rails community in favor of RSpec or Shoulda?

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• CSS semantics; selecting elements directly or via order

  - by Joshua Cody

  Perhaps this question has been asked elsewhere, but I'm unable to find it. With HTML5 and CSS3 modules inching closer, I'm getting interested in a discussion about the way we write CSS. Something like this where selection is done via element order and type is particularly fascinating. The big advantage to this method seems to be complete modularization of HTML and CSS to make tweaks and redesigns simpler. At the same time, semantic IDs and classes seem advantageous for sundry reasons. Particularly, direct linking, JS targeting, and shorter CSS selectors. Also, it seems selector length might be an issue. For instance, I just wrote the following, which would be admittedly easier using some semantic HTML5 elements: body>div:nth-child(2)>div:nth-child(2)>ul:nth-child(2)>li:last-child So what say you, Stack Overflow? Is the future of CSS writing focused on element order and type? Or are IDs and classes and the current ways here to stay? (I'm well aware the IDs and classes have their place, although I am interested to hear more ways you think they'll continue to be necessary. The discussion I'm interested in is bigger-picture and the ways writing CSS is changing.)

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• SQLite on iPhone - Techniques for tracking down multithreading-related bugs

  - by Jasarien

  Hey guys, I'm working with an Objective-C wrapper around SQLite that I didn't write, and documentation is sparse... It's not FMDB. The people writing this wrapper weren't aware of FMDB when writing this code. It seems that the code is suffering from a bug where database connections are being accessed from multiple threads -- which according to the SQLite documentation won't work if the if SQLite is compiled with SQLITE_THREADSAFE 2. I have tested the libsqlite3.dylib provided as part of the iPhone SDK and seen that it is compiled in this manner, using the sqlite_threadsafe() routine. Using the provided sqlite library, the code regularly hits SQLITE_BUSY and SQLITE_LOCKED return codes when performing routines. To combat this, I added some code to wait a couple of milliseconds and try again, with a maximum retry count of 50. The code didn't contain any retry logic prior to this. Now when a sqlite call returns SQLITE_BUSY or SQLITE_LOCKED, the retry loop is invoked and the retry returns SQLITE_MISUSE. Not good. Grasping at straws, I replaced the provided sqlite library with a version compiled by myself setting SQLITE_THREADSAFE to 1 - which according to the documentation means sqlite is safe to be used in a multithreaded environment, effectively serialising all of the operations. It incurs a performance hit, that which I haven't measured, but it ridded the app of the SQLITE_MISUSE happening and seemed to not need the retry logic as it never hit a busy or locked state. What I would rather do is fix the problem of accessing a single db connection from multiple threads, but I can't for the life of me find where it's occurring. So if anyone has any tips on locating multithreaded bugs I would be extremely appreciative. Thanks in advance.

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• I/O between AIR client using Native process and executable java .jar

  - by aseem behl

  I am using Adobe AIR 2.0 native process API to launch a java executable jar. I/O is handled by writing to the input stream of the java process and reading from the output stream. The application is event based where several events are fired from the server. We catch these events in java code, handle them and write the output to the outputstream using the synchronized static method below. public class ReaderWriter { static Logger logger = Logger.getLogger(ReaderWriter.class); public synchronized static void writeToAir(String output){ try{ byte[] byteArray = output.getBytes(); DataOutputStream dataOutputStream = new DataOutputStream(System.out); dataOutputStream.write(byteArray); dataOutputStream.flush(); } catch (IOException e) { logger.info("Exception while writing the output. " + e); } } } The issue is that some messages are lost between the transfer and not all messages reach the AIR client. If I run the java application from the console I am receiving all the messages. It would be great if somebody could point out what I am missing. Following are some of the listeners used to send the event data to the AIR client. // class used to process Shutdown events from the Session private class SessionShutdownListener implements SessionListener{ public void onEvent(Event e) { Session.Shutdown sd = (Session.Shutdown) e; Session.ShutdownReason sr = sd.getReason(); String eventOutput = "eo;" + "Session Shutdown event ocurred reason=" + sr.strValue() + "\n"; ReaderWriter.writeToAir(eventOutput); } } // class used to process OperationSucceeded events from the Session private class SessionOperationSucceededListener implements SessionListener{ public void onEvent(Event e) { Session.OperationSucceeded os = (Session.OperationSucceeded) e; String eventOutput = "eo;" + "Session OperationSucceeded event ocurred" + "\n"; ReaderWriter.writeToAir(eventOutput); } }

