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  • Understanding run time code interpretation and execution

    - by Bob
    I'm creating a game in XNA and was thinking of creating my own scripting language (extremely simple mind you). I know there's better ways to go about this (and that I'm reinventing the wheel), but I want the learning experience more than to be productive and fast. When confronted with code at run time, from what I understand, the usual approach is to parse into a machine code or byte code or something else that is actually executable and then execute that, right? But, for instance, when Chrome first came out they said their JavaScript engine was fast because it compiles the JavaScript into machine code. This implies other engines weren't compiling into machine code. I'd prefer not compiling to a lower language, so are there any known modern techniques for parsing and executing code without compiling to low level? Perhaps something like parsing the code into some sort of tree, branching through the tree, and comparing each symbol and calling some function that handles that symbol? (Wild guessing and stabbing in the dark)

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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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  • 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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  • Placement of defensive structures in a game

    - by Martin
    I am working on an AI bot for the game Defcon. The game has cities, with varying populations, and defensive structures with limited range. I'm trying to work out a good algorithm for placing defence towers. Cities with higher populations are more important to defend Losing a defence tower is a blow, so towers should be placed reasonably close together Towers and cities can only be placed on land So, with these three rules, we see that the best kind of placement is towers being placed in a ring around the largest population areas (although I don't want an algorithm just to blindly place a ring around the highest area of population, sometime there might be 2 sets of cities far apart, in which case the algorithm should make 2 circles, each one half my total towers). I'm wondering what kind of algorithms might be used for determining placement of towers?

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  • How do you reproduce bugs that occur sporadically?

    - by furtelwart
    We have a bug in our application that does not occur every time and therefore we don't know its "logic". I don't even get it reproduced in 100 times today. Disclaimer: This bug exists and I've seen it. It's not a pebkac or something similar. What are common hints to reproduce this kind of bug?

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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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  • 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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  • What do we log and why do we log it?

    - by Lucas
    This has been bugging me for quite some time. Reading various questions on SO, blogs and listening to colleagues, I keep hearing how important "logging" is. How various logging frameworks stack up against each other, and how there are so many to pick from it's (apparently) ridiculous. Now, I know what logging is. What I don't know is what is supposed to be logged and why. Sure, I can guess. Exceptions? Sounds like something one might want to log... but which exceptions? And is it only exceptions? And what do I do with the logged information? If it's an in-house app, then that could probably be put to good use, but if it's a commercial desktop application, how is the log of... whatever... helping anyone? I doubt regular users would be peeking inside. Is it then something you ask the users to provide on request? I'm deeply frustrated by my own ignorance in this. It's also surprising how little information there is about this. The info on the websites of the various logging frameworks is all written for an audience that already knows what it wants to log, and knows why it needs to do so. Same things goes for the various discussions on SO about logging, like for instance this highly voted up question on Logging best practices. For a question with so many votes, it's almost comical how there's next to nothing in there that would answer my what and why questions. So being finally fed up, I'm asking here: what do people log, and why do they log it?

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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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  • 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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  • Statements and state

    - by FredOverflow
    Is there any deeper meaning in the fact that the word "statement" starts with the word "state", or is that just a curious coincidence? Note that english is not my native language, so the answer might be obvious to you, but not me ;)

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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 any valid reason radians are used as the inputs to trig function in many modern languages?

    - by johnmortal
    Is there any pressing reason trig functions should use radian inputs in modern programming languages? As far as I know radians are typically ugly to deal with except in three cases: (1) You want to compute an arc length and you know the angle of the arc and (2) You need to do symbolic calculus with trig functions (3) certain infinite series expansion look prettier if the input is in radians. None of these scenarios seem like a worthy justification for every programming language I am familiar with using radian inputs for Sin, Cos, Tangent, etc... The third one sounds good because it might mean one gets faster computations using radians (very slightly faster- the cost of one additional floating point multiplication ) , but I am dubious even of that because most commonly the developer had to take an extra step to put the angle in radians in the first place. The other two are ridiculous justifications for all the added obscurity.

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  • What is the most efficient way to store a mapping "key -> event stream"?

    - by jkff
    Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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  • How do we achieve "substring-match" under O(n) time?

