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  • How to change password hashing algorithm when using spring security?

    - by harry
    I'm working on a legacy Spring MVC based web Application which is using a - by current standards - inappropriate hashing algorithm. Now I want to gradually migrate all hashes to bcrypt. My high level strategy is: New hashes are generated with bcrypt by default When a user successfully logs in and has still a legacy hash, the app replaces the old hash with a new bcrypt hash. What is the most idiomatic way of implementing this strategy with Spring Security? Should I use a custom Filter or my on AccessDecisionManager or …?

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  • Recursive algorithm for coalescing / collapsing list of dates into ranges.

    - by Dycey
    Given a list of dates 12/07/2010 13/07/2010 14/07/2010 15/07/2010 12/08/2010 13/08/2010 14/08/2010 15/08/2010 19/08/2010 20/08/2010 21/08/2010 I'm looking for pointers towards a recursive pseudocode algorithm (which I can translate into a FileMaker custom function) for producing a list of ranges, i.e. 12/07/2010 to 15/07/2010, 12/08/2010 to 15/08/2010, 19/08/2010 to 20/08/2010 The list is presorted and de-deuplicated. I've tried starting from both the first value and working forwards, and the last value and working backwards but I just can't seem to get it to work. Having one of those frustrating days... It would be nice if the signature was something like CollapseDateList( dateList, separator, ellipsis ) :-)

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  • Spring @Value annotation not using defaults when property is not present

    - by garyj
    Hi All I am trying to use @Value annotation in the parameters of a constructor as follows: @Autowired public StringEncryptor( @Value("${encryptor.password:\"\"}") String password, @Value("${encryptor.algorithm:\"PBEWithMD5AndTripleDES\"}") String algorithm, @Value("${encryptor.poolSize:10}") Integer poolSize, @Value("${encryptor.salt:\"\"}") String salt) { ... } When the properties file is present on the classpath, the properties are loaded perfectly and the test executes fine. However when I remove the properties file from the classpath, I would have expected that the default values would have been used, for example poolSize would be set to 10 or algorithm to PBEWithMD5AndTripleDES however this is not the case. Running the code through a debugger (which would only work after changing @Value("${encryptor.poolSize:10}") Integer poolSize to @Value("${encryptor.poolSize:10}") String poolSize as it was causing NumberFormatExceptions) I find that the defaults are not being set and the parameters are in the form of: poolSize = ${encryptor.poolSize:10} or algorithm = ${encryptor.algorithm:"PBEWithMD5AndTripleDES"} rather than the expected poolSize = 10 or algorithm = "PBEWithMD5AndTripleDES" Based on SPR-4785 the notation such as ${my.property:myDefaultValue} should work. Yet it's not happening for me! Thank you

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  • What's the largest (most complex) PHP algorithm ever implemented in a single monolithic PHP script?

    - by Alex R
    I'm working on a tool which converts PHP code to Scala. As one of the finishing touches, I'm in need of a really good (er, somewhat biased) benchmark. By dumb luck my first benchmark attempt was with some code which uses bcmath extensively, which unfortunately is 1000x slower in Java, making the Scala code 22x slower overall than the original PHP. So I'm looking for some meaningful PHP benchmark with the following characteristics: The source needs to be in a single file. I need it to be simple to setup - no databases, hard-to-find input files, etc. Simple text input and output preferred. It should not use features that are slow in Java (BigInteger, trigonometric functions, etc). It should not use exoteric or dynamic PHP functions (e.g. no "eval" or "variable vars"). It should not over-rely on built-in libraries, e.g. MD5, crypt, etc. It should not be I/O bound. A CPU-bound memory-hungry algorithm is preferred. Basically, intensive OO operations, integer and string manipulation, recursion, etc would be great. Thanks

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  • Is there an algorithm for finding an item that matches certain properties, like a 20 questions game?