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• Can pdflatex (or any tex package) automatically rescale included images which have been reduced in s

  - by drfrogsplat

  I'm writing my thesis in LaTeX, generating it with pdflatex. I have a large number of figures, many of which are bitmaps (as opposed to SVG) in PNG/JPEG format. I've generally created them to be fairly high resolution (say 1600x1200-ish) to ensure that whatever size they end up in the document, they'll be at least 300dpi when printed. As I'm writing/laying out the document, I'm including graphics (using \includegraphics from the graphicx package) and setting widths/heights as appropriate (e.g. subfigures are quite small). I don't need the images to be any more than about 300 dpi at best, so where I have shrunk a 1600x1200 image down to say 5cm, the image is now at 800 dpi. So despite including some very small (on the page) images, the PDF is becoming quite large. Is there a way to tell pdflatex or graphicx (or something else involved?) to convert all images to a maximum of 300 dpi, based on the dimensions I'm setting with say \includegraphics[width=2in]{filename}? i.e. so it scales the image to a max of 600x600 pixels as it includes it in the PDF (leaving the original file untouched). I know I can resize the original images with various command line applications, and include the pre-resized versions, but given the images vary in size considerably, it wouldn't be as simple as making sure they're all 300dpi for a constant printed size. It'd also be nice to be able to easily create different versions of PDFs (web vs final print) without resizing images manually, so that the 'web' PDF capped images at say 72-100 dpi while the final print one could cap at 600 (if at all).

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• How do I lock the workstation from a windows service?

  - by Brad Mathews

  Hello, I need to lock the workstation from a windows service written in VB.Net. I am writing the app on Windows 7 but it needs to work under Vista and XP as well. User32 API LockWorkStation does not work as it requires an interactive desktop and I get return value of 0. I tried calling %windir%\System32\rundll32.exe user32.dll,LockWorkStation from both a Process and from Shell, but still nothing happens. Setting the service to interact with the desktop is a no-go as I am running the service under the admin account so it can do some other stuff that requires admin rights - like disabling the network, and you can only select the interact with desktop option if running under Local System Account. That would be secondary question - how to run another app with admin rights from a service running under Local System Account without bugging the user. I am writing an app to control my kids computer/internet access (which I plan to open source when done) so I need everything to happen as stealthily as possible. I have a UI that handles settings and status notifications in the taskbar, but that is easy to kill and thus defeat the locking. I could make another hidden Windows Forms app to handle the locking, but that just seems a rather inelegant solution. Better ideas anyone? Thanks! Brad

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• Map element position in data file to class property

  - by Augusto

  I need to read/write files, following a format provided by a third party specification. The specification itself is pretty simple: it says the position and the size of the data that will be saved in the file. For example: Position Size Description -------------------------------------------------- 0001 10 Device serial number 0011 02 Hour 0013 02 Minute 0015 02 Second 0017 02 Day 0019 02 Month 0021 02 Year The list is very long, it has about 400 elements. But lots of them can be combined. For example, hour, minute, second, day, month and year can be combined in a single DateTime object. I've splitted the elements into about 4 categories, and created separeted classes for holding the data. So, instead of a big structure representing the data, I have some smaller classes. I've also created different classes for reading and writing the data. The problem is: how to map the positions in the file to the objects properties, so that I don't need to repeat the values in the reading/writing class? I could use some custom attributes and retrieve them via reflection. But since the code will be running on devices with small memory and processor, it would be nice to find another way. My current read code looks like this: public void Read() { DataFile dataFile = new DataFile(); // the arguments are: position, size dataFile.SerialNumber = ReadLong(1, 10); //... } Any ideas on this one? Thanks!

