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  • Odd optimization problem under MSVC

    - by Goz
    I've seen this blog: http://igoro.com/archive/gallery-of-processor-cache-effects/ The "weirdness" in part 7 is what caught my interest. My first thought was "Thats just C# being weird". Its not I wrote the following C++ code. volatile int* p = (volatile int*)_aligned_malloc( sizeof( int ) * 8, 64 ); memset( (void*)p, 0, sizeof( int ) * 8 ); double dStart = t.GetTime(); for (int i = 0; i < 200000000; i++) { //p[0]++;p[1]++;p[2]++;p[3]++; // Option 1 //p[0]++;p[2]++;p[4]++;p[6]++; // Option 2 p[0]++;p[2]++; // Option 3 } double dTime = t.GetTime() - dStart; The timing I get on my 2.4 Ghz Core 2 Quad go as follows: Option 1 = ~8 cycles per loop. Option 2 = ~4 cycles per loop. Option 3 = ~6 cycles per loop. Now This is confusing. My reasoning behind the difference comes down to the cache write latency (3 cycles) on my chip and an assumption that the cache has a 128-bit write port (This is pure guess work on my part). On that basis in Option 1: It will increment p[0] (1 cycle) then increment p[2] (1 cycle) then it has to wait 1 cycle (for cache) then p[1] (1 cycle) then wait 1 cycle (for cache) then p[3] (1 cycle). Finally 2 cycles for increment and jump (Though its usually implemented as decrement and jump). This gives a total of 8 cycles. In Option 2: It can increment p[0] and p[4] in one cycle then increment p[2] and p[6] in another cycle. Then 2 cycles for subtract and jump. No waits needed on cache. Total 4 cycles. In option 3: It can increment p[0] then has to wait 2 cycles then increment p[2] then subtract and jump. The problem is if you set case 3 to increment p[0] and p[4] it STILL takes 6 cycles (which kinda blows my 128-bit read/write port out of the water). So ... can anyone tell me what the hell is going on here? Why DOES case 3 take longer? Also I'd love to know what I've got wrong in my thinking above, as i obviously have something wrong! Any ideas would be much appreciated! :) It'd also be interesting to see how GCC or any other compiler copes with it as well! Edit: Jerry Coffin's idea gave me some thoughts. I've done some more tests (on a different machine so forgive the change in timings) with and without nops and with different counts of nops case 2 - 0.46 00401ABD jne (401AB0h) 0 nops - 0.68 00401AB7 jne (401AB0h) 1 nop - 0.61 00401AB8 jne (401AB0h) 2 nops - 0.636 00401AB9 jne (401AB0h) 3 nops - 0.632 00401ABA jne (401AB0h) 4 nops - 0.66 00401ABB jne (401AB0h) 5 nops - 0.52 00401ABC jne (401AB0h) 6 nops - 0.46 00401ABD jne (401AB0h) 7 nops - 0.46 00401ABE jne (401AB0h) 8 nops - 0.46 00401ABF jne (401AB0h) 9 nops - 0.55 00401AC0 jne (401AB0h) I've included the jump statetements so you can see that the source and destination are in one cache line. You can also see that we start to get a difference when we are 13 bytes or more apart. Until we hit 16 ... then it all goes wrong. So Jerry isn't right (though his suggestion DOES help a bit), however something IS going on. I'm more and more intrigued to try and figure out what it is now. It does appear to be more some sort of memory alignment oddity rather than some sort of instruction throughput oddity. Anyone want to explain this for an inquisitive mind? :D Edit 3: Interjay has a point on the unrolling that blows the previous edit out of the water. With an unrolled loop the performance does not improve. You need to add a nop in to make the gap between jump source and destination the same as for my good nop count above. Performance still sucks. Its interesting that I need 6 nops to improve performance though. I wonder how many nops the processor can issue per cycle? If its 3 then that account for the cache write latency ... But, if thats it, why is the latency occurring? Curiouser and curiouser ...

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  • Identify the checkbox that is checked

    - by lucky
    Hello Everyone, I have 2 checkboxes in a form and onclick of these, some php code needs to be executed and based on the result of the code, the checkbox is checked or unchecked. So i have written onclick = document.formName.submit(); Now it is triggering the same page and i am able to write the code. I am not able to differentiate which checkbox is checked. I don't want to use the procedure of:- calling javascript and then storing the value of the checkbox in a variable and making this variable as invisible. I would like to write something like document.formName.submit('checkbox1'). So that i should be able to handle the value of this or i dont know. Please suggest me an alternative method or better approach.

