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• Need Help finding an appropriate task asignment algoritm for a collage project involving coordinatin

  - by Trif Mircea

  Hello. I am a long time lurker here and have found over time many answers regarding jquery and web development topics so I decided to ask a question of my own. This time I have to create a c++ project for collage which should help manage the workflow of a company providing all kinds of services through in the field teams. The ideas I have so far are: client-server application; the server is a dispatcher where all the orders from clients get and the clients are mobile devices (PDAs) each team in the field having one a order from a client is a task. Each task is made up of a series of subtasks. You have a database with estimations on how long a task should take to complete you also know what tasks or subtasks each team on the field can perform based on what kind of specialists made up the team (not going to complicate the problem by adding needed materials, it is considered that if a member of a team can perform a subtask he has the stuff needed) Now knowing these factors, what would a good task assignment algorithm be? The criteria is: how many tasks can a team do, how many tasks they have in the queue, it could also be location, how far away are they from the place but I don't think I can implement that.. It needs to be efficient and also to adapt quickly is the human dispatcher manually assigns a task. Any help or leads would be really appreciated. Also I'm not 100% sure in the idea so if you have another way you would go about creating such an application please share, even if it just a quick outline. I have to write a theoretical part too so even if the ideas are far more complex that what i outlined that would be ok ; I'd write those and implement what I can.

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• UITableView with dynamic cell heights -- what do I need to do to fix scrolling down?

  - by Ian Terrell

  I am building a teensy tiny little Twitter client on the iPhone. Naturally, I'm displaying the tweets in a UITableView, and they are of course of varying lengths. I'm dynamically changing the height of the cell based on the text quite fine: - (CGFloat)heightForTweetCellWithString:(NSString *)text { CGFloat height = Buffer + [text sizeWithFont:Font constrainedToSize:Size lineBreakMode:LineBreakMode].height; return MAX(height, MinHeight); } - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath { NSString *text = // get tweet text for this indexpath return [self heightForTweetCellWithString:text]; } } I'm displaying the actual tweet cell using the algorithm in the PragProg book: - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"TweetCell"; TweetCell *cell = (TweetCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [self createNewTweetCellFromNib]; } cell.tweet.text = // tweet text // set other labels, etc return cell; } When I boot up, all the tweets visible display just fine. However, when I scroll down, the tweets below are quite mussed up -- it appears that once a cell has scrolled off the screen, the cell height for the one above it gets resized to be larger than it should be, and obscures part of the cell below it. When the cell reaches the top of the view, it resets itself and renders properly. Scrolling up presents no difficulties. Here is a video that shows this in action: http://screencast.com/t/rqwD9tpdltd I've tried quite a bit already: resizing the cell's frame on creation, using different identifiers for cells with different heights (i.e. [NSString stringWithFormat:@"Identifier%d", rowHeight]), changing properties in Interface Builder... If there are additional code snippets I can post, please let me know. Thanks in advance for your help!

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• Join two list comparing their elements properties

  - by 100r

  public class Person() { int ID; string Name; DateTime ChangeDate } var list1 = new List<Person> { new Person { ID= 1, Name = "Peter", ChangeDate= "2011-10-21" }, new Person { ID= 2, Name = "John", ChangeDate= "2011-10-22" }, new Person { ID= 3, Name = "Mike", ChangeDate= "2011-10-23" }, new Person { ID= 4, Name = "Dave", ChangeDate= "2011-10-24" } }; var list2 = new List<Person> { new Person { ID= 1, Name = "Pete", ChangeDate= "2011-10-21" }, new Person { ID= 2, Name = "Johny", ChangeDate= "2011-10-20" }, new Person { ID= 3, Name = "Mikey", ChangeDate= "2011-10-24" }, new Person { ID= 5, Name = "Larry", ChangeDate= "2011-10-27" } }; As output I would like to have list1 + list2 = Person { ID= 1, Name = "Peter", ChangeDate= "2011-10-21" }, Person { ID= 2, Name = "John", ChangeDate= "2011-10-22" }, Person { ID= 3, Name = "Mikey", ChangeDate= "2011-10-24" }, Person { ID= 4, Name = "Dave", ChangeDate= "2011-10-24" } Person { ID= 5, Name = "Larry", ChangeDate= "2011-10-27" } And the Algorithm is like this. Join two list. If elements of lists have same ID, compare them by ChangeDate and take the ond with bigger date. If ChangeDate are equeal take any of them but not both. Maybe its easier to concat both lists and than to filter them with lambda. I tried, but always came out with some ugly code :/ Anyone have any idea?

