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  • 'Fixed' for loop - what is more efficient?

    - by pimvdb
    I'm creating a tic-tac-toe game, and one of the functions has to iterate through each of the 9 fields (tic-tac-toe is played on a 3x3 grid). I was wondering what is more efficient (which one is perhaps faster, or what is the preferred way of scripting in such situation) - using two for nested loops like this: for(var i=0; i<3; i++) { for(var j=0; j<3; j++) { checkField(i, j); } } or hard-coding it like this: checkField(0, 0); checkField(0, 1); checkField(0, 2); checkField(1, 0); checkField(1, 1); checkField(1, 2); checkField(2, 0); checkField(2, 1); checkField(2, 2); As there are only 9 combinations, it would be perhaps overkill to use two nested for loops, but then again this is clearer to read. The for loop, however, will increment variables and check whether i and j are smaller than 3 every time as well. In this example, the time saving at least might be negligible, but what is the preferred way of coding in this case? Thanks.

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  • Most efficient way to update attribute of one instance

    - by Begbie00
    Hi all - I'm creating an arbitrary number of instances (using for loops and ranges). At some event in the future, I need to change an attribute for only one of the instances. What's the best way to do this? Right now, I'm doing the following: 1) Manage the instances in a list. 2) Iterate through the list to find a key value. 3) Once I find the right object within the list (i.e. key value = value I'm looking for), change whatever attribute I need to change. for Instance within ListofInstances: if Instance.KeyValue == SearchValue: Instance.AttributeToChange = 10 This feels really inefficient: I'm basically iterating over the entire list of instances, even through I only need to change an attribute in one of them. Should I be storing the Instance references in a structure more suitable for random access (e.g. dictionary with KeyValue as the dictionary key?) Is a dictionary any more efficient in this case? Should I be using something else? Thanks, Mike

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  • More efficient comparison of numbers

    - by Pez Cuckow
    I have an array which is part of a small JS game I am working on I need to check (as often as reasonable) that each of the elements in the array haven't left the "stage" or "playground", so I can remove them and save the script load I have coded the below and was wondering if anyone knew a faster/more efficient way to calculate this. This is run every 50ms (it deals with the movement). Where bots[i][1] is movement in X and bots[i][2] is movement in Y (mutually exclusive). for (var i in bots) { var left = parseInt($("#" + i).css("left")); var top = parseInt($("#" + i).css("top")); var nextleft = left + bots[i][1]; var nexttop = top + bots[i][2]; if(bots[i][1]>0&&nextleft>=PLAYGROUND_WIDTH) { remove_bot(i); } else if(bots[i][1]<0&&nextleft<=-GRID_SIZE) { remove_bot(i); } else if(bots[i][2]>0&&nexttop>=PLAYGROUND_HEIGHT) { remove_bot(i); } else if(bots[i][2]<0&&nexttop<=-GRID_SIZE) { remove_bot(i); } else { //alert(nextleft + ":" + nexttop); $("#" + i).css("left", ""+(nextleft)+"px"); $("#" + i).css("top", ""+(nexttop)+"px"); } } On a similar note the remove_bot(i); function is as below, is this correct (I can't splice as it changes all the ID's of the elements in the array. function remove_bot(i) { $("#" + i).remove(); bots[i] = false; } Many thanks for any advice given!

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  • Efficient way to store order in mySQL for list of items

    - by ninumedia
    I want to code cleaner and more efficiently and I wanted to know any other suggestions for the following problem: I have a mySQL database that holds data about a set of photograph names. Oh, say 100 photograph names Table 1: (photos) has the following fields: photo_id, photo_name Ex data: 1 | sunshine.jpg 2 | cloudy.jpg 3 | rainy.jpg 4 | hazy.jpg ... Table 2: (categories) has the following fields: category_id, category_name, category_order Ex data: 1 | Summer Shots | 1,2,4 2 | Winter Shots | 2,3 3 | All Seasons | 1,2,3,4 ... Is it efficient to store the order of the photos in this manner per entry via comma delimited values? It's one approach I have seen used before but I wanted to know if something else is faster in run time. Using this way I don't think it is possible to do a direct INNER JOIN on the category table and photo table to get a single matched list of all the photographs per category. Ex: Summer shots - sunshine.jpg, cloudy.jpg, hazy.jpg because it was matched against 1,2,4 The iteration through all the categories and then the photos will have a O(n^2) and there has to be a better/faster way. Please educate me :)

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  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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  • Most efficient way to bind a Listbox with SelectionMode=Multiple

    - by Draak
    Hi, I have an ASP.NET webform that has a listbox (lbxRegions) with multi-select option enabled. In my db, I have a table with an xml field that holds a list of regions. I need to populate the listbox with all available regions and then "check off" the list items that match the regions in the db table. The list options also need to be ordered by region name. So, I wrote the following code that works just fine -- no problems. But I was wondering if anyone can think of a better (more succinct, more efficient) way to have done the same thing. Thanks in advance. Dim allRegions = XElement.Load(Server.MapPath(Request.ApplicationPath) & "\Regions.xml").<country>.<regions>.<region> Dim selectedRegions = (From ev In dc.Events Where ev.EventId = 2951).Single.CEURegions.<country>.<regions>.<region> Dim unselectedRegions = allRegions.Except(selectedRegions) Dim selectedItems = From x In selectedRegions Select New ListItem() _ With {.Value = x.@code, .Text = x.Value, .Selected = True} Dim unselectedItems = From x In unselectedRegions Select New ListItem() _ With {.Value = x.@code, .Text = x.Value} Dim allItems = selectedItems.Union(unselectedItems).OrderBy(Function(x) x.Text) lbxRegions.Items.AddRange(allItems.ToArray()) P.S. You can post code in C# if you like.