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• Rails model relations depending on count of nested relations

  - by Lowgain

  I am putting together a messaging system for a rails app I am working on. I am building it in a similar fashion to facebook's system, so messages are grouped into threads, etc. My related models are: MsgThread - main container of a thread Message - each message/reply in thread Recipience - ties to user to define which users should subscribe to this thread Read - determines whether or not a user has read a specific message My relationships look like class User < ActiveRecord::Base #stuff... has_many :msg_threads, :foreign_key => 'originator_id' #threads the user has started has_many :recipiences has_many :subscribed_threads, :through => :recipiences, :source => :msg_thread #threads the user is subscribed to end class MsgThread < ActiveRecord::Base has_many :messages has_many :recipiences belongs_to :originator, :class_name => "User", :foreign_key => "originator_id" end class Recipience < ActiveRecord::Base belongs_to :user belongs_to :msg_thread end class Message < ActiveRecord::Base belongs_to :msg_thread belongs_to :author, :class_name => "User", :foreign_key => "author_id" end class Read < ActiveRecord::Base belongs_to :user belongs_to :message end I'd like to create a new selector in the user sort of like: has_many :updated_threads, :through => :recipiencies, :source => :msg_thread, :conditions => {THREAD CONTAINS MESSAGES WHICH ARE UNREAD (have no 'read' models tying a user to a message)} I was thinking of either writing a long condition with multiple joins, or possibly writing giving the model an updated_threads method to return this, but I'd like to see if there is an easier way first. Any ideas? Also, if there is something fundamentally wrong with my structure for this functionality let me know! Thanks!!

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• C# - File Encoding Problem.

  - by user301330

  Hello, I'm have a StringBuilder that is writing content to a file. Towards the end of each file, I'm writing the copyright symbol. Oddly, I have noticed that whenever the copyright symbol is written, it is preceeded by a "Â". My code that generates the content of the file looks like this: using (StringWriter stringWriter = new StringWriter()) { stringWriter = GetFileContent(); string targetPath = ConfigurationManager.AppSettings["TargetPath"]; using (StreamWriter streamWriter = new StreamWriter(targetPath, false)) { StringBuilder sb = new StringBuilder(stringWriter.ToString()); // Attempted fix string content = sb.ToString(); content = content.Replace("Â", ""); streamWriter.Write(content); } } As you can tell, I tried to do a find-and-replace. In the process, I noticed that a "Â" was not in the content itself. This makes me believe there is something occurring in the streamWriter. However, I'm not sure what it could be. Can someone please tell me why a "Â" would be popping up before the "©" symbol and how to fix it? I believe it has something to do with encoding, but I'm not sure Thank you!

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• Zend: Fetching row from session db table after generating session id

  - by Nux

  Hi, I'm trying to update the session table used by Zend_Session_SaveHandler_DbTable directly after authenticating the user and writing the session to the DB. But I can neither update nor fetch the newly inserted row, even though the session id I use to check (Zend_Session::getId()) is valid and the row is indeed inserted into the table. Upon fetching all session ids (on the same request) the one I newly inserted is missing from the results. It does appear in the results if I fetch it with something else. I've checked whether it is a problem with transactions and that does not seem to be the problem - there is no active transaction when I'm fetching the results. I've also tried fetching a few seconds after writing using sleep(), which doesn't help. $auth->getStorage()->write($ident); //sleep(1) $update = $this->db->update('session', array('uid' => $ident->user_id), 'id='.$this->db->quote(Zend_Session::getId())); $qload = 'SELECT id FROM session'; $load = $this->db->fetchAll($qload); echo $qload; print_r($load); $update fails. $load doesn't contain the row that was written with $auth-getStorage()-write($identity). $qload does contain the correct query - copying it to somewhere else leads to the expected result, that is the inserted row is included in the results. Database used is MySQL - InnoDB. If someone knows how to directly fix this (i.e. on the same request, not doing something like updating after redirecting to another page) without modifying Zend_Session_SaveHandler_DbTable: Thank you very much!

