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• Determining whether a file is a duplicate

  - by Todd R

  Is there a reliable way to determine whether or not two files are the same? For example, two files with the same size and type may or may not be the same binarilly (yeah, I know it's not really a word). I assume that comparing one or two checksums of the files will help, but I wonder: How reliable are checksums at determining whether two files are different; what are the chances of two different files having the same checksum? Would reliability increase by applying additional checksum comparisons? Which checksum algorithm(s) would be the most efficient and/or reliable? Any ideas, suggestions or thoughts are appreciated! P.S. The code for this is being written in Java running on a nix system, but generic or platform agnostic input is most helpful.

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• Python: Huge file reading by using linecache Vs normal file access open()

  - by user335223

  Hi, I am in a situation where multiple threads reading the same huge file with mutliple file pointers to same file. The file will have atleast 1 million lines. Eachline's length varies from 500 characters to 1500 characters. There won't "write" operations on the file. Each thread will start reading the same file from different lines. Which is the efficient way..? Using the Python's linecache or normal readline() or is there anyother effient way?

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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• Database design for a Fantasy league

  - by Samidh T

  Here's the basic schema for my database Table user{ userid numeber primary key, count number } Table player{ pid number primary key, } Table user-player{ userid number primary key foreign key(user), pid number primary key foreign key(player) } Table temp{ pid number primary key, points number } Here's what I intend to do... After every match the temp table is updated which holds the id of players that played the last match and the points they earned. Next run a procedure that will match the pid from temp table with every uid of user-player table having the same pid. add the points from temp table to the count of user table for every matching uid. empty temp table. My questions is considering 200 players and 10000 users,Will this method be efficient? I am going to be using mysql for this.

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• Opinions regarding C++ programming practice

  - by Sagar

  I have a program that I am writing, not too big. Apart from the main function, it has about 15 other functions that called for various tasks at various times. The code works just fine all in one file, and as it is right now. However, I was wondering if anyone had any advice on whether it is smarter/more efficient/better programming to put those functions in a separate file different from where main is, or whether it even matters at all. If yes, why? If no, why not? I am not new at C++, but definitely not an expert either, so if you think this question is stupid, feel free to tell me so. Thanks for your time!

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• Facebook user_id as MongoDB BSON ObjectId?

  - by MattDiPasquale

  I'm rebuilding Lovers on Facebook with Sinatra & Redis. I like Redis because it doesn't have the long (12-byte) BSON ObjectIds and I am storing sets of Facebook user_ids for each user. The sets are requests_sent, requests_received, & relationships, and they all contain Facebook user ids. I'm thinking of switching to MongoDB because I want to use it's geospatial indexing. If I do, I'd want to use the FB user ids as the _id field because I want the sets to be small and I want the JSON responses to be small. But, is the BSON ObjectId better (more efficient for MongoDB) to use than just an integer (fb user_id)?

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• a completely decoupled OO system ?

  - by shrini1000

  To make an OO system as decoupled as possible, I'm thinking of the following approach: 1) we run an RMI/directory like service where objects can register and discover each other. They talk to this service through an interface 2) we run a messaging service to which objects can publish messages, and register subscription callbacks. Again, this happens through interfaces 3) when object A wants to invoke a method on object B, it discovers the target object's unique identity through #1 above, and publishes a message on the message service for object B 4) message services invokes B's callback to give it the message 5) B processes the request and sends the response for A on message service 6) A's callback is called and it gets the response. I feel this system is as decoupled as practically possible, but it has the following problems: 1) communication is typically asynchronous 2) hence it's non real time 3) the system as a whole is less efficient. Are there any other practical problems where this design obviously won't be applicable ? What are your thoughts on this design in general ?

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• Write data into .txt file created by CFileDialog, in C++

  - by younevertell

  I wanna Write data into .txt file created by CFileDialog, in C++. The problem I am facing is that below codes doesn't work, although there is no build error. The .txt file created by CFileDialog can not be found for some reason. What's wrong the code? what's the efficient way to Write data into .txt file created by CFileDialog, in C++? Thanks CFileDialog dlg(FALSE, NULL, NULL, OFN_OVERWRITEPROMPT, _T("My Data File (*.txt)|*.txt||")); if(dlg.DoModal() != IDOK) return; CString filename = dlg.GetPathName(); ofstream outfile (filename); int mydata = 10; outfile << "my data:" << mydata << endl; outfile.close();

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• java statistics collection for performance evaluation

  - by user384706

  What is the most efficient way to collect and report performance statistic analysis from an application? If I have an application that uses a series of network apis, and I want to report statistics at runtime, e.g. Method doA() was called 3 times and consumed on avg 500ms Method doB() was called 5 times and consumed on avg 1200ms etc Then, I thought of using a well defined data structure (of collection) that each thread updates per remote call, and this can be used for the report. But I think that it will make the performance worse, for the time spend for statistics collection. Am I correct? How would I procceed if I used a background thread for this, and the other threads that did the remote calls were unaware of this collection gathering? Thanks

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• How to initialise a STL vector/list with a class without invoking the copy constructor

  - by Warpspace

  I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks when you need a deep copy. I would love to have the constructor of my class new something and not have to implement a copy constructor just to allocate my memory for the second time and waste runtime. I'd also rather not have to immediately find the class instance from the vector/list and then manually allocate the memory (or do something horrible like allocate the memory in the copy constructor itself). Is there any way around this (I'm not using Visual Studio BTW)?