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  • Efficient database access when dealing with multiple abstracted repositories

    - by Nathan Ridley
    I want to know how most people are dealing with the repository pattern when it involves hitting the same database multiple times (sometimes transactionally) and trying to do so efficiently while maintaining database agnosticism and using multiple repositories together. Let's say we have repositories for three different entities; Widget, Thing and Whatsit. Each repository is abstracted via a base interface as per normal decoupling design processes. The base interfaces would then be IWidgetRepository, IThingRepository and IWhatsitRepository. Now we have our business layer or equivalent (whatever you want to call it). In this layer we have classes that access the various repositories. Often the methods in these classes need to do batch/combined operations where multiple repositories are involved. Sometimes one method may make use of another method internally, while that method can still be called independently. What about, in this scenario, when the operation needs to be transactional? Example: class Bob { private IWidgetRepository _widgetRepo; private IThingRepository _thingRepo; private IWhatsitRepository _whatsitRepo; public Bob(IWidgetRepository widgetRepo, IThingRepository thingRepo, IWhatsitRepository whatsitRepo) { _widgetRepo = widgetRepo; _thingRepo= thingRepo; _whatsitRepo= whatsitRepo; } public void DoStuff() { _widgetRepo.StoreSomeStuff(); _thingRepo.ReadSomeStuff(); _whatsitRepo.SaveSomething(); } public void DoOtherThing() { _widgetRepo.UpdateSomething(); DoStuff(); } } How do I keep my access to that database efficient and not have a constant stream of open-close-open-close on connections and inadvertent invocation of MSDTS and whatnot? If my database is something like SQLite, standard mechanisms like creating nested transactions are going to inherently fail, yet the business layer should not have to be concerning itself with such things. How do you handle such issues? Does ADO.Net provide simple mechanisms to handle this or do most people end up wrapping their own custom bits of code around ADO.Net to solve these types of problems?

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  • Most efficient way of checking if Date object and Calendar object are in the same month

    - by Indigenuity
    I am working on a project that will run many thousands of comparisons between dates to see if they are in the same month, and I am wondering what the most efficient way of doing it would be. This isn't exactly what my code looks like, but here's the gist: List<Date> dates = getABunchOfDates(); Calendar month = Calendar.getInstance(); for(int i = 0; i < numMonths; i++) { for(Date date : dates) { if(sameMonth(month, date) .. doSomething } month.add(Calendar.MONTH, -1); } Creating a new Calendar object for every date seems like a pretty hefty overhead when this comparison will happen thousands of times, soI kind of want to cheat a bit and use the deprecated method Date.getMonth() and Date.getYear() public static boolean sameMonth(Calendar month, Date date) { return month.get(Calendar.YEAR) == date.getYear() && month.get(Calendar.MONTH) == date.getMonth(); } I'm pretty close to just using this method, since it seems to be the fastest, but is there a faster way? And is this a foolish way, since the Date methods are deprecated? Note: This project will always run with Java 7

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  • Efficient way to get highly correlated pairs from large data set in Python or R

    - by Akavall
    I have a large data set (Let's say 10,000 variables with about 1000 elements each), we can think of it as 2D list, something like: [[variable_1], [variable_2], ............ [variable_n] ] I want to extract highly correlated variable pairs from that data. I want "highly correlated" to be a parameter that I can choose. I don't need all pairs to be extracted, and I don't necessarily want the most correlated pairs. As long as there is an efficient method that gets me highly correlated pairs I am happy. Also, it would be nice if a variable does not show up in more than one pair. Although this might not be crucial. Of course, there is a brute force way to finding such pairs, but it is too slow for me. I've googled around for a bit and found some theoretical work on this issue, but I wasn't able for find a package that could do what I am looking for. I mostly work in python, so a package in python would be most helpful, but if there exists a package in R that does what I am looking for it will be great. Does anyone know of a package that does the above in Python or R? Or any other ideas? Thank You in Advance

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  • Most Efficient way to deal with multiple CCSprites?

