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• How to compile scheme into native binary files ?

  - by Joe

  I am very new to scheme. And now I am trying to compile some scheme code into binary file which will be loaded faster into interpreter. (The interpreter is a hybrid interpreter)Some one told me that I can compile the code into native binary file and then load it into interperter. And my question is: 1. What is the native binary file? 2. How can I compile the scheme code into a native binary file? 3. How can I load native bianry file into scheme interpreter? Thanks in advance. Joe Suggested that I want to compile below code into native binary file: (define test (lambda() (display "this is a test")) And then load the bianry file into interpreter and call the function "test".

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• One table, need multiple values from different rows/tuples

  - by WmasterJ

  I have tables like: 'profile_values' userID | fid | value -------+---------+------- 1 | 3 | [email protected] 1 | 45 | 203-234-2345 3 | 3 | [email protected] 1 | 45 | 123-456-7890 And: 'users' userID | name -------+------- 1 | joe 2 | jane 3 | jake I want to join them and have one row with two of the values like: 'profile_values' userID | name | email | phone -------+-------+----------------+-------------- 1 | joe | [email protected] | 203-234-2345 2 | jane | [email protected] | 123-456-7890 I have solved it but it feels clumsy and I want to know if there is a better way to do it. Meaning solutions that are either more readable or faster(optimized) or simply best-practice. Current solution: multiple tables selected, many conditional statements: SELECT u.userID AS memberid, u.name AS first_name, pv1.value AS fname, pv2.value as lname FROM users AS u, profile_values AS pv1, profile_values AS pv2, WHERE u.userID = pv1.userID AND pv1.fid = 3 AND u.userID = pv2.userID AND pv2.fid = 45; Thanks for the help!

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• How to reduce compilation times with Boost Asio

  - by Artyom

  Boost.Asio is great library but it has one huge drawback -- extreamly slow compilation times. A simple implementation (really simple) of HTTP protocol (about 1k lines of code) requires about 13.5s to compile under GCC 4.4! I tryed to use PCH but it does not improve compilation times too much (about 1s. only). So are there any tutorials on how to make Boost.Asio compilation times faster? For example what headers should I exactly include for what class. I use for example: io_service, tcp::ip::sockets, tcp::ip::acceptor, deadline_timer, buffers and few functions like async_read, async_write. Any suggestions? P.S.: I do use pimpl whenever I can.

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• How do people prove the correctness of Computer Vision methods?

  - by solvingPuzzles

  I'd like to pose a few abstract questions about computer vision research. I haven't quite been able to answer these questions by searching the web and reading papers. How does someone know whether a computer vision algorithm is correct? How do we define "correct" in the context of computer vision? Do formal proofs play a role in understanding the correctness of computer vision algorithms? A bit of background: I'm about to start my PhD in Computer Science. I enjoy designing fast parallel algorithms and proving the correctness of these algorithms. I've also used OpenCV from some class projects, though I don't have much formal training in computer vision. I've been approached by a potential thesis advisor who works on designing faster and more scalable algorithms for computer vision (e.g. fast image segmentation). I'm trying to understand the common practices in solving computer vision problems.

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• Why doesn't Linux use the hardware context switch via the TSS?

  - by smwikipedia

  Hi guys! I read the following statement: The x86 architecture includes a specific segment type called the Task State Segment (TSS), to store hardware contexts. Although Linux doesn't use hardware context switches, it is nonetheless forced to set up a TSS for each distinct CPU in the system. I am wondering: Why doesn't Linux use the hardware support for context switch? Isn't the hardware approach much faster than the software approach? Is there any OS which does take advantage of the hardware context switch? Does windows use it? At last and as usual, thanks for your patience and reply.

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• How can you increase timeout in Linq2Entities?

  - by Russell Steen

  I'm doing a basic select against a view. Unfortunately the result can be slow and I'm getting timeout errors intermittently. How can I increase the timeout? Using .NET 3.5, Sql Server 2000, Linq2Entities I'm using the very basic query List<MyData> result = db.MyData.Where(x.Attribute == search).ToList(); Fixing the query so that it's faster on the DB side is not an option here. Exact Error: "Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding." Update: I'd prefer to just change it for this one query.