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• How to properly translate the "var" result of a lambda expression to a concrete type?

  - by CrimsonX

  So I'm trying to learn more about lambda expressions. I read this question on stackoverflow, concurred with the chosen answer, and have attempted to implement the algorithm using a console app in C# using a simple LINQ expression. My question is: how do I translate the "var result" of the lambda expression into a usable object that I can then print the result? I would also appreciate an in-depth explanation of what is happening when I declare the outer => outer.Value.Frequency (I've read numerous explanations of lambda expressions but additional clarification would help) C# //Input : {5, 13, 6, 5, 13, 7, 8, 6, 5} //Output : {5, 5, 5, 13, 13, 6, 6, 7, 8} //The question is to arrange the numbers in the array in decreasing order of their frequency, preserving the order of their occurrence. //If there is a tie, like in this example between 13 and 6, then the number occurring first in the input array would come first in the output array. List<int> input = new List<int>(); input.Add(5); input.Add(13); input.Add(6); input.Add(5); input.Add(13); input.Add(7); input.Add(8); input.Add(6); input.Add(5); Dictionary<int, FrequencyAndValue> dictionary = new Dictionary<int, FrequencyAndValue>(); foreach (int number in input) { if (!dictionary.ContainsKey(number)) { dictionary.Add(number, new FrequencyAndValue(1, number) ); } else { dictionary[number].Frequency++; } } var result = dictionary.OrderByDescending(outer => outer.Value.Frequency); // How to translate the result into something I can print??

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• Sending files using Winsock - optimal send() data length?

  - by Meta

  I am using Winsock with non-blocking sockets to send a file to a client. The way I'm doing it right now is that I read a chunk of 8192 bytes from the file, and then loop until all of it successfully goes through send() (obviously handling WSAEWOULDBLOCK as it occurs). I then move on and read the next 8192 bytes, and so on... Although I can use any other number than 8192 when I test the transfer on my local machine, once I try it over a network, it seems like 8191 is the largest number I can use. When I try to use any number higher than 8191 (starting with 8192), the file transfer becomes extremely slow (about 5 times slower). Is there any reason why 8191 is so special? I've done some more testing and it turns out that using 8000 is slightly faster (by 0.5%). If you understand why 8191 is so special, can you tell me if there is a number better than the others (better than 8000)? I have a feeling that it has something to do with the fact that the default send buffer allocated to the socket by Winsock is 8KB, but I don't understand why. It might also have something to do with the Nagle algorithm, but again, I'm not sure how. Note that I have not modified the SO_SNDBUF option nor the TCP_NODELAY option. Or am I doing this all wrong? What's the best way of sending a file over a non-blocking socket?

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• String Manipulation in C

  - by baris_a

  Hi guys, I am helping my nephew for his C lab homework, it is a string manipulation assignment and applying Wang's algorithm. Here is the BNF representation for the input. <sequent> ::= <lhs> # <rhs> <lhs> ::= <formulalist>| e <rhs> ::= <formulalist>| e <formulalist> ::= <formula>|<formula> , <formulalist> <formula> ::= <letter>| - <formula>| (<formula><in?xop><formula>) <in?xop> ::= & | | | > <letter> ::= A | B | ... | Z What is the best practice to handle and parse this kind of input in C? How can I parse this structure without using struct? Thanks in advance.

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• How to change the date/time in Python for all modules?

