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  • How to make a big switch control structure with variable check values?

    - by mystify
    For example, I have a huge switch control structure with a few hundred checks. They're an animation sequence, which is numbered from 0 to n. Someone said I can't use variables with switch. What I need is something like: NSInteger step = 0; NSInteger i = 0; switch (step) { case i++: // do stuff break; case i++: // do stuff break; case i++: // do stuff break; case i++: // do stuff break; } The point of this is, that the animation system calls a method with this big switch structure, giving it a step number. I want to be able to simply cut-copy-paste large blocks and put them in a different position inside the switch. for example, the first 50 blocks to the end. I could do that easily with a huge if-else structure, but it would look ugly and something tells me switch is much faster. How to?

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  • Use a vector to index a matrix without linear index

    - by David_G
    G'day, I'm trying to find a way to use a vector of [x,y] points to index from a large matrix in MATLAB. Usually, I would convert the subscript points to the linear index of the matrix.(for eg. Use a vector as an index to a matrix in MATLab) However, the matrix is 4-dimensional, and I want to take all of the elements of the 3rd and 4th dimensions that have the same 1st and 2nd dimension. Let me hopefully demonstrate with an example: Matrix = nan(4,4,2,2); % where the dimensions are (x,y,depth,time) Matrix(1,2,:,:) = 999; % note that this value could change in depth (3rd dim) and time (4th time) Matrix(3,4,:,:) = 888; % note that this value could change in depth (3rd dim) and time (4th time) Matrix(4,4,:,:) = 124; Now, I want to be able to index with the subscripts (1,2) and (3,4), etc and return not only the 999 and 888 which exist in Matrix(:,:,1,1) but the contents which exist at Matrix(:,:,1,2),Matrix(:,:,2,1) and Matrix(:,:,2,2), and so on (IRL, the dimensions of Matrix might be more like size(Matrix) = (300 250 30 200) I don't want to use linear indices because I would like the results to be in a similar vector fashion. For example, I would like a result which is something like: ans(time=1) 999 888 124 999 888 124 ans(time=2) etc etc etc etc etc etc I'd also like to add that due to the size of the matrix I'm dealing with, speed is an issue here - thus why I'd like to use subscript indices to index to the data. I should also mention that (unlike this question: Accessing values using subscripts without using sub2ind) since I want all the information stored in the extra dimensions, 3 and 4, of the i and jth indices, I don't think that a slightly faster version of sub2ind still would not cut it..

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  • Flipping View transition becomes clunky when using UIPickerViews with a large number of elements

    - by user302246
    I have a very simple app created with the Utility Application project template on XCode. My MainView has two UIPickerView components and two buttons. The FlipSideView has another UIPickerView. The pickers on the main view each have 4 segments and each segment has 8 rows. The picker on the flip side has just 1 segment with 8 rows. All rows on all pickers are just text. With just this setup, pressing the button to flip the view back and forth displays a noticeable delay before the animation actually starts, and then the animation actually seems to go faster than what it should, like it's trying to make up for the lost time. I removed the pickers in interface builder and loaded the app on the phone and the animation now seems natural. I also tried just one picker (the flipside one) and things still seem normal. So my current theory is that the number of objects involved in the main view is the cause. The thing is that I don't think it's that many (4 x 8 x 2 = 64), but I could be completely wrong. This is pretty much my first app so maybe I'm just doing something grossly wrong, or maybe the phone is has a lot more limited processing than I thought. I am thinking of creating the picker views with pickerView:viewForRow:forComponent:reusingView: to see if this hopefully performs better, but I'm not sure if this is just a waste of time. Any suggestions? Thanks Ruy P.S.: Testing on a 3G phone on 3.1.2

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  • How to speed up the reading of innerHTML in IE8?