    - by nardsurfer
    I have four different types of objects within my environment(box2d), each type of object having multiple instances of itself, and would like to find the most efficient way to deal with adding and manipulating all the CCSprites. The sprites are all from different files, so would it be best to create each sprite and add it to a data structure (NSMutableArray) or would I use a CCSpriteBatchNode even though each CCSprite file is different (for each type of object)? Thanks. @interface LevelScene : CCLayer { b2World* world; GLESDebugDraw *m_debugDraw; CCSpriteBatchNode *ballBatch; CCSpriteBatchNode *blockBatch; CCSpriteBatchNode *springBatch; CCSprite *goal; } +(id) scene; // adds a new sprite at a given coordinate -(void) addNewBallWithCoords:(CGPoint)p; // loads the objects (blocks, springs, and the goal), returns the Level Object -(Level) loadLevel:(int)level; @end or using NSMutableArray objects within the Level object... @interface zLevel : zThing { NSMutableArray *springs; NSMutableArray *blocks; NSMutableArray *balls; zGoal *goal; int levelNumber; } @property(nonatomic,retain)NSMutableArray *springs; @property(nonatomic,retain)NSMutableArray *blocks; @property(nonatomic,retain)NSMutableArray *balls; @property(nonatomic,retain)zGoal *goal; @property(nonatomic,assign)int levelNumber; -(void)initWithLevel:(int)level; -(void)loadLevelThings; @end

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  • The most efficient way to calculate an integral in a dataset range

    - by Annalisa
    I have an array of 10 rows by 20 columns. Each columns corresponds to a data set that cannot be fitted with any sort of continuous mathematical function (it's a series of numbers derived experimentally). I would like to calculate the integral of each column between row 4 and row 8, then store the obtained result in a new array (20 rows x 1 column). I have tried using different scipy.integrate modules (e.g. quad, trpz,...). The problem is that, from what I understand, scipy.integrate must be applied to functions, and I am not sure how to convert each column of my initial array into a function. As an alternative, I thought of calculating the average of each column between row 4 and row 8, then multiply this number by 4 (i.e. 8-4=4, the x-interval) and then store this into my final 20x1 array. The problem is...ehm...that I don't know how to calculate the average over a given range. The question I am asking are: Which method is more efficient/straightforward? Can integrals be calculated over a data set like the one that I have described? How do I calculate the average over a range of rows?

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  • Efficient way to call .Sum() on multiple properties

    - by SherCoder
    I have a function that uses Linq to get data from the database and then I call that function in another function to sum all the individual properties using .Sum on each individual property. I was wondering if there is an efficient way to sum all the properties at once rather than calling .Sum() on each individual property. I think the way I am doing as of right now, is very slow (although untested). public OminitureStats GetAvgOmnitureData(int? fnsId, int dateRange) { IQueryable<OminitureStats> query = GetOmnitureDataAsQueryable(fnsId, dateRange); int pageViews = query.Sum(q => q.PageViews); int monthlyUniqueVisitors = query.Sum(q => q.MonthlyUniqueVisitors); int visits = query.Sum(q => q.Visits); double pagesPerVisit = (double)query.Sum(q => q.PagesPerVisit); double bounceRate = (double)query.Sum(q => q.BounceRate); return new OminitureStats(pageViews, monthlyUniqueVisitors, visits, bounceRate, pagesPerVisit); }

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  • Java: Efficient Equivalent to Removing while Iterating a Collection

    - by Claudiu
    Hello everyone. We all know you can't do this: for (Object i : l) if (condition(i)) l.remove(i); ConcurrentModificationException etc... this apparently works sometimes, but not always. Here's some specific code: public static void main(String[] args) { Collection<Integer> l = new ArrayList<Integer>(); for (int i=0; i < 10; ++i) { l.add(new Integer(4)); l.add(new Integer(5)); l.add(new Integer(6)); } for (Integer i : l) { if (i.intValue() == 5) l.remove(i); } System.out.println(l); } This, of course, results in: Exception in thread "main" java.util.ConcurrentModificationException ...even though multiple threads aren't doing it... Anyway. What's the best solution to this problem? "Best" here means most time and space efficient (I realize you can't always have both!) I'm also using an arbitrary Collection here, not necessarily an ArrayList, so you can't rely on get.

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  • Game loop and time tracking

    - by David Brown
    Maybe I'm just an idiot, but I've been trying to implement a game loop all day and it's just not clicking. I've read literally every article I could find on Google, but the problem is that they all use different timing mechanisms, which makes them difficult to apply to my particular situation (some use milliseconds, other use ticks, etc). Basically, I have a Clock object that updates each time the game loop executes. internal class Clock { public static long Timestamp { get { return Stopwatch.GetTimestamp(); } } public static long Frequency { get { return Stopwatch.Frequency; } } private long _startTime; private long _lastTime; private TimeSpan _totalTime; private TimeSpan _elapsedTime; /// <summary> /// The amount of time that has passed since the first step. /// </summary> public TimeSpan TotalTime { get { return _totalTime; } } /// <summary> /// The amount of time that has passed since the last step. /// </summary> public TimeSpan ElapsedTime { get { return _elapsedTime; } } public Clock() { Reset(); } public void Reset() { _startTime = Timestamp; _lastTime = 0; _totalTime = TimeSpan.Zero; _elapsedTime = TimeSpan.Zero; } public void Tick() { long currentTime = Timestamp; if (_lastTime == 0) _lastTime = currentTime; _totalTime = TimestampToTimeSpan(currentTime - _startTime); _elapsedTime = TimestampToTimeSpan(currentTime - _lastTime); _lastTime = currentTime; } public static TimeSpan TimestampToTimeSpan(long timestamp) { return TimeSpan.FromTicks( (timestamp * TimeSpan.TicksPerSecond) / Frequency); } } I based most of that on the XNA GameClock, but it's greatly simplified. Then, I have a Time class which holds various times that the Update and Draw methods need to know. public class Time { public TimeSpan ElapsedVirtualTime { get; internal set; } public TimeSpan ElapsedRealTime { get; internal set; } public TimeSpan TotalVirtualTime { get; internal set; } public TimeSpan TotalRealTime { get; internal set; } internal Time() { } internal Time(TimeSpan elapsedVirtualTime, TimeSpan elapsedRealTime, TimeSpan totalVirutalTime, TimeSpan totalRealTime) { ElapsedVirtualTime = elapsedVirtualTime; ElapsedRealTime = elapsedRealTime; TotalVirtualTime = totalVirutalTime; TotalRealTime = totalRealTime; } } My main class keeps a single instance of Time, which it should constantly update during the game loop. So far, I have this: private static void Loop() { do { Clock.Tick(); Time.TotalRealTime = Clock.TotalTime; Time.ElapsedRealTime = Clock.ElapsedTime; InternalUpdate(Time); InternalDraw(Time); } while (!_exitRequested); } The real time properties of the time class turn out great. Now I'd like to get a proper update/draw loop working so that the state is updated a variable number of times per frame, but at a fixed timestep. At the same time, the Time.TotalVirtualTime and Time.ElapsedVirtualTime should be updated accordingly. In addition, I intend for this to support multiplayer in the future, in case that makes any difference to the design of the game loop. Any tips or examples on how I could go about implementing this (aside from links to articles)?

