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• Fast modulo 3 or division algorithm?

  - by aaa

  Hello is there a fast algorithm, similar to power of 2, which can be used with 3, i.e. n%3. Perhaps something that uses the fact that if sum of digits is divisible by three, then the number is also divisible. This leads to a next question. What is the fast way to add digits in a number? I.e. 37 - 3 +7 - 10 I am looking for something that does not have conditionals as those tend to inhibit vectorization thanks

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• Send and recieve multiple ssh commands via java runtime and cygwin

  - by Moustachio

  Hey I have run into the following problem when attempting to build a program in java which executes commands on a remote linux server and returns the output for processing... Basically I have installed Cygwin with an SSH client and want to do the following: Open Cygwin, Send command "user@ip"; Return output; Send command "password"; Return output; Send multiple other commands, Return output; ...etc... So far: Process proc = Runtime.getRuntime().exec("C:/Power Apps/Cygwin/Cygwin.bat"); Works nicely except I am at a loss as to how to attempt the next steps. Any help?

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• Laws of Computer Science and Programming

  - by Jonas

  We have Amdahl's law that basically states that if your program is 10% sequential you can get a maximum 10x performance boost by parallelizing your application. Another one is Wadler's law which states that In any language design, the total time spent discussing a feature in this list is proportional to two raised to the power of its position. 0. Semantics 1. Syntax 2. Lexical syntax 3. Lexical syntax of comments My question is this: What are the most important (or at least significant / funny but true / sad but true) laws of Computer Science and programming? I want named laws, and not random theorems, So an answer should look something like Surname's (law|theorem|conjecture|corollary...) Please state the law in your answer, and not only a link. Edit: The name of the law does not need to contain it's inventors surname. But I do want to know who stated (and perhaps proved) the law

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• git status: how to ignore some changes

  - by Mr Fooz

  Is there a way to have git status ignore certain changes within a file? Background I have some files in my repository that are auto-generated (yes, I know that's typically not recommended, but I have no power to change this). Whenever I build my tree, these auto-generated files have status information updated in them (who generated them, a timestamp, etc.). When I say git status, I'd like it to run a filter on these generated files that strips out this transient status information. I only want it to show up in the "Changed but not updated:" section of git's output if there are other, real changes. Using the .gitattributes approach found at http://progit.org/book/ch7-2.html, I am able to get git diff to ignore these status line changes using a simple egrep filter. I'd like to get git status to also use textconv filters (or something equivalent). I'd prefer it if merges aren't affected by any of this filtering.

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• 16 bit processor , memory addressing and memory cells

  - by Zia ur Rahman

  Suppose the accumulater register of the processor is of 16 bit , now we can call this processor as 16 bit processor, that is this processor supports 16 bit addressing. now my question is how we can calculate the number of memory cells that can be addressed by 16 bit addressing? according to my calculation 2 to the power 16 becomes 65055 it means the memory have 65055 cells now if we take 1KB=1000 Bytes then this becomes 65055/1000=65.055 now this means that 65 kilo bytes memory can be used with the processor having 16 bit addressing. now if we take 1KB=1024 Bytes then this becomes 65055/1024=63.5 ,it means that 63 kilo bytes memory can be used with this processor, but people say that 64 kilo bytes memory can be used. Now tell me am i right or wrong and why i am wrong why people say that 64kb memory can be used with the processor having 16 bit addressing?

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• Why does my UITableView change from UITableViewStyleGrouped to UITableViewStylePlain

  - by casper

  My application has a view controller that extends UITableViewController. The initialization method looks like this: - (id)initWithCoder:(NSCoder*)coder { if (self = [super initWithCoder:coder]) { self.tableView = [[UITableView alloc] initWithFrame:self.tableView.frame style:UITableViewStyleGrouped]; } return self; } When the view is initially loaded, it's displayed as UITableViewStyleGrouped. However, if my app ever receives a low memory warning, the above view changes to UITableViewStylePlain. There is no associated xib file with the View/Controller. The viewDidUnload and didReceiveMemoryWarning methods are straightforward: - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; } My question is, why does the table style change when I receive a memory warning?

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• Fastest sort of fixed length 6 int array

  - by kriss

  Answering to another StackOverflow question (this one) I stumbled upon an interresting sub-problem. What is the fastest way to sort an array of 6 ints ? As the question is very low level (will be executed by a GPU): we can't assume libraries are available (and the call itself has it's cost), only plain C to avoid emptying instruction pipeline (that has a very high cost) we should probably minimize branches, jumps, and every other kind of control flow breaking (like those hidden behind sequence points in && or ||). room is constrained and minimizing registers and memory use is an issue, ideally in place sort is probably best. Really this question is a kind of Golf where the goal is not to minimize source length but execution speed. I call it 'Zening` code as used in the title of the book Zen of Code optimization by Michael Abrash and it's sequels.