    - by Dennis Cheung
    I am using JQuery with the DataTable plugin, and now I have a big performnce issue on the following line. aLocalData[jInner] = nTds[j].innerHTML; // jquery.dataTables.js:2220 I have a ajax call, and result string in HTML format. I convert them into HTML nodes, and that part is ok. var $result = $('<div/>').html(result).find("*:first"); // simlar to $result=$(result) but much more faster in Fx Then I activate enable the result from a plain table to a sortable datatable. The speed is acceptable in Fx (around 4sec for 900 rows), but unacceptable in IE8 (more then 100 seconds). I check it deep using the buildin profiler, and found the above single line take all 99.9% of the time, how can I speed it up? anything I missed? nTrs = oSettings.nTable.getElementsByTagName('tbody')[0].childNodes; for ( i=0, iLen=nTrs.length ; i<iLen ; i++ ) { if ( nTrs[i].nodeName == "TR" ) { iThisIndex = oSettings.aoData.length; oSettings.aoData.push( { "nTr": nTrs[i], "_iId": oSettings.iNextId++, "_aData": [], "_anHidden": [], "_sRowStripe": '' } ); oSettings.aiDisplayMaster.push( iThisIndex ); aLocalData = oSettings.aoData[iThisIndex]._aData; nTds = nTrs[i].childNodes; jInner = 0; for ( j=0, jLen=nTds.length ; j<jLen ; j++ ) { if ( nTds[j].nodeName == "TD" ) { aLocalData[jInner] = nTds[j].innerHTML; // jquery.dataTables.js:2220 jInner++; } } } }

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  • JavaScript: Achieving precise animation end values?

    - by bobthabuilda
    I'm currently trying to write my own JavaScript library. I'm in the middle of writing an animation callback, but I'm having trouble getting precise end values, especially when animation duration times are smaller. Right now, I'm only targeting positional animation (left, top, right, bottom). When my animations complete, they end up having an error margin of 5px~ on faster animations, and 0.5px~ on animations 1000+ ms or greater. Here's the bulk of the callback, with notes following. var current = parseFloat( this[0].style[prop] || 0 ) // If our target value is greater than the current , gt = !!( value > current ) , delta = ( Math.abs(current - value) / (duration / 13) ) * (gt ? 1 : -1) , elem = this[0] , anim = setInterval( function(){ elem.style[prop] = ( current + delta ) + 'px'; current = parseFloat( elem.style[prop] ); if ( gt && current >= value || !gt && current <= value ) clearInterval( anim ); }, 13 ); this[0] and elem both reference the target DOM element. prop references the property to animate, left, top, bottom, right, etc. current is the current value of the DOM element's property. value is the desired value to animate to. duration is the specified duration (in ms) that the animation should last. 13 is the setInterval delay (which should roughly be the absolute minimal for all browsers). gt is a var that is true if value exceeds the initial current, else it is false. How can I resolve the error margin?

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  • How to Use Calculated Color Values with ColorMatrix?

    - by Otaku
    I am changing color values of each pixel in an image based on a calculation. The problem is that this takes over 5 seconds on my machine with a 1000x1333 image and I'm looking for a way to optimize it to be much faster. I think ColorMatrix may be an option, but I'm having a difficult time figure out how I would get a set of pixel RGB values, use that to calculate and then set the new pixel value. I can see how this can be done if I was just modifying (multiplying, subtracting, etc.) the original value with ColorMatrix, but now how I can use the pixels returned value to use it to calculate and new value. For example: Sub DarkenPicture() Dim clrTestFolderPath = "C:\Users\Me\Desktop\ColorTest\" Dim originalPicture = "original.jpg" Dim Luminance As Single Dim bitmapOriginal As Bitmap = Image.FromFile(clrTestFolderPath + originalPicture) Dim Clr As Color Dim newR As Byte Dim newG As Byte Dim newB As Byte For x = 0 To bitmapOriginal.Width - 1 For y = 0 To bitmapOriginal.Height - 1 Clr = bitmapOriginal.GetPixel(x, y) Luminance = ((0.21 * (Clr.R) + (0.72 * (Clr.G)) + (0.07 * (Clr.B))/ 255 newR = Clr.R * Luminance newG = Clr.G * Luminance newB = Clr.B * Luminance bitmapOriginal.SetPixel(x, y, Color.FromArgb(newR, newG, newB)) Next Next bitmapOriginal.Save(clrTestFolderPath + "colorized.jpg", ImageFormat.Jpeg) End Sub The Luminance value is the calculated one. I know I can set ColorMatrix's M00, M11, M22 to 0, 0, 0 respectively and then put a new value in M40, M41, M42, but that new value is calculated based of a value multiplication and addition of that pixel's components (((0.21 * (Clr.R) + (0.72 * (Clr.G)) + (0.07 * (Clr.B)) and the result of that - Luminance - is multiplied by the color component). Is this even possible with ColorMatrix?

