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  • approximating log10[x^k0 + k1]

    - by Yale Zhang
    Greetings. I'm trying to approximate the function Log10[x^k0 + k1], where .21 < k0 < 21, 0 < k1 < ~2000, and x is integer < 2^14. k0 & k1 are constant. For practical purposes, you can assume k0 = 2.12, k1 = 2660. The desired accuracy is 5*10^-4 relative error. This function is virtually identical to Log[x], except near 0, where it differs a lot. I already have came up with a SIMD implementation that is ~1.15x faster than a simple lookup table, but would like to improve it if possible, which I think is very hard due to lack of efficient instructions. My SIMD implementation uses 16bit fixed point arithmetic to evaluate a 3rd degree polynomial (I use least squares fit). The polynomial uses different coefficients for different input ranges. There are 8 ranges, and range i spans (64)2^i to (64)2^(i + 1). The rational behind this is the derivatives of Log[x] drop rapidly with x, meaning a polynomial will fit it more accurately since polynomials are an exact fit for functions that have a derivative of 0 beyond a certain order. SIMD table lookups are done very efficiently with a single _mm_shuffle_epi8(). I use SSE's float to int conversion to get the exponent and significand used for the fixed point approximation. I also software pipelined the loop to get ~1.25x speedup, so further code optimizations are probably unlikely. What I'm asking is if there's a more efficient approximation at a higher level? For example: Can this function be decomposed into functions with a limited domain like log2((2^x) * significand) = x + log2(significand) hence eliminating the need to deal with different ranges (table lookups). The main problem I think is adding the k1 term kills all those nice log properties that we know and love, making it not possible. Or is it? Iterative method? don't think so because the Newton method for log[x] is already a complicated expression Exploiting locality of neighboring pixels? - if the range of the 8 inputs fall in the same approximation range, then I can look up a single coefficient, instead of looking up separate coefficients for each element. Thus, I can use this as a fast common case, and use a slower, general code path when it isn't. But for my data, the range needs to be ~2000 before this property hold 70% of the time, which doesn't seem to make this method competitive. Please, give me some opinion, especially if you're an applied mathematician, even if you say it can't be done. Thanks.

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  • Lisp data security/validation

    - by Wayne Werner
    This is really just a conceptual question for me at this point. In Lisp, programs are data and data are programs. The REPL does exactly that - reads and then evaluates. So how does one go about getting input from the user in a secure way? Obviously it's possible - I mean viaweb - now Yahoo!Stores is pretty secure, so how is it done?

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  • How can I get Pinch to Zoom back in Desktop mode?

    - by Ben Brocka
    Windows 7 had an old implimentation of Pinch to Zoom where bringing your fingers apart/together would act similar to ctrl + +/-, the standard zoom. It's not as nice as granular zoom (like iOS/Android use) but it worked. Most notably it doesn't work in Chrome (did before) but I haven't noticed it working in any other apps. In windows 8 desktop mode, pinch to zoom doesn't seem to work at all. It doesn't even work in One Note 2010, which, if I recall correctly, had granular zoom in Windows 7. I have an (older) 2 touch point multi-touch monitor, and I can see the visual feedback that the two touch points and coming closer/farther apart, but it doesn't zoom. Note I'm using the touchscreen, not a touchpad or the Arch mouse or other peripherals. Can I enable this somehow or is it gone from Desktop mode? It works fine in Metro apps. Additionally I get weird visual feedback when placing my second finger on the screen; a shrinking transparent square appears somewhere between the two fingers, visually similar to the Right Click visual queue when long-pressing. It's not a right click though, I can't tell what, if anything, it's doing.

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  • Regular Expression - Match only 7 chars?

    - by Simon
    I'm trying to match a SEDOL (exactly 7 chars: 6 alpha-numeric chars followed by 1 numeric char) My regex ([A-Z 0-9]{6})[0-9]{1} matches correctly but strings greater than 7 chars that begin with a valid match also match (if you see what I mean :)). For example: B3KMJP4 matches correctly but so does: B3KMJP4x which shouldn't match. Can anyone show me how to avoid this?

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  • When does a PHP script end?

    - by allyourcode
    In my mind, a web app something that runs continuously; therefore, I'm confused by documentation pages that talk about the "end" of a PHP script (eg this one). Such references seem to refer to the end of each web request, but if the script ends there, doesn't that mean that the OS has to setup a whole new process for each request? That seems unlikely, because spinning up a whole new process is expensive, and be very inefficient for the whole site.

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  • GKSession sendDataToAllPeers including sendee?

