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• Dealing with UIImagePickerController to minimize memory useage

  - by Gordon Fontenot

  So, I have read the SO post on UIImagePickerController, UIImage, Memory and More, and I read the post on Memory Leak Problems with UIImagePickerController in iPhone. I have VASTLY increased my memory efficiency between these 2 posts, and I thank the OPs and the people that provided the answers. I just had a question on the answer provided in the Memory Leak question, which was (essentially): only have one instance of the controller throughout the programs runtime What would be the best way to go about this without causing memory leaks? Right now I am initiating it and releasing it on every use from within the view, and I am seeing exactly what the answer describes (Memory warnings and a crash after about 20 uses). Should I initiate the UIImagePickerController when I need it, but use a seperate class unrelated to the view to control it? How should I deal with releasing the controller if I do it this way?

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• Base-camp Style Subdomains and IDs of Models

  - by Newy

  I have an app that has Basecamp-style subdomains, that is, I have Projects, Users, Apples and Oranges. The Users, Apples and Oranges are all keyed to a Project and only exist in the http://project.myapp.com. I added a project_id to Users, Apples and Oranges and everything works, except of course that the ids of those three objects increment globally, and throughout my app I lookup objects by that id. This doesn't seem like best practice. Should I instead do lookups by a secondary key? How does that affect efficiency? If there's a good blog post that covers this, would be wesome.

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• Pre-allocate memory between HostApp and DLL

  - by Leo

  I have a DLL which provided a decoding function, as follows: function MyDecode (Source: PChar; SourceLen: Integer; var Dest: PChar; DestLen: Integer): Boolean; stdcall; The HostApp call "MyDecode", and transfer into the Source, SourceLen and Dest parameters, the DLL returns decoded Dest and DestLen. The problem is: The HostApp impossible to know decoded Dest length, and therefore would not know how to pre-allocated Dest's memory. I know that can split "MyDecode" into two functions: function GetDecodeLen (Source: PChar; SourceLen: Integer): Integer; stdcall; // Return the Dest's length function MyDecodeLen (Source: PChar; SourceLen: Integer; var Dest: PChar): Boolean; stdcall; But, My decoding process is very complicated, so if split into two functions will affect the efficiency. Is there a better solution?

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• binary file formats: need for error correction?

  - by Jason S

  I need to serialize some data in a binary format for efficiency (datalog where 10-100MB files are typical), and I'm working out the formatting details. I'm wondering if realistically I need to worry about file corruption / error correction / etc. What are circumstances where file corruption can happen? Should I be building robustness to corruption into my binary format? Or should I wrap my nonrobust-to-corruption stream of bytes with some kind of error correcting code? (any suggestions? I'm using Java) Or should I just not worry about this?

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• Tips for optimizing C#/.NET programs

  - by Bob

  It seems like optimization is a lost art these days. Wasn't there a time when all programmers squeezed every ounce of efficiency from their code? Often doing so while walking 5 miles in the snow? In the spirit of bringing back a lost art, what are some tips that you know of for simple (or perhaps complex) changes to optimize C#/.NET code? Since it's such a broad thing that depends on what one is trying to accomplish it'd help to provide context with your tip. For instance: When concatenating many strings together use StringBuilder instead. If you're only concatenating a handful of strings it's ok to use the + operator. Use string.Compare to compare 2 strings instead of doing something like string1.ToLower() == string2.ToLower()

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• From interpeted to native code: "dynamic" languages compiler support

  - by Daniel

  First, I am aware that dynamic languages is a term used mainly by a vendor; I am using it just to have a container word to include languages like Perl (a favorite of mine), Python, Tcl, Ruby, PHP and so on. They are interpreted but I am interested here to refer to languages featuring strong capability to support the programmer efficiency and the support for typical constructs of modern interpreted languages My question is: there are dynamic languages can be compiled efficiently in native executable code - typically for Windows platforms? Which ones? Maybe using some third part ad-hoc tools? I am not talking about huge executables carrying with them a full interpreter or some similar tricks nor some smart module able to include its own dependances or some required modules, but a honest, straight, standard, solid executable code. If not, there is some technical reason inhibiting the availability of such a best-of-both-world feature? Thanks! Daniel

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• How to scroll and zoom in/out large images on iPhone?

