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  • Compression Array of Bytes

    - by Pedro Magalhaes
    Hi, My problem is: I want to store a array of bytes in compressed file, and then I want to read it with a good performance. So I create a array of bytes then pass to a ZLIB algorithm then store it in the file. For my surprise the algorithm doesn't work well., probably because the array is a random sample. Using this approach, it will will be ber easy to read. Just copy the stream to memory, decompress them and copy it to a array of bytes. But i need to compress the file. Do I have to use a algorithm, like RLE, for compresse the byte array? I think that I can store the byte array like a string and then compress it. But i think I am going to have a poor performance on reading data. Sorry for my poor english. Thanks

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  • Why do people still use C these days? [closed]

    - by Joshua
    C++ is clearly a far superior language than C, since it has many features that C lacks (although, C++'s object model isn't as ideal as say C#'s). With the coming off the new C++0x standard, why hasn't C been phased out to obscurity? C++ has been around for so long, since the '80s. The Linux kernel has already been ported to C++ with negligible performance differences. I believe, with no evidence, that larger program structures benefit in performance if written in C++ than in C, if only because of object interaction. Don't get me started on "objects-in-C!" libraries, which are all a terrible hack. (Not that C++'s object model is the most ideal, but it is almost up to snuff with C# using common ad-hoc techniques.)

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  • Comparison of collection datatypes in C#

    - by Joel in Gö
    Does anyone know of a good overview of the different C# collection types? I am looking for something showing which basic operations such as Add, Remove, RemoveLast etc. are supported, and giving the relative performance. It would be particularly interesting for the various generic classes - and even better if it showed eg. if there is a difference in performance between a List<T> where T is a class and one where T is a struct. A start would be a nice cheat-sheet for the abstract data structures, comparing Linked Lists, Hash Tables etc. etc. Thanks!

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  • segmented reduction with scattered segments

    - by Christian Rau
    I got to solve a pretty standard problem on the GPU, but I'm quite new to practical GPGPU, so I'm looking for ideas to approach this problem. I have many points in 3-space which are assigned to a very small number of groups (each point belongs to one group), specifically 15 in this case (doesn't ever change). Now I want to compute the mean and covariance matrix of all the groups. So on the CPU it's roughly the same as: for each point p { mean[p.group] += p.pos; covariance[p.group] += p.pos * p.pos; ++count[p.group]; } for each group g { mean[g] /= count[g]; covariance[g] = covariance[g]/count[g] - mean[g]*mean[g]; } Since the number of groups is extremely small, the last step can be done on the CPU (I need those values on the CPU, anyway). The first step is actually just a segmented reduction, but with the segments scattered around. So the first idea I came up with, was to first sort the points by their groups. I thought about a simple bucket sort using atomic_inc to compute bucket sizes and per-point relocation indices (got a better idea for sorting?, atomics may not be the best idea). After that they're sorted by groups and I could possibly come up with an adaption of the segmented scan algorithms presented here. But in this special case, I got a very large amount of data per point (9-10 floats, maybe even doubles if the need arises), so the standard algorithms using a shared memory element per thread and a thread per point might make problems regarding per-multiprocessor resources as shared memory or registers (Ok, much more on compute capability 1.x than 2.x, but still). Due to the very small and constant number of groups I thought there might be better approaches. Maybe there are already existing ideas suited for these specific properties of such a standard problem. Or maybe my general approach isn't that bad and you got ideas for improving the individual steps, like a good sorting algorithm suited for a very small number of keys or some segmented reduction algorithm minimizing shared memory/register usage. I'm looking for general approaches and don't want to use external libraries. FWIW I'm using OpenCL, but it shouldn't really matter as the general concepts of GPU computing don't really differ over the major frameworks.

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  • Extract a sentence out of sentences separated by delimitors

    - by Laura
    Below is a sample line I have extracted from a website: below a satisfactory level; &quot;an off year for tennis&quot;; &quot;his performance was off&quot; The output displays as: below a satisfactory level; "an off year for tennis"; "his performance was off" I want to get only the first sentence "below a satisfactory level"; Here is the code I have tried after exploring many stackoverflow posts: $data=explode('; ',$str); echo $data[0]; But somehow it is not working. Thanks in advance.