  - by Felix Schwarz

  When I write with business logic, my code often depends on the current time. For example the algorithm which looks at each unfinished order and checks if an invoice should be sent (which depends on the no of days since the job was ended). In these cases creating an invoice is not triggered by an explicit user action but by a background job. Now this creates a problem for me when it comes to testing: I can test invoice creation itself easily However it is hard to create an order in a test and check that the background job identifies the correct orders at the correct time. So far I found two solutions: In the test setup, calculate the job dates relative to the current date. Downside: The code becomes quite complicated as there are no explicit dates written anymore. Sometimes the business logic is pretty complex for edge cases so it becomes hard to debug due to all these relative dates. I have my own date/time accessor functions which I use throughout my code. In the test I just set a current date and all modules get this date. So I can simulate an order creation in February and check that the invoice is created in April easily. Downside: 3rd party modules do not use this mechanism so it's really hard to integrate+test these. The second approach was way more successful to me after all. Therefore I'm looking for a way to set the time Python's datetime+time modules return. Setting the date is usually enough, I don't need to set the current hour or second (even though this would be nice). Is there such a utility? Is there an (internal) Python API that I can use?

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• How do I optimize this postfix expression tree for speed?

  - by Peter Stewart

  Thanks to the help I received in this post: I have a nice, concise recursive function to traverse a tree in postfix order: deque <char*> d; void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } d.push_front(cargo); return; }; This is an expression tree. The branch nodes are operators randomly selected from an array, and the leaf nodes are values or the variable 'x', also randomly selected from an array. char *values[10]={"1.0","2.0","3.0","4.0","5.0","6.0","7.0","8.0","9.0","x"}; char *ops[4]={"+","-","*","/"}; As this will be called billions of times during a run of the genetic algorithm of which it is a part, I'd like to optimize it for speed. I have a number of questions on this topic which I will ask in separate postings. The first is: how can I get access to each 'cargo' as it is found. That is: instead of pushing 'cargo' onto a deque, and then processing the deque to get the value, I'd like to start processing it right away. I don't yet know about parallel processing in c++, but this would ideally be done concurrently on two different processors. In python, I'd make the function a generator and access succeeding 'cargo's using .next(). But I'm using c++ to speed up the python implementation. I'm thinking that this kind of tree has been around for a long time, and somebody has probably optimized it already. Any Ideas? Thanks

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• d2: assigning ranges/iterators to array slices

  - by modchan

  Consider following code: enum size = 16; double[size] arr1 = [...]; double[size] arr2 = [...]; process = (double x) { return (x + 1); }; arr2[] = map!(process)(arr1[]); // here I have trouble converting results of map back to my plain array. Problem applies not only to map, but also to take, repeat and all those fine tools from std.algorithm and std.range that operate on ranges. On this assignment, I get Error: cannot implicitly convert expression (map(arr1[])) of type Result to double[]. How can I evaluate range to array without using uint i = 0; foreach (x; map!(process)(arr1[])) { arr2[i] = x; i++; } ? Additionally, can someone please explain, why I must call map!(process)(arr1[]) instead of map!(process)(arr1) with static arrays? Shouldn't static arrays be compatible with dynamic for means of iteration, or I don't get something? Also, it seems that straightforward enumeration syntax foreach (index, item; sequence) does not work for ranges - are there workarounds? I guess the reason is the same as why ranges cannot be assigned to array slices.

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• Are these two functions the same?

  - by Ranhiru

  There is a function in the AES algorithm, to multiply a byte by 2 in Galois Field. This is the function given in a website private static byte gfmultby02(byte b) { if (b < 0x80) return (byte)(int)(b <<1); else return (byte)( (int)(b << 1) ^ (int)(0x1b) ); } This is the function i wrote. private static byte MulGF2(byte x) { if (x < 0x80) return (byte)(x << 1); else { return (byte)((x << 1) ^ 0x1b); } } What i need to know is, given any byte whether this will perform in the same manner. Actually I am worried about the extra conversion of to int and then again to byte. So far I have tested and it looks fine. Does the extra cast to int and then to byte make a difference?

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• Vehicle License Plate Detection