    - by Typeoneerror
    I've got a number of devices connected over wifi using GameKit. I have a simple UIAlertView popping up when peers receive data. All but the sendee show this alert view when data is sent, so I'm wondering if that's a bug in my app or if that's expected behavior. Should call a method manually at the same on the sendee device? For example, if I wanted to send a "GameStart" packet to the 4 phones, the peers would call startGame: in the receiveData:fromPeer:inSession:context: method when it receives that packet and the sendee would just sendData and call startGame: on itself. Does that sound right or is there a way to include the sendee in the sendData list so that it responds exactly the same as all connected peers?

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  • Enabling depth testing when using CAOpenGLLayer

    - by Andrew
    If one is using a subclass of NSOpenGLView then one enables depth testing by selecting a 16/24/32 bit buffer from the attributes menu in Xcode, and then adding glEnable(GL_DEPTH_TEST); glClear(GL_DEPTH_BUFFER_BIT); to the drawRect method. However, in the application I'm creating I'm rendering OpenGL content via the drawInCGLContext method of a CAOpenGLLayer which is contained within a subclass of NSView. This means that it is no longer possible to create a depth buffer via the inspector. Does anyone know how I can achieve this in such a situation?

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  • Adding Multiline html content using javascript

    - by pokrate
    Hi, I have created a usercontrol and I want to put its generated html using a javascript file in a webpage. But couldnt do so. Like <script src='file.aspx'></script> should add the html from the usercontrol to the container div. The file "file.aspx" has its content-type set to "text/javascript". And using LoadControl() method I am loading the usercontrol, and then using its RenderControl method, I am able to get its generated html. But I couldnt show it up in the webpage. But I am able to add single line html content , but multiline consumed my whole day :( .

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  • Saving auto increment in MySQL

    - by oshafran
    Hello, I am trying to sync between 2 tables: I have active table where has auto_increment, and I have archive table with the same values. I would like both ID's to be unique (between the tables as well) - I mean, I would like to save auto incremenet, and if I UNION both table I still have uniqness. How can I do that? Is there a possibility to save auto increment when mysql is off?

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  • Just a small problem regarding javscript BOM question

    - by caramel1991
    The question is this: Create a page with a number of links. Then write code that fires on the window onload event, displaying the href of each of the links on the page. And this is my solution <html> <body language="Javascript" onload="displayLink()"> <a href="http://www.google.com/">First link</a> <a href="http://www.yahoo.com/">Second link</a> <a href="http://www.msn.com/">Third link</a> <script type="text/javascript" language="Javascript"> function displayLink() { for(var i = 0;document.links[i];i++) { alert(document.links[i].href); } } </script> </body> </html> This is the answer provided by the book <html> <head> <script language=”JavaScript” type=”text/javascript”> function displayLinks() { var linksCounter; for (linksCounter = 0; linksCounter < document.links.length; linksCounter++) { alert(document.links[linksCounter].href); } } </script> </head> <body onload=”displayLinks()”> <A href=”link0.htm” >Link 0</A> <A href=”link1.htm”>Link 2</A> <A href=”link2.htm”>Link 2</A> </body> </html> Before I get into the javascript tutorial on how to check user browser version or model,I was using the same method as the example,by acessing the length property of the links array for the loop,but after I read through the tutorial,I find out that I can also use this alternative ways,by using the method that the test condition will evalute to true only if the document.links[i] return a valid value,so does my code is written using the valid method??If it's not,any comment regarding how to write a better code??Correct me if I'm wrong,I heard some of the people say "a good code is not evaluate solely on whether it works or not,but in terms of speed,the ability to comprehend the code,and could posssibly let others to understand the code easily".Is is true??

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  • How to preserve object identity across different VMs

    - by wheleph
    To be specific let me illustrate the question with Spring http-remoting example. Suppose we have such implementation of a simple interface: public SearchServiceImpl implements SearchService { public SearchJdo processSearch(SearchJdo search) { search.name = "a funky name"; return search; } } SearchJdo is itself a simple POJO. Now when we call the method from a client through http-remoting we'll get: public class HTTPClient { public static void main(final String[] arguments) { final ApplicationContext context = new ClassPathXmlApplicationContext( "spring-http-client-config.xml"); final SearchService searchService = (SearchService) context.getBean("searchService"); SearchJdo search = new SearchJdo(); search.name = "myName"; // this method actually returns the same object it gets as an argument SearchJdo search2 = searchService.processSearch(search); System.out.println(search == search2); // prints "false" } } The problem is that the search objects are different because of serializaton although from logical prospective they are the same. The question is whether there are some technique that allows to support or emulate object identity across VMs.

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  • What's the best way to unit test code that generates random output?