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  • C++ Access to MSSQL from Linux

    - by Meloun
    Hi, I need to write some data to mssql database from linux in c++. I found this sqlapi.com But I think, at first ODBC driver has to be installed an has to work. I folowed this adminlife.net/allgemein/mssql-zugriff-unter-debian-etch-mit-unixodbc-und-freetds/ or this http://b.gil.megiteam.pl/2009/11/linux-odbc-to-mssql/ But it didnt work, the port 1433 seems to be closed ($ sudo nmap -PN -sU -p 1433 192.168.56.101 - port "filtered") isql -v sqlexpress sa - wait with no response or get "coulndt connect to sql" From other PC with Windows I have no problem to write data in mssql, so server should be right configured to remote access. any idea?

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  • Writing to the middle of the file (without overwriting data)

    - by Andreas Bonini
    In windows is it possible through an API to write to the middle of a file without overwriting any data and without having to rewrite everything after that? If it's possible then I believe it will obviously fragment the file; how many times can I do it before it becomes a serious problem? If it's not possible what approach/workaround is usually taken? Re-writing everything after the insertion point becomes prohibitive really quickly with big (ie, gigabytes) files. Note: I can't avoid having to write to the middle. Think of the application as a text editor for huge files where the user types stuff and then saves. I also can't split the files in several smaller ones.

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  • use qt and django to create desktop apps

    - by sandra
    Hi guys, I had this idea of creating desktop apps using django. The principe being: - Write the django app, and use something like cherrypy to serve it. - Write a Qt app in C++ to access it and this by using QtWebview (webkit) I'd like to "bundle" this in a single app. The lighter, the better :) So here are my questions and if you have better ideas and suggestions, please share them :) Is it possible to serve a django app with a c++ one? (a c++ server embedding python)? anyone did this before? Do you have some articles, blog posts? Thanks a lot!

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  • How to open save dialog box for saving pdf

    - by Mutturaj Bali
    I truly appreciate your suggestions. I am using MVC3 and I want user to save to his own path by opening a dialog with password protected. Can you guys please help me on this. Below is my code: mydoc.GenerateLetter(PdfData); string WorkingFolder = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments); using (MemoryStream m = new MemoryStream()) { m.Write(mydoc.DocumentBytes, 0, mydoc.DocumentBytes.Length); m.Seek(0, SeekOrigin.Begin); string OutputFile = Path.Combine(WorkingFolder, PdfData.Name + ".pdf"); using (Stream output = new FileStream(OutputFile, FileMode.Create, FileAccess.Write, FileShare.None)) { PdfReader reader = new PdfReader(m); PdfEncryptor.Encrypt(reader, output, true, "abc123", "secret", PdfWriter.ALLOW_SCREENREADERS); } }

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  • Can you create a HIPAA compliant Amazon S3 Web Application?

    - by xkingpin
    I am facing some questions when trying to design an S3 application using ASP.NET MVC and trying to stay HIPAA compliant. My initial plan was to require an SSL connection to my web server, encrypt the images on my server, then send them to s3 using my private keys. Here's my obvious concerns: You cannot store unencrypted images in any temporary file cache when client views images within the browser. Even if I setup an ashx to generically handle the image in memory, couldn't this get stored in cache? Saying the images will be encrpyted because you will be connecting to my server via https still does not guarantee all browsers will not cache data. It's not possible to even consider the "Query String" with expiration option since data will be encrypted before being stored on disk at s3, and will again be decrypted at my server in memory. I think my only option would be to write/purchase some sort of ActiveX component that will not expose the image as a simple html image source or write my app as a client side WinForm application.

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  • For what programs are Objective C and Ruby ideal on the Mac?

    - by Kurt
    Hi, as a Mac outsider it seems that two popular programming languages on the Mac appear to be Objective C and Ruby. From what I understand the main API Cocoa seems to be written in and optimized for Objective C, but it is also possible to use Ruby for that. Are there different areas where each language is ideal, for example, I could imagine Objective C could be ideal for a GUI layer, or standalone desktop app, and Ruby could be good for web services etc. What about classic business logic, or data access layers? What language would be a good choice for a library of services for example? Can we write a library in one language and link to it from a main program written in the other language? If I wanted to write a layered enterprise application using domain driven design and dependency injection which languages could support each concerns? Are things like DDD and DI common amongst Mac devs? Just a curious outsider.