  - by Ash

  Hey all Basically for my final project at university, I'm developing a vehicle license plate detection application. Now I consider myself an intermediate programmer, however my mathematics knowledge lacks anything above secondary school, therefore producing detection formulae is basically impossible. I've spend a good amount of time looking up academic papers such as: http://www.scribd.com/doc/266575/Detecting-Vehicle-License-Plates-in-Images http://www.cic.unb.br/~mylene/PI_2010_2/ICIP10/pdfs/0003945.pdf http://www.eurasip.org/Proceedings/Eusipco/Eusipco2007/Papers/d3l-b05.pdf When it comes to the maths, I'm lost. Due to this testing various graphic images proved productive, for example: to However this approach is only catered to that particular image, and if the techniques were applied to different images, I'm sure a different, most likely poorer conversion would occur. I've read about a formula called the bottom hat morphology transform, which according to the first does the following: "Basically, the trans- formation keeps all the dark details of the picture, and eliminates everything else (including bigger dark regions and light regions)." Sadly I can't find much information on this, however the image within the documentation near the end of the report shows it's effectiveness. I'm aware this is complicated and vast, I'd just appreciate a little advice, even in terms of what transformation techniques I should focus on developing, or algorithm regarding edge detection or pixel detection. Few things I need to add Developing in C Sharp Confining the project to UK registration plates only I can basically choose the images to convert as a demonstration Thanks

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• Thread management advice - Is TPL a good idea?

  - by Ian

  I'm hoping to get some advice on the use of thread managment and hopefully the task parallel library, because I'm not sure I've been going down the correct route. Probably best is that I give an outline of what I'm trying to do. Given a Problem I need to generate a Solution using a heuristic based algorithm. I start of by calculating a base solution, this operation I don't think can be parallelised so we don't need to worry about. Once the inital solution has been generated, I want to trigger n threads, which attempt to find a better solution. These threads need to do a couple of things: They need to be initalized with a different 'optimization metric'. In other words they are attempting to optimize different things, with a precedence level set within code. This means they all run slightly different calculation engines. I'm not sure if I can do this with the TPL.. If one of the threads finds a better solution that the currently best known solution (which needs to be shared across all threads) then it needs to update the best solution, and force a number of other threads to restart (again this depends on precedence levels of the optimization metrics). I may also wish to combine certain calculations across threads (e.g. keep a union of probabilities for a certain approach to the problem). This is probably more optional though. The whole system needs to be thread safe obviously and I want it to be running as fast as possible. I tried quite an implementation that involved managing my own threads and shutting them down etc, but it started getting quite complicated, and I'm now wondering if the TPL might be better. I'm wondering if anyone can offer any general guidance? Thanks...

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• Thread-safety of read-only memory access

  - by Edmund

  I've implemented the Barnes-Hut gravity algorithm in C as follows: Build a tree of clustered stars. For each star, traverse the tree and apply the gravitational forces from each applicable node. Update the star velocities and positions. Stage 2 is the most expensive stage, and so is implemented in parallel by dividing the set of stars. E.g. with 1000 stars and 2 threads, I have one thread processing the first 500 stars and the second thread processing the second 500. In practice this works: it speeds the computation by about 30% with two threads on a two-core machine, compared to the non-threaded version. Additionally, it yields the same numerical results as the original non-threaded version. My concern is that the two threads are accessing the same resource (namely, the tree) simultaneously. I have not added any synchronisation to the thread workers, so it's likely they will attempt to read from the same location at some point. Although access to the tree is strictly read-only I am not 100% sure it's safe. It has worked when I've tested it but I know this is no guarantee of correctness! Questions Do I need to make a private copy of the tree for each thread? Even if it is safe, are there performance problems of accessing the same memory from multiple threads?

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• What about race condition in multithreaded reading?

  - by themoob

  Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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• Is learning C++ a good idea?

  - by chang

  The more I hear and read about C++ (e.g. this: http://lwn.net/Articles/249460/), I get the impression, that I'd waste my time learning C++. I some wrote network routing algorithm in C++ for a simulator, and it was a pain (as expected, especially coming from a perl/python/Java background ...). I'm never happy about giving up on some technology, but I would be happy, if I could limit my knowledge of C-family languages to just C, C# and Objective-C (even OS Xs Cocoa, which is huge and takes a lot of time to learn looks like joy compared to C++ ...). Do I need to consider myself dumb or unwilling, just because I'm not partial to the pain involved learning this stuff? Technologies advance and there will be options other than C++, when deciding on implementation languages, or not? And for speed: If speed were that critical, I'd go for a plain C implementation instead, or write C extensions for much more productive languages like ruby or python ... The one-line version of the above: Will C++ stay such a relevant language that every committed programmer should be familiar with it? [ edit / thank you very much for your interesting and useful answers so far .. ] [ edit / .. i am accepting the top-rated answer; thanks again for all answers! ]