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  • Problems setting NTP sever with w32tm for a DC that is a Hyper-V guest

    - by R.Tonheim
    Hello ! I have tried to sett my DC to get its time from several NTP severs. I follow this answer (http://serverfault.com/questions/24298/w32time-sync-problems-for-hyper-v-guests-w32time-event-ids-38-24-29-35/24299#24299) to do it. First I disable Time Synchronization in the Hyper-V Integration Services for each guest. Then restart the Windows Time serviceon the guest. I had before this used this command: w32tm /config /manualpeerlist:"ntp.uio.no;timekeeper. uio.no;nissen.uio.no;0.no.pool.ntp.org;1.no.pool.ntp.org;2.no.pool.ntp.org" /syn cfromflags:manual /reliable:yes /update And the cmd sad: The command completed successfully. But the time was still 10 min wrong... I run w32tm again after restarted the DC without it having any effect. The w32tm /query /status still say: "Source: Local CMOS Clock" FROM MY CMD: Microsoft Windows [Version 6.0.6002] Copyright (c) 2006 Microsoft Corporation. All rights reserved. C:\Users\Administrator.MHGw32tm /query /status Leap Indicator: 0(no warning) Stratum: 1 (primary reference - syncd by radio clock) Precision: -6 (15.625ms per tick) Root Delay: 0.0000000s Root Dispersion: 10.0000000s ReferenceId: 0x4C4F434C (source name: "LOCL") Last Successful Sync Time: 05.09.2009 20:06:21 Source: Local CMOS Clock Poll Interval: 6 (64s) C:\Users\Administrator.MHGw32tm /config /manualpeerlist:"ntp.uio.no;timekeeper. uio.no;nissen.uio.no;0.no.pool.ntp.org;1.no.pool.ntp.org;2.no.pool.ntp.org" /syn cfromflags:manual /reliable:yes /update The command completed successfully. C:\Users\Administrator.MHGw32tm /query /status Leap Indicator: 0(no warning) Stratum: 1 (primary reference - syncd by radio clock) Precision: -6 (15.625ms per tick) Root Delay: 0.0000000s Root Dispersion: 10.0000000s ReferenceId: 0x4C4F434C (source name: "LOCL") Last Successful Sync Time: 05.09.2009 20:06:21 Source: Local CMOS Clock Poll Interval: 6 (64s) C:\Users\Administrator.MHG

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  • ntpd on Fedora Core 6 with high negative time rest values

    - by Mark White
    The basic problem is we have a FC6 server instance running on a virtual machine, and the system time seems to have been slowly varying until it is now causing a problem. The server runs 24/7 and has been up for 155 days. It has been changed to show GMT, and reports the time as (example) 00:15:15 GMT whereas the actual time is 00:00:00 GMT. This is an offset of 915 seconds. selinux has been changed to 'setenforce 0' for testing and I am running as root. I stop the ntpd service and change the time in System|Administration|Date & Time. The time still shows the same with 'date' in bash. There are no error logs. I change the date with 'date --set' in bash. The response confirms the changed date. I run 'date' and the incorrect date is shown. There are no error logs. I start the ntpd service and /var/log/messages shows success with 'time reset -915.720139s'. The date remains unchanged. ntpq -p shows three three time servers all have offsets of around -915 seconds. I stop ntpd service and try 'ntpd -gqx' and get the same result as above - success, but a large negative time reset. I've tried varying combinations of the above, and a few more settings in System|Administration|Date & Time - no change. I just need to reset the system time to GMT. No offset. But I can't wait for ntpd to slew the time over the next few weeks. Any advice is welcome, cheers! Sure this shouldn't be this difficult... Mark...

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  • Can parser combinators be made efficient?