    - by Flynn1179
    Specifically, I've got a method picks n items from a list in such a way that a% of them meet one criterion, and b% meet a second, and so on. A simplified example would be to pick 5 items where 50% have a given property with the value 'true', and 50% 'false'; 50% of the time the method would return 2 true/3 false, and the other 50%, 3 true/2 false. Statistically speaking, this means that over 100 runs, I should get about 250 true/250 false, but because of the randomness, 240/260 is entirely possible. What's the best way to unit test this? I'm assuming that even though technically 300/200 is possible, it should probably fail the test if this happens. Is there a generally accepted tolerance for cases like this, and if so, how do you determine what that is?

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  • Java HashSet is allowing dupes; problem with comparable?

    - by IVR Avenger
    Hi, all. I've got a class, "Accumulator", that implements the Comparable compareTo method, and I'm trying to put these objects into a HashSet. When I add() to the HashSet, I don't see any activity in my compareTo method in the debugger, regardless of where I set my breakpoints. Additionally, when I'm done with the add()s, I see several duplicates within the Set. What am I screwing up, here; why is it not Comparing, and therefore, allowing the dupes? Thanks, IVR Avenger

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  • Using type hints in Clojure for Java return values

    - by mikera
    I'm working on some Java / Clojure interoperability and came across a reflection warning for the following code: (defn load-image [resource-name] (javax.imageio.ImageIO/read (.getResource (class javax.imageio.ImageIO) resource-name))) => Reflection warning, clojure/repl.clj:37 - reference to field read can't be resolved. I'm surprised at this because getResource always returns a URL and I would therefore expect the compiler to use the appropriate static method in javax.imageio.ImageIO/read. The code works fine BTW so it is clearly finding the right method at run time. So two questions: Why is this returning a reflection warning? What type hint do I need to fix this?

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  • Is there an easy way to change iPhone Application Settings from within an application?

    - by Matt
    I've got application settings working just fine. However, I'd like to be able to change my app settings from within my app. It seems as though there should be some kind of generic way to add this functionality to my app without having to recreate all the controls myself. I mean, the code is already written in apple's settings app. Maybe someone wrote this code and open sourced it? (if it is not already available)

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  • how to return the current object?

    - by ajsie
    in code igniter you can type: $query = $this->db->query("YOUR QUERY"); foreach ($query->result() as $row) { echo $row->title; echo $row->name; echo $row->body; } i guess that the query method returns the object it's part of. am i correct? if i am, how do you type the line where it returns the object? so what i wonder is how it looks like inside the query method for the above code to be functional. public function query($sql) { // some db logic here with the $sql and saves the values to the properties (title, name and body) return X } with other words, what should X be?

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  • Why use event listeners over function calls?

    - by Organiccat
    I've been studying event listeners lately and I think I've finally gotten them down. Basically, they are functions that are called on another object's method. My question is, why create an event listener when calling the function will work just fine? Example, I want to call player.display_health(), and when this is fired, the method player.get_health() should be fired and stored so that display_health() has access to it. Why should I use an event listener over simply calling the function? Even if display_health() were in another object, this still doesn't appear to be a problem to me. If you have another example that fits the usage better, please let me know. Perhaps particular languages don't benefit from it as much? (Javascript, PHP, ASP?)

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  • CGContextShowTextAtPoint: invalid context

    - by coure06
    I want to call a method responsible for drawing text on screen after each 5 seconds. Here is my code -(void) handleTimer: (NSTimer *)timer { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetLineWidth(context, 2.0); CGContextSetStrokeColorWithColor(context, currentColor.CGColor); CGContextTranslateCTM(context, 145.0, 240.0); CGContextScaleCTM(context, 1.0, -1.0); CGContextSelectFont(context, "Arial", 18, kCGEncodingMacRoman); CGContextSetCharacterSpacing(context, 1); CGContextSetTextDrawingMode(context, kCGTextFillStroke); CGContextSetRGBStrokeColor(context, 0.5,0.5,1,1); CGContextShowTextAtPoint(context, 100, 100, "01", 2); } But after 5 seconds when this method is called i am getting this error CGContextShowTextAtPoint: invalid context Another thing is how to show a thinner font?

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  • File details from a string in C#

    - by acadia
    Hello, I have a string in C# String file="\\mserver-80\docs\somedoc.doc" Now How do I get fileInfo from the above sting. What I mean is, I want to declare something like FileInfo fInfo = new FileInfo(file); fileExtn = fInfo.Extension;

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  • Path Problem in ASP.net

    - by Hany
    Hi I am trying to do the following I am building asp.net website with c# language I want to read a text file from my project(the file is inside the project) I tried to get the file Path by this way : string path=Request.PhysicalApplicationPath+"filename.txt"; but I can't use The "Request" object from separated C# file ?? note: separated C3 file,I mean it's not related with aspx file can you help me with my way or do you have another way ?? thx

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