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• Faking a Single Address Space

  - by dsimcha

  I have a large scientific computing task that parallelizes very well with SMP, but at too fine grained a level to be easily parallelized via explicit message passing. I'd like to parallelize it across address spaces and physical machines. Is it feasible to create a scheduler that would parallelize already multithreaded code across multiple physical computers under the following conditions: The code is already multithreaded and can scale pretty well on SMP configurations. The fact that not all of the threads are running in the same address space or on the same physical machine must be transparent to the program, even if this comes at a significant performance penalty in some use cases. You may assume that all of the physical machines involved are running operating systems and CPU architectures that are binary compatible. Things like locks and atomic operations may be slow (having network latency to deal with and all) but must "just work".

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• JavaScript pack("d") - binary strings

  - by Tim Whitlock

  I'm trying to replicate the Perl and PHP style pack and unpack functions in JavaScript. Unsigned integers were easy enough, so my pack('n') and pack('N') are ok. But my lack of a computer science background is a hurdle now and I don't know where to start with pack('d') for packing JavaScript's standard floating point. Is there a JavaScript library for this out there? If not, is there a good resource where I can learn how to do this? I am fine with bitwise and binary level operations in JS, I just don't know where to start with the logic. Thanks.

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• Is there a Windows utility that will let me do multiple programmatic find/replaces on text that I cu

  - by billmaya

  I've inherited some C# code that contains about a thousand lines of source that I need to modify, transforming it from this: newDataRow["to_dir"] = comboBox108.Text; To this: assetAttributes.Add("to_dir", comboBox108.Text); The lines occur in various places throughout the application in groups of 40 or 50. Modifying each line by hand in Visual Studio 2008 can be done but it's labor intensive and prone to errors. Is there a Windows utility out there that will let me cut and paste groups of code into it and then run some sort of reg-ex expression to transform the individual lines one-by-one? I'd also be willing to use some sort of VS 2008 add-in that performed the same set of reg-ex operations against a selection of code. Thanks in advance.

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• PHP: Simulate multiple MySQL connections to same database

  - by Varun

  An insert query is constantly getting logged in my MySQL slow query log. I want to see how much time the INSERT query is taking with 100 simultaneous insert operations(to the same table). So I need to simulate the follwoing. 500 different simultaneous connections from PHP to the same database on a mysql server, all of which are inserting a row(simultaneously) to the same table. DO I need to use any load testing tool? Or Can I simply write a PHP script to do this? Any thoughts?

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• Simple integer encryption

  - by tloflin

  Is there a simple algorithm to encrypt integers? That is, a function E(i,k) that accepts an n-bit integer and a key (of any type) and produces another, unrelated n-bit integer that, when fed into a second function D(i,k) (along with the key) produces the original integer? Obviously there are some simple reversible operations you can perform, but they all seem to produce clearly related outputs (e.g. consecutive inputs lead to consecutive outputs). Also, of course, there are cryptographically strong standard algorithms, but they don't produce small enough outputs (e.g. 32-bit). I know any 32-bit cryptography can be brute-forced, but I'm not looking for something cryptographically strong, just something that looks random. Theoretically speaking it should be possible; after all, I could just create a dictionary by randomly pairing every integer. But I was hoping for something a little less memory-intensive.

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• Identify a non-computer network device?

  - by Avilan

  I'm current working on a program that scans my network and discoveres computers and devices on the network. I use various operations to find data on the devices I discover, but want to distinguish the network devices from computers. And I'm wondering if anyone knows how I could do this? I looked a bit at SNMP, and tried connecting to my network printer, router and modem. But I seem to only be able to connect to the printer, neither the router or modem responds. Is there another way to identify what kind of a device an IP address belongs to?

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• A window that behaves both modally and non-modally

  - by Chris

  I want to create a WPF window that behaves as a modal dialogue box while at the same time facilitating selected operations on certain other windows of the same application. An example of this behaviour can be seen in Adobe Photoshop, which offers several dialogues that allow the user to use an eyedropper tool to make selections from an image while disabling virtually all other application features. I'm guessing that the way forward is to create a non-modal, always-on-top dialogue and programmatically disable those application features that are not applicable to the dialogue. Is there an easy way to achieve this in WPF? Or perhaps there's a design pattern I could adopt.