    - by lala
    A question about 20 questions games was asked here: However, if I'm understanding it correctly, the answers seem to assume that each question will go down a hierarchal branching tree. A binary tree should work if the game went like this: Is it an animal? Yes. Is it a mammal? Yes. Is it a feline? Yes. Because feline is an example of a mammal and mammal is an example of an animal. But what if the questions go like this? Is it a mammal? Yes. Is it a predator? Yes. Does it have a long nose? No. You can't branch down a tree with those kinds of questions, because there are plenty of predators that aren't mammals. So you can't have your program just narrow it down to mammal and have predators be a subset of mammals. So is there a way to use a binary search tree that I'm not understanding or is there a different algorithm for this problem?

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  • How to specify hash algorithm when updating LDAP via Java?

    - by JuanZe
    Is there a way to specify the hash algorithm (MD5, SHA1, etc.) to use for storing the passwords when you update an Open LDAP directory using Java APIs with code like this: private void resetPassword(String principal, String newPassword) throws NamingException { InitialDirContext ctxAdmin = null; Hashtable<String, String> ctxData = new Hashtable<String, String>(); ctxData.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory"); ctxData.put(Context.PROVIDER_URL, "ldap://myserver:389"); ctxData.put(Context.SECURITY_AUTHENTICATION, "simple"); ctxData.put(Context.SECURITY_PRINCIPAL, "admin_dn"); ctxData.put(Context.SECURITY_CREDENTIALS, "admin_passwd"); InitialDirContext ctxAdmin = new InitialDirContext(ctxData); if (newPassword == null || newPassword.equals("")) { String msg = "Password can't be null"; throw new NamingException(msg); } else { if (principal == null || principal.equals("")) { String msg = "Principal can't be null"; throw new NamingException(msg); } else { if (ctxAdmin == null) { String errCtx = "Can't get LDAP context"; throw new NamingException(errCtx); } } } BasicAttribute attr = new BasicAttribute("userpassword", newPassword); ModificationItem modItem = new ModificationItem(DirContext.REPLACE_ATTRIBUTE, attr); ModificationItem[] items = new ModificationItem[1]; items[0] = modItem; ctxAdmin.modifyAttributes("cn=" + principal + ",ou=Users,dc=com", items); }

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  • is there a simple timed lock algorithm avoiding deadlock on multiple mutexes?

    - by Vicente Botet Escriba
    C++0x thread library or Boost.thread define a non-member variadic template function that locks all mutex at once that helps to avoid deadlock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); The same can be applied to a non-member variadic template function try_lock_until, which locks all the mutex until a given time is reached that helps to avoid deadlock like lock(...). template <class Clock, class Duration, class L1, class L2, class... L3> void try_lock_until( const chrono::time_point<Clock,Duration>& abs_time, L1&, L2&, L3&...); I have an implementation that follows the same design as the Boost function boost::lock(...). But this is quite complex. As I can be missing something evident I wanted to know if: is there a simple timed lock algorithm avoiding deadlock on multiple mutexes? If no simple implementation exists, can this justify a proposal to Boost? P.S. Please avoid posting complex solutions.

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  • emule algorithm and how to get fast download speed.

    - by Benjamin
    Actually, I use amule in ubuntu. Because emule users are much more, I wrote emule in this title. But whatever emule or amule, it's okay. Both of them are very similar. I want to get fast-download speed as much as I can. But I don't understand emule(or amule)'s detail functions and algorithms. These are always very qurious to me. If I provide higher upload-speed or more valuable files to other people, can I get benefit?(My download speed) Is serverlist important? Does it cause my download-speed? I captured a image for my amule. Please explain these columns and let me know your tips for getting fast speed. What does 8/9+23 mean in the Source column? What does 294/300(1) mean in the Source column? What does QR:608(0) mean in the Priority? What do I do for getting fast download speed as much as I can get? You can also explain other columns.

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  • Is (Ubuntu) Linux file copying algorithm better than Windows 7?

    - by Sarath
    Windows Copying is a real mess ever since Windows Vista. Even Microsoft claims they've improved the performance, from a user perspective, it's not quite visible. Even with single file the copying window appears too much time for 'Calculating' and then finishing the copy(Even after 100% completion some times the dialog remains active). At the same time, I was backing up some files in Ubuntu Linux. I felt it's really fast. Might be a feeling caused by faster UI updates. I read an informative post from Jeff Atwood few years back on Windows File Copying. but what my specific questions are Is (Ubuntu) Linux file performance is better than Windows-7? Are both algorithms, Windows and Linux is making use of multiple threads and pipelining mechanism to improve the speed? If yes, which one is better?