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  • How to handle pagination queries properly with mongodb and php?

    - by luckytaxi
    Am I doing this right? I went to look at some old PHP code w/ MySQL and I've managed to get it to work, however I'm wondering if there's a much "cleaner" and "faster" way of accomplishing this. First I would need to get the total number of "documents" $total_documents = $collection->find(array("tags" => $tag, "seeking" => $this->session->userdata('gender'), "gender" => $this->session->userdata('seeking')))->count(); $skip = (int)($docs_per_page * ($page - 1)); $limit = $docs_per_page; $total_pages = ceil($total_documents / $limit); // Query to populate array so I can display with pagination $data['result'] = $collection->find(array("tags" => $tag, "seeking" => $this->session->userdata('gender'), "gender" => $this->session->userdata('seeking')))->limit($limit)->skip($skip)->sort(array("_id" => -1)); My question is, can I run the query in one shot? I'm basically running the same query twice, except the second time I'm passing the value to skip between records.

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  • Cross-Platform Language + GUI Toolkit for Prototyping Multimedia Applications

    - by msutherl
    I'm looking for a language + GUI toolkit for rapidly prototyping utility applications for multimedia installations. I've been working with Max/MSP/Jitter for many years, but I'd like to add a text-based language to my 'arsenal' for tasks apart from 'content production'. (When it comes to actual media synthesis, my choices are clear [SuperCollider + MSP for audio, Jitter + Quartz + openFrameworks for video]). I'm looking for something that maintains some of the advantages of Max, but is lower-level, faster, more cross-platfrom (Linux support), and text-based. Integration with powerful sound/video libraries is not a requirement. Some requirements: Cross-platform (at least OSX and Linux, Windows is a plus) Fast and easy cross-platform GUIs with no platform-specific modification GUI code separated from backend code as much as possible Good for interfacing with external serial devices (micro-controllers) Good network support (UDP/TCP) Good libraries for multi-media (video, sound, OSC) are a plus Asynchronous synchronous UNIX integration is a plus The options that come to mind: AS3/Flex (not a fan of AS3 or the idea of running in the Flash Player) openFrameworks (C++ framework, perhaps a bit too low level [looking for fast development time] and biased toward video work) Java w/ Processing libraries (like openFrameworks, just slower) Python + Qt (is Qt appropriate for rapid prototyping?) Python + Another GUI toolkit SuperCollider + Swing (yucky GUI development) Java w/ SWT Any other options? What do you recommend?

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  • Drawing half of a Bezier path in Raphael

    - by Fibericon
    Let's say I have a cubic Bezier path as follows (formatted for use with the Raphael path function): M55 246S55 247 55 248 Just an example. This was taken from my drawing application, where I use the cursor to draw a line when the user holds the mouse button down, kind of like a pencil or marker. I'm using jquery's mousemove event to draw the line between two points every time the user moves the mouse. There is another (the reference point) that is taken before the line is drawn, so that the Bezier curve can be created. Here's my question: is it possible to make Raphael only draw half of a given path? I'm aware of the getSubpath() function, but if my understanding of Bezier curves is correct, it would be rather difficult to calculate the second argument. The problem with the animate function is that it creates double lines (that is, it creates the curved line that I want, and the boxy line around it which should not be shown, possibly because the mouse is being moved faster than the animation can handle). Of course, if my approach itself is flawed in some way (or my understanding of the possible solutions), I'd like to hear it. Any help would be appreciated.

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  • Fast, very lightweight algorithm for camera motion detection?

    - by Ertebolle
    I'm working on an augmented reality app for iPhone that involves a very processor-intensive object recognition algorithm (pushing the CPU at 100% it can get through maybe 5 frames per second), and in an effort to both save battery power and make the whole thing less "jittery" I'm trying to come up with a way to only run that object recognizer when the user is actually moving the camera around. My first thought was to simply use the iPhone's accelerometers / gyroscope, but in testing I found that very often people would move the iPhone at a consistent enough attitude and velocity that there wouldn't be any way to tell that it was still in motion. So that left the option of analyzing the actual video feed and detecting movement in that. I got OpenCV working and tried running their pyramidal Lucas-Kanade optical flow algorithm, which works well but seems to be almost as processor-intensive as my object recognizer - I can get it to an acceptable framerate if I lower the depth levels / downsample the image / track fewer points, but then accuracy suffers and it starts to miss some large movements and trigger on small hand-shaking-y ones. So my question is, is there another optical flow algorithm that's faster than Lucas-Kanade if I just want to detect the overall magnitude of camera movement? I don't need to track individual objects, I don't even need to know which direction the camera is moving, all I really need is a way to feed something two frames of video and have it tell me how far apart they are.