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• LINQ : How to query how to sort result by most similarity/equality

  - by aNui

  I want to do a search for Music instruments which has its informations Name, Category and Origin as I asked in my post. But now I want to sort/group the result by similarity/equality to the keyword such as. If I have the list { Harp, Piano, Drum, Guitar, Guitarrón } and if I queried "p" the result should be { Piano, Harp } but it shows Harp first because of the list's sequence and if I add {Grand Piano} to the list and query "piano" the result shoud be like { Piano, Grand Piano } here's my code static IEnumerable<MInstrument> InstrumentsSearch(IEnumerable<MInstrument> InstrumentsList, string query, MInstrument.Category[] SelectedCategories, MInstrument.Origin[] SelectedOrigins) { var result = InstrumentsList .Where(item => SelectedCategories.Contains(item.category)) .Where(item => SelectedOrigins.Contains(item.origin)) .Where(item => { if ( (" " + item.Name.ToLower()).Contains(" " + query.ToLower()) || item.Name.IndexOf(query) != -1 ) { return true; } return false; } ) .Take(30); return result.ToList<MInstrument>(); } Or the result may be like my old self-invented algorithm that I called "by order of occurence", that is just OK to me. Is there any way to do that, please tell me. Thanks in advance.

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• How does mercurial's bisect work when the range includes branching?

  - by Joshua Goldberg

  If the bisect range includes multiple branches, how does hg bisect's search work. Does it effectively bisect each sub-branch (I would think that would be inefficient)? For instance, borrowing, with gratitude, a diagram from an answer to this related question, what if the bisect got to changeset 7 on the "good" right-side branch first. @ 12:8ae1fff407c8:bad6 | o 11:27edd4ba0a78:bad5 | o 10:312ba3d6eb29:bad4 |\ | o 9:68ae20ea0c02:good33 | | | o 8:916e977fa594:good32 | | | o 7:b9d00094223f:good31 | | o | 6:a7cab1800465:bad3 | | o | 5:a84e45045a29:bad2 | | o | 4:d0a381a67072:bad1 | | o | 3:54349a6276cc:good4 |/ o 2:4588e394e325:good3 | o 1:de79725cb39a:good2 | o 0:2641cc78ce7a:good1 Will it then look only between 7 and 12, missing the real first-bad that we care about? (thus using "dumb" numerical order) or is it smart enough to use the full topography and to know that the first bad could be below 7 on the right-side branch, or could still be anywhere on the left-side branch. The purpose of my question is both (a) just to understand the algorithm better, and (b) to understand whether I can liberally extend my initial bisect range without thinking hard about what branch I go to. I've been in high-branching bisect situations where it kept asking me after every test to extend beyond the next merge, so that the whole procedure was essentially O(n). I'm wondering if I can just throw the first "good" marker way back past some nest of merges without thinking about it much, and whether that would save time and give correct results.

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• Tail recursion and memoization with C#

  - by Jay

  I'm writing a function that finds the full path of a directory based on a database table of entries. Each record contains a key, the directory's name, and the key of the parent directory (it's the Directory table in an MSI if you're familiar). I had an iterative solution, but it started looking a little nasty. I thought I could write an elegant tail recursive solution, but I'm not sure anymore. I'll show you my code and then explain the issues I'm facing. Dictionary<string, string> m_directoryKeyToFullPathDictionary = new Dictionary<string, string>(); ... private string ExpandDirectoryKey(Database database, string directoryKey) { // check for terminating condition string fullPath; if (m_directoryKeyToFullPathDictionary.TryGetValue(directoryKey, out fullPath)) { return fullPath; } // inductive step Record record = ExecuteQuery(database, "SELECT DefaultDir, Directory_Parent FROM Directory where Directory.Directory='{0}'", directoryKey); // null check string directoryName = record.GetString("DefaultDir"); string parentDirectoryKey = record.GetString("Directory_Parent"); return Path.Combine(ExpandDirectoryKey(database, parentDirectoryKey), directoryName); } This is how the code looked when I realized I had a problem (with some minor validation/massaging removed). I want to use memoization to short circuit whenever possible, but that requires me to make a function call to the dictionary to store the output of the recursive ExpandDirectoryKey call. I realize that I also have a Path.Combine call there, but I think that can be circumvented with a ... + Path.DirectorySeparatorChar + .... I thought about using a helper method that would memoize the directory and return the value so that I could call it like this at the end of the function above: return MemoizeHelper( m_directoryKeyToFullPathDictionary, Path.Combine(ExpandDirectoryKey(database, parentDirectoryKey)), directoryName); But I feel like that's cheating and not going to be optimized as tail recursion. Any ideas? Should I be using a completely different strategy? This doesn't need to be a super efficient algorithm at all, I'm just really curious. I'm using .NET 4.0, btw. Thanks!

