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  • Plotting an Arc in Discrete Steps

    - by phobos51594
    Good afternoon, Background My question relates to the plotting of an arbitrary arc in space using discrete steps. It is unique, however, in that I am not drawing to a canvas in the typical sense. The firmware I am designing is for a gcode interpreter for a CNC mill that will translate commands into stepper motor movements. Now, I have already found a similar question on this very site, but the methodology suggested (Bresenham's Algorithm) appears to be incompatable for moving an object in space, as it only relies on the calculation of one octant of a circle which is then mirrored about the remaining axes of symmetry. Furthermore, the prescribed method of calculation an arc between two arbitrary angles relies on trigonometry (I am implementing on a microcontroller and would like to avoid costly trig functions, if possible) and simply not taking the steps that are out of the range. Finally, the algorithm only is designed to work in one rotational direction (e.g. counterclockwise). Question So, on to the actual question: Does anyone know of a general-purpose algorithm that can be used to "draw" an arbitrary arc in discrete steps while still giving respect to angular direction (CW / CCW)? The final implementation will be done in C, but the language for the purpose of the question is irrelevant. Thank you in advance. References S.O post on drawing a simple circle using Bresenham's Algorithm: "Drawing" an arc in discrete x-y steps Wiki page describing Bresenham's Algorithm for a circle http://en.wikipedia.org/wiki/Midpoint_circle_algorithm Gcode instructions to be implemented (see. G2 and G3) http://linuxcnc.org/docs/html/gcode.html

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  • Articles about replication schemes/algorithms?

    - by jkff
    I'm designing an hierarchical distributed system (every node has zero or more "master" nodes to which it propagates its current data). The data gets continuously updated and I'd like to guarantee that at least N nodes have almost-current data at any given time. I do not need complete consistency, only eventual consistency (t.i. for any time instant, the current snapshot of data should eventually appear on at least N nodes. It is tricky to define the term "current" here, but still). Nodes may fail and go back up at any moment, and there is no single "central" node. O overflowers! Point me to some good papers describing replication schemes. I've so far found one: Consistency Management in Optimistic Replication Algorithms

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  • How to write a spinlock without using CAS

    - by Martin
    Following on from a discussion which got going in the comments of this question. How would one go about writing a Spinlock without CAS operations? As the other question states: The memory ordering model is such that writes will be atomic (if two concurrent threads write a memory location at the same time, the result will be one or the other). The platform will not support atomic compare-and-set operations.

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  • The Implications of Modern Day Software Development Abstractions

    - by Andreas Grech
    I am currently doing a dissertation about the implications or dangers that today's software development practices or teachings may have on the long term effects of programming. Just to make it clear: I am not attacking the use abstractions in programming. Every programmer knows that abstractions are the bases for modularity. What I want to investigate with this dissertation are the positive and negative effects abstractions can have in software development. As regards the positive, I am sure that I can find many sources that can confirm this. But what about the negative effects of abstractions? Do you have any stories to share that talk about when certain abstractions failed on you? The main concern is that many programmers today are programming against abstractions without having the faintest idea of what the abstraction is doing under-the-covers. This may very well lead to bugs and bad design. So, in you're opinion, how important is it that programmers actually know what is going below the abstractions? Taking a simple example from Joel's Back to Basics, C's strcat: void strcat( char* dest, char* src ) { while (*dest) dest++; while (*dest++ = *src++); } The above function hosts the issue that if you are doing string concatenation, the function is always starting from the beginning of the dest pointer to find the null terminator character, whereas if you write the function as follows, you will return a pointer to where the concatenated string is, which in turn allows you to pass this new pointer to the concatenation function as the *dest parameter: char* mystrcat( char* dest, char* src ) { while (*dest) dest++; while (*dest++ = *src++); return --dest; } Now this is obviously a very simple as regards abstractions, but it is the same concept I shall be investigating. Finally, what do you think about the issue that schools are preferring to teach Java instead of C and Lisp ? Can you please give your opinions and your says as regards this subject? Thank you for your time and I appreciate every comment.