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  • Java (or possibly other languages) learning path

    - by bgo
    I am familiar (as a self-learner) with C, python and php such that i can solve some problems involving simple steps (for example, i easily do calculations for physics lab reports with python which normally would take 4x-5x times longer with a calculator). The point here is, as doing such things, i learnt the idea / concepts of programming language and problem solving along with oop or fuctional programming etc. Recently i have started Java and, with the familiarity of other languages, i am doing well for starters but i need guidence. -I am thinking of learning syntax from sun java tutorials and then practicing with codingbat.com or similar sites. I need a reference book that i can study deeper aspects of the topics i am learning. What do you suggest about these? -The problem is (and always have been) the lack of practice. I need coding and problem-solving practices sources. I stuck at the point where i can't figure out what to do next. Can you suggest any source (possibly like codingbat)? If i could plan a learning trail, i can progress faster and efficiently. So i need ideas, comments, suggestions. Thanks in advance.

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  • How to use VC++ intrinsic functions w/o run-time library

    - by Adrian McCarthy
    I'm involved in one of those challenges where you try to produce the smallest possible binary, so I'm building my program without the C or C++ run-time libraries (RTL). I don't link to the DLL version or the static version. I don't even #include the header files. I have this working fine. For some code constructs, the compiler generates calls to memset(). For example: struct MyStruct { int foo; int bar; }; MyStruct blah = {}; // calls memset() Since I don't include the RTL, this results in a missing symbol at link time. I've been getting around this by avoiding those constructs. For the given example, I'll explicitly initialize the struct. MyStruct blah; blah.foo = 0; blah.bar = 0; But memset() can be useful, so I tried adding my own implementation. It works fine in Debug builds, even for those places where the compiler generates an implicit call to memset(). But in Release builds, I get an error saying that I cannot define an intrinsic function. You see, in Release builds, intrinsic functions are enabled, and memset() is an intrinsic. I would love to use the intrinsic for memset() in my release builds, since it's probably inlined and smaller and faster than my implementation. But I seem to be a in catch-22. If I don't define memset(), the linker complains that it's undefined. If I do define it, the compiler complains that I cannot define an intrinsic function. I've tried adding #pragma intrinsic(memset) with and without declarations of memset, but no luck. Does anyone know the right combination of definition, declaration, #pragma, and compiler and linker flags to get an intrinsic function without pulling in RTL overhead? Visual Studio 2008, x86, Windows XP+.

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  • How do i make a allocation table?

    - by david
    I have build a grid of div's as playground for some visual experiments. In order to use that grid, i need to know the x and y coordinates of each div. That's why i want to create a table with the X and Y position of each div. X:0 & Y:0 = div:eq(0), X:0 Y:1 = div:eq(1), X:0 Y:2 = div:eq(2), X:0 Y:3 = div:eq(3), X:1 Y:0 = div:eq(4) etc.. What is the best way to do a table like that? Creating a OBJECT like this: { 00: 0, 01: 1, 02: 2, etc.. } or is it better to create a array? position[0][0] = 0 the thing is i need to use the table in multiple way's.. for example the user clicked the div nb: 13 what are the coordinates of this div or what is the eq of the div x: 12 y: 5. Thats how i do it right now: var row = 0 var col = 0 var eq = 0 c.find('div').each(function(i){ // c = $('div#stage') if (i !=0 && $(this).offset().top != $(this).prev().offset().top){ row++ col = 0 } $(this).attr({'row': row, 'col': col }) col++ }) I think it would be faster to build a table with the coordinates, instead of adding them as attr or data to the DOM. but i cant figure out how to do this technically. How would you solve this problem width JS / jQuery?