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• Iterate attributes and IBOutlets of a UIViewController

  - by Espuz

  I've a generic UIViewController on my app. All the UIViewController on the app inherits from this generic one. I'm trying to automate the deallocation and releasing of attributes and IBOutlets as properties. I'm doing the first (attributes) on dealloc method and the second (IBOutlets as properties) on viewDidUnload. - (void) dealloc { [_att1 release]; _att1 = nil; [_att2 release]; _att2 = nil; // ... } - (void) viewDidUnload { self.att1 = nil; // att1 is an IBOutlet self.att2 = nil; // att2 is an IBOutlet // ... } Is there any way to iterate all my attributes and IBOutlets to simplify this operations? I want to avoid do it for each outlet and attribute and delegate it to the generic UIViewController. Thanks.

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• Do I need to syncronize thread access to an int

  - by Martin Harris

  I've just written a method that is called by multiple threads simultaneously and I need to keep track of when all the threads have completed, the code uses this pattern: private void RunReport() { _reportsRunning++; try { //code to run the report } finally { _reportsRunning--; } } This is the only place within the code that _reportsRunning's value is changed, and the method takes about a second to run. Occasionally when I have more than six or so threads running reports together the final result for _reportsRunning can get down to -1, if I wrap the calls to _runningReports++ and _runningReports-- in a lock then the behaviour appears to be correct and consistant. So, to the question: When I was learning multithreading in C++ I was taught that you didn't need to synchronize calls to increment and decrement operations because they were always one assembly instruction and therefore it was impossible for the thread to be switched out mid-call. Was I taught correctly, and if so how come that doesn't hold true for C#?

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• Optimality of Binary Search

  - by templatetypedef

  Hello all- This may be a silly question, but does anyone know of a proof that binary search is asymptotically optimal? That is, if we are given a sorted list of elements where the only permitted operation on those objects is a comparison, how do you prove that the search can't be done in o(lg n)? (That's little-o of lg n, by the way.) Note that I'm restricting this to elements where the only operation permitted operation is a comparison, since there are well-known algorithms that can beat O(lg n) on expectation if you're allowed to do more complex operations on the data (see, for example, interpolation search). Thanks so much! This has really been bugging me since it seems like it should be simple but has managed to resist all my best efforts. :-)

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• C++ / Java: Toggle boolean statement?

  - by Martijn Courteaux

  Hi, Is there a short way to toggle a boolean? With integers we can do operations like this: int i = 4; i *= 4; // equals 16 /* Which is equivalent to */ i = i * 4; So is there also something for booleans (like the *= operator for ints)? In C++: bool booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something? In Java: boolean booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something?

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• Reading files with Java

  - by sikas

  I would like to know how can I read a file byte by byte then perform some operation every n bytes. for example: Say I have a file of size = 50 bytes, I want to divide it into blocks each of n bytes. Then each block is sent to a function for some operations to be done on those bytes. The blocks are to be created during the read process and sent to the function when the block reaches n bytes so that I don`t use much memory for storing all blocks. I want the output of the function to be written/appended on a new file. This is what I've reached to read, yet I don't know it it is right: fc = new JFileChooser(); File f = fc.getSelectedFile(); FileInputStream in = new FileInputStream(f); byte[] b = new byte[16]; in.read(b); I haven't done anything yet for the write process.

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• Construction an logical expression which will count bits in a byte.

  - by danatel

  When interviewing new candidates, we usually ask them to write a piece of C code to count the number of bits with value 1 in a given byte variable (e.g. the byte 3 has two 1-bits). I know all the common answers, such as right shifting eight times, or indexing constant table of 256 precomputed results. But, is there a smarter way without using the precomputed table? What is the shortest combination of byte operations (AND, OR, XOR, +, -, binary negation, left and right shift) which computes the number of bites?

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• IDL-like parser that turns a document definition into powerful classes?