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• How to improve multi-threaded access to Cache (custom implementation)

  - by Andy

  I have a custom Cache implementation, which allows to cache TCacheable<TKey> descendants using LRU (Least Recently Used) cache replacement algorithm. Every time an element is accessed, it is bubbled up to the top of the LRU queue using the following synchronized function: // a single instance is created to handle all TCacheable<T> elements public class Cache() { private object syncQueue = new object(); private void topQueue(TCacheable<T> el) { lock (syncQueue) if (newest != el) { if (el.elder != null) el.elder.newer = el.newer; if (el.newer != null) el.newer.elder = el.elder; if (oldest == el) oldest = el.newer; if (oldest == null) oldest = el; if (newest != null) newest.newer = el; el.newer = null; el.elder = newest; newest = el; } } } The bottleneck in this function is the lock() operator, which limits cache access to just one thread at a time. Question: Is it possible to get rid of lock(syncQueue) in this function while still preserving the queue integrity?

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• Simplification / optimization of GPS track

  - by GreyCat

  I've got a GPS track, produces by gpxlogger(1) (supplied as a client for gpsd). GPS receiver updates its coordinates every 1 second, gpxlogger's logic is very simple, it writes down location (lat, lon, ele) and a timestamp (time) received from GPS every n seconds (n = 3 in my case). After writing down a several hours worth of track, gpxlogger saves several megabyte long GPX file that includes several thousands of points. Afterwards, I try to plot this track on a map and use it with OpenLayers. It works, but several thousands of points make using the map a sloppy and slow experience. I understand that having several thousands of points of suboptimal. There are myriads of points that can be deleted without losing almost anything: when there are several points making up roughly the straight line and we're moving with the same constant speed between them, we can just leave the first and the last point and throw anything else. I thought of using gpsbabel for such track simplification / optimization job, but, alas, it's simplification filter works only with routes, i.e. analyzing only geometrical shape of path, without timestamps (i.e. not checking that the speed was roughly constant). Is there some ready-made utility / library / algorithm available to optimize tracks? Or may be I'm missing some clever option with gpsbabel?

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• Can't decrypt after encrypting with blowfish Java

  - by user2030599

  Hello i'm new to Java and i have the following problem: i'm trying to encrypt the password of a user using the blowfish algorithm, but when i try to decrypt it back to check the authentication it fails to decrypt it for some reason. public static String encryptBlowFish(String to_encrypt, String salt){ String dbpassword = null; try{ SecretKeySpec skeySpec = new SecretKeySpec( salt.getBytes(), "Blowfish" ); // Instantiate the cipher. Cipher cipher = Cipher.getInstance("Blowfish/CBC/PKCS5Padding"); cipher.init(Cipher.ENCRYPT_MODE, skeySpec); //byte[] encrypted = cipher.doFinal( URLEncoder.encode(data).getBytes() ); byte[] encrypted = cipher.doFinal( to_encrypt.getBytes() ); dbpassword = new String(encrypted); } catch (Exception e) { System.out.println("Exception while encrypting"); e.printStackTrace(); dbpassword = null; } finally { return dbpassword; } } public static String decryptBlowFish(String to_decrypt, String salt){ String dbpassword = null; try{ SecretKeySpec skeySpec = new SecretKeySpec( salt.getBytes(), "Blowfish" ); // Instantiate the cipher. Cipher cipher = Cipher.getInstance("Blowfish/CBC/PKCS5Padding"); cipher.init(Cipher.DECRYPT_MODE, skeySpec); //byte[] encrypted = cipher.doFinal( URLEncoder.encode(data).getBytes() ); byte[] encrypted = cipher.doFinal( to_decrypt.getBytes() ); dbpassword = new String(encrypted); } catch (Exception e) { System.out.println("Exception while decrypting"); e.printStackTrace(); dbpassword = null; } finally { return dbpassword; } } When i call the decrypt function it gives me the following error: java.security.InvalidKeyException: Parameters missing Any ideas? Thank you

