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• How to implement square root and exponentiation on arbitrary length numbers?

  - by tomp

  I'm working on new data type for arbitrary length numbers (only non-negative integers) and I got stuck at implementing square root and exponentiation functions (only for natural exponents). Please help. I store the arbitrary length number as a string, so all operations are made char by char. Please don't include advices to use different (existing) library or other way to store the number than string. It's meant to be a programming exercise, not a real-world application, so optimization and performance are not so necessary. If you include code in your answer, I would prefer it to be in either pseudo-code or in C++. The important thing is the algorithm, not the implementation itself. Thanks for the help.

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• Self-Configuring Classes W/ Command Line Args: Pattern or Anti-Pattern?

  - by dsimcha

  I've got a program where a lot of classes have really complicated configuration requirements. I've adopted the pattern of decentralizing the configuration and allowing each class to take and parse the command line/configuration file arguments in its c'tor and do whatever it needs with them. (These are very coarse-grained classes that are only instantiated a few times, so there is absolutely no performance issue here.) This avoids having to do shotgun surgery to plumb new options I add through all the levels they need to be passed through. It also avoids having to specify each configuration option in multiple places (where it's parsed and where it's used). What are some advantages/disadvantages of this style of programming? It seems to reduce separation of concerns in that every class is now doing configuration stuff, and to make programs less self-documenting because what parameters a class takes becomes less explicit. OTOH, it seems to increase encapsulation in that it makes each class more self-contained because no other part of the program needs to know exactly what configuration parameters a class might need.

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• Which is the best API/Library to use when accessing a WebCam in .Net?

  - by Doctor Jones

  Which is the best API to use when accessing a WebCam in .Net? (I know they can be webcam specific, I am willing to buy a new webcam if it means better results). I want to write a desktop application that will take video from a webcam and store it in MPEG4 formats (DivX, Xvid, etc...). I would also like to access bitmap stills from the device so I can do image comparison between frames. I have tried various libraries, and none have really been a great fit (some have performance issues (very inconsistent framerates), some have image quality limitations, some just crash out for seemingly no reason. I want to get high quality video (as high as I can get) and a decent framerate. My webcam is more than up to the job and I was hoping that there would be a nice Managed .Net library around that would help my cause. Are webcam APIs all just incredibly bad?

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• postgres SQL - pg_class question

  - by Sachin Chourasiya

  PostgreSQL stores statistics about tables in the system table called pg_class. The query planner accesses this table for every query. These statistics may only be updated using the analyze command. If the analyze command is not run often, the statistics in this table may not be accurate and the query planner may make poor decisions which can degrade system performance. Another strategy is for the query planner to generate these statistics for each query (including selects, inserts, updates, and deletes). This approach would allow the query planner to have the most up-to-date statistics possible. Why postgres always rely on pg_class instead?

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• Tips for a successful AppStore submission?

  - by Andrew Grant

  In a day or two I'll be ready to submit my iPhone app to the AppStore and I'm curious whether people who have gone through this process have any tips / suggestions for a smooth submission process. Here's things I've covered; No memory leaks Tested performance on an actual device Doesn't crash :) Using correct certificates / profile What I'm a little unsure about are how to configure the "Bundle Display Name" /"Bundle Identifier" and "Bundle Name" in info.plist. I understand the first is the text that's shown on the iPhone itself, but what about the last? Does this have to match Bundle Identifier? Are there any other things I should add to the info.plist? I've noticed that when built for Adhoc distribution my app does not have any author/title information in iTunes.

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• How can I configure different worker pools using celery?

  - by Chris R

  I need to deploy a queued execution service with (generally) the following three classes of worker: A periodic, low-priority job class that takes a long time and can be processed serially; these jobs should only use 0..2 workers in the system at most. A periodic, deadline-sensitive job class that take a short to medium amount of time (say, topping out at 5 minutes) An ad-hoc job class, that is higher priority than #1, but can interleave with #2. Any workers from class #2 that are inactive when this type of job comes in should handle it, without ever starving the pool of workers for #2 All three job classes are the same task, the only difference between them is how they're requested; they'll take the same input and generate the same output, but each one has different performance guarantees. How can I implement this using celery?

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• How do I view how many concurrent long polling requests there are on my server?

  - by Pascal

  My host is Joyent. My host says I have 15 process limit and prstat -J shows those processes but that doesn't tell me how many long polling requests are currently being served. I could record it myself but that would add alot of performance overhead. I need to know when the server is at its long polling limits. I know this limit occurs far before the memory or CPU is used up. From experimentation, I've already verified that the number of long polls open is NOT equivalant to the number of processes running, probably because each process has multiple threads, each serving a request. thanks.

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• BDD-testing using a UI driver (e.g. Selenium for a web-application)

  - by jonathanconway

  Can BDD (Behavior Driven Design) tests be implemented using a UI driver? For example, given a web application, instead of: Writing tests for the back-end, and then more tests in Javascript for the front-end Should I: Write the tests as Selenium macros, which simulate mouse-clicks, etc in the actual browser? The advantages I see in doing it this way are: The tests are written in one language, rather than several They're focussed on the UI, which gets developers thinking outside-in They run in the real execution environment (the browser), which allows us to Test different browsers Test different servers Get insight into real-world performance Thoughts?