  - by paniq

  I am looking for an IDL-like (or whatever) translator which turns a DOM- or JSON-like document definition into classes which are accessible from both C++ and Python, within the same application expose document properties as ints, floats, strings, binary blobs and compounds: array, string dict (both nestable) (basically the JSON type feature set) allow changes to be tracked to refresh views of an editing UI provide a change history to enable undo/redo operations can be serialized to and from JSON (can also be some kind of binary format) allow to keep large data chunks on disk, with parts only loaded on demand provide non-blocking thread-safe read/write access to exchange data with realtime threads allow multiple editors in different processes (or even on different machines) to view and modify the document The thing that comes closest so far is the Blender 2.5 DNA/RNA system, but it's not available as a separate library, and badly documented. I'm most of all trying to make sure that such a lib does not exist yet, so I know my time is not wasted when I start to design and write such a thing. It's supposed to provide a great foundation to write editing UI components.

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• Reranging a uitableview

  - by Nicolay

  Hallo @ All I ran into the same problem as desciped in http://stackoverflow.com/questions/1884491/crashing-while-trying-to-move-uitableview-rows! All I want to do is on specific reranging operations insert a new cell or delet the selected one! Sometimes I get a * Assertion failure in -[_UITableViewUpdateSupport _setupAnimationForReorderingRow], /SourceCache/UIKit/UIKit-963.10/UITableViewSupport.m:295 Attempt to create two animations for cell exception and when I want to reload my data by calling [self.tableView reloadData] I get a * Terminating app due to uncaught exception 'NSRangeException', reason: '* -[NSCFArray objectAtIndex:]: index (0) beyond bounds (0)' This is quiet anoying! Is there anybody out there who knows how to handle this problem? Please help me!

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• Calling asynchronous methods from wcf service

  - by hima

  In my asp.net application, I am using wcf service to get all the business logic. I am using that service reference in my application to work with that. Now adding that service reference is giving another option Update service reference is giving Generate asynchronous operations. If I check the option and add the service will it generate asynchronous methods for my existing service. If so how do I use the metohd. Let me know the way for that. Thanks, Hima.

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• g++: Use ZIP files as input

  - by Notinlist

  We have the Boost library in our side. It consists of huge amount of files which are not changing ever and only a tiny portion of it is used. We swap the whole boost directory if we are changing versions. Currently we have the Boost sources in our SVN, file by file which makes the checkout operations very slow, especially on Windows. It would be nice if there were a notation / plugin to address C++ files inside ZIP files, something like: // @ZIPFS ASSIGN 'boost' 'boost.zip/boost' #include <boost/smart_ptr/shared_ptr.hpp> Are there any support for compiler hooks in g++? Are there any effort regarding ZIP support? Other ideas?

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• python parallel computing: split keyspace to give each node a range to work on

  - by MatToufoutu

  My question is rather complicated for me to explain, as i'm not really good at maths, but i'll try to be as clear as possible. I'm trying to code a cluster in python, which will generate words given a charset (i.e. with lowercase: aaaa, aaab, aaac, ..., zzzz) and make various operations on them. I'm searching how to calculate, given the charset and the number of nodes, what range each node should work on (i.e.: node1: aaaa-azzz, node2: baaa-czzz, node3: daaa-ezzz, ...). Is it possible to make an algorithm that could compute this, and if it is, how could i implement this in python? I really don't know how to do that, so any help would be much appreciated

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• How to detect if breaking an edge will make a graph disjoint?

  - by the_graph_guy

  I have a graph that starts off with a single, root node. Nodes are added one by one to the graph. At node creation time, they have to be linked either to the root node, or to another node, by a single edge. Edges can also be created and deleted (one by one, between any two nodes). Nodes can be deleted one at a time. Node and edge creation, deletion operations can happen in any arbitrary order. OK, so here's my question: When an edge is deleted, is it possible do determine, in constant time (i.e. with an O(1) algorithm), if doing this will divide the graph into two disjoint subgraphs? If it will, then which side of the edge will the root node belong? I'm willing to maintain, within reasonable limits, any additional data structure that can facilitate the derivation of this information. Maybe it is not possible to do it in O(1), if so any pointers to literature will be appreciated.