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• Parse a CSV file using python (to make a decision tree later)

  - by Margaret

  First off, full disclosure: This is going towards a uni assignment, so I don't want to receive code. :). I'm more looking for approaches; I'm very new to python, having read a book but not yet written any code. The entire task is to import the contents of a CSV file, create a decision tree from the contents of the CSV file (using the ID3 algorithm), and then parse a second CSV file to run against the tree. There's a big (understandable) preference to have it capable of dealing with different CSV files (I asked if we were allowed to hard code the column names, mostly to eliminate it as a possibility, and the answer was no). The CSV files are in a fairly standard format; the header row is marked with a # then the column names are displayed, and every row after that is a simple series of values. Example: # Column1, Column2, Column3, Column4 Value01, Value02, Value03, Value04 Value11, Value12, Value13, Value14 At the moment, I'm trying to work out the first part: parsing the CSV. To make the decisions for the decision tree, a dictionary structure seems like it's going to be the most logical; so I was thinking of doing something along these lines: Read in each line, character by character If the character is not a comma or a space Append character to temporary string If the character is a comma Append the temporary string to a list Empty string Once a line has been read Create a dictionary using the header row as the key (somehow!) Append that dictionary to a list However, if I do things that way, I'm not sure how to make a mapping between the keys and the values. I'm also wondering whether there is some way to perform an action on every dictionary in a list, since I'll need to be doing things to the effect of "Everyone return their values for columns Column1 and Column4, so I can count up who has what!" - I assume that there is some mechanism, but I don't think I know how to do it. Is a dictionary the best way to do it? Would I be better off doing things using some other data structure? If so, what?

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• Parallel.For Batching

  - by chibacity

  Is there built-in support in the TPL for batching operations? I was recently playing with a routine to carry out character replacement on a character array which required a lookup table i.e. transliteration: for (int i = 0; i < chars.Length; i++) { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } } I could see that this could be trivially parallelized, so jumped in with a first stab which I knew would perform worse as the tasks were too fine-grained: Parallel.For(0, chars.Length, i => { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } }); I then reworked the algorithm to use batching so that the work could be chunked onto different threads in less fine-grained batches. This made use of threads as expected and I got some near linear speed up. I'm sure that there must be built-in support for batching in the TPL. What is the syntax, and how do I use it? const int CharBatch = 100; int charLen = chars.Length; Parallel.For(0, ((charLen / CharBatch) + 1), i => { int batchUpper = ((i + 1) * CharBatch); for (int j = i * CharBatch; j < batchUpper && j < charLen; j++) { char replaceChar; if (lookup.TryGetValue(chars[j], out replaceChar)) { chars[j] = replaceChar; } } });

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• Flushing writes in buffer of Memory Controller to DDR device

  - by Rohit

  At some point in my code, I need to push the writes in my code all the way to the DIMM or DDR device. My requirement is to ensure the write reaches the row,ban,column of the DDR device on the DIMM. I need to read what I've written to the main memory. I do not want caching to get me the value. Instead after writing I want to fetch this value from main memory(DIMM's). So far I've been using Intel's x86 instruction wbinvd(write back and invalidate cache). However this means the caches and TLB are flushed. Write-back requests go to the main memory. However, there is a reasonable amount of time this data might reside in the write buffer of the Memory Controller( Intel calls it integrated memory controller or IMC). The Memory Controller might take some more time depending on the algorithm that runs in the Memory Controller to handle writes. Is there a way I force all existing or pending writes in the write buffer of the memory controller to the DRAM devices ?? What I am looking for is something more direct and more low-level than wbinvd. If you could point me to right documents or specs that describe this I would be grateful. Generally, the IMC has a several registers which can be written or read from. From looking at the specs for that for the chipset I could not find anything useful. Thanks for taking the time to read this.

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