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  • Technical choices in unmarshaling hash-consed data

    - by Pascal Cuoq
    There seems to be quite a bit of folklore knowledge floating about in restricted circles about the pitfalls of hash-consing combined with marshaling-unmarshaling of data. I am looking for citable references to these tidbits. For instance, someone once pointed me to library aterm and mentioned that the authors had clearly thought about this and that the representation on disk was bottom-up (children of a node come before the node itself in the data stream). This is indeed the right way to do things when you need to re-share each node (with a possible identical node already in memory). This re-sharing pass needs to be done bottom-up, so the unmarshaling itself might as well be, too, so that it's possible to do everything in a single pass. I am in the process of describing difficulties encountered in our own context, and the solutions we found. I would appreciate any citable reference to the kind of aforementioned folklore knowledge. Some people obviously have encountered the problems before (the aterm library is only one example). But I didn't find anything in writing. Even the little piece of information I have about aterm is hear-say. I am not worried it's not reliable (you can't make this up), but "personal communication" and "look how it's done in the source code" are considered poor form in citations. I have enough references on hash-consing alone. I am only interested in references where it interferes with other aspects of programming, such as marshaling or distribution.

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  • Why is processing a sorted array faster than an unsorted array?

    - by GManNickG
    Here is a piece of code that shows some very peculiar performance. For some strange reason, sorting the data miraculously speeds up the code by almost 6x: #include <algorithm> #include <ctime> #include <iostream> int main() { // generate data const unsigned arraySize = 32768; int data[arraySize]; for (unsigned c = 0; c < arraySize; ++c) data[c] = std::rand() % 256; // !!! with this, the next loop runs faster std::sort(data, data + arraySize); // test clock_t start = clock(); long long sum = 0; for (unsigned i = 0; i < 100000; ++i) { // primary loop for (unsigned c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } double elapsedTime = static_cast<double>(clock() - start) / CLOCKS_PER_SEC; std::cout << elapsedTime << std::endl; std::cout << "sum = " << sum << std::endl; } Without std::sort(data, data + arraySize);, the code runs in 11.54 seconds. With the sorted data, the code runs in 1.93 seconds. Initially I thought this might be just a language or compiler anomaly. So I tried it Java... import java.util.Arrays; import java.util.Random; public class Main { public static void main(String[] args) { // generate data int arraySize = 32768; int data[] = new int[arraySize]; Random rnd = new Random(0); for (int c = 0; c < arraySize; ++c) data[c] = rnd.nextInt() % 256; // !!! with this, the next loop runs faster Arrays.sort(data); // test long start = System.nanoTime(); long sum = 0; for (int i = 0; i < 100000; ++i) { // primary loop for (int c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } System.out.println((System.nanoTime() - start) / 1000000000.0); System.out.println("sum = " + sum); } } with a similar but less extreme result. My first thought was that sorting brings the data into cache, but my next thought was how silly that is because the array was just generated. What is going on? Why is a sorted array faster than an unsorted array? The code is summing up some independent terms, the order should not matter.

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  • Do you ever feel confident in your skills?

    - by Gary Willoughby
    As a self taught developer i always find myself questioning my skill and knowledge and always feel like i am falling behind in using new technology. Over a period of nearly 9 years i've studied most mainstream languages (especially C based ones), used lots of different OSes, read and absorbed many books and even written one myself. But i still feel i'm usless! Do professional developers ever get to the stage where they feel confident that they know what they are doing and are confident when submitting solutions/code? When do you know you're good enough?

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  • The Definitive Guide To Website Authentication (beta)

    - by Michiel de Mare
    Form Based Authentication For Websites Please help us create the definitive resource for this topic. We believe that stackoverflow should not just be a resource for very specific technical questions, but also for general guidelines on how to solve variations on common problems. "Form Based Authentication For Websites" should be a fine topic for such an experiment. It should include topics such as: how to log in how to remain logged in how to store passwords using secret questions forgotten password functionality OpenID "Remember me" checkbox Browser autocompletion of usernames and passwords secret urls (public urls protected by digest) checking password strength email validation and much more It should not include things like: roles and authorization http basic authentication Please help us by Suggesting subtopics Submitting good articles about this subject Editing the official answer (as soon as you have enough karma) UPDATE: See the terrific 7-part series by Jens Roland below.