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  • [iPhone] UIScrollView notifications

    - by ryyst
    Hi, I'm coding an app that works much like Apple's Weather.app: There's a UIPageControl at the bottom and a UIScrollView in the middle of the screen. In my code, I implemented the - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView method to figure out when the user did move to a new page. If they move to a new page, I load the adjacent pages' data, as to make further page-switching faster. (In one of Apple's examples, the - (void)scrollViewDidScroll:(UIScrollView *)sender is used, but that causes my app to shortly hang when loading a new page, so it's not suitable.) That code works very well. I'm using scrollRectToVisible:: to programmatically scroll inside the scrollview when the user clicks the UIPageControl. The problem is that the scrollRectToVisible: doesn't post a notification to the UIScrollViewDelegate when it's done scrolling - so the code responsible for loading adjacent pages never get's called when using the UIPageControl. Is there any way to make the UIScrollView notify its delegate when it gets called by the scrollRectToVisible: method? Or will I have to use threads in order to prevent my app from freezing? Thanks! -- Ry

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  • Java: Efficiency of the readLine method of the BufferedReader and possible alternatives

    - by Luhar
    We are working to reduce the latency and increase the performance of a process written in Java that consumes data (xml strings) from a socket via the readLine() method of the BufferedReader class. The data is delimited by the end of line separater (\n), and each line can be of a variable length (6KBits - 32KBits). Our code looks like: Socket sock = connection; InputStream in = sock.getInputStream(); BufferedReader inputReader = new BufferedReader(new InputStreamReader(in)); ... do { String input = inputReader.readLine(); // Executor call to parse the input thread in a seperate thread }while(true) So I have a couple of questions: Will the inputReader.readLine() method return as soon as it hits the \n character or will it wait till the buffer is full? Is there a faster of picking up data from the socket than using a BufferedReader? What happens when the size of the input string is smaller than the size of the Socket's receive buffer? What happens when the size of the input string is bigger than the size of the Socket's receive buffer? I am getting to grips (slowly) with Java's IO libraries, so any pointers are much appreciated. Thank you!

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  • Is there a fast alternative to creating a Texture2D from a Bitmap object in XNA?

    - by Matthew Bowen
    I've looked around a lot and the only methods I've found for creating a Texture2D from a Bitmap are: using (MemoryStream s = new MemoryStream()) { bmp.Save(s, System.Drawing.Imaging.ImageFormat.Png); s.Seek(0, SeekOrigin.Begin); Texture2D tx = Texture2D.FromFile(device, s); } and Texture2D tx = new Texture2D(device, bmp.Width, bmp.Height, 0, TextureUsage.None, SurfaceFormat.Color); tx.SetData<byte>(rgbValues, 0, rgbValues.Length, SetDataOptions.NoOverwrite); Where rgbValues is a byte array containing the bitmap's pixel data in 32-bit ARGB format. My question is, are there any faster approaches that I can try? I am writing a map editor which has to read in custom-format images (map tiles) and convert them into Texture2D textures to display. The previous version of the editor, which was a C++ implementation, converted the images first into bitmaps and then into textures to be drawn using DirectX. I have attempted the same approach here, however both of the above approaches are significantly too slow. To load into memory all of the textures required for a map takes for the first approach ~250 seconds and for the second approach ~110 seconds on a reasonable spec computer. If there is a method to edit the data of a texture directly (such as with the Bitmap class's LockBits method) then I would be able to convert the custom-format images straight into a Texture2D and hopefully save processing time. Any help would be very much appreciated. Thanks

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  • How do you efficiently bulk index lookups?