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  • A* algorithm works OK, but not perfectly. What's wrong?

    - by Bart van Heukelom
    This is my grid of nodes: I'm moving an object around on it using the A* pathfinding algorithm. It generally works OK, but it sometimes acts wrongly: When moving from 3 to 1, it correctly goes via 2. When going from 1 to 3 however, it goes via 4. When moving between 3 and 5, it goes via 4 in either direction instead of the shorter way via 6 What can be wrong? Here's my code (AS3): public static function getPath(from:Point, to:Point, grid:NodeGrid):PointLine { // get target node var target:NodeGridNode = grid.getClosestNodeObj(to.x, to.y); var backtrace:Map = new Map(); var openList:LinkedSet = new LinkedSet(); var closedList:LinkedSet = new LinkedSet(); // begin with first node openList.add(grid.getClosestNodeObj(from.x, from.y)); // start A* var curNode:NodeGridNode; while (openList.size != 0) { // pick a new current node if (openList.size == 1) { curNode = NodeGridNode(openList.first); } else { // find cheapest node in open list var minScore:Number = Number.MAX_VALUE; var minNext:NodeGridNode; openList.iterate(function(next:NodeGridNode, i:int):int { var score:Number = curNode.distanceTo(next) + next.distanceTo(target); if (score < minScore) { minScore = score; minNext = next; return LinkedSet.BREAK; } return 0; }); curNode = minNext; } // have not reached if (curNode == target) break; else { // move to closed openList.remove(curNode); closedList.add(curNode); // put connected nodes on open list for each (var adjNode:NodeGridNode in curNode.connects) { if (!openList.contains(adjNode) && !closedList.contains(adjNode)) { openList.add(adjNode); backtrace.put(adjNode, curNode); } } } } // make path var pathPoints:Vector.<Point> = new Vector.<Point>(); pathPoints.push(to); while(curNode != null) { pathPoints.unshift(curNode.location); curNode = backtrace.read(curNode); } pathPoints.unshift(from); return new PointLine(pathPoints); } NodeGridNode::distanceTo() public function distanceTo(o:NodeGridNode):Number { var dx:Number = location.x - o.location.x; var dy:Number = location.y - o.location.y; return Math.sqrt(dx*dx + dy*dy); }

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  • Can python and php work together?

    - by user71741
    I am having a mobile app created for ios. The developers built the app in php. The app requires an algorithm so I found another programmer to develop it. The algorithm programmer built the algorithm in python. The developers refuse to finish the app because they say it won't work with python, while the programmer insist it will. The programmer says put the algorithm in its on server and connect then over http. Will this work and I'd so how risky is it to future problems?

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  • Is chess-like AI really inapplicable in turn-based strategy games?

    - by Joh
    Obviously, trying to apply the min-max algorithm on the complete tree of moves works only for small games (I apologize to all chess enthusiasts, by "small" I do not mean "simplistic"). For typical turn-based strategy games where the board is often wider than 100 tiles and all pieces in a side can move simultaneously, the min-max algorithm is inapplicable. I was wondering if a partial min-max algorithm which limits itself to N board configurations at each depth couldn't be good enough? Using a genetic algorithm, it might be possible to find a number of board configurations that are good wrt to the evaluation function. Hopefully, these configurations might also be good wrt to long-term goals. I would be surprised if this hasn't been thought of before and tried. Has it? How does it work?

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  • Why using the word "mechanism" in CS?

    - by Nick Rosencrantz
    I'm not sure about the usage of the word "mechanism" when in fact most of the time what is meant is an algorithm. For instance there's talk about Java's "thread-scheduling mechanism" - why not call it an algorithm and why borrow a term from mechanics where relations sometimes are the opposites than of computer science? I'm aware that an algorithm is considered a "mechanical solution" but is this really the case in fact when a lot of algorithm don't have mechanical representations for instance a file-sharing network that gets quicker and faster as the usage grows, that would be the reverse of a mechanical structure that would go slower when usage grows.