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

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  • efficient android rendering

    - by llll
    I've read quite a few tutorials on game programming on android, and all of them provide basically the same solution as to drawing the game, that is having a dedicated thread spinning like this: public void run() { while(true) { if(!surfaceHolder.getSurface().isValid()) continue; Canvas canvas = surfaceHolder.lockCanvas(); drawGame(canvas); /* do actual drawing here */ surfaceHolder.unlockCanvasAndPost(canvas); } } now I'm wondering, isn't this wasteful? Suppose I've a game with very simple graphics, so that the actual time in drawGame is little; then I'm going to draw the same things on and on, stealing cpu from the other threads; a possibility could be skipping the drawing and sleeping a bit if the game state hasn't changed, which I could check by having the state update thread mantaining a suitable status flag. But maybe there are other options. For example, couldn'it be possible to synchronize with rendering, so that I don't post updates too often? Or am I missing something and that is precisely what lockCanvas does, that is it blocks and burns no cpu until proper time? Thanks in advance L.

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  • Efficient (basic) regular expression implementation for streaming data

    - by Brendan Dolan-Gavitt
    I'm looking for an implementation of regular expression matching that operates on a stream of data -- i.e., it has an API that allows a user to pass in one character at a time and report when a match is found on the stream of characters seen so far. Only very basic (classic) regular expressions are needed, so a DFA/NFA based implementation seems like it would be well-suited to the problem. Based on the fact that it's possible to do regular expression matching using a DFA/NFA in a single linear sweep, it seems like a streaming implementation should be possible. Requirements: The library should try to wait until the full string has been read before performing the match. The data I have really is streaming; there is no way to know how much data will arrive, it's not possible to seek forward or backward. Implementing specific stream matching for a couple special cases is not an option, as I don't know in advance what patterns a user might want to look for. For the curious, my use case is the following: I have a system which intercepts memory writes inside a full system emulator, and I would like to have a way to identify memory writes that match a regular expression (e.g., one could use this to find the point in the system where a URL is written to memory). I have found (links de-linkified because I don't have enough reputation): stackoverflow.com/questions/1962220/apply-a-regex-on-stream stackoverflow.com/questions/716927/applying-a-regular-expression-to-a-java-i-o-stream www.codeguru.com/csharp/csharp/cs_data/searching/article.php/c14689/Building-a-Regular-Expression-Stream-Search-with-the-NET-Framework.htm But all of these attempt to convert the stream to a string first and then use a stock regular expression library. Another thought I had was to modify the RE2 library, but according to the author it is architected around the assumption that the entire string is in memory at the same time. If nothing's available, then I can start down the unhappy path of reinventing this wheel to fit my own needs, but I'd really rather not if I can avoid it. Any help would be greatly appreciated!

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  • Datastructure choices for highspeed and memory efficient detection of duplicate of strings

    - by Jonathan Holland
    I have a interesting problem that could be solved in a number of ways: I have a function that takes in a string. If this function has never seen this string before, it needs to perform some processing. If the function has seen the string before, it needs to skip processing. After a specified amount of time, the function should accept duplicate strings. This function may be called thousands of time per second, and the string data may be very large. This is a highly abstracted explanation of the real application, just trying to get down to the core concept for the purpose of the question. The function will need to store state in order to detect duplicates. It also will need to store an associated timestamp in order to expire duplicates. It does NOT need to store the strings, a unique hash of the string would be fine, providing there is no false positives due to collisions (Use a perfect hash?), and the hash function was performant enough. The naive implementation would be simply (in C#): Dictionary<String,DateTime> though in the interest of lowering memory footprint and potentially increasing performance I'm evaluating a custom data structures to handle this instead of a basic hashtable. So, given these constraints, what would you use? EDIT, some additional information that might change proposed implementations: 99% of the strings will not be duplicates. Almost all of the duplicates will arrive back to back, or nearly sequentially. In the real world, the function will be called from multiple worker threads, so state management will need to be synchronized.

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  • C# Proposal: Compile Time Static Checking Of Dynamic Objects

    - by Paulo Morgado
    C# 4.0 introduces a new type: dynamic. dynamic is a static type that bypasses static type checking. This new type comes in very handy to work with: The new languages from the dynamic language runtime. HTML Document Object Model (DOM). COM objects. Duck typing … Because static type checking is bypassed, this: dynamic dynamicValue = GetValue(); dynamicValue.Method(); is equivalent to this: object objectValue = GetValue(); objectValue .GetType() .InvokeMember( "Method", BindingFlags.InvokeMethod, null, objectValue, null); Apart from caching the call site behind the scenes and some dynamic resolution, dynamic only looks better. Any typing error will only be caught at run time. In fact, if I’m writing the code, I know the contract of what I’m calling. Wouldn’t it be nice to have the compiler do some static type checking on the interactions with these dynamic objects? Imagine that the dynamic object that I’m retrieving from the GetValue method, besides the parameterless method Method also has a string read-only Property property. This means that, from the point of view of the code I’m writing, the contract that the dynamic object returned by GetValue implements is: string Property { get; } void Method(); Since it’s a well defined contract, I could write an interface to represent it: interface IValue { string Property { get; } void Method(); } If dynamic allowed to specify the contract in the form of dynamic(contract), I could write this: dynamic(IValue) dynamicValue = GetValue(); dynamicValue.Method(); This doesn’t mean that the value returned by GetValue has to implement the IValue interface. It just enables the compiler to verify that dynamicValue.Method() is a valid use of dynamicValue and dynamicValue.OtherMethod() isn’t. If the IValue interface already existed for any other reason, this would be fine. But having a type added to an assembly just for compile time usage doesn’t seem right. So, dynamic could be another type construct. Something like this: dynamic DValue { string Property { get; } void Method(); } The code could now be written like this; DValue dynamicValue = GetValue(); dynamicValue.Method(); The compiler would never generate any IL or metadata for this new type construct. It would only thee used for compile type static checking of dynamic objects. As a consequence, it makes no sense to have public accessibility, so it would not be allowed. Once again, if the IValue interface (or any other type definition) already exists, it can be used in the dynamic type definition: dynamic DValue : IValue, IEnumerable, SomeClass { string Property { get; } void Method(); } Another added benefit would be IntelliSense. I’ve been getting mixed reactions to this proposal. What do you think? Would this be useful?