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  • How to sum up an array of integers in C#

    - by Filburt
    Is there a better shorter way than iterating over the array? int[] arr = new int[] { 1, 2, 3 }; int sum = 0; for (int i = 0; i < arr.Length; i++) { sum += arr[i]; } clarification: Better primary means cleaner code but hints on performance improvement are also welcome. (Like already mentioned: splitting large arrays). It's not like I was looking for killer performance improvement - I just wondered if this very kind of syntactic sugar wasn't already available: "There's String.Join - what the heck about int[]?".

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  • Remove items from SWT tables

    - by Dima
    This is more of an answer I'd like to share for the problem I was chasing for some time in RCP application using large SWT tables. The problem is the performance of SWT Table.remove(int start, int end) method. It gives really bad performance - about 50msec per 100 items on my Windows XP. But the real show stopper was on Vista and Windows 7, where deleting 100 items would take up to 5 seconds! Looking into the source code of the Table shows that there are huge amount of windowing events flying around in this call.. That brings the windowing system to its knees. The solution was to hide the damn thing during this call: table.setVisible(false); table.remove(from, to); table.setVisible(true); That does wonders - deleting 500 items on both XP & Windows7 takes ~15msec, which is just an overhead for printing out time stamps I used. nice :)

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  • Custom onsynctopreference for XUL textbox

    - by Alexey Romanov
    I wanted to enable custom shortcuts in my Firefox extension. The idea is that the user just focuses on a textbox, presses key combination, and it's shown in the textbox and saved to a preference. However, I couldn't get it to work. With this XUL <?xml version="1.0"?> <?xml-stylesheet href="chrome://global/skin/" type="text/css"?> <?xml-stylesheet href="chrome://mozapps/skin/pref/pref.css" type="text/css"?> <!DOCTYPE window SYSTEM "chrome://nextplease/locale/nextplease.dtd"> <prefwindow id="nextpleaseprefs" title="&options.title;" buttons="accept, cancel" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"> <prefpane id="nextplease.general" label="&options.general.title;" image="chrome://nextplease/skin/Sound Mixer.png"> <preferences> <preference id="nextkey" name="nextplease.nextkey" type="int"/> </preferences> <vbox flex="1"> <hbox align="center"> <label value="&options.general.nextKey;" /> <textbox id="nextkey" flex="1" editable="false" onkeyup="return nextplease.handleKeySelection(this, event);" preference-editable="true" preference="nextkey" onsynctopreference="alert('syncing'); return nextplease.syncKeySelector(this);"/> </hbox> </vbox> </prefpane> <script type="application/x-javascript" src="chrome://nextplease/content/nextpleaseCommon.js" /> <script type="application/x-javascript" src="chrome://nextplease/content/nextpleaseOptions.js" /> </prefwindow> the event in onkeyup works. But when I click the OK button, I don't see a "syncing" alert. Why isn't onsynctopreference working? Is it impossible to have custom onsynctopreference attribute for a textbox?

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  • Haskell maps returning a monad

    - by sabauma
    The lookup function in Data.Map and Data.IntMap currently return values wrapped in Maybe with the type signature lookup :: Ord k => k -> Map k a -> Maybe a It used to have the more general type of lookup :: (Monad m, Ord k) => k -> Map k a -> m a I realize the former likely reduces the need of extra type specification, but the latter would make it much more general and allow lookup to be used in list comprehensions. Is there any way to mimic this behavior with the newer version, or would I have to use an older version of the library?

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  • Do you know Best Practise and Design Patterns for Adobe Air/Flex Applications?

    - by Julian
    I'm going to write an application with the Air/Flex-Framework. I'm looking for Best Practise and general Design Patterns for designing software especially in Air/Flex. I have experience with this framework but never had the pleasure to write a piece of software from scratch. For instance: I stumbled across lots of software written in Air/Flex with nearly infinity global vars :-) Most of the software I saw was not object-oriented How can I pack the asynchronous method calls nicely? I'm familiar with general design patterns by gamma. I'm looking more for advise in designing good quality software with Adobe Air/Flex.

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  • What tricks can be used to type and edit code faster?