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  • Clean way to output values in ASP.NET MVC Views when value is not null

    - by Swoop
    Is there a better way to write the code below? I have quite a few blocks that are similar, and this is making the code in the Viewpage very messy to work with. The data value with the associated label only needs to be output when certain conditions are met, which is almost always if the value is not null. The options I can think is to use a response.write to atleast minimize the usage of the ASP script tags, or to format the webpage is such a way that the label displays with an appropriate n/a type value. <% if (myData.Balance != null) { %> Balance: <%= String.Format("{0:C}", (myData.Balance))%> <% } %>

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  • SNMP in Java, specifically to be JMX adapter.

    - by Ben
    Hi, I have a few JAVA application that I monitor using JMX. I would like to write an SNMP client for these applications that wraps the JMX interface and by discovery exposes the same attributes that are exposed in JMX, through SNMP. I have no problem writing the client if I just figure out how to write SNMP clients in JAVA. Is there a free SNMP library for JAVA that I can use? Is there a good free SNMP adapter for JMX? (Tried "WebNMS SNMP Adapter for JMX" trial unsuccessfully) Thank you!

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  • what kind of credentials/prerequisites do you need to be a professional penetration tester ?

    - by dfafa
    does it take more than knowing Bt4 ? are there any one that just runs a scanner and no real labor involved ? would you be expected to be able to code your own exploits without having to dl from milw0rm and discover entry into a system by yourself, in other words, do you have to think outside the box even when there's so many tools that makes the job a lot easier ? would you ever be expected to be able to write your own scanners, exploits and etc ? i am also curious how people are able to write long pages of hex address, that magically causes some type of memory overflow...how are people guessing at the hex values for game hacks for instance ? are certification important ? what about formal school education ? I am a CS major.

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  • Do people create and use Web Parts connections?

    - by Javaman59
    I've been writing some SharePoint web parts wich connect (as providers and consumers). I've found many difficulties, and (comparatively*) little material from the web, from books, or from microsoft.com, which is quite surprising as Web Parts have been around since 2003. This is making me think that although web part connections look like a first class feature in SharePoint, that in practice few people write connecting web parts, and few SharePoint users use them. Is this the case - that few developers write connecting web parts, and few users use them? *comparitively: A subjective impression. With each specific problem i usually find only a handful of web pages which address it, and as my problems seem to be fundamental ones (such which data type to wrap in an IWebPartRow), I expect a lot more search results.

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  • How can I avoid mutable variables in Scala when using ZipInputStreams and ZipOutpuStreams?

    - by pr1001
    I'm trying to read a zip file, check that it has some required files, and then write all valid files out to another zip file. The basic introduction to java.util.zip has a lot of Java-isms and I'd love to make my code more Scala-native. Specifically, I'd like to avoid the use of vars. Here's what I have: val fos = new FileOutputStream("new.zip"); val zipOut = new ZipOutputStream(new BufferedOutputStream(fos)); while (zipIn.available == 1) { val entry = zipIn.getNextEntry if (entryIsValid(entry)) { val fos = new FileOutputStream("subdir/" + entry.getName()); val dest = new BufferedOutputStream(fos); // read data into the data Array var data: Array[Byte] = null var count = zip.read(data) while (count != -1) { dest.write(data, 0, count) count = zip.read(data) } dest.flush dest.close } }

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  • One blank line in list item

    - by rima
    Hi there. I try to write a code to fill my list item in oracle form builder. I do it by write a function to handle this. list_index number(10) := 1; clear_list(list_item1); FOR I IN (Select id,desc FORM table1) LOOP ADD_LIST_ELEMENT('list_item1',list_index,desc,id); list_index := list_index + 1; END LOOP list_item1 := get_list_element_value('list_item1',1); my result in output is like this: x1 x2 x3 x4 <a blank field> but in my database table I just have x1 x2 x3 x4 would you help me please to how find what's my problem that I have one more space in my list item.

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  • Sending Variables in Post without the input tag

    - by abhishekgupta92
    I want to send only one variable via the post method. I have queried the database and have to post $row[id] variable to the page along with the form. To send the user's input we simply write like <input type="text" name="xyz"></input> and then we access it as $_POST[xyz]. This way we can send a variable that a user write. But, I want to send something that user has not written but there in my sending file as $row['id']. So, I want to send this variable as well. How can I do that? And also how will I be able to access that?