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• Performance Tricks for C# Logging

  - by Charles

  I am looking into C# logging and I do not want my log messages to spend any time processing if the message is below the logging threshold. The best I can see log4net does is a threshold check AFTER evaluating the log parameters. Example: _logger.Debug( "My complicated log message " + thisFunctionTakesALongTime() + " will take a long time" ) Even if the threshold is above Debug, thisFunctionTakesALongTime will still be evaluated. In log4net you are supposed to use _logger.isDebugEnabled so you end up with if( _logger.isDebugEnabled ) _logger.Debug( "Much faster" ) I want to know if there is a better solution for .net logging that does not involve a check each time I want to log. In C++ I am allowed to do LOG_DEBUG( "My complicated log message " + thisFunctionTakesALongTime() + " will take no time" ) since my LOG_DEBUG macro does the log level check itself. This frees me to have a 1 line log message throughout my app which I greatly prefer. Anyone know of a way to replicate this behavior in C#?

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• process taking high time on Itanium server

  - by Vishwa

  Hi, we have an application which is recently migrated from PA-Risk server to itanium server. After migration we noticed that there is significant increase in time taken to complete a process. when we tracked the time taken by each part we found that the system time is 7.590000, user time is 3.990000 but elapsed time is 70.434882!! Due to this huge elapsed time, overall performance of the application has gone very low. i wrote a small progrms to perform I/O operations on Itanium. these scripts working faster on Itanium compared to PA-Risk. what could be the reason for this high elapsed time of this process?

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• How to pre-process CSV data for FasterCSV?

  - by Katherine Chalmers

  We're having a significant number of problems creating a bulk upload function for our little app. We're using the FasterCSV gem to upload data to a MySQL database but he Faster CSV is so twitchy and precise in its requirements that it constantly breaks with malformed CSV errors and time out errors. The csv files are generally created by users' pasting text from their web sites or from Microsoft Word docs so it is not reasonable to expect that there will never be odd characters like smart quotes or accents in the data. Also users aren't going to be readily able to identify whether their data is perfect enough for FasterCSV or not. We need to find a way to fix it for them automatically. Is there a good way or a reliable tool for pre-processing CSV data to fix any nits in the data before having the FasterCSV gem process it?

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• Alternative to BitConverter.ToInt32

  - by MusiGenesis

  I'm using BitConverter.ToInt32 to pack 3 byte values into an int, like so: byte R = 0; byte G = 0; byte B = 0; int i = BitConverter.ToInt32(new byte[] { R, G, B, 0 }, 0); Is there a faster way to do this that doesn't involve the creation of a new int each time? Getting the bytes out of an int is easy: int i = 34234; byte B = (byte)(i >> 0); byte G = (byte)(i >> 8); byte R = (byte)(i >> 16); Is there a simple way to reverse this process and use bit-shifting to write the RGB bytes back over an existing int?

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• Efficient algorithm to generate all solutions of a linear diophantine equation with ai=1

  - by Ben

  I am trying to generate all the solutions for the following equations for a given H. With H=4 : 1) ALL solutions for x_1 + x_2 + x_3 + x_4 =4 2) ALL solutions for x_1 + x_2 + x_3 = 4 3) ALL solutions for x_1 + x_2 = 4 4) ALL solutions for x_1 =4 For my problem, there are always 4 equations to solve (independently from the others). There are a total of 2^(H-1) solutions. For the previous one, here are the solutions : 1) 1 1 1 1 2) 1 1 2 and 1 2 1 and 2 1 1 3) 1 3 and 3 1 and 2 2 4) 4 Here is an R algorithm which solve the problem. library(gtools) H<-4 solutions<-NULL for(i in seq(H)) { res<-permutations(H-i+1,i,repeats.allowed=T) resum<-apply(res,1,sum) id<-which(resum==H) print(paste("solutions with ",i," variables",sep="")) print(res[id,]) } However, this algorithm makes more calculations than needed. I am sure it is possible to go faster. By that, I mean not generating the permutations for which the sums is H Any idea of a better algorithm for a given H ?

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• INNER JOIN vs LEFT JOIN performance in SQL Server

  - by Ekkapop

  I've created SQL command that use INNER JOIN for 9 tables, anyway this command take a very long time (more than five minutes). So my folk suggest me to change INNER JOIN to LEFT JOIN because the performance of LEFT JOIN is better, at first time its despite what I know. After I changed, the speed of query is significantly improve. I want to know why LEFT JOIN is faster than INNER JOIN? My SQL command look like below: SELECT * FROM A INNER JOIN B ON ... INNER JOIN C ON ... INNER JOIN D and so no

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• multiple modules under one solution

  - by Vicky

  I have a project under which various distributed applications are placed; the whole project is under a single dll. Hence, if any issue occurs we need to re-build the whole application to run or import to our server. I am looking for the best possible way to make the build process faster and also bit worried about the size of the DLL. Is it a good way to have separate dll for all the modules or split the application in multiple projects??? Can, anyone suggest the best way or example to deal with this situation. Any help would be appreciated. Thanks in advance.