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• Base class deleted before subclass during python __del__ processing

  - by Oddthinking

  Context I am aware that if I ask a question about Python destructors, the standard argument will be to use contexts instead. Let me start by explaining why I am not doing that. I am writing a subclass to logging.Handler. When an instance is closed, it posts a sentinel value to a Queue.Queue. If it doesn't, a second thread will be left running forever, waiting for Queue.Queue.get() to complete. I am writing this with other developers in mind, so I don't want a failure to call close() on a handler object to cause the program to hang. Therefore, I am adding a check in __del__() to ensure the object was closed properly. I understand circular references may cause it to fail in some circumstances. There's not a lot I can do about that. Problem Here is some simple example code: explicit_delete = True class Base: def __del__(self): print "Base class cleaning up." class Sub(Base): def __del__(self): print "Sub-class cleaning up." Base.__del__(self) x = Sub() if explicit_delete: del x print "End of thread" When I run this I get, as expected: Sub-class cleaning up. Base class cleaning up. End of thread If I set explicit_delete to False in the first line, I get: End of thread Sub-class cleaning up. Exception AttributeError: "'NoneType' object has no attribute '__del__'" in <bound method Sub.__del__ of <__main__.Sub instance at 0x00F0B698>> ignored It seems the definition of Base is removed before the x._del_() is called. The Python Documentation on _del_() warns that the subclass needs to call the base-class to get a clean deletion, but here that appears to be impossible. Can you see where I made a bad step?

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• How do I supply extra info to IApplicationSettingsProvider class?

  - by joebeazelman

  Perhaps this question has been asked before in a different way, but I haven’t been able to find it. I have one or more plugin adapter assemblies in my application all having the type IPlugin, for instance. Each adapter has its own settings structures stored in a common directory. Whether they are stored in one contiguous file or in separate ones doesn’t matter. Each adapter can have one or more settings associated with it. The settings will have both a name and the Plugin it will be used for. How would I create such a configuration system using the following requirements: I want to use .NETs built in settings system and avoid writing one from scratch The host application will be responsible for locating the plugin settings and passing it to the plugin Each plugin will be responsible for reading and writing its own settings to separate concerns. The host application should call Plugin.Save(thePath) and it does its thing. All settings are user scoped So far, I realize that I would need to write my own SettingsProvider, but the provider seems to work in isolation in that there’s no way to pass it parameters such as the path of the plugin directory and the name of the settings. All of the example code I've seen has the provider getting the data from the runtime environment.

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• Qt Socket blocking functions required to run in QThread where created. Any way past this?

  - by Alexander Kondratskiy

  The title is very cryptic, so here goes! I am writing a client that behaves in a very synchronous manner. Due to the design of the protocol and the server, everything has to happen sequentially (send request, wait for reply, service reply etc.), so I am using blocking sockets. Here is where Qt comes in. In my application I have a GUI thread, a command processing thread and a scripting engine thread. I create the QTcpSocket in the command processing thread, as part of my Client class. The Client class has various methods that boil down to writing to the socket, reading back a specific number of bytes, and returning a result. The problem comes when I try to directly call Client methods from the scripting engine thread. The Qt sockets randomly time out and when using a debug build of Qt, I get these warnings: QSocketNotifier: socket notifiers cannot be enabled from another thread QSocketNotifier: socket notifiers cannot be disabled from another thread Anytime I call these methods from the command processing thread (where Client was created), I do not get these problems. To simply phrase the situation: Calling blocking functions of QAbstractSocket, like waitForReadyRead(), from a thread other than the one where the socket was created (dynamically allocated), causes random behaviour and debug asserts/warnings. Anyone else experienced this? Ways around it? Thanks in advance.

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• Linear feedback shift register?

  - by Mattia Gobbi

  Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. So I wanted to write some small code for a program that worked like a LFSR. To be more precise, that somehow showed how a LFSR works. Here's the cleanest thing I could come up with after some lenghtier attempts (Python): def lfsr(seed, taps): sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor sr, xor = str(xor) + sr[:-1], 0 print sr if sr == seed: break lfsr('11001001', (8,7,6,1)) #example I named "xor" the output of the XOR function, not very correct. However, this is just meant to show how it circles through its possible states, in fact you noticed the register is represented by a string. Not much logical coherence. This can be easily turned into a nice toy you can watch for hours (at least I could :-) def lfsr(seed, taps): import time sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor print time.sleep(0.75) sr, xor = str(xor) + sr[:-1], 0 print sr print time.sleep(0.75) Then it struck me, what use is this in writing software? I heard it can generate random numbers; is it true? how? So, it would be nice if someone could: explain how to use such a device in software development come up with some code, to support the point above or just like mine to show different ways to do it, in any language Also, as theres not much didactic stuff around about this piece of logic and digital circuitry, it would be nice if this could be a place for noobies (like me) to get a better understanding of this thing, or better, to understand what it is and how it can be useful when writing software. Should have made it a community wiki? That said, if someone feels like golfing... you're welcome.