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  • how to start stop tomcat server using CMD?

    - by ali
    i set the path for the tomcat and set all variables like 1.JAVA_HOME=C:\Program Files (x86)\Java\jdk1.6.0_22 2.CATALINA_HOME=G:\springwork\server\apache-tomcat-6.0.29 3.CLASSPATH=G:\springwork\server\apache-tomcat-6.0.29\lib\servlet-api.jar;G:\springwork\server\apache-tomcat-6.0.29\lib\jsp-api.jar;.; when i go to bin folder and double click on startup.bat then my tomcat start and when i double click on shutdown.bat tomcat is stop. But I want using CMD start and stop the tomcat. And in any folder i write command startup.bat the server will start and when i write the server will stop...... Thanks in advace..........

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  • python: multiline regular expression

    - by facha
    Hi, everyone I have a piece of text and I've got to parse usernames and hashes out of it. Right now I'm doing it with two regular expressions. Could I do it with just one multiline regular expression? #!/usr/bin/env python import re test_str = """ Hello, UserName. Please read this looooooooooooooooong text. hash Now, write down this hash: fdaf9399jef9qw0j. Then keep reading this loooooooooong text. Hello, UserName2. Please read this looooooooooooooooong text. hash Now, write down this hash: gtwnhton340gjr2g. Then keep reading this loooooooooong text. """ logins = re.findall('Hello, (?P<login>.+).',test_str) hashes = re.findall('hash: (?P<hash>.+).',test_str)

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  • Pass HTML form entries into a Javascript array to then be written to a client side cookie?

    - by Tom
    I'm building a bit of a test-case JS application, something very basic, but have run into some problems. I'm trying to use a HTML form for a user to enter a number, which is then written to a Javascript Array. The user then has the option to write that same array to a local (client side) cookie. (I understand the security implications of this - it's a test-case and not for commercial use.) However, I can't make the connection - how can I capture the HTML entry, press 'submit' which will send it to a JS array, where the user can then press a different 'submit' which will write the array to a text file? If anyone can help I'd appreciate it because it's been nearly 6 hours and it's not funny anymore.

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  • mysqli and php requesting rows returned in object oriented scripting...

    - by Matt
    in object oriented php mysqli I am trying to request a username, and return if it matches a row, without actually returning any user data. How would I write this?...so far I have... $sql = "SELECT NULL FROM database WHERE usernick=?"; $stmt = $link->prepare($sql) $stmt->bind_param('s', $snr); $stmt->execute(); After this step I need to see if a row matched the query...but I have no idea how to write it, everyone here pretty much writes in mysql if I dont mention I want object oriented mysqli :S

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  • how to manage formating of text when read a save file?

    - by moon
    hello i have a java applet application in which i use rich text area . i write URDU the national language of PAKISTAN. i managed to do so with uni codes. the problem is, when i write urdu in text area and select a font and color for each line it do all of this but when i save this file using UTF-8 encoding and then open it again it shows all text formatted as i choose format of last line. my requirement is to open file as it is saved. i mean each file should have same formatting as i done before saving.

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  • how to use variable from runscript command

    - by poe
    I get some text from a web page 5,19 € 3,50 € I want to split this text after "€". for that I'm using this command runScript|javascript{var prices = storedVars['price'].split("€"); document.write(prices[0]); document.write(prices[1])}; after done that try this command getEval|alert(storedVars['prices[0]']) the answer is that prices is undefined. what is the problem here? how can I get this variable from a runScript command? thanks for helping me!

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  • Literate Haskell (.lhs) and Haddock

    - by finnsson
    At the moment I'm only using Haddock but after seeing some really interesting examples (e.g. this gist ) of literate Haskell I'm interested in trying it out in a project. The questions I got are: What do you write as Haddock comments and what do you write in the literate part? How do you scale literate programming to multiple files? Can anyone point me to an example where literate programming is used in a package with multiple modules? What is your experience of using literate programming in larger packages? Which flavour (markdown, latex, ...) of literate Haskell is preferred? Why are you programming in literate Haskell or plain vanilla Haskell? Are you programming in both styles and if so why? Do you prefer block-style (\begin{code}) or Bird-style (>)? Why?

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