  - by Horace Ho

  I have a large image, size around 30000 (w) x 6000 (h) pixels. You may consider it's like a big map. I assume I need to crop it up into smaller tiles. Questions: what are the right ViewControllers to use? (link) what is the tile strategy? (I put this in another question, as it's not iPhone specific) Requirements: whole image (though cropped) can be scrolled up/down/left/right by swipes zoom in (up to pixel-to-pixel) out (down to screen-fit-by-height) by the 2-finger operation memory efficiency by lazy loading tiles Bonus requirements: automatic scroll, say from left to right slowly and smoothly Thanks!

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• Retail knowledge inference

  - by blueomega

  So i am doing a research on how can i infer knowledge from reports (not with a specific format), but after pre processing, i should have some kind of formatted data. A fairly basic inference would be: "Retailer has X stock." and "X is sellable." - "Retailer sells X" the knowledge i focus is retail domain oriented, and if possible i should improve its efficiency with each iteration. Is this scifi(some of my friends think it is)? The related stuff i find online are "expert systems" that find anomalies, fuzzy inference systems and some rants about "easy knowledge". Can you help me with some points for me to focus or orient me in some research directions? blueomega

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• Filter zipcodes by proximity in Django with the Spherical Law of Cosines

  - by spiffytech

  I'm trying to handle proximity search for a basic store locater in Django. Rather than haul PostGIS around with my app just so I can use GeoDjango's distance filter, I'd like to use the Spherical Law of Cosines distance formula in a model query. I'd like all of the calculations to be done in the database in one query, for efficiency. An example MySQL query from The Internet implementing the Spherical Law of Cosines like this: SELECT id, ( 3959 * acos( cos( radians(37) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians(-122) ) + sin( radians(37) ) * sin( radians( lat ) ) ) ) AS distance FROM stores HAVING distance < 25 ORDER BY distance LIMIT 0 , 20; The query needs to reference the Zipcode ForeignKey for each store's lat/lng values. How can I make all of this work in a Django model query?

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• Effective methods for reading and writing large files in C

  - by Bertholt Stutley Johnson

  I'm writing an application that deals with very large user-generated input files. The program will copy about 95 percent of the file, effectively duplicating it and switching a few words and values in the copy, and then appending the copy (in chunks) to the original file, such that each block (consisting of between 10 and 50 lines) in the original is followed by the copied and modified block, and then the next original block, and so on. The user-generated input conforms to a certain format, and it is highly unlikely that any line in the original file is longer than 100 characters long. Which would be the better approach? a) To use one file pointer and use variables that hold the current position of how much has been read and where to write to, seeking the file pointer back and forth to read and write; or b) To use multiple file pointers, one for reading and one for writing. I am mostly concerned with the efficiency of the program, as the input files will reach up to 25,000 lines, each about 50 characters long. Thanks!

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

  - by Pacerier

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

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• code throws std::bad_alloc, not enough memory or can it be a bug?

  - by Andreas

  I am parsing using a pretty large grammar (1.1 GB, it's data-oriented parsing). The parser I use (bitpar) is said to be optimized for highly ambiguous grammars. I'm getting this error: 1terminate called after throwing an instance of 'std::bad_alloc' what(): St9bad_alloc dotest.sh: line 11: 16686 Aborted bitpar -p -b 1 -s top -u unknownwordsm -w pos.dfsa /tmp/gsyntax.pcfg /tmp/gsyntax.lex arbobanko.test arbobanko.results Is there hope? Does it mean that it has ran out of memory? It uses about 15 GB before it crashes. The machine I'm using has 32 GB of RAM, plus swap as well. It crashes before outputting a single parse tree. The parser is an efficient CYK chart parser using bit vector representations; I presume it is already near the limit of memory efficiency. If it really requires too much memory I could sample from the grammar rules, but this will decrease parse accuracy of course.

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• HTML 5 Canvas - Get pixel data for a path

  - by Mikey S.

  I wonder if is there any way I can get pixel data for the currently drawn path in the canvas tag. I can calculate the pixel data on my own when drawing simple shapes like square or a line, but things get messy with more complicated shapes like ellipse or even a simple circle. The reason i'm asking this is because I'm working on a web application which involves sending canvas pixels data to the server when I add a path to the canvas. The server needs to keep it's own copy of the entire canvas, and I really don't want to send the ENTIRE canvas image every single change, but only the delta for efficiency reasons... Thanks.