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• Remove first 'n' elements from list without itterating

  - by Eldhose M Babu

  I need an efficient way of removing items from list. If some condition happens, I need to remove first 'n' elements from a list. Can some one suggest the best way to do this? Please keep in mind: performance is a factor for me, so I need a faster way than itterating. Thanks. I'm thinking of a way through which the 'n'th item can be made as the starting of the list so that the 0-n items will get garbage collected. Is it possible?

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• Optimize SQL with Interbase

  - by Roland Bengtsson

  I was inspired by the good answers from my previous question about SQL. Now this SQL is run on a DB with Interbase 2009. It is about 21 GB in size. SELECT DistanceAsMeters, Bold_Id, Created, AddressFrom.CityName_CO as FromCity, AddressTo.CityName_CO as ToCity FROM AddrDistance LEFT JOIN Address AddressFrom ON AddrDistance.FromAddress = AddressFrom.Bold_Id LEFT JOIN Address AddressTo ON AddrDistance.ToAddress = AddressTo.Bold_Id Where DistanceAsMeters = 0 and PseudoDistanceAsCostKm = 0 and not AddrDistance.bold_id in (select bold_id from DistanceQueryTask) Order By Created Desc There are 840000 rows with AddrDistance 190000 rows with Address and 4 with DistanceQueryTask. The question is, can this be done faster? I guess, the same query is run many times select bold_id from DistanceQueryTask. Note that I'm not interested in stored procedures, just plain SQL :)

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• Is there a way to tell JVM to optimize my code before processing?

  - by Rogach

  I have a method, which takes much time to execute first time. But after several invocations, it takes about 30 times less time. So, to make my application respond to user interaction faster, I "warm-up" this method (5 times) with some sample data on initialization of application. But this increases app start-up time. I read, that JVM's can optimize and compile my java code to native, thus speeding things up. I wanted to know - maybe there is some way to explicitly tell JVM that I want this method to be compiled on startup of application?

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• How do I get Java to use my multi-core processor?

  - by Rudiger

  I'm using a GZIPInputStream in my program, and I know that the performance would be helped if I could get Java running my program in parallel. In general, is there a command-line option for the standard VM to run on many cores? It's running on just one as it is. Thanks! Edit I'm running plain ol' Java SE 6 update 17 on Windows XP. Would putting the GZIPInputStream on a separate thread explicitly help? No! Do not put the GZIPInputStream on a separate thread! Do NOT multithread I/O! Edit 2 I suppose I/O is the bottleneck, as I'm reading and writing to the same disk... In general, though, is there a way to make GZIPInputStream faster? Or a replacement for GZIPInputStream that runs parallel? Edit 3 Code snippet I used: GZIPInputStream gzip = new GZIPInputStream(new FileInputStream(INPUT_FILENAME)); DataInputStream in = new DataInputStream(new BufferedInputStream(gzip));

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• Sorting objects in Python

  - by Curious2learn

  I want to sort objects using by one of their attributes. As of now, I am doing it in the following way USpeople.sort(key=lambda person: person.utility[chosenCar],reverse=True) This works fine, but I have read that using operator.attrgetter() might be a faster way to achieve this sort. First, is this correct? Assuming that it is correct, how do I use operator.attrgetter() to achieve this sort? I tried, keyFunc=operator.attrgetter('utility[chosenCar]') USpeople.sort(key=keyFunc,reverse=True) However, I get an error saying that there is no attribute 'utility[chosenCar]'. The problem is that the attribute by which I want to sort is in a dictionary. For example, the utility attribute is in the following form: utility={chosenCar:25000,anotherCar:24000,yetAnotherCar:24500} I want to sort by the utility of the chosenCar using operator.attrgetter(). How could I do this? Thanks in advance.

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• Is writing to a socket an arbitrary limitation of the sendfile() syscall?

  - by Sufian

  Prelude sendfile() is an extremely useful syscall for two reasons: First, it's less code than a read()/write() (or recv()/send() if you prefer that jive) loop. Second, it's faster (less syscalls, implementation may copy between devices without buffer, etc...) than the aforementioned methods. Less code. More efficient. Awesome. In UNIX, everything is (mostly) a file. This is the ugly territory from the collision of platonic theory and real-world practice. I understand that sockets are fundamentally different than files residing on some device. I haven't dug through the sources of Linux/*BSD/Darwin/whatever OS implements sendfile() to know why this specific syscall is restricted to writing to sockets (specifically, streaming sockets). I just want to know... Question What is limiting sendfile() from allowing the destination file descriptor to be something besides a socket (like a disk file, or a pipe)?