    - by Liron Shapira
    I have these entity kinds: Molecule Atom MoleculeAtom Given a list(molecule_ids) whose lengths is in the hundreds, I need to get a dict of the form {molecule_id: list(atom_ids)}. Likewise, given a list(atom_ids) whose length is in the hunreds, I need to get a dict of the form {atom_id: list(molecule_ids)}. Both of these bulk lookups need to happen really fast. Right now I'm doing something like: atom_ids_by_molecule_id = {} for molecule_id in molecule_ids: moleculeatoms = MoleculeAtom.all().filter('molecule =', db.Key.from_path('molecule', molecule_id)).fetch(1000) atom_ids_by_molecule_id[molecule_id] = [ MoleculeAtom.atom.get_value_for_datastore(ma).id() for ma in moleculeatoms ] Like I said, len(molecule_ids) is in the hundreds. I need to do this kind of bulk index lookup on almost every single request, and I need it to be FAST, and right now it's too slow. Ideas: Will using a Molecule.atoms ListProperty do what I need? Consider that I am storing additional data on the MoleculeAtom node, and remember it's equally important for me to do the lookup in the molecule-atom and atom-molecule directions. Caching? I tried memcaching lists of atom IDs keyed by molecule ID, but I have tons of atoms and molecules, and the cache can't fit it. How about denormalizing the data by creating a new entity kind whose key name is a molecule ID and whose value is a list of atom IDs? The idea is, calling db.get on 500 keys is probably faster than looping through 500 fetches with filters, right?

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  • Did the Unity Team fix that "generics handling" bug back in 2008?

    - by rasx
    At my level of experience with Unity it might be faster to ask whether the "generics handling" bug acknowledged by ctavares back in 2008 was fixed in a public release. Here was the problem (which might be my problem today): Hi, I get an exception when using .... container.RegisterType(typeof(IDictionary<,), typeof(Dictionary<,)); The exception is... "Resolution of the dependency failed, type = \"IDictionary2\", name = \"\". Exception message is: The current build operation (build key Build Key[System.Collections.Generic.Dictionary2[System.String,System.String], null]) failed: The current build operation (build key Build Key[System.Collections.Generic.Dictionary2[System.String,System.String], null]) failed: The type Dictionary2 has multiple constructors of length 2. Unable to disambiguate. When I attempt... IDictionary myExampleDictionary = container.Resolve(); Here was the moderated response: There are no books that'll help, Unity is a little too new for publishers to have caught up yet. Unfortunately, you've run into a bug in our generics handling. This is currently fixed in our internal version, but it'll be a little while before we can get the bits out. In the meantime, as a workaround you could do something like this instead: public class WorkaroundDictionary : Dictionary { public WorkaroundDictionary() { } } container.RegisterType(typeof(IDictionary<,),typeof(WorkaroundDictionary<,)); The WorkaroundDictionary only has the default constructor so it'll inject no problem. Since the rest of your app is written in terms of IDictionary, when we get the fixed version done you can just replace the registration with the real Dictionary class, throw out the workaround, and everything will still just work. Sorry about the bug, it'll be fixed soon!

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  • Oracle output: cursor, file, or very long string?

    - by Klay
    First, the setup: I have a table in an Oracle10g database with spatial columns. I need to be able to pass in a spatial reference so that I can reproject the geometry into an arbitrary coordinate system. Ultimately, I need to compress the results of this projection to a zip file and make it available for download through a Silverlight project. I would really appreciate ideas as to the best way to accomplish this. In the examples below, the SRID is the Spatial reference ID integer used to convert the geometric points into a new coordinate system. In particular, I can see a couple of possibilities. There are many more, but this is an idea of how I'm thinking: a) Pass SRID to a dynamic view -- perform projection, output a cursor -- send cursor to UTL_COMPRESS -- write output to a file (somehow) -- send URL to Silverlight app b) Use SRID to call Oracle function from Silverlight app -- perform projection, output a string -- build strings into a file -- compress file using SharpZipLib library in .NET -- send bytestream back to Silverlight app I've done the first two steps of b), and the conversion of 100 points took about 7 seconds, which is unacceptably slow. I'm hoping it would be faster doing the processing totally in Oracle. If anyone can see potential problems with either way of doing this, or can suggest a better way, it would be very helpful. Thanks!

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  • Benefits of migrating my work to a new web development framework?

    - by John
    When I first started programming with PHP, I was ignorant of other php frameworks (like code igniter, cake php, etc...). So I fell into the trap of re-inventing wheels, which had the benefit of being "fun" and "educational". Overtime, I discovered other open source products that I found useful, like smarty templating engine, jquery library, tcpdf library, fdf etc...so I started bundling these technologies along with things I've built over the years into a LAMP development framework to make life easier for myself. This pass year, I've been having fun developing on the code igniter framework. It does many of the things I do in my framework. Coding in CI feels natural because the MVC and ORM feels similar to the MVC and ORM of my framework. So now I'm contemplating migrating a lot of the plugins in my framework over to CI. The pros and cons I can think of for such a project are: Pros: benefit from the vast community of CI developers lots of other developers will be familiar with it better documentation Cons: I've built a lot of useful plugins against my own framework, and it will take a lot of time to move even just the essential ones at the moment, I still, work faster against my own framework than CI, just because I'm more familiar with it even if I did migrate to CI, there will always be newer and better frameworks in the near future, and i'll be contemplating this scenario again So my question is the following: perhaps I should leave my old framework as is, and for each new project I receive, I make a decision on whether the requirements are best served by developing with CI or my own framework. Is this the right approach?