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• calling template function without <>; type inference

  - by Oops

  Hi, if I have a function template with typename T, where the compiler can set the type by itself, I do not have to write the type explicitely when I call the function like: template < typename T > T min( T v1, T v2 ) { return ( v1 < v2 ) ? v1: v2; } int i1 = 1, i2 = 2; int i3 = min( i1, i2 ); //no explicit <type> but if I have a function template with two different typenames like... template < typename TOut, typename TIn > TOut round( TIn v ) { return (TOut)( v + 0.5 ); } double d = 1.54; int i = round<int>(d); //explicit <int> Is it true that I have to specify at least 1 typename, always? I assume the reason is because C++ can not distinguish functions between different return types, true? but if I use a void function and handover a reference, again I must not explicitely specify the return typename: template < typename TOut, typename TIn > void round( TOut & vret, TIn vin ) { vret = (TOut)(vin + 0.5); } double d = 1.54; int i; round(i, d); //no explicit <int> should the conclusion be to avoid functions with return and more prefer void functions that return via a reference when writing templates? Or is there a possibility to avoid explicitely writing the return type? something like "type inference" for templates... is "type inference" possible in C++0x? I hope I was not too unclear. many thanks in advance Oops

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• Bioperl, equivalent of IO::ScalarArray for array of Seq objects?

  - by Ryan Thompson

  In perl, we have IO::ScalarArray for treating the elements of an array like the lines of a file. In BioPerl, we have Bio::SeqIO, which can produce a filehandle that reads and writes Bio::Seq objects instead of strings representing lines of text. I would like to do a combination of the two: I would like to obtain a handle that reads successive Bio::Seq objects from an array of such objects. Is there any way to do this? Would it be trivial for me to implement a module that does this? My reason for wanting this is that I would like to be able to write a subroutine that accepts either a Bio::SeqIO handle or an array of Bio::Seq objects, and I'd like to avoid writing separate loops based on what kind of input I get. Perhaps the following would be better than writing my own IO module? sub process_sequences { my $input = $_[0]; # read either from array of Bio::Seq or from Bio::SeqIO my $nextseq; if (ref $input eq 'ARRAY') { my $pos = 0 $nextseq = sub { return $input->[$pos++] if $pos < @$input}; } } else { $nextseq = sub { $input->getline(); } } while (my $seq = $nextseq->()) { do_cool_stuff_with($seq) } }

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• Misalignement in the output Bitmap created from a byte array

  - by Daniel

  I am trying to understand why I have troubles creating a Bitmap from a byte array. I post this after a careful scrutiny of the existing posts about Bitmap creation from byte arrays, like the followings: Creating a bitmap from a byte[], Working with Image and Bitmap in c#?, C#: Bitmap Creation using bytes array My code is aimed to execute a filter on a digital image 8bppIndexed writing the pixel value on a byte [] buffer to be converted again (after some processing to manage gray levels) in a 8BppIndexed Bitmap My input image is a trivial image created by means of specific perl code: https://www.box.com/shared/zqt46c4pcvmxhc92i7ct Of course, after executing the filter the output image has lost the first and last rows and the first and last columns, due to the way the filter manage borders, so from the original 256 x 256 image i get a 254 x 254 image. Just to stay focused on the issue I have commented the code responsible for executing the filter so that the operation really performed is an obvious: ComputedPixel = InputImage.GetPixel(myColumn, myRow).R; I know, i should use lock and unlock but I prefer one headache one by one. Anyway this code should be a sort of identity transform, and at last i use: private unsafe void FillOutputImage() { OutputImage = new Bitmap (OutputImageCols, OutputImageRows , PixelFormat .Format8bppIndexed); ColorPalette ncp = OutputImage.Palette; for (int i = 0; i < 256; i++) ncp.Entries[i] = Color .FromArgb(255, i, i, i); OutputImage.Palette = ncp; Rectangle area = new Rectangle(0, 0, OutputImageCols, OutputImageRows); var data = OutputImage.LockBits(area, ImageLockMode.WriteOnly, OutputImage.PixelFormat); Marshal .Copy (byteBuffer, 0, data.Scan0, byteBuffer.Length); OutputImage.UnlockBits(data); } The output image I get is the following: https://www.box.com/shared/p6tubyi6dsf7cyregg9e It is quite clear that I am losing a pixel per row, but i cannot understand why: I have carefully controlled all the parameters: OutputImageCols, OutputImageRows and the byte [] byteBuffer length and content even writing known values as way to test. The code is nearly identical to other code posted in stackOverflow and elsewhere. Someone maybe could help to identify where the problem is? Thanks a lot