    - by Pacerier
    I have an assignment that requires reading a huge file of random inputs, for example: Adana Izmir Adnan Menderes Apt Addis Ababa Aden ADIYAMAN ALDAN Amman Marka Intl Airport Adak Island Adelaide Airport ANURADHAPURA Kodiak Apt DALLAS/ADDISON Ardabil ANDREWS AFB etc.. If I specify a search term, the program is supposed to find the lines whereby a substring occurs. For example, if the search term is "uradha", the program is supposed to show ANURADHAPURA. If the search term is "airport", the program is supposed to show Amman Marka Intl Airport, Adelaide Airport A quote from the assignment specs: "You are to program this application taking efficiency into account as though large amounts of data and processing is involved.." I could easily achieve this functionality using a loop but the performance would be O(n). I was thinking of using a trie but it seems to only work if the substring starts from index 0. I was wondering what solutions are there which gives a performance better than O(n)?

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  • Compiler Construction course

    - by donpal
    I'm looking for a course (preferably video, much preferably) like MIT's video courses on Compiler Construction. Can someone point me to some decent resources or help material (preferably video)?

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  • How should I implement items that are normalized in the Database, in Object Oriented Design?

    - by Jonas
    How should I implement items that are normalized in the Database, in Object Oriented classes? In the database I have a big table of items and a smaller of groups. Each item belong to one group. This is how my database design look like: +----------------------------------------+ | Inventory | +----+------+-------+----------+---------+ | Id | Name | Price | Quantity | GroupId | +----+------+-------+----------+---------+ | 43 | Box | 34.00 | 456 | 4 | | 56 | Ball | 56.50 | 3 | 6 | | 66 | Tin | 23.00 | 14 | 4 | +----+------+-------+----------+---------+ Totally 3000 lines +----------------------+ | Groups | +---------+------+-----+ | GroupId | Name | VAT | +---------+------+-----+ | 4 | Mini | 0.2 | | 6 | Big | 0.3 | +---------+------+-----+ Totally 10 lines I will use the OOP classes in a GUI, where the user can edit Items and Groups in the inventory. It should also be easy to do calculations with a bunch of items. The group information like VAT are needed for the calculations. I will write an Item class, but do I need a Group class? and if I need it, should I keep them in a global location or how do I access it when I need it for Item-calculations? Is there any design pattern for this case?

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  • Need some help understanding this problem

    - by Legend
    I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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  • Code Golf: Print the entire "12 Days of Christmas" song in the fewest lines of code.

    - by fizzer
    Print all 12 verses of the popular holiday song. By 12 verses I mean the repetition of each line as is sung in the song, ie Verse One: On the first day of Christmas my true love gave to me a partridge in a pear tree. Verse Two On the second day of Christmas my true love gave to me two turtle doves and a partridge in a pear tree. ... Verse N: On the nth day of Christmas my true love gave to me (Verse N-1 without the first line) (line added in verse N)

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  • Bulding an multi-platform SWT application using Ant

    - by Mridang Agarwalla
    I'm writing an SWT application which can be used on Windows (32/64 bit) and Mac OSX (32/64 bit). Apart from the JRE I rely on the SWT library found here. I can find four versions of the SWT library depending upon my target platforms (as mentioned above). When building my application, how can I compile using the correct SWT Jar? If possible, I'd like to try and avoid hard-coding the Jar version, platform and architecture. The SWT Jars are named like this: swt-win32-x86_64.jar swt-win32-x86_32.jar swt-macosx-x86_32.jar swt-macosx-x86_64.jar (My project will be an open source project. I'd like people to be able to download the source and build it and therefore I've thought of including all the four versions of the SWT Jars in the source distribution. I hope this is the correct approach of publishing code relying on third-part libraries.) Thanks everyone.

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  • Beginner's resources/introductions to classification algorithms.

    - by Dirk
    Hi, everybody. I am entirely new to the topic of classification algorithms, and need a few good pointers about where to start some "serious reading". I am right now in the process of finding out, whether machine learning and automated classification algorithms could be a worthwhile thing to add to some application of mine. I already scanned through "How to Solve It: Modern heuristics" by Z. Michalewicz and D. Fogel (in particular, the chapters about linear classifiers using neuronal networks), and on the practical side, I am currently looking through the WEKA toolkit source code. My next (planned) step would be to dive into the realm of Bayesian classification algorithms. Unfortunately, I am lacking a serious theoretical foundation in this area (let alone, having used it in any way as of yet), so any hints at where to look next would be appreciated; in particular, a good introduction of available classification algorithms would be helpful. Being more a craftsman and less a theoretician, the more practical, the better... Hints, anyone?

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