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  • How does loop address alignment affect the speed on Intel x86_64?

    - by Alexander Gololobov
    I'm seeing 15% performance degradation of the same C++ code compiled to exactly same machine instructions but located on differently aligned addresses. When my tiny main loop starts at 0x415220 it's faster then when it is at 0x415250. I'm running this on Intel Core2 Duo. I use gcc 4.4.5 on x86_64 Ubuntu. Can anybody explain the cause of slowdown and how I can force gcc to optimally align the loop? Here is the disassembly for both cases with profiler annotation: 415220 576 12.56% |XXXXXXXXXXXXXX 48 c1 eb 08 shr $0x8,%rbx 415224 110 2.40% |XX 0f b6 c3 movzbl %bl,%eax 415227 0.00% | 41 0f b6 04 00 movzbl (%r8,%rax,1),%eax 41522c 40 0.87% | 48 8b 04 c1 mov (%rcx,%rax,8),%rax 415230 806 17.58% |XXXXXXXXXXXXXXXXXXX 4c 63 f8 movslq %eax,%r15 415233 186 4.06% |XXXX 48 c1 e8 20 shr $0x20,%rax 415237 102 2.22% |XX 4c 01 f9 add %r15,%rcx 41523a 414 9.03% |XXXXXXXXXX a8 0f test $0xf,%al 41523c 680 14.83% |XXXXXXXXXXXXXXXX 74 45 je 415283 ::Run(char const*, char const*)+0x4b3 41523e 0.00% | 41 89 c7 mov %eax,%r15d 415241 0.00% | 41 83 e7 01 and $0x1,%r15d 415245 0.00% | 41 83 ff 01 cmp $0x1,%r15d 415249 0.00% | 41 89 c7 mov %eax,%r15d 415250 679 13.05% |XXXXXXXXXXXXXXXX 48 c1 eb 08 shr $0x8,%rbx 415254 124 2.38% |XX 0f b6 c3 movzbl %bl,%eax 415257 0.00% | 41 0f b6 04 00 movzbl (%r8,%rax,1),%eax 41525c 43 0.83% |X 48 8b 04 c1 mov (%rcx,%rax,8),%rax 415260 828 15.91% |XXXXXXXXXXXXXXXXXXX 4c 63 f8 movslq %eax,%r15 415263 388 7.46% |XXXXXXXXX 48 c1 e8 20 shr $0x20,%rax 415267 141 2.71% |XXX 4c 01 f9 add %r15,%rcx 41526a 634 12.18% |XXXXXXXXXXXXXXX a8 0f test $0xf,%al 41526c 749 14.39% |XXXXXXXXXXXXXXXXXX 74 45 je 4152b3 ::Run(char const*, char const*)+0x4c3 41526e 0.00% | 41 89 c7 mov %eax,%r15d 415271 0.00% | 41 83 e7 01 and $0x1,%r15d 415275 0.00% | 41 83 ff 01 cmp $0x1,%r15d 415279 0.00% | 41 89 c7 mov %eax,%r15d

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  • Can parser combinators be made efficient?