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• Dealing with Windows line-endings in Python

  - by Adam Nelson

  I've got a 700MB XML file coming from a Windows provider. As one might expect, the line endings are '\r\n' (or ^M in vi). What is the most efficient way to deal with this situation aside from getting the supplier to send over '\n' :-) Use os.linesep Use rstrip() (requiring opening the file ... which seems crazy) Using Universal newline support is not standard on my Mac Snow Leopard - so isn't an option. I'm open to anything that requires Python 2.6+ but it needs to work on Snow Leopard and Ubuntu 9.10 with minimal external requirements. I don't mind a small performance penalty but I am looking for the standard best way to deal with this.

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• Android image scaling to support multiple resolutions

  - by tyuo9980

  I've coded my game for 320x480 and I figure that the easiest way to support multiple resolutions is to scale the end image. What are your thoughts on this? Would it be cpu efficient to do it this way? I have all my images placed in the mdpi folder, I'll have it drawn unscaled on the screen onto a buffer, then scale it to fit the screen. all the user inputs will be scaled as well. I have these 2 questions: -How do you draw a bitmap without android automatically scaling it -How do you scale a bitmap?

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• Please suggest me the best way to design my database.

  - by Raymond Ho

  I have a table named "Pages" and a table named "Categories". Each entry of the table "Pages" is linked to the table "Categories". The "Categories" table have 5 entries, they are: "Car", "Websites", "Technology", "Mobile Phones", and "Interest". So each time I put an entry to the "Pages" table, I need to map it to the "Categories" table so are arranged properly. Here's my table: Pages ______ id [PK] name url Categories ______ id [PK] Categoryname Pages2Categories ______ Pages.id Categories.id So my question is, is this the most efficient way to create this kind of relationships between tables? It seems very amateur

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• High level programming logic, design, pattern

  - by Muhammad Shahzad

  I have been doing programming from last 7 years, getting better and better, but still i think that am lacking something. I have been doing work in JOOMLA, MAGENTO, WP, Custom PHP, Opencart, laravel, codeignitor. Sometimes i need to design logic for a huge database application, in the applications we need nesting loops and queries, although i follow OOPS standards, ORM etc, still i feel i need more robust coding designs. I need to know how can i improve these things, so that code remain neat, efficient and faster. Also how big webapps like facebook twitter tests there code speed? How high level programmers choose design patterns. If you can help me find something useful with examples?

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• JPA in distributed Java EE configuration

  - by sof

  Hello, I'm developing a JEE application to run on Glassfish: Database (javaDB, MS SQL, MySQL or Oracle) EJB layer with JPA (Toplink essentials - from Glassfish) for database access JSF/Icefaces based web UI accessing the EJB layer The application will have a lot of concurrent web client, so I want to run it on different physical servers and use a load-balancer. My problem is now how to keep the applications synchronized. I intend to set up multiple servers, each running Glassfish with my EAR app installed. Whenever on one of the servers data is added to or removed from the database (via JPA, no direct SQL queries), this change should be reflected in the JPA layer on the other servers. I've been looking around for solutions to this, but couldn't find anything I really like (the full Toplink from Oracle claims to have a solution, but don't know). Doing a refresh before every access to a JPA entity could work, but is far from efficient. Are there any patterns, libraries, ... that could help here? Thanks a lot!

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• PHP Array Efficiency and Memory Clarification

  - by CogitoErgoSum

  When declaring an Array in PHP, the index's may be created out of order...I.e Array[1] = 1 Array[19] = 2 Array[4] = 3 My question. In creating an array like this, is the length 19 with nulls in between? If I attempted to get Array[3] would it come as undefined or throw an error? Also, how does this affect memory. Would the memory of 3 index's be taken up or 19? Also currently a developer wrote a script with 3 arrays FailedUpdates[] FailedDeletes[] FailedInserts[] Is it more efficient to do it this way, or do it in the case of an associative array controlling several sub arrays "Failures" array(){ ["Updates"] => array(){ [0] => 12 [1] => 41 } ["Deletes"] => array(){ [0] => 122 [1] => 414 [1] => 43 } ["Inserts"] => array(){ [0] => 12 } }

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• How do I create a point system in a Rails app that assigns points to users and non-authenticated-use

  - by codyvbrown

  I'm building a question and answer application on top of twitter and I'm hitting some snags because I'm inevitably dealing with two classes of users: authenticated and non-authenticated. The site enable users to give points to other users, who may or may not be authenticated, and I want to create a site-wide point system where the application stores and displays this information on their profile. I want to save this point data to the user because that would be faster and more efficient but non-authenticated users aren't in our system, we only have the twitter handle. So instead we display the points in our system like this: @points = point.all( :select => "tag, count(*) AS count", # Return tag and count :group => 'tag', # Group by the tag :order => "2 desc", :conditions => {:twitter_handle => params[:username]}) Is there a better way to do this? Is there a better way to associate data with non-authenticated users?