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• Help replace this SQL cursor with better code

  - by user318573

  Can anyone give me a hand improving the performance of this cursor logic from SQL 2000. It runs great in SQl2005 and SQL2008, but takes at least 20 minutes to run in SQL 2000. BTW, I would never choose to use a cursor, and I didn't write this code, just trying to get it to run faster. Upgrading this client to 2005/2008 is not an option in the immediate future. ------------------------------------------------------------------------------- ------- Rollup totals in the chart of accounts hierarchy ------------------------------------------------------------------------------- DECLARE @B_SubTotalAccountID int, @B_Debits money, @B_Credits money, @B_YTDDebits money, @B_YTDCredits money DECLARE Bal CURSOR FAST_FORWARD FOR SELECT SubTotalAccountID, Debits, Credits, YTDDebits, YTDCredits FROM xxx WHERE AccountType = 0 AND SubTotalAccountID Is Not Null and (abs(credits)+abs(debits)+abs(ytdcredits)+abs(ytddebits)<>0) OPEN Bal FETCH NEXT FROM Bal INTO @B_SubTotalAccountID, @B_Debits, @B_Credits, @B_YTDDebits, @B_YTDCredits --For Each Active Account WHILE @@FETCH_STATUS = 0 BEGIN --Loop Until end of subtotal chain is reached WHILE @B_SubTotalAccountID Is Not Null BEGIN UPDATE xxx2 SET Debits = Debits + @B_Debits, Credits = Credits + @B_Credits, YTDDebits = YTDDebits + @B_YTDDebits, YTDCredits = YTDCredits + @B_YTDCredits WHERE GLAccountID = @B_SubTotalAccountID SET @B_SubTotalAccountID = (SELECT SubTotalAccountID FROM xxx2 WHERE GLAccountID = @B_SubTotalAccountID) END FETCH NEXT FROM Bal INTO @B_SubTotalAccountID, @B_Debits, @B_Credits, @B_YTDDebits, @B_YTDCredits END CLOSE Bal DEALLOCATE Bal

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• In Subversion, I know when a file was added, what's the quickest way to find out when it was deleted

  - by Eric Johnson

  OK, so suppose I know I added file "foo.txt" to my Subversion repository at revision 500. So I can do a svn log -v http://svnrepo/path/foo.txt@500, and that shows all the files added at the same time. What's the fastest way to find when the file was deleted after it was added? I tried svn log -r500:HEAD -v http://svnrepo/path/foo.txt@500, but that gives me "path not found" - perhaps obviously, because the file "foo.txt" doesn't exist at "HEAD". I can try a binary search algorithm going forward through revisions (and that would certainly be faster than typing this question), but is there a better way?

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• Efficiently detect corrupted jpeg file?

  - by Jacco

  Is there an efficient way of detecting if a jpeg file is corrupted? Background info:   solutions needs to work from within a php script   the jpeg files are on disk   manual checking is no option (user uploaded data) I know that imagecreatefromjpeg(string $filename); can do it. But it is quite slow at doing so. Does anybody know a faster/more efficient solutions?

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• Advantage of using a static member function instead of an equivalent non-static member function?

  - by jonathanasdf

  I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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• File system to choose for NAS box based on FreeNAS or OpenFiler [closed]

  - by Chris

  I'm a photographer and I have a requirement find a better method of storing my photos other than multiple USB2 drives via USB hubs. Currently I use a Macbook Pro and 6 external drives connected via USB2 or FW800. 3 are a copy of the first three, kept up to day manually by running an rsync backup. I'd like to run a FreeNAS or OpenFiler NAS box using 2TB drives mirrored via software RAID. But - I would like to have the flexibility of also plugging into the drive physically for the faster throughput when necessary. So. My question is, is there a file system that both *nix and Mac OSX will play nice with? Many thanks, Chris.

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• exchanging 2 memory positions

  - by Jordi

  I am working with OpenCV and Qt, Opencv use BGR while Qt uses RGB , so I have to swap those 2 bytes for very big images. There is a better way of doing the following? I can not think of anything faster but looks so simple and lame... int width = iplImage->width; int height = iplImage->height; uchar *iplImagePtr = (uchar *) iplImage->imageData; uchar buf; int limit = height * width; for (int y = 0; y < limit; ++y) { buf = iplImagePtr[2]; iplImagePtr[2] = iplImagePtr[0]; iplImagePtr[0] = buf; iplImagePtr += 3; } QImage img((uchar *) iplImage->imageData, width, height, QImage::Format_RGB888);

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