    - by Jon Harrop
    Around 6 years ago, I benchmarked my own parser combinators in OCaml and found that they were ~5× slower than the parser generators on offer at the time. I recently revisited this subject and benchmarked Haskell's Parsec vs a simple hand-rolled precedence climbing parser written in F# and was surprised to find the F# to be 25× faster than the Haskell. Here's the Haskell code I used to read a large mathematical expression from file, parse and evaluate it: import Control.Applicative import Text.Parsec hiding ((<|>)) expr = chainl1 term ((+) <$ char '+' <|> (-) <$ char '-') term = chainl1 fact ((*) <$ char '*' <|> div <$ char '/') fact = read <$> many1 digit <|> char '(' *> expr <* char ')' eval :: String -> Int eval = either (error . show) id . parse expr "" . filter (/= ' ') main :: IO () main = do file <- readFile "expr" putStr $ show $ eval file putStr "\n" and here's my self-contained precedence climbing parser in F#: let rec (|Expr|) (P(f, xs)) = Expr(loop (' ', f, xs)) and loop = function | ' ' as oop, f, ('+' | '-' as op)::P(g, xs) | (' ' | '+' | '-' as oop), f, ('*' | '/' as op)::P(g, xs) -> let h, xs = loop (op, g, xs) let op = match op with | '+' -> (+) | '-' -> (-) | '*' -> (*) | '/' -> (/) loop (oop, op f h, xs) | _, f, xs -> f, xs and (|P|) = function | '('::Expr(f, ')'::xs) -> P(f, xs) | c::xs when '0' <= c && c <= '9' -> P(int(string c), xs) My impression is that even state-of-the-art parser combinators waste a lot of time back tracking. Is that correct? If so, is it possible to write parser combinators that generate state machines to obtain competitive performance or is it necessary to use code generation?

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  • Should I persist images on EBS or S3?

    - by javanes
    I am migrating my Java,Tomcat, Mysql server to AWS EC2. I have already attached EBS volume for storing MySql data. In my web application people may upload images. So I should persist them. There are 2 alternatives in my mind: Save uploaded images to EBS volume. Use the S3 service. The followings are my notes, please be skeptic about them, as my expertise is not on servers, but software development. EBS plus: S3 storage is more expensive. (0.15 $/Gb 0.1$/Gb) S3 plus: Serving statics from EBS may influence my web server's performance negatively. Is this true? Does Serving images affect server performance notably? For S3 my server will not be responsible for serving statics. S3 plus: Serving statics from EBS may result I/O cost, probably it will be minor. EBS plus: People say EBS is faster. S3 plus: People say S3 is more safe for persistence. EBS plus: No need to learn API, it is straight forward to save the images to EBS volume. Namely I can not decide, will be happy if you guide. Thanks

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  • Reading text files line by line, with exact offset/position reporting

    - by Benjamin Podszun
    Hi. My simple requirement: Reading a huge ( a million) line test file (For this example assume it's a CSV of some sorts) and keeping a reference to the beginning of that line for faster lookup in the future (read a line, starting at X). I tried the naive and easy way first, using a StreamWriter and accessing the underlying BaseStream.Position. Unfortunately that doesn't work as I intended: Given a file containing the following Foo Bar Baz Bla Fasel and this very simple code using (var sr = new StreamReader(@"C:\Temp\LineTest.txt")) { string line; long pos = sr.BaseStream.Position; while ((line = sr.ReadLine()) != null) { Console.Write("{0:d3} ", pos); Console.WriteLine(line); pos = sr.BaseStream.Position; } } the output is: 000 Foo 025 Bar 025 Baz 025 Bla 025 Fasel I can imagine that the stream is trying to be helpful/efficient and probably reads in (big) chunks whenever new data is necessary. For me this is bad.. The question, finally: Any way to get the (byte, char) offset while reading a file line by line without using a basic Stream and messing with \r \n \r\n and string encoding etc. manually? Not a big deal, really, I just don't like to build things that might exist already..

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  • Finding a MIME type for a file on windows

    - by rmeador
    Is there a way to get a file's MIME type using some system call on Windows? I'm writing an IIS extension in C++, so it must be callable from C++, and I do have access to IIS if there is some functionality exposed. Obviously, IIS itself must be able to do this, but my googling has been unable to find out how. I did find this .net related question here on SO, but that doesn't give me much hope (as neither a good solution nor a C++ solution is mentioned there). I need it so I can serve up dynamic files using the appropriate content type from my app. My plan is to first consult a list of MIME types within my app, then fall back to the system's MIME type listing (however that works; obviously it exists since it's how you associate files with programs). I only have a file extension to work with in some cases, but in other cases I may have an actual on-disk file to examine. Since these will not be user-uploaded files, I believe I can trust the extension and I'd prefer an extension-only lookup solution since it seems simpler and faster. Thanks!

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