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• Is the web hosting location important these days?

  - by kristof

  I was recently looking at some web hosting solutions and some of the providers offered various hosting locations e.g. US or UK based servers. My question is: does it really make a difference from the performance point of view? Lets say that I am expecting most of the traffic coming from continental Europe? Would the fact that the servers are based in UK make bigger difference if the traffic was coming from the UK. Any pros and cons of having a website hosted in the same county as the most of the expected traffic?

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• Element point map for html5 canvas element, need algorithm

  - by Artiom Chilaru

  I'm currently working on a pure html 5 canvas implementation of the "flying tag cloud sphere", which many of you have undoubtedly seen as a flash object in some pages. The tags are drawn fine, and the performance is satisfactory, but there's one thing in the canvas element that's kind of breaking this idea: you can't identify the objects that you've drawn on a canvas, as it's just a simple flat "image".. What I have to do in this case is catch the click event, and try to "guess" which element was clicked. So I have to have some kind of matrix, which stores a link to a tag object for each pixel on the canvas, AND I have to update this matrix on every redraw. Now this sounds incredibly inefficient, and before I even start trying to implement this, I want to ask the community - is there some "well known" algorithm that would help me in this case? Or maybe I'm just missing something, and the answer is right behind the corner? :)

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• How do I calculate a good hash code for a list of strings?

  - by Ian Ringrose

  Background: I have a short list of strings. The number of strings is not always the same, but are nearly always of the order of a “handful” In our database will store these strings in a 2nd normalised table These strings are never changed once they are written to the database. We wish to be able to match on these strings quickly in a query without the performance hit of doing lots of joins. So I am thinking of storing a hash code of all these strings in the main table and including it in our index, so the joins are only processed by the database when the hash code matches. So how do I get a good hashcode? I could: Xor the hash codes of all the string together Xor with multiply the result after each string (say by 31) Cat all the string together then get the hashcode Some other way So what do people think? (If you care we are using .NET and SqlServer)

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• Should I use a hosted version of JQuery? Which one?

  - by ataylor

  Should I use a local copy of jquery, or should I link to a copy provided by Google or Microsoft? I'm primarily concerned about speed. I've heard that just pulling content from other domains can have performance advantages related to how browsers limit connections. In particular, has anyone benchmarked the speed and latency of Google vs. Microsoft vs. local? Also, do I have to agree to any conditions or licenses to link from a third-party?

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• Emulating a transaction-safe SEQUENCE in MySQL

  - by Michael Pliskin

  We're using MySQL with InnoDB storage engine and transactions a lot, and we've run into a problem: we need a nice way to emulate Oracle's SEQUENCEs in MySQL. The requirements are: - concurrency support - transaction safety - max performance (meaning minimizing locks and deadlocks) We don't care if some of the values won't be used, i.e. gaps in sequence are ok. There is an easy way to archieve that by creating a separate InnoDB table with a counter, however this means it will take part in transaction and will introduce locks and waiting. I am thinking to try a MyISAM table with manual locks, any other ideas or best practices?

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• data between pages: $_SESSION vs. $_GET ?

  - by Haroldo

  Ok, firstly this is not about forms this is about consistent layout as a user explores a site. let me explain: If we imagine a (non-ajax) digital camera online store, say someone was on the DSLR section and specified to view the cameras in Gallery mode and order by price. They then click onto the Compact camera's page. It would be in the users interests if the 'views' they selected we're carried over to this new page. Now, i'd say use a session - am i wrong? are there performance issues i should be aware of for a few small session vars ( ie view=1 , orderby=price) ?

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• How can I measure TForm deserialization time in Delphi?

  - by mjustin

  For performance tests I need a way to measure the time needed for a form to load its definition from the DFM. All existing forms inherit a custom form class. To capture the current time, this base class needs overriden methods as "extension points": before the beginning of the deserialization process after the completion of deserialization (can be implemented by overriding the Loaded procedure) the moment just before the execution of the OnFormCreate event Which TObject (or TComponent) methods are best suited? Maybe there are other extension points in the form creation process, please feel free to make suggestions.

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• Multimedia content in REST responce(XML/JSON)

  - by Koushik

  In my thesis I need to test different architectures. A request to a REST web service developed using Apache CXF and Spring MVC with MySQL as back end serving references(a field in database) to images,audio and video files stored in file system. In the response message, what is the best method to send the content to the client(another application using the service which I developed). URI: http://www.filmservices.com/film/{id} A client here is not the end user. Send the encoded hyperlink's(where the content is stored in the file system) to the client, so that the client renders the response and displays it to the browser. Use Base64 to encode the message(image,audio,video) and send it to the client. Main concern is performance.