    - by Thomas
    As Jeff Atwood noted, we are typists first, programmers second. Fast typing and editing may not be essential to be a good programmer, but it certainly helps. I noticed that I consciously and subconsciously use various tricks to get my intent across to the computer as fast as possible. What tricks can be used to type and edit code faster? I'm hoping to collect a nice list here that we can all learn from, so that we can be ever so slightly more productive. One trick per answer please! (This is not about typing speed in general. There are other questions about that. It's also not about general answers like "learn your editor's shortcut keys". Think of this topic as micro-optimizations for specific cases. See my own answers for examples of what I mean.)

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  • Database indexes and their Big-O notation

    - by miket2e
    I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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  • which is better, creating a materialized view or a new table?

    - by Carson
    I have some demanding mysql queries that are needed to grap same up-to-date datasets from 5-7 mysql tables. I am thinking of creating a table or materialized view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create materialized view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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  • CLI design and implementation?

    - by Majid
    I am developing a time management tool for my personal use. I prefer using keyboard over mouse, and on the interface have a general purpose text box which will act like a command line. I have just started thinking about what commands I need, what to use for the command names, how to pass in switches and parameters, and so forth. I wonder if some of you have come across a good read along these lines; something that describes the choices you have for designing a cli, and how those affect the complexity of the interpreter, and extendability of the commands. It makes no difference if the descriptions are language-specific or in general terms. However, my implementation will be with javascript. Thank you.

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  • How to integrate access control with my ORM in a .net windows form application?

    - by Ying
    I am developing a general database query tools, a .Net 3.5 Windows Form application. In order to make the presentation layer is independent of the database layer. I use an ORM framework, XPO from DevExpress. But, I have no access control function built in. I surfed Internet and I found in WCF Data Services, there is an interesting concept, Interceptor, which is following AOP(Aspect Oriented Programming). I am wondering who has such an experience to build access control in ORM. My basic requirement is : It should be a general method and controlled by users in runtime. So any hard coding is not acceptable. It could be based on attribute, database table, or even an external assembly. I am willing to buy a ready solution. According to the idea of AOP, an access control function can be integrated with existing functions easily and nearly not knowingly to the previous developer;) Any suggestions are welcome.

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  • Is there a module that implements an efficient array type in Erlang?

    - by dsmith
    I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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  • Emails, a different 'reply to' address then sender address.

    - by dcrodjer
    I have a contact form on a website (a general form: name, email, subject, message) in which mails are sent using google apps smtp to the admins. Currently if an administrator wants to reply to the mail directly selecting the reply option, the person's reply's To field will be filled by the sender's address automatically. What I wan't to ask is, Is there any standardized way to pass on some additional info with the mail which would define any reply to the mail should go to this address instead of the sender's? It does seems that there is a little chance for this option as it may lead to some problems due to spammers (They may define a custom reply field in their mail and a general user might not look where they are replying). So as an alternative what I thought is to find a way to create a filter with sender's account which figures out the reply email address from the format and forwards the mail (Doesn't seems like a good solution and I have no idea how to achieve this). I have tagged django, though this is not directly related with this, as I will finally implement this through django.

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  • What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

    - by Robert S. Barnes
    Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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  • Inline function and calling cost in C

    - by Eonil
    I'm making a vector/matrix library. (GCC, ARM NEON, iPhone) typedef struct{ float v[4]; } Vector; typedef struct{ Vector v[4]; } Matrix; I passed struct data as pointer to avoid performance degrade from data copying when calling function. So I thought designed function like this: void makeTranslation(const Vector* factor, Matrix* restrict result); But, if function is inline, is there any reason to pass values as pointer for performance? Do those variables copied too? How about register and caches? inline Matrix makeTranslation(Vector factor) __attribute__ ((always_inline)); How do you think about calling costs of each cases?

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  • Model of hql query firing at back end by hql engine?

    - by Maddy.Shik
    I want to understand how hibernate execute hql query internally or in other models how hql query engine works. Please suggest some good links for same? One of reason for reading is following problem. Class Branch { //lazy loaded @joincolumn(name="company_id") Company company; } Since company is heavy object so it is lazy loaded. now i have hql query "from Branch as branch where branch.Company.id=:companyId" my concern is that if for firing above query, hql engine has to retrieve company object then its a performance hit and i would prefer to add one more property in Branch class i.e. companyId. So in this case hql query would be "from Branch as branch where branch.companyId=:companyId" If hql engine first generate sql from hql followed by firing of sql query itself, then there should be no performance issue. Please let me know if problem is not understandable.

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