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• How to find a binary logarithm very fast? (O(1) at best)

  - by psihodelia

  Is there any very fast method to find a binary logarithm of an integer number? For example, given a number x=52656145834278593348959013841835216159447547700274555627155488768 such algorithm must find y=log(x,2) which is 215. x is always a power of 2. The problem seems to be really simple. All what is required is to find the position of the most significant 1 bit. There is a well-known method FloorLog, but it is not very fast especially for the very long multi-words integers. What is the fastest method?

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• Replace values in a dataframe based on another factor which contains NA's in R

  - by PaulHurleyuk

  I have a dataframe which contains (among other things) a numeric column with a concentration, and a factor column with a status flag. This status flag contains NA's. Here's an example df<-structure(list(conc = c(101.769, 1.734, 62.944, 92.697, 25.091, 27.377, 24.343, 55.084, 0.335, 23.280), status = structure(c(NA, NA, NA, NA, NA, NA, 2L, NA, 1L, NA), .Label = c("<LLOQ", "NR"), class = "factor")), .Names = c("conc", "status"), row.names = c(NA, -10L), class = "data.frame") I want to replace the concentration column with a string for some values of the flag column, or with the concentration value formatted to a certain number of significant digits. When I try this ifelse(df$status=="NR","NR",df$conc) The NA's in the status flag don't trigger either the true or false condition (and return NA) - as the documentation suggests it will. I could loop over the rows and use IF then else on each one but this seems inefficient. Am I missing something ? I've tried as.character(df$status) as well which doesn't work. My mojo must be getting low....

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• Is it possible to force an error in an Integration Services data flow to demonstrate its rollback?

  - by Matt

  I have been tasked with demoing how Integration Services handles an error during a data flow to show that no data makes it into the destination. This is an existing package and I want to limit the code changes to the package as much as possible (since this is most likely a one time deal). The scenario that is trying to be understood is a "systemic" failure - the source file disappears midstream, or the file server loses power, etc. I know I can make this happen by having the Error Output of the source set to Failure and introducing bad data but I would like to do something lighter than that. I suppose I could add a Script Transform task and look for a certain value and throw an error but I was hoping someone has come up with something easier / more elegant. Thanks, Matt

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• Troubles configuring SSL for an Apache host

  - by Ryan

  I configured it on Friday night and all worked well. Today for some reason it stopped working and I can't figure out why. When you goto the secure page it's acting like I have a self-signed certificate and I don't. I have the host configured like so ServerAdmin [email protected] DocumentRoot "/path/to/site" Servername www.mydomain.com ServerAlias mydomain.com DirectoryIndex index.cfm index.htm SSLEngine on SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL SSLCertificateFile /etc/httpd/path/to/mydomain.com.crt SSLCertificateKeyFile /etc/httpd/path/to/www.mydomain.com.key SSLCertificateChainFile /etc/httpd/path/to/gd_bundle.crt Apache starts with no errors and I can't seem to find anything meaningful in any of the logs. It's got to be something minor but I can't seem to see it. It's an updated Centos/Apache VM. I have worn Google out.

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• How do You Get a Specific Value From a System.Data.DataTable Object?

  - by Giffyguy

  I'm a low-level algorithm programmer, and databases are not really my thing - so this'll be a n00b question if ever there was one. I'm running a simple SELECT query through our development team's DAO. The DAO returns a System.Data.DataTable object containing the results of the query. This is all working fine so far. The problem I have run into now: I need to pull a value out of one of the fields of the first row in the resulting DataTable - and I have no idea where to even start. Microsoft is so confusing about this! Arrrg! Any advice would be appreciated. I'm not providing any code samples, because I believe that context is unnecessary here. I'm assuming that all DataTable objects work the same way, no matter how you run your queries - and therefore any additional information would just make this more confusing for everyone.