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  • Converting a bounded knapsack problem to 0/1 knapsack problem

    - by Ants
    I ran across a problem where goal was to use dynamic programming (instead of other approaches). There is a distance to be spanned, and a set of cables of different lengths. What is the minimum number of cables needed to span the distance exactly? To me this looked like a knapsack problem, but since there could be multiples of a particular length, it was a bounded knapsack problem, rather than a 0/1 knapsack problem. (Treat the value of each item to be its weight.) Taking the naive approach (and not caring about the expansion of the search space), the method I used to convert the bounded knapsack problem into a 0/1 knapsack problem, was simply break up the multiples into singles and apply the well-known dynamic programming algorithm. Unfortunately, this leads to sub-optimal results. For example, given cables: 1 x 10ft, 1 x 7ft, 1 x 6ft, 5 x 3ft, 6 x 2ft, 7 x 1ft If the target span is 13ft, the DP algorithm picks 7+6 to span the distance. A greedy algorithm would have picked 10+3, but it's a tie for minimum number of cables. The problem arises, when trying to span 15ft. The DP algorithm ended up picking 6+3+3+3 to get 4 cables, while the greedy algorithm correctly picks 10+3+2 for only 3 cables. Anyway, doing some light scanning of converting bounded to 0/1, it seems like the well-known approach to convert multiple items to { p, 2p, 4p ... }. My question is how does this conversion work if p+2p+4p does not add up to the number of multiple items. For example: I have 5 3ft cables. I can't very well add { 3, 2x3, 4x3 } because 3+2x3+4x3 5x3. Should I add { 3, 4x3 } instead? [I'm currently trying to grok the "Oregon Trail Knapsack Problem" paper, but it currently looks like the approach used there is not dynamic programming.]

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  • Marching squares: Finding multiple contours within one source field?

    - by TravisG
    Principally, this is a follow-up-question to a problem from a few weeks ago, even though this is about the algorithm in general without application to my actual problem. The algorithm basically searches through all lines in the picture, starting from the top left of it, until it finds a pixel that is a border. In pseudo-C++: int start = 0; for(int i=0; i<amount_of_pixels; ++i) { if(pixels[i] == border) { start = i; break; } } When it finds one, it starts the marching squares algorithm and finds the contour to whatever object the pixel belongs to. Let's say I have something like this: Where everything except the color white is a border. And have found the contour points of the first blob: For the general algorithm it's over. It found a contour and has done its job. How can I move on to the other two blobs to find their contours as well?

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  • Design pattern: static function call with input/output containers?

    - by Pavlo Dyban
    I work for a company in software research department. We use algorithms from our real software and wrap them so that we can use them for prototyping. Every time an algorithm interface changes, we need to adapt our wrappers respectively. Recently all algorithms have been refactored in such a manner that instead of accepting many different inputs and returning outputs via referenced parameters, they now accept one input data container and one output data container (the latter is passed by reference). Algorithm interface is limited to a static function call like that: class MyAlgorithm{ static bool calculate(MyAlgorithmInput input, MyAlgorithmOutput &output); } This is actually a very powerful design, though I have never seen it in a C++ programming environment before. Changes in the number of parameters and their data types are now encapsulated and they don't change the algorithm callback. In the latest algorithm which I have developed I used the same scheme. Now I want to know if this is a popular design pattern and what it is called.

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  • Is the Leptonica implementation of 'Modified Median Cut' not using the median at all?