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• Is Work Stealing always the most appropriate user-level thread scheduling algorithm?

  - by Il-Bhima

  I've been investigating different scheduling algorithms for a thread pool I am implementing. Due to the nature of the problem I am solving I can assume that the tasks being run in parallel are independent and do not spawn any new tasks. The tasks can be of varying sizes. I went immediately for the most popular scheduling algorithm "work stealing" using lock-free deques for the local job queues, and I am relatively happy with this approach. However I'm wondering whether there are any common cases where work-stealing is not the best approach. For this particular problem I have a good estimate of the size of each individual task. Work-stealing does not make use of this information and I'm wondering if there is any scheduler which will give better load-balancing than work-stealing with this information (obviously with the same efficiency). NB. This question ties up with a previous question.

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• Complicated parsing in python

  - by Quazi Farhan

  I have a weird parsing problem with python. I need to parse the following text. Here I need only the section between(not including) "pre" tag and column of numbers (starting with 205 4 164). I have several pages in this format. <html> <pre> A Short Study of Notation Efficiency CACM August, 1960 Smith Jr., H. J. CA600802 JB March 20, 1978 9:02 PM 205 4 164 210 4 164 214 4 164 642 4 164 1 5 164 </pre> </html>

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• DDD: Trying to code sorting and filtering as it pertains to Poco, Repository, DTO, and DAO using C#?

  - by Dr. Zim

  I get a list of items from my Repository. Now I need to sort and filter them, which I believe would be done in the Repository for efficiency. I think there would be two ways of doing this in a DDD way: Send a filter and a sort object full of conditions to the Repository (What is this called)? Repository result would produce an object with .filter and .sort methods? (This wouldn't be a POJO/POCO because it contains more than one object?). So is the answer 1, 2, or other? Could you explain why? I am leaning toward #1 because the Repository would be able to only send the data I want (or will #2 be able to delay accessing data like a LazyList?) A code example (or website link) would be very helpful. Example: Product product = repo.GetProducts(mySortObject, myFilterObject); // List of Poco product.AddFilter("price", "lessThan", "3.99"); product.AddSort("price", "descending");

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• How do I know if I'm being truly clever and not just "clever"?

  - by Covar

  If there's one thing I've learned from programming is that there are clever solutions to problems, and then there are "clever" solutions to problems. One is an intelligent solution to a difficult problem that results in improved efficiency and a better way to to do something and the other will wind up on The Daily WTF, and result in headaches and pain for anyone else involved. My question is how do you distinguish between one and the other? How do you figure out if you've over thought the solution? How do you stop yourself from throwing away truly clever solutions, thinking they were "clever"?

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• File Explorer using Java - how to go about it?

  - by user299988

  Hi, I am set to create a file explorer using Java. The aim is to emulate the behavior of the default explorer as closely as possible, whatever may be the underlying OS. I have done NO GUI programming in Java. I have looked-up Swing, SWT and JFace, and I am beginning my project with this tutorial: http://www.ibm.com/developerworks/opensource/library/os-ecgui1/ I would like to know your opinions about the best approach to tackle this problem. If you could comment on complexity of coding, portability and OS-independence, and efficiency, it would be great. Is there anything else I should know? Do some other ways exist? Thanks a lot!

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• How do you write an idiomatic Scala Quicksort function?

  - by Don Mackenzie

  I recently answered a question with an attempt at writing a quicksort function in scala, I'd seen something like the code below written somewhere. def qsort(l: List[Int]): List[Int] = { l match { case Nil => Nil case pivot::tail => qsort(tail.filter(_ < pivot)) ::: pivot :: qsort(tail.filter(_ >= pivot)) } } My answer received some constructive criticism pointing out that List was a poor choice of collection for quicksort and secondly that the above wasn't tail recursive. I tried to re-write the above in a tail recursive manner but didn't have much luck. Is it possible to write a tail recursive quicksort? or, if not, how can it be done in a functional style? Also what can be done to maximise the efficiency of the implementation? Thanks in advance.

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• Rejigging a floating point equation ...

  - by Jamie

  I'd like to know if there is a way to improve the accuracy of calculating a slope. (This came up a few months back here). It seems by changing: float get_slope(float dXa, float dXb, float dYa, float dYb) { return (dXa - dXb)/(dYa - dYb); } to float get_slope(float dXa, float dXb, float dYa, float dYb) { return dXa/(dYa - dYb) - dXb/(dYa - dYb); } might be an improvement. Suggestions? Edit: It's precision I'm after, not efficiency.