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  • Help finding time of collision

    - by WannaBe
    I am making a simple game right now and am struggling with collision response. My goal is to someday be able to turn it into a 2D platformer but I have a long way to go. I am currently making this in JavaScript and using the canvas element so (0,0) is in the top left and positive X is to the right and positive Y is down. I read a helpful post on StackExchange that got me started on this but I can't seem to get the algorithm 100% correct. How to deal with corner collisions in 2D? I can detect the collision fine but I can't seem to get the response right. The goal is to detect which side the player hit first since minimum displacement doesn't always work. The X response seems to work fine but the Y only works when I am far from the corners. Here is a picture showing what happens Here is the code var bx = box.x; var by = box.y; var bw = box.width; var bh = box.height; var boxCenterX = bx + (bw/2); var boxCenterY = by + (bh/2); var playerCenterX = player.x + player.xvel + (player.width/2); var playerCenterY = player.y + player.yvel + (player.height/2); //left = negative and right = positve, 0 = middle var distanceXin = playerCenterX - boxCenterX; var distanceYin = playerCenterY - boxCenterY; var distanceWidth = Math.abs(distanceXin); var distanceHeight = Math.abs(distanceYin); var halfWidths = (bw/2) + (player.width/2); var halfHeights = (bh/2) + (player.height/2); if(distanceWidth < halfWidths){ //xcollision if(distanceHeight < halfHeights){ //ycollision if(player.xvel == 0){ //adjust y if(distanceYin > 0){ //bottom player.y = by + bh; player.yvel = 0; }else{ player.y = by - player.height; player.yvel = 0; } }else if(player.yvel == 0){ //adjust x if(distanceXin > 0){ //right player.x = bx + bw; player.xvel = 0; }else{ //left player.x = bx - player.width; player.xvel = 0; } }else{ var yTime = distanceYin / player.yvel; var xTime = distanceXin / player.xvel; if(xTime < yTime){ //adjust the x it collided first if(distanceXin > 0){ //right player.x = bx + bw; player.xvel = 0; }else{ //left player.x = bx - player.width; player.xvel = 0; } }else{ //adjust the y it collided first if(distanceYin > 0){ //bottom player.y = by + bh; player.yvel = 0; }else{ player.y = by - player.height; player.yvel = 0; } } } } } And here is a JSFiddle if you would like to see the problem yourself. http://jsfiddle.net/dMumU/ To recreate this move the player to here And press up and left at the same time. The player will jump to the right for some reason. Any advice? I know I am close but I can't seem to get xTime and yTime to equal what I want every time.

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  • Bridging the Gap in Cloud, Big Data, and Real-time

    - by Dain C. Hansen
    Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";} With all the buzz of around big data and cloud computing, it is easy to overlook one of your most precious commodities—your data. Today’s businesses cannot stand still when it comes to data. Market success now depends on speed, volume, complexity, and keeping pace with the latest data integration breakthroughs. Are you up to speed with big data, cloud integration, real-time analytics? Join us in this three part blog series where we’ll look at each component in more detail. Meet us online on October 24th where we’ll take your questions about what issues you are facing in this brave new world of integration. Let’s start first with Cloud. What happens with your data when you decide to implement a private cloud architecture? Or public cloud? Data integration solutions play a vital role migrating data simply, efficiently, and reliably to the cloud; they are a necessary ingredient of any platform as a service strategy because they support cloud deployments with data-layer application integration between on-premise and cloud environments of all kinds. For private cloud architectures, consolidation of your databases and data stores is an important step to take to be able to receive the full benefits of cloud computing. Private cloud integration requires bidirectional replication between heterogeneous systems to allow you to perform data consolidation without interrupting your business operations. In addition, integrating data requires bulk load and transformation into and out of your private cloud is a crucial step for those companies moving to private cloud. In addition, the need for managing data services as part of SOA/BPM solutions that enable agile application delivery and help build shared data services for organizations. But what about public Cloud? If you have moved your data to a public cloud application, you may also need to connect your on-premise enterprise systems and the cloud environment by moving data in bulk or as real-time transactions across geographies. For public and private cloud architectures both, Oracle offers a complete and extensible set of integration options that span not only data integration but also service and process integration, security, and management. For those companies investing in Oracle Cloud, you can move your data through Oracle SOA Suite using REST APIs to Oracle Messaging Cloud Service —a new service that lets applications deployed in Oracle Cloud securely and reliably communicate over Java Messaging Service . As an example of loading and transforming data into other public clouds, Oracle Data Integrator supports a knowledge module for Salesforce.com—now available on AppExchange. Other third-party knowledge modules are being developed by customers and partners every day. To learn more about how to leverage Oracle’s Data Integration products for Cloud, join us live: Data Integration Breakthroughs Webcast on October 24th 10 AM PST.