    - by TheCodeJunkie
    I'm playing around a bit with image processing and decided to read up on how color quantization worked and after a bit of reading I found the Modified Median Cut Quantization algorithm. I've been reading the code of the C implementation in Leptonica library and came across something I thought was a bit odd. Now I want to stress that I am far from an expert in this area, not am I a math-head, so I am predicting that this all comes down to me not understanding all of it and not that the implementation of the algorithm is wrong at all. The algorithm states that the vbox should be split along the lagest axis and that it should be split using the following logic The largest axis is divided by locating the bin with the median pixel (by population), selecting the longer side, and dividing in the center of that side. We could have simply put the bin with the median pixel in the shorter side, but in the early stages of subdivision, this tends to put low density clusters (that are not considered in the subdivision) in the same vbox as part of a high density cluster that will outvote it in median vbox color, even with future median-based subdivisions. The algorithm used here is particularly important in early subdivisions, and 3is useful for giving visible but low population color clusters their own vbox. This has little effect on the subdivision of high density clusters, which ultimately will have roughly equal population in their vboxes. For the sake of the argument, let's assume that we have a vbox that we are in the process of splitting and that the red axis is the largest. In the Leptonica algorithm, on line 01297, the code appears to do the following Iterate over all the possible green and blue variations of the red color For each iteration it adds to the total number of pixels (population) it's found along the red axis For each red color it sum up the population of the current red and the previous ones, thus storing an accumulated value, for each red note: when I say 'red' I mean each point along the axis that is covered by the iteration, the actual color may not be red but contains a certain amount of red So for the sake of illustration, assume we have 9 "bins" along the red axis and that they have the following populations 4 8 20 16 1 9 12 8 8 After the iteration of all red bins, the partialsum array will contain the following count for the bins mentioned above 4 12 32 48 49 58 70 78 86 And total would have a value of 86 Once that's done it's time to perform the actual median cut and for the red axis this is performed on line 01346 It iterates over bins and check they accumulated sum. And here's the part that throws me of from the description of the algorithm. It looks for the first bin that has a value that is greater than total/2 Wouldn't total/2 mean that it is looking for a bin that has a value that is greater than the average value and not the median ? The median for the above bins would be 49 The use of 43 or 49 could potentially have a huge impact on how the boxes are split, even though the algorithm then proceeds by moving to the center of the larger side of where the matched value was.. Another thing that puzzles me a bit is that the paper specified that the bin with the median value should be located, but does not mention how to proceed if there are an even number of bins.. the median would be the result of (a+b)/2 and it's not guaranteed that any of the bins contains that population count. So this is what makes me thing that there are some approximations going on that are negligible because of how the split actually takes part at the center of the larger side of the selected bin. Sorry if it got a bit long winded, but I wanted to be as thoroughas I could because it's been driving me nuts for a couple of days now ;)

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  • Optimizing processing and management of large Java data arrays

    - by mikera
    I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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  • Generic Event Generator and Handler from User Supplied Types?

    - by JaredBroad
    I'm trying to allow the user to supply custom data and manage the data with custom types. The user's algorithm will get time synchronized events pushed into the event handlers they define. I'm not sure if this is possible but here's the "proof of concept" code I'd like to build. It doesn't detect T in the for loop: "The type or namespace name 'T' could not be found" class Program { static void Main(string[] args) { Algorithm algo = new Algorithm(); Dictionary<Type, string[]> userDataSources = new Dictionary<Type, string[]>(); // "User" adding custom type and data source for algorithm to consume userDataSources.Add(typeof(Weather), new string[] { "temperature data1", "temperature data2" }); for (int i = 0; i < 2; i++) { foreach (Type T in userDataSources.Keys) { string line = userDataSources[typeof(T)][i]; //Iterate over CSV data.. var userObj = new T(line); algo.OnData < typeof(T) > (userObj); } } } //User's algorithm pattern. interface IAlgorithm<TData> where TData : class { void OnData<TData>(TData data); } //User's algorithm. class Algorithm : IAlgorithm<Weather> { //Handle Custom User Data public void OnData<Weather>(Weather data) { Console.WriteLine(data.date.ToString()); Console.ReadKey(); } } //Example "user" custom type. public class Weather { public DateTime date = new DateTime(); public double temperature = 0; public Weather(string line) { Console.WriteLine("Initializing weather object with: " + line); date = DateTime.Now; temperature = -1; } } }

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  • Cooperative linux vs vm

    - by Rhythmic Algorithm
    What are the advantages / disadvantages of using cooperative linux like portable ubuntu for example compared to a qemu or any other virtual machine installation. Is one option notably faster than the other plus and other things that should be taken into consideration.

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