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  • Choosing a method for a webservice

    - by Wrikken
    I'm asked to set up a new webservice which should be easily usable in whatever language (php, .NET, Java, etc.) possible. Of course rolling my own can be done, accepting different content-types (xml / x-www-form-urlencoded (normal post) / json / etc.), but an existing method or mechanism would of course be prefered, cutting down time spent on development for the consumers of the service. The webservice does accept modifications / sets (it is not only simply data retrieval), but those will most likely be quite a lot less then gets (we estimate about 2.5% sets, 97.5 gets). The term webservice here indicates the protocol should go over HTTP, not being able to implement it totally client sided (javascript in the end-users browser etc.), as it needs specific user authentication. Both gets and sets are pretty light on the parameter count (usually 1 to 4). Methods like REST (which I'd prefer for only gets), XML-RPC & SOAP (might be a bit overkill, but has the advantage of explicitly defined methods and returns) are the usual suspects. What in your opinion / experience is the most widely 'spoken' and most easily implementable protocol in different languages (seen from the consumers' viewpoint) which could fullfill this need?

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  • How to notice unusual news activity

    - by ??iu
    Suppose you were able keep track of the news mentions of different entities, like say "Steve Jobs" and "Steve Ballmer". What are ways that could you tell whether the amount of mentions per entity per a given time period was unusual relative to their normal degree of frequency of appearance? I imagine that for a more popular person like Steve Jobs an increase of like 50% might be unusual (an increase of 1000 to 1500), while for a relatively unknown CEO an increase of 1000% for a given day could be possible (an increase of 2 to 200). If you didn't have a way of scaling that your unusualness index could be dominated by unheard-ofs getting their 15 minutes of fame.

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  • Develop an classic UI or be bold with a newer design?

    - by DeanMc
    Forgive me if this is the wrong place but I am curious as to how other programmers feel about this topic: I am currently working on my portfolio site, it is being designed and built in silverlight 4. I initially started off with a typical stylised e-folio theme much like a standard website in terms of layout and flow. As I work more in the concept stages something has struck me. Am I trying to shoe-horn yesterday into today? What I am talking about is UI expectations. I'm all for clean user interfaces but that does not mean they should not take advantage of new concepts in presentation right? If you where to develop a site in silverlight as your own portfolio piece would you stick to the tried and tested "website" feel or would you try to come up with a UI that is intuitive and complements the technology? I feel that UI discussions are all the more important now that all forms of web development are allowing better methods to engage the user.

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  • What's the best example of pure show-off code you've seen?

    - by Damovisa
    Let's face it, programmers can be show-offs. I've seen a lot of code that was only done a particular way to prove how smart the person who wrote it was. What's the best example of pure show-off code you've seen (or been responsible for) in your time? For me, it'd have to be the guy who wrote FizzBuzz in one line on a whiteboard during a programming interview. Not really that impressive in the scheme of things, but completely unnecessary and pure, "look-what-I-can-do". I've lost the original code, but I think it was something like this (linebreaks for readability): Enumerable.Range(1,100).ToList().ForEach( n => Console.WriteLine( (n%3==0) ? (n%5==0) ? "FizzBuzz" : "Fizz" : (n%5==0) ? "Buzz" : n ) );

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  • Semantically linking to code snippets

    - by Tim
    What's the most simple and semantic way of presenting code snippets in HTML? Possible XHTML syntax <a href="code_sample.php" type="text/x-php"> Example of widget creation </a> Example of linked file (code_sample.php): // Create a new widget $widget = new widget(); Pros: Semantically uses title to describe the source code being referenced Up to the client to render snippet Having very many custom server-side implementations tells me it should be standardized Browsers can have plug-ins for copy+paste, download, etc Seems to me this is where it belongs (not in Javascript) Degradation: non-compliant browsers receive a link to the associated content Cons: Not semantic enough? Seems wrong to replace hyperlinks with source code for presentation <object> might be better, but wouldn't degrade as nicely. Background I'm trying to create a "personal" XHTML standard for storing notes (wow, this is probably among the nerdiest things I've said). Since notes are just "scratch" it needs to be very lightweight. SO's markdown is very lightweight but not semantic enough for my needs. Plus, now I'm just curious. What's the most ideal syntax for linking to client-rendered code-snippets?