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• Reinforcement learning with neural networks

  - by Betamoo

  I am working on a project with RL & NN I need to determine the action vector structure which will be fed to a neural network.. I have 3 different actions (A & B & Nothing) each with different powers (e.g A100 A50 B100 B50) I wonder what is the best way to feed these actions to a NN in order to yield best results? 1- feed A/B to input 1, while action power 100/50/Nothing to input 2 2- feed A100/A50/Nothing to input 1, while B100/B50/Nothing to input 2 3- feed A100/A50 to input 1, while B100/B50 to input 2, while Nothing flag to input 3 4- Also to feed 100 & 50 or normalize them to 2 & 1 ? I need reasons why to choose one method Any suggestions are recommended Thanks

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• Rapidly prototype GUI's...

  - by Donovan

  G'Day, I am looking to prototype a windows based GUI. Ideally I would like: Be able create new GUI's and change existing ones quickly The resulting "thing" to be self contained Have the ability to include limited data where necessary ie. When showing a grid including the headers and perhaps a few rows of data for the grid. Allow clickable hotspots that either allow a new screen to be shown or perhaps an explanation hint. I have been using Visio 2003 for this kind of thing and then producing a PDF. However it has some disadvantages: Including data for grids is not possible You cannot include hotspots to allow changing of tabs within the workbook. eg Click on a button and it opens a different tab. If possible a free / open source application would be preferable but a low priced commercial application would also be good. All pointers and suggestions greatly appreciated.Rapid

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• How do I make "simple" throughput servlet-filter?

  - by Tommy

  I'm looking to create a filter that can give me two things: number of request pr minute, and average responsetime pr minute. I already got the individual readings, I'm just not sure how to add them up. My filter captures every request, and it records the time each request takes: public void doFilter(ServletRequest request, ...() { long start = System.currentTimeMillis(); chain.doFilter(request, response); long stop = System.currentTimeMillis(); String time = Util.getTimeDifferenceInSec(start, stop); } This information will be used to create some pretty Google Chart charts. I don't want to store the data in any database. Just a way to get current numbers out when requested As this is a high volume application; low overhead is essential. I'm assuming my applicationserver doesn't provide this information.

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• What HTML is permitted within Flash text fields.

  - by JasonS

  Hi, Could someone clarify for me what input Flash accepts for its text fields? I am tasked with managing a content management system, this then generates XML which power's flash sites. I have nothing to do with Flash. I work with PHP. Currently we use a rather temperamental Flash Text Editor which is prone to all sorts of troubles. I tried to plug-in tinyMce but it broke the Flash templates. I then recently spoke to someone who said that flash should take any HTML. Now I am confused as this would point to a dodgy template. Can someone clarify. Do Flash text fields handle all HTML or just a limited subset of HTML. If it is the latter, what happens if it comes across a tag it doesn't recognise? Does it display the tag or break? Thanks, Jason

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• ASP.Net MVC and N-Tier

  - by Damien

  Greetings, Apologies in advance that I have not researched this toughly enough to answer the question myself, but I imagine it would take me some time and I would rather know now before I invest more time in learning it. I couldn't find anything in my initial research.. Why use ASP.Net MVC if your already using a multi-tier architecture (Data Layer, Logic Layer, Presentation Layer)? Other than the fact the controller has more power than the logic layer. Am I right in thinking I can use nHibernate and all my data access classes, entities, and mappings in the Model part of the MVC? When using controllers, is it best to separate a lot of the logic into a separate class so I can call it from multiple controllers? Or can I call them from the controllers themselves, considering the fact that I would not want all of them to be Actions, just normal methods. Thanks

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• Why darcs instead of git?

  - by Ctrl Alt D-1337

  Using pure functional languages can have a lot of benefits over using impure imperatives but low level systems languages will generally allow you to achieve much greater performance especially when they are imperative because it allows you to specify the exact steps in how the cpu should compute the result. If there is ever list of tools where high performance is an absolute must then I would put source version controls systems right at the top of that list and git achieves this very well but performance is not it's only advantage over many other other types of version control systems anyway. The git team are handling the unsafe c code very well and I never worry about my type system or any other features of the language it is written in so why is it that there is a lot of haskell developers that must use darcs when they will only be using the finished product?

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• Minimum Acceptable Code Coverage Numbers in the real world.

  - by Pita.O

  Hi, I am in the middle of putting together some guidelines around code coverage and I want to specify a number that really makes sense. It's easy to repeat the 100% mantra that I see all over the internet without considering the cost benefit analysis and when diminishing returns actually sets in. I solicit comments from persons who have actually reported code coverage on real-life, medium/large-sized projects. What percentages were you seeing? How much is too much? I really want some balance (in figures) that will help developers produce hight quality code. Is 65% coverage too low to expect? Is 80% too high?