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• Is F# a good language for card game AI?

  - by Anthony Brien

  I'm writing a Mahjong Game in C# (the Chinese traditional game, not the solitaire kind). While writing the code for the bot player's AI, I'm wondering if a functional language like F# would be a more suitable language than what I currently use which is C# with a lot of Linq. I don't know much about F# which is why I ask here. To illustrate what I try to solve, here's a quick summary of Mahjong: Mahjong plays a bit like Gin Rummy. You have 13 tiles in your hand, and each turn, you draw a tile and discard another one, trying to improve your hand towards a winning Mahjong hand, which consists or 4 sets and a pair. Sets can be a 3 of a kind (pungs), 4 of a kind (kongs) or a sequence of 3 consecutive tiles (chows). You can also steal another player's discard, if it can complete one of your sets. The code I had to write to detect if the bot can declare 3 consecutive tiles set (chow) is pretty tedious. I have to find all the unique tiles in the hand, and then start checking if there's a sequence of 3 tiles that contain that one in the hand. Detecting if the bot can go Mahjong is even more complicated since it's a combination of detecting if there's 4 sets and a pair in his hand. And that's just a standard Mahjong hand. There's also numerous "special" hands that break those rules but are still a Mahjong hand. For example, "13 unique wonders" consists of 13 specific tiles, "Jade Empire" consists of only tiles colored green, etc. In a perfect world, I'd love to be able to just state the 'rules' of Mahjong, and have the language be able to match a set of 13 tiles against those rules to retrieve which rules it fulfills, for example, checking if it's a Mahjong hand or if it includes a 4 of a kind. Is this something F#'s pattern matching feature can help solve?

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• Is there a website to look up common, already written functions?

  - by pinnacler

  I'm sitting here writing a function that I'm positive has been written before, somewhere on earth. It's just too common to have not been attempted, and I'm wondering why I can't just go to a website and search for a function that I can then copy and paste into my project in 2 seconds, instead of wasting my day reinventing the wheel. Sure there are certain libraries you can use, but where do you find these libraries and when they are absent, is there a site like I'm describing? Possibly a wiki of some type that contains free code that anybody can edit and improve? Edit: I can code things fine, I just don't know HOW to do them. So for example, right now, I'm trying to localize a robot/car/point in space. I KNOW there is a way to do it, just based off of range and distance. Triangulation and Trilateration. How to code that is a different story. A site that could have psuedo code, step by step how to do that would be ridiculously helpful. It would also ensure the optimal solution since everybody can edit it. I'm also writing in Matlab, which I hate because it's quirky, adding to my desire for creating a website like I describe.

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• Solver Foundation Optimization - 1D Bin Packing

  - by Val Nolav

  I want to optimize loading marbles into trucks. I do not know, if I can use Solver Foundation class for that purpose. Before, I start writing code, I wanted to ask it here. 1- Marbles can be in any weight between 1 to 24 Tons. 2 - A truck can hold maximum of 24 Tons. 3- It can be loaded as many marble cubes, as it can take for upto 24 tones, which means there is no Volume limitation. 4- There can be between 200 up to 500 different marbles depending on time. GOAL - The goal is to load marbles in minimum truck shipment. How can I do that without writing a lot of if conditions and for loops? Can I use Microsoft Solver Foundation for that purpose? I read the documentation provided by Microsoft however, I could not find a scenario similar to mine. M1+ M2 + M3 + .... Mn <=24 this is for one truck shipment. Let say there are 200 different Marbles and Marble weights are Float. Thanks

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