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• What's the proper way to use sqlite on the iPhone?

  - by Elliot Chen

  Hi, Experts: Can you please give some suggestions on sqlite using on the iPhone? Within my application, I use a sqlite DB to store all local data. Two methods can be used to retrieve those data during running time. 1, Load all the data into memory at initialization stage. (More memory used, less DB open/close operation needed) 2, Read corresponding records when necessary, free the occupied memory after using. (Good habit for memory using, but much DB open/close operations needs). I prefer to use method 2, but not sure whether too many DB opening/closing operations could affect app's efficiency. Or do you think I can 'upgrade' method 2 by opening DB when app launches and closing DB when app quits? Thanks for your suggestions very much!

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• How efficient is an if statement compared to a test that doesn't use an if? (C++)

  - by Keand64

  I need a program to get the smaller of two numbers, and I'm wondering if using a standard "if x is less than y" int a, b, low; if (a < b) low = a; else low = a; is more or less efficient than this: int a, b, low; low = b + ((a - b) & ((a - b) >> 31)); (or the variation of putting int delta = a - b at the top and rerplacing instances of a - b with that). I'm just wondering which one of these would be more efficient (or if the difference is to miniscule to be relevant), and the efficiency of if-else statements versus alternatives in general.

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• Base64 Encoded Data - DB or Filesystem

  - by Marty

  I have a new program that will be generating a lot of Base64 encoded audio and image data. This data will be served via HTTP in the form of XML and the Base64 data will be inline. These files will most likely break 20MB and higher. Would it be more efficient to serve these files directly from the filesystem or would it be feasible to store the data in a MySQL database? Caching will be set up but overall unnecessary because it is likely that this data will be purged shortly after it is created and served. i know that storing binary data in the DB is frowned upon in most circumstances but since this will all be character data I want to see what the consensus is. As of now, I am leaning toward storing them in the filesystem for efficiency reasons but if it is feasible to store them in a database it would be much easier to manage the data.

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• Aggregate functions in ANSI SQL

  - by morpheous

  I want to use multiple aggregate functions in a query. All the examples i have seem on aggregate functions however, are trivial. Typically, they are of the form: SELECT field1,agg_func1, agg_func2 GROUP BY SOME_COLUMNS HAVING agg_func1 OP SOME_SCALAR Where: OP: is a boolean operator (e.g. <, = etc) SOME_SCALAR: is a scalar (i.e. a constant number) What I want to know is if it is possible to write (IN ANSI SQL) queries like: SELECT field1,agg_func1, agg_func2, agg_func3 GROUP BY SOME_COLUMNS HAVING (agg_func1 OP1 agg_func2) OP2 (agg_func2 OP3 agg_func3) Where: OP[N] are boolean operators or ANSI SQL clause operators like 'BETWEEN', 'LIKE', 'IN' etc. Also, assuming this is possible (I have not seen any documentation saying otherwise) are there any efficiency/performance considerations (i.e. penalties) when the HAVING clause consists of a boolean expression combining the output of the aggregate functions - instead of the normal comparison of the output of the aggregate with a constant number (e.g. min('salary') 100 ) - which is often used in the most banal examples involving aggregate functions?

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• Make a usable Join relationship with LINQ on top of a database CSV design error

  - by jdk

  I'm looking for a way to fix and/or abstract away a comma-separated values (CSV) list in a database field in order to reconstruct a usable relationship such that I can properly join the two tables below and query them using LINQ and its Join method. Following is a sample showing the Person table and CsvArticleIds field having a CSV value to represent a one-to-many association with Article records. TABLE [dbo].[Person] Id Name CsvArticleIds -- ---------- -------- 1 Joe "15,22" 5 Ed "22" 10 Arnie "8,15,22" ^^^(Of course a link table should have been created; nonetheless the relationship with articles is trapped inside that list of CSV values.) TABLE [dbo].[Article] Id Title -- ---------- 8 Beginning C# 15 A Historic look at Programming in the 90s 22 Gardening in January Additional Info the fix can be at any level: C#.NET or SQL Server something easy because I will be repeating the solution for many other CSV values in other tables. Elegant is nice too. not looking for efficiency because this is part of a one-time data migration task and can take as long as it wants to run.

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