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• How to prevent DOS attacks using image resizing in an ASP.NET application?

  - by Waleed Eissa

  I'm currently developing a site where users can upload images to use as avatars, I know this makes me sound a little paranoid but I was wondering what if a malicious user uploads an image with incredibly large dimensions that will eat the server memory (as a DOS attack), I already have a limit on the file size that can be uploaded (250 k) but even that size can allow for an image with incredibly large dimensions if the image for example is a JPEG that contains one color and created with a very low quality setting. Taking into consideration that the image is uploaded as a bitmap in memory when being resized (ie. not compressed), I wonder if such DOS attacks occur, even to check the image dimensions it has to be uploaded in memory first, did you hear about any attacks that exploited this? Am I too worried?

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• ASP.Net ITemplate - ways of declaring

  - by Mahes

  when we want to define a Template in our user controls we declare a field like this in our user controls public ITemplate MyTemplate { get; set; } so that the user defined templates contents will be represented in MyTemplate, and you can use it. and there are ways to customize the templates, for example [TemplateInstanceAttribute(TemplateInstance.Single)] public ITemplate MyTemplate { get; set; } the above example will enable defines single instance Templates(http://www.nikhilk.net/SingleInstanceTemplates.aspx). i accidentally came across single instance templates and blown away by the power of it. my question is what are all the things possible with ITemplates?? how do we define(use) them (more specifically thru annotations). is there any good documentation available for ITemplates?? (please dont point to msdn)

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• Difference between Document-oriented-DB and Bigtable clones

  - by chen

  We are looking for a suitable storage engine for our weblog history data. We looked at Bigtable's paper and understand it is suitable to us well. However, I also understand that Document-oriented-DB such as MongoDB seems to provide a little more powerful schema power -- i.e, it can model our data as well. I wonder how nowadays ppl choose a scalable NoSQL DB --- I read enough articles like "we looked at A, B and C, and we decided to use C". But I'd like to see some benchmark number. What I am saying is that if MongoDB and the like can provide same level of performance as Bigtable clones, why don't web companies choose it (preparing to deal with various potentially more complex data problem)? Thanks, By the way, I read an article (which convinced me at the moment) saying Cassandra does not fit the M/R operation, any comments?

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• What is the underlying reason for not being able to put arrays of pointers in unsafe structs in C#?

  - by cons

  If one could put an array of pointers to child structs inside unsafe structs in C# like one could in C, constructing complex data structures without the overhead of having one object per node would be a lot easier and less of a time sink, as well as syntactically cleaner and much more readable. Is there a deep architectural reason why fixed arrays inside unsafe structs are only allowed to be composed of "value types" and not pointers? I assume only having explicitly named pointers inside structs must be a deliberate decision to weaken the language, but I can't find any documentation about why this is so, or the reasoning for not allowing pointer arrays inside structs, since I would assume the garbage collector shouldn't care what is going on in structs marked as unsafe. Digital Mars' D handles structs and pointers elegantly in comparison, and I'm missing not being able to rapidly develop succinct data structures; by making references abstract in C# a lot of power seems to have been removed from the language, even though pointers are still there at least in a marketing sense. Maybe I'm wrong to expect languages to become more powerful at representing complex data structures efficiently over time.

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• Is it naughty to have a large utility file?

  - by banister

  In my C project I have quite a large utils.c file. It is really full of many utilities of different sorts. I feel a bit naughty just stuffing different miscellaneous functions in there. For example it has some utilities related to low level stuff such as a lowercase() function, and it also has some quite sophisticated utilities such as converting to/from different colour formats. My question is, is it very naughty to have such a large utils.c with many different types of utilities in it? Should I break it up into many different kinds of utility files? Such as graphics_utils.c and so on What do you think?

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• Microsoft BizTalk Server vNext (after 2009 R2) - Feature Request

  - by Saravana Kumar

  All, This post is not a question; it’s more of asking for feed back and future request. The product team is always looking for feed back to facilitate the future direction of the product. Some of us as BizTalk Server MVP’s/partners get that privilege to work with the product team closely to give our feedback regularly based on our real world experience. But I believe there is a much wider BizTalk community out there working on closed door project that tests the strength of the product to extreme levels. I would like those passionate people to come forward and put their feature request. Let’s use the power of StackOverflow to help us here. We can vote up and down on each feature request, and see what's going to top the chart. I hope this will be a useful exercise. Updated 24th Feb: If you got more than one request, please post it as separate answers. So, its easy to vote against them.

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