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• How do I determine darker or lighter color variant of a given color?

  - by Nidonocu

  Given a source color of any hue by the system or user, I'd like a simple algorithm I can use to work out a lighter or darker variants of the selected color. Similar to effects used on Windows Live Messenger for styling the user interface. Language is C# with .net 3.5. Responding to comment: Color format is (Alpha)RGB. With values as bytes or floats. Marking answer: For the context of my use (a few simple UI effects), the answer I'm marking as accepted is actually the most simple for this context. However, I've given up votes to the more complex and accurate answers too. Anyone doing more advanced color operations and finding this thread in future should definitely check those out. Thanks SO. :)

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• Cross-referencing UML models in VS 2010

  - by cheaster

  I am just starting to explore/use the UML modeling support in Visual Studio 2010 Umltimate. I have created two model projects within a single solution. Let's call them Model A and Model B. I have some data types (classes) defined in Model B. I want to use them as return types for operations in Model A. However, I cannot figure out how to make the types defined in Model B show up in Model A when attempting to set return type on an operation. Any help/suggestions would be greatly appreciated! Thanks!

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• Combining XSLT transforms

  - by Flynn1179

  Is there a way to combine two XSLT documents into a single XSLT document that does the same as transforming using the original two in sequence? i.e. Combining XSLTA and XSLTB into XSLTC such that XSLTB( XSLTA( xml )) == XSLTC( xml )? There's three reasons I'd like to be able to do this: Simplifies development; some operations need sequential transforms, and although I can generate a combined one by hand, it's a lot more difficult to maintain that two much simpler, separate transforms. Speed; one transform is in most cases hopefully faster than two. I'm currently working on a program that literally just transforms a data file in XML into an XHTML page capable of editing it using one XSLT, and a second XSLT that transforms the XHTML page back into the data file when it's saved. One test I hope to be able to do is to combine the two, and easily confirm that the 'combined' XSLT should leave the data unchanged.

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• Should I denormalize a has_many has_many?

  - by Cameron

  I have this: class User < ActiveRecord::Base has_many :serials has_many :sites, :through => :series end class Serial < ActiveRecord::Base belongs_to :user belongs_to :site has_many :episodes end class Site < ActiveRecord::Base has_many :serials has_many :users, :through => :serials end class Episode < ActiveRecord::Base belongs_to :serial end I would like to do some operations on User.serials.episodes but I know this would mean all sorts of clever tricks. I could in theory just put all the episode data into serial (denormalize) and then group_by Site when needed. If I have a lot of episodes that I need to query on would this be a bad idea? thanks

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• Are spinlocks a good choice for a memory allocator?

  - by dsimcha

  I've suggested to the maintainers of the D programming language runtime a few times that the memory allocator/garbage collector should use spinlocks instead of regular OS critical sections. This hasn't really caught on. Here are the reasons I think spinlocks would be better: At least in synthetic benchmarks that I did, it's several times faster than OS critical sections when there's contention for the memory allocator/GC lock. Edit: Empirically, using spinlocks didn't even have measurable overhead in a single-core environment, probably because locks need to be held for such a short period of time in a memory allocator. Memory allocations and similar operations usually take a small fraction of a timeslice, and even a small fraction of the time a context switch takes, making it silly to context switch in the case of contention. A garbage collection in the implementation in question stops the world anyhow. There won't be any spinning during a collection. Are there any good reasons not to use spinlocks in a memory allocator/garbage collector implementation?

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• C# eval equivalent?

  - by Adhip Gupta

  I can do an eval("something()"); to execute the code dynamically in JavaScript. Is there a way for me to do the same thing in C#? What I am exactly trying to do is that I have an integer variable (say i) and I have multiple properties by the names: "Property1","Property2","Property3" etc. Now, I want to perform some operations on the " Propertyi " property depending on the value of i. This is really simple with Javascript. Is there any way to do this with C#? Edit: Oh, and I am using C# 2.0

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