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• Fast, Vectorizable method of taking floating point number modulus of special primes?

  - by caffiend

  Is there a fast method for taking the modulus of a floating point number? With integers, there are tricks for Mersenne primes, so that its possible to calculate y = x MOD 2^31 without needing division. Can any similar tricks be applied for floating point numbers? Preferably, in a way that can be converted into vector/SIMD operations, or moved into GPGPU code. The primes I'm interested in would be 2^7 and 2^31, although if there are more efficient ones for floating point numbers, those would be welcome.

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• Prims vs Polys: what are the pros and cons of each?

  - by Richard Inglis

  I've noticed that most 3d gaming/rendering environments represent solids as a mesh of (usually triangular) 3d polygons. However some examples, such as Second Life, or PovRay use solids built from a set of 3d primitives (cube, sphere, cone, torus etc) on which various operations can be performed to create more complex shapes. So my question is: why choose one method over the other for representing 3d data? I can see there might be benefits for complex ray-tracing operations to be able to describe a surface as a single mathematical function (like PovRay does), but SL surely isn't attempting anything so ambitious with their rendering engine. Equally, I can imagine it might be more bandwidth-efficient to serve descriptions of generalised solids instead of arbitrary meshes, but is it really worth the downside that SL suffers from (ie modelling stuff is really hard, and usually the results are ugly) - was this just a bad decision made early in SL's development that they're now stuck with? Or is it an artefact of what's easiest to implement in OpenGL?

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• What is faster: multiple `send`s or using buffering?

  - by dauerbaustelle

  I'm playing around with sockets in C/Python and I wonder what is the most efficient way to send headers from a Python dictionary to the client socket. My ideas: use a send call for every header. Pros: No memory allocation needed. Cons: many send calls -- probably error prone; error management should be rather complicated use a buffer. Pros: one send call, error checking a lot easier. Cons: Need a buffer :-) malloc/realloc should be rather slow and using a (too) big buffer to avoid realloc calls wastes memory. Any tips for me? Thanks :-)

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• 2 Select or 1 Join query ?

  - by xRobot

  I have 2 tables: book ( id, title, age ) ---- 100 milions of rows author ( id, book_id, name, born ) ---- 10 millions of rows Now, supposing I have a generic id of a book. I need to print this page: Title: mybook authors: Tom, Graham, Luis, Clarke, George So... what is the best way to do this ? 1) Simple join like this: Select book.title, author.name From book, author WHERE ( author.book_id = book.id ) AND ( book.id = 342 ) 2) For avoid the join, I could make 2 simple query: Select title FROM book WHERE id = 342 Select name FROM author WHERE book_id = 342 What is the most efficient way ?

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• NASM: Count how many bits in a 32 Bit number are set to 1.

  - by citronas

  I have a 32 Bit number and want to count know how many bits are 1. I'm thinking of this pseudocode: mov eax, [number] while(eax != 0) { div eax, 2 if(edx == 1) { ecx++; } shr eax, 1 } Is there a more efficient way? I'm using NASM on a x86 processor. (I'm just beginning with assembler, so please do not tell me to use code from extern libraries, because I do not even know how to include them ;) ) (I just found http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer which also contains my solution. There are other solutions posted, but unfortunatly I can't seem to figure out, how I would write them in assembler)

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• Pass Session data to a Class Library without using a bunch of constructors?

  - by sah302

  Hi all, I've got my application here where literally every object has a lastUpdatedBy property. The information I put into here is the person's username, which is retrieved from the session("username") variable. How can I pass this data to my DAL in the class library? At first I was just passing in the value into each method, but this is ridiculous I thought, there should be no reason to do that every time a method is called. Then I thought well if I just put it in a constructor for each of the DAL related classes, that will make it even easier. However, even still on any given page, I've got a plethora of New() declarations, for which every single line I need to pass in the session username casted as a string. Is there an even still more efficient way of doing this so that I could only declare this in one place, and everything will know what it is and I can pass it to classes in a class library?

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• Workstation hardware at does your company buy developers?

  - by Bosh

  I'm curious to know what workstation hardware companies are devoting to you, as a developer -- and how much they're spending. I'd consider this thread a big success if I could shed some light on these questions: Do engineers at big companies use substantially different hardware than engineers at start-ups companies? Does a fresh developer recruit at Google get substantially different hardware from someone in the same position at Microsoft or Yahoo!? Do programmers in more senior positions have more powerful hardware on their desks? Does anyone think faster hardware makes more efficient engineers?

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• Logging NHibernate SQL queries

  - by GuestMVCAsync

  Is there a way to access the full SQL query, including the values, inside my code? I am able to log SQL queries using log4net: <logger name="NHibernate.SQL" additivity="false"> <level value="ALL"/> <appender-ref ref="NHibernateSQLFileLog"/> </logger> However, I would like to find a way to log SQL queries from the code also. This way I will log the specific SQL query that causes an exception in my try/catch statement. Right now I have to data-mine the SQLFileLog to find the query that caused the exception when an exception occurs and it is not efficient.

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