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• Finding the lowest average Hamming distance when the order of the strings matter

  - by user1049697

  I have a sequence of binary strings that I want to find a match for among a set of longer sequences of binary strings. A match means that the compared sequence gives the lowest average Hamming distance when all elements in the shorter sequence have been matched against a sequence in one of the longer sets. Let me try to explain with an example. I have a set of video frames that have been hashed using a perceptual hashing algorithm so that the video frames that look the same has roughly the same hash. I want to match a short video clip against a set of longer videos, to see if the clip is contained in one of these. This means that I need to find out where the sequence of the hashed frames in the short video has the lowest average Hamming distance when compared with the long videos. The short video is the sub strings Sub1, Sub2 and Sub3, and I want to match them against the hashes of the long videos in Src. The clue here is that the strings need to match in the specific order that they are given in, e.g. that Sub1 always has to match the element before Sub2, and Sub2 always has to match the element before Sub3. In this example it would map thusly: Sub1-Src3, Sub2-Src4 and Sub3-Src5. So the question is this: is there an algorithm for finding the lowest average Hamming distance when the order of the elements compared matter? The naïve approach to compare the substring sequence to every source string won't cut it of course, so I need something that preferably can match a (much) shorter sub string to a set of million of elements. I have looked at MVP-trees, BK-trees and similar, but everything seems to only take into account one binary string and not a sequence of them. Sub1: 100111011111011101 Sub2: 110111000010010100 Sub3: 111111010110101101 Src1: 001011010001010110 Src2: 010111101000111001 Src3: 101111001110011101 Src4: 010111100011010101 Src5: 001111010110111101 Src6: 101011111111010101 I have added a calculation of the examples below. (The Hamming distances aren't correct, but it doesn't matter) **Run 1.** dist(Sub1, Src1) = 8 dist(Sub2, Src2) = 10 dist(Sub3, Src3) = 12 average = 10 **Run 2.** dist(Sub1, Src2) = 10 dist(Sub2, Src3) = 12 dist(Sub3, Src4) = 10 average = 11 **Run 3.** dist(Sub1, Src3) = 7 dist(Sub2, Src4) = 6 dist(Sub3, Src5) = 10 average = 8 **Run 4.** dist(Sub1, Src3) = 10 dist(Sub2, Src4) = 4 dist(Sub3, Src5) = 2 average = 5 So the winner here is sequence 4 with an average distance of 5.

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• How to calculate the hamming distance of two binary sequences in PHP?

  - by user198729

  hamming('10101010','01010101') The result of the above should be 8. How to implement it?

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• Why does iChat Server keep connecting to proxy.eu.jabber.org?

  - by Tom Hamming

  I have OS X Server 10.6.5 running on a new Mac Mini (server model), serving several functions among which is iChat Server (iChat and Pidgin on Windows as clients). In the iChat log in Server Admin, I kept seeing entries about connecting to proxy.eu.jabber.org. It's for our office network and I wasn't excited about external access to it, so I disabled server-to-server XMPP federation and now the connections just time out. But why is it doing that in the first place? Sample log entry: (datetime) (servername)jabberd/resolver[portnum]: [xmpp-server._tcp.proxy.eu.jabber.org resolved to 208.68.163.220:5269 (300 seconds to live) then: sending dialback auth request for route '(full server hostname)/proxy.eu.jabber.org' A couple minutes later, it comes back with: dialback for outgoing route '(full server hostname)/proxy.eu.jabber.org' timed out

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• Why does iChat Server keep connecting to proxy.eu.jabber.org?

  - by Tom Hamming

  I have OS X Server 10.6.5 running on a new Mac Mini (server model), serving several functions among which is iChat Server (iChat and Pidgin on Windows as clients). In the iChat log in Server Admin, I kept seeing entries about connecting to proxy.eu.jabber.org. It's for our office network and I wasn't excited about external access to it, so I disabled server-to-server XMPP federation and now the connections just time out. But why is it doing that in the first place? Sample log entry: (datetime) (servername)jabberd/resolver[portnum]: [xmpp-server._tcp.proxy.eu.jabber.org resolved to 208.68.163.220:5269 (300 seconds to live) then: sending dialback auth request for route '(full server hostname)/proxy.eu.jabber.org' A couple minutes later, it comes back with: dialback for outgoing route '(full server hostname)/proxy.eu.jabber.org' timed out

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• Getting MATLAB variable (string) from C

  - by Hamming

  Hi! I'm writing a small C application that launchs a Matlab script (.m file). I need to exchange some variables and I don't know how to get an array of chars that exists in Matlab. I'm doing something like this: enter code here result = engGetVariable(ep,"X"); if (!result) { printf ("Error..."); exit -1; } int n = mxGetN(result); char *varx = NULL; memcpy(varx, mxGetData(result),n*sizeof(char)); It doesn't work. Does someone know how to get a Matlab string in C? I've read Matlab documentation about engGetVariable() and the provided example but any of this things clarify me.