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• Monitoring .NET ASP.NET Applications

  - by James Hollingworth

  I have a number of applications running on top of ASP.NET I want to monitor. The main things I care about are: Exceptions: We currently some custom code which will email us when an exception occurs. If the application is failing hard it will crash our outlook... I know (and use) elmah which partly solves the problem however it is still just a big table of exceptions with a pretty(ish) UI. I want something that makes sense of all of these exceptions (e.g. groups exceptions, alerts when new ones occur, tells me what the common ones are that I should fix, etc) Logging: We currently log to files which are then accessible via a shared folder which dev's grep & tail. Does anyone know of better ways of presenting this information. In an ideal world I want to associate it with exceptions. Performance: Request times, memory usage, cpu, etc. whatever stats I can get I'm guessing this is probably going to be solved by a number of tools, has anyone got any suggestions?

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• Should we use a CSS frame work ? Are they worth it ?

  - by Gaurav M

  CSS frameworks have nice styles inbuilt and ask you to focuses on the grids but still there is a bit of dependency and lack of freedom it provide.. If I need to generate a webpage by looking on a PSD based mockup screen ..either i will use the classes provided by the framework but if that actual measurements does not exist I need to again specify my own rules that will add upto my CSS filesize and if performance is a constraint as always it is...you need not a big size file..though its in kb but every drop counts. Any comments and suggestions to use the framework in a best possible way.

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• Has Object in VB 2010 received the same optimalization as dynamic in C# 4.0?

  - by Abel

  Some people have argued that the C# 4.0 feature introduced with the dynamic keyword is the same as the "everything is an Object" feature of VB. However, any call on a dynamic variable will be translated into a delegate once and from then on, the delegate will be called. In VB, when using Object, no caching is applied and each call on a non-typed method involves a whole lot of under-the-hood reflection, sometimes totaling a whopping 400-fold performance penalty. Have the dynamic type delegate-optimization and caching also been added to the VB untyped method calls, or is VB's untyped Object still so slow?

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• What could be adding "Pragma:no-cache" to my response Headers? (Apache, PHP)

  - by Daniel Magliola

  I have a website whose maintenance I've inherited, which is a big hairy mess. One of the things i'm doing is improving performance. Among other things, I'm adding Expires headers to images. Now, there are some images that are served through a PHP file, and I notice that they do have the Expires header, but they also get loaded every time. Looking at Response Headers, I see this: Expires Wed, 15 Jun 2011 18:11:55 GMT Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma no-cache Which obviously explains the problem. Now, i've looked all over the code base, and it doesn't say "pragma" anywhere. .htaccess doesn't seem to have anything related either. Any ideas who could be setting those "pragma" (and "cache-control") headers, and how I can avoid it? Thanks! Daniel

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• Is it possible to find out what FlashBuilder is doing during compilation?

  - by justkevin

  I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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• Rails/mysql SUM distinct records - optimization

  - by pepernik

  Hey. How would you optimize this SQL SELECT SUM(tmp.cost) FROM ( SELECT DISTINCT clients.id as client, countries.credits_cost AS cost FROM countries INNER JOIN clients ON clients.country_id = countries.id INNER JOIN clients_groups ON clients_groups.client_id=clients.id WHERE clients_groups.group_id IN (1,2,3,4,5,6,7,8,9) GROUP BY clients.id ) AS tmp; I'm using this example as part of my Ruby on Rails project. Note that my nested SQL (tmp) can have more then 10 milion records. You can split that in more SQLs if the performance is better. Should I add any indexes to make it quicker (i have it on IDs)?

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• How to correct this glitch

  - by Rebol Tutorial

  I removed background: url(none); in my stylesheet because of load performance http://stackoverflow.com/questions/2577422/why-firebug-pretends-that-my-stylesheet-is-calling-my-xmlrpc The problem is that it now causes some glitch on css list. Any idea how to fix this ? Thanks. Update: picture below Tried to put background: none as suggested but didn't solve the problem/ ul.sidebar_list li ul li ul { margin: 0px; padding: 0px!important; float: left; width: 100%; list-style-type: none; background: none; }

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• Seeking tutorial: introduction to ODBC with Delphi

  - by mawg

  I have a lot of embedded C/C++/Ada experience and an outdated smattering of Delphi plus some database stuff. Now I have to implement an app in Delphi which can manipulate MySql, Oracle, maybe MS Access. In short, I need ODBC. I need to programmatically created a database, define its structure and populate its contents, then later query its existence and programmatically search. I would prefer not to use 3rd party components, unless there is a compelling reason to do so (performance ought not to be an issue for the app, it won't have much data or be run often, at least not in v1.0) . Can anyone point me at a tutorial which can get me up to speed? Thanks

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• ContextSwitchDeadlock Was Detected error in C#

  - by assassin

  Hi, I am running a C# application, and during run-time I get the following error: The CLR has been unable to transition from COM context 0x20e480 to COM context 0x20e5f0 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations. Can anyone please help me out with the problem here? Thanks a lot.

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