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  • Slow Ubuntu 10.04 after long time unused

    - by Winston Ewert
    I'm at spring break so I'm back at my parent's house. I've turned my computer on which has been off since January and its unusably slow. This was not the case when I last used the computer in January. It is running 10.04, Memory: 875.5 MB CPU: AMD Athlon 64 X2 Dual Core Processor 4400+ Available Disk Space: 330.8 GB I'm not seeing a large usage of either memory or Disk I/O. If I look at my list of processes there is only a very small amount of CPU usage. However, if I hover over the CPU usage graph that I've on the top bar, I sometimes get really high readings like 100%. It took a long time to boot, to open firefox, to open a link in firefox. As far as I can tell everything that the computer tries to do is just massively slow. Right now, I'm apt-get dist-upgrading to install any updates that I will have missed since last time this computer was on. Any ideas as to what is going on here? UPDATE: I thought to check dmesg and it has a lot of entries like this: [ 1870.142201] ata3.00: exception Emask 0x0 SAct 0x7 SErr 0x0 action 0x0 [ 1870.142206] ata3.00: irq_stat 0x40000008 [ 1870.142210] ata3.00: failed command: READ FPDMA QUEUED [ 1870.142217] ata3.00: cmd 60/08:10:c0:4a:65/00:00:03:00:00/40 tag 2 ncq 4096 in [ 1870.142218] res 41/40:00:c5:4a:65/00:00:03:00:00/40 Emask 0x409 (media error) <F> [ 1870.142221] ata3.00: status: { DRDY ERR } [ 1870.142223] ata3.00: error: { UNC } [ 1870.143981] ata3.00: SB600 AHCI: limiting to 255 sectors per cmd [ 1870.146758] ata3.00: SB600 AHCI: limiting to 255 sectors per cmd [ 1870.146761] ata3.00: configured for UDMA/133 [ 1870.146777] ata3: EH complete [ 1872.092269] ata3.00: exception Emask 0x0 SAct 0x7 SErr 0x0 action 0x0 [ 1872.092274] ata3.00: irq_stat 0x40000008 [ 1872.092278] ata3.00: failed command: READ FPDMA QUEUED [ 1872.092285] ata3.00: cmd 60/08:00:c0:4a:65/00:00:03:00:00/40 tag 0 ncq 4096 in [ 1872.092287] res 41/40:00:c5:4a:65/00:00:03:00:00/40 Emask 0x409 (media error) <F> [ 1872.092289] ata3.00: status: { DRDY ERR } [ 1872.092292] ata3.00: error: { UNC } [ 1872.094050] ata3.00: SB600 AHCI: limiting to 255 sectors per cmd [ 1872.096795] ata3.00: SB600 AHCI: limiting to 255 sectors per cmd [ 1872.096798] ata3.00: configured for UDMA/133 [ 1872.096814] ata3: EH complete [ 1874.042279] ata3.00: exception Emask 0x0 SAct 0x7 SErr 0x0 action 0x0 [ 1874.042285] ata3.00: irq_stat 0x40000008 [ 1874.042289] ata3.00: failed command: READ FPDMA QUEUED [ 1874.042296] ata3.00: cmd 60/08:10:c0:4a:65/00:00:03:00:00/40 tag 2 ncq 4096 in [ 1874.042297] res 41/40:00:c5:4a:65/00:00:03:00:00/40 Emask 0x409 (media error) <F> [ 1874.042300] ata3.00: status: { DRDY ERR } [ 1874.042302] ata3.00: error: { UNC } [ 1874.044048] ata3.00: SB600 AHCI: limiting to 255 sectors per cmd [ 1874.046837] ata3.00: SB600 AHCI: limiting to 255 sectors per cmd [ 1874.046840] ata3.00: configured for UDMA/133 [ 1874.046861] sd 2:0:0:0: [sda] Unhandled sense code [ 1874.046863] sd 2:0:0:0: [sda] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 1874.046867] sd 2:0:0:0: [sda] Sense Key : Medium Error [current] [descriptor] [ 1874.046872] Descriptor sense data with sense descriptors (in hex): [ 1874.046874] 72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00 [ 1874.046883] 03 65 4a c5 [ 1874.046886] sd 2:0:0:0: [sda] Add. Sense: Unrecovered read error - auto reallocate failed [ 1874.046892] sd 2:0:0:0: [sda] CDB: Read(10): 28 00 03 65 4a c0 00 00 08 00 [ 1874.046900] end_request: I/O error, dev sda, sector 56969925 [ 1874.046920] ata3: EH complete I'm not certain, but that looks like my problem may be a failing hard drive. But the drive is less then a year old, it really shouldn't be failing now...