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  • Are there any good sites for blogging about programming?

    - by Jacques Bosch
    I have a few programming articles I would like to write, but I do not have a site of my own - yet ;). Is there a site that is specifically geared toward technical / programming topics, with great functionality and style? Or will I have to go with things like wordpress or blogspot? I would like a site that can track number of views and that has an intuitive commenting system. Any thoughts would be appreciated.

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  • Is there anyone out there that codes like I do?

    - by Jacob Relkin
    Hi, Some people have told me that my coding style is a lot different than theirs. I think I am somewhat neurotic when it comes to spacing and indenting though. Here's a snippet to show you what I mean: - ( void ) applicationDidFinishLaunching: ( UIApplication *) application { SomeObject *object = [ [ SomeObject alloc ] init ]; int x = 100 / 5; object.someInstanceVariable = ( ( 4 * x ) + rand() ); [ object someMethod ]; } Notice how I space out all of my brackets/parentheses, start curly braces on the same line, "my code has room to breathe", so to speak. So my questions are a) is this normal and b) What's your coding style?

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  • What programming language is this?

    - by Richard M.
    I recently stumbled over a very odd source listing on a rather old programming-related site (lost it somewhere in my browser history as I didn't care about it at first). I think that this is part of a simple (console-based?) snake game. I searched and searched but didn't find a language that looked somwhat like this. This seems like a mix of Python, Ruby and C++. What the hell? What programming-language is the below source listing written in? Maybe you can figure it out? my Snake.hasProps { length parts xDir yDir } & hasMethods { init: length = 0 parts[0].x,y = 5 move: parts[ 0 ].x,y.!add xDir | yDir # Move the head map parts(i,v): parts[ i ] = parts[ i + 1 ] checkBiteSelf checkFeed checkBiteSelf: part } my SnakePart.hasProps { x y } fork SnakePart to !Feed my Game.hasProps { frameTime = 30 } & hasMethods { init: mainloop mainloop: sys.util.sleep frameTime Snake.move Field.getInput -> Snake.xDir | Snake.yDir Field.reDraw with Snake & Feed & Game # For FPS } main.isMethod { game.init }

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  • Shortest distance between a point and a line segment

    - by Eli Courtwright
    I need a basic function to find the shortest distance between a point and a line segment. Feel free to write the solution in any language you want; I can translate it into what I'm using (Javascript). EDIT: My line segment is defined by two endpoints. So my line segment AB is defined by the two points A (x1,y1) and B (x2,y2). I'm trying to find the distance between this line segment and a point C (x3,y3). My geometry skills are rusty, so the examples I've seen are confusing, I'm sorry to admit.

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  • How a servlet can get the absolute path to a file outside of the servlet?

    - by WolfmanDragon
    We have been using System.getProperties("user.dir") to get the location of a properties file. Now that it has been deployed on Tomcat(via servlet), the System call is giving the location as tomcat and not at the location at where the properties file exist. How can we call the the properties file dynamically? Given: Tomcat is not the only way the app will be deployed We have no control on where the app may be placed. Relative paths will not work as that Vista is being used and Vista breaks relative paths. This must work on all OS, including(but not limited to) Linux, XP and Vista. EDIT I implied this, but in case I was not clear enough, I have no way of knowing the path String.

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  • Calculate date from numeric value

    - by elias
    The number 71867806 represents the present day, with the smallest unit of days. How can I calculate the currente date from it? (or) convert it into an Unix timestamp? Solution shouldn't use language depending features. Thanks!

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