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  • Quaternion dfference + time --> angular velocity (gyroscope in physics library)

    - by AndrewK
    I am using Bullet Physic library to program some function, where I have difference between orientation from gyroscope given in quaternion and orientation of my object, and time between each frame in milisecond. All I want is set the orientation from my gyroscope to orientation of my object in 3D space. But all I can do is set angular velocity to my object. I have orientation difference and time, and from that I calculate vector of angular velocity [Wx,Wy,Wz] from that formula: W(t) = 2 * dq(t)/dt * conj(q(t)) My code is: btQuaternion diffQuater = gyroQuater - boxQuater; btQuaternion conjBoxQuater = gyroQuater.inverse(); btQuaternion velQuater = ((diffQuater * 2.0f) / d_time) * conjBoxQuater; And everything works well, till I get: 1 rotating around Y axis, angle about 60 degrees, then I have these values in 2 critical frames: x: -0.013220 y: -0.038050 z: -0.021979 w: -0.074250 - diffQuater x: 0.120094 y: 0.818967 z: 0.156797 w: -0.538782 - gyroQuater x: 0.133313 y: 0.857016 z: 0.178776 w: -0.464531 - boxQuater x: 0.207781 y: 0.290452 z: 0.245594 - diffQuater -> euler angles x: 3.153619 y: -66.947929 z: 175.936615 - gyroQuater -> euler angles x: 4.290697 y: -57.553043 z: 173.320053 - boxQuater -> euler angles x: 0.138128 y: 2.823307 z: 1.025552 w: 0.131360 - velQuater d_time: 0.058000 x: 0.211020 y: 1.595124 z: 0.303650 w: -1.143846 - diffQuater x: 0.089518 y: 0.771939 z: 0.144527 w: -0.612543 - gyroQuater x: -0.121502 y: -0.823185 z: -0.159123 w: 0.531303 - boxQuater x: nan y: nan z: nan - diffQuater -> euler angles x: 2.985240 y: -76.304405 z: -170.555054 - gyroQuater -> euler angles x: 3.269681 y: -65.977966 z: 175.639420 - boxQuater -> euler angles x: -0.730262 y: -2.882153 z: -1.294721 w: 63.325996 - velQuater d_time: 0.063000 2 rotating around X axis, angle about 120 degrees, then I have these values in 2 critical frames: x: -0.013045 y: -0.004186 z: -0.005667 w: -0.022482 - diffQuater x: -0.848030 y: -0.187985 z: 0.114400 w: 0.482099 - gyroQuater x: -0.834985 y: -0.183799 z: 0.120067 w: 0.504580 - boxQuater x: 0.036336 y: 0.002312 z: 0.020859 - diffQuater -> euler angles x: -113.129463 y: 0.731925 z: 25.415056 - gyroQuater -> euler angles x: -110.232368 y: 0.860897 z: 25.350458 - boxQuater -> euler angles x: -0.865820 y: -0.456086 z: 0.034084 w: 0.013184 - velQuater d_time: 0.055000 x: -1.721662 y: -0.387898 z: 0.229844 w: 0.910235 - diffQuater x: -0.874310 y: -0.200132 z: 0.115142 w: 0.426933 - gyroQuater x: 0.847352 y: 0.187766 z: -0.114703 w: -0.483302 - boxQuater x: -144.402298 y: 4.891629 z: 71.309158 - diffQuater -> euler angles x: -119.515343 y: 1.745076 z: 26.646086 - gyroQuater -> euler angles x: -112.974533 y: 0.738675 z: 25.411509 - boxQuater -> euler angles x: 2.086195 y: 0.676526 z: -0.424351 w: 70.104248 - velQuater d_time: 0.057000 2 rotating around Z axis, angle about 120 degrees, then I have these values in 2 critical frames: x: -0.000736 y: 0.002812 z: -0.004692 w: -0.008181 - diffQuater x: -0.003829 y: 0.012045 z: -0.868035 w: 0.496343 - gyroQuater x: -0.003093 y: 0.009232 z: -0.863343 w: 0.504524 - boxQuater x: -0.000822 y: -0.003032 z: 0.004162 - diffQuater -> euler angles x: -1.415189 y: 0.304210 z: -120.481873 - gyroQuater -> euler angles x: -1.091881 y: 0.227784 z: -119.399445 - boxQuater -> euler angles x: 0.159042 y: 0.169228 z: -0.754599 w: 0.003900 - velQuater d_time: 0.025000 x: -0.007598 y: 0.024074 z: -1.749412 w: 0.968588 - diffQuater x: -0.003769 y: 0.012030 z: -0.881377 w: 0.472245 - gyroQuater x: 0.003829 y: -0.012045 z: 0.868035 w: -0.496343 - boxQuater x: -5.645197 y: 1.148993 z: -146.507187 - diffQuater -> euler angles x: -1.418294 y: 0.270319 z: -123.638245 - gyroQuater -> euler angles x: -1.415183 y: 0.304208 z: -120.481873 - boxQuater -> euler angles x: 0.017498 y: -0.013332 z: 2.040073 w: 148.120056 - velQuater d_time: 0.027000 The problem is the most visible in diffQuater - euler angles vector. Can someone tell me why it is like that? and how to solve that problem? All suggestions are welcome.

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