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• Implement "tail -f" in C++

  - by Hamming

  Hi! I want to create a small code in C++ with the same functionality as "tail-f": watch for new lines in a text file and show them in the standard output. The idea is to have a thread that monitors the file Is there an easy way to do it without opening and closing the file each time?

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• Best way to convert Stream (of unknown length) to byte array, in .NET?

  - by Frank Hamming

  Hello, I have the following code to read data from a Stream (in this case, from a named pipe) and into a byte array: // NPSS is an instance of NamedPipeServerStream int BytesRead; byte[] StreamBuffer = new byte[BUFFER_SIZE]; // defined elsewhere (less than total possible message size, though) MemoryStream MessageStream = new MemoryStream(); do { BytesRead = NPSS.Read(StreamBuffer, 0, StreamBuffer.Length); MessageStream.Write(StreamBuffer, 0, BytesRead); } while (!NPSS.IsMessageComplete); byte[] Message = MessageStream.ToArray(); // final data Could you please take a look and let me know if it can be done more efficiently or neatly? Seems a bit messy as it is, using a MemoryStream. Thanks!

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• Audio Detection in Matlab

  - by insane-36

  I am writing a matlab code that would be able to read the audio file and then compare it to the another audio and recognize if those audio are the voice of the same person. In both type of the audio, would have the same word utterance and the audio is about 1 minutes long. I have come to know that the approach of sliding windows using hamming window would work best on this approach but have a very little idea on this. The simple code to read an audio file and then display a portion of 10s is as below : [x,fs, nbits]= wavread('01-AudioTrack 01.wav'); subplot(211) plot(x) title('Entire Wave') smallRange = 1:100000; subplot(212) plot(smallRange,x(smallRange)) How do I make Hamming window each of 10ms in this case and what approaches should I take to deal with this problem ?

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• Algorithm for performing decentralized search in social networks

  - by Jack

  I want to find out all the existing decentralized algorithms that exploit the structural properties of social networks. So far I know the following algorithms - 1) Best connected search - Adamic et al 2) Random Walk (does not exploit any structural property but still it is decentralized) 3) Hamming distance search 4) Weak/Strong tie search Any help would be appreciated

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• What kind of data processing problems would CUDA help with?

  - by Chris McCauley

  Hi, I've worked on many data matching problems and very often they boil down to quickly and in parallel running many implementations of CPU intensive algorithms such as Hamming / Edit distance. Is this the kind of thing that CUDA would be useful for? What kinds of data processing problems have you solved with it? Is there really an uplift over the standard quad-core intel desktop? Chris

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• Issue in understanding how to compare performance of classifier using ROC

  - by user1214586

  I am trying to demystify pattern recognition techniques and understood few of them. I am trying to design a classifier M. A gesture is classified based on the hamming distance between the sample time series y and the training time series x. The result of the classifier are probabilistic values. There are 3 classes/categories with labels A,B,C which classifies hand gestures where there are 100 samples for each class which are to be classified (single feature and data length=100). The data are different time series (x coordinate vs time). The training set is used to assign probabilities indicating which gesture has occured how many times. So,out of 10 training samples if gesture A appeared 6 times then probability that a gesture falls under category A is P(A)=0.6 similarly P(B)=0.3 and P(C)=0.1 Now, I am trying to compare the performance of this classifier with Bayes classifier, K-NN, Principal component analysis (PCA) and Neural Network. On what basis,parameter and method should I do it if I consider ROC or cross validate since the features for my classifier are the probabilistic values for the ROC plot hence what shall be the features for k-nn,bayes classification and PCA? Is there a code for it which will be useful. What should be the value of k is there are 3 classes of gestures? Please help. I am in a fix.

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• CodePlex Daily Summary for Tuesday, February 08, 2011

  CodePlex Daily Summary for Tuesday, February 08, 2011Popular ReleasesyoutubeFisher: youtubeFisher 3.0 [beta]: What's new: Supports YouTube's new layout Complete internal refactoringNearforums - ASP.NET MVC forum engine: Nearforums v5.0: Version 5.0 of the ASP.NET MVC Forum Engine, containing the following improvements: .NET 4.0 as target framework using ASP.NET MVC 3. All views migrated to Razor for cleaner markup. Alternate template (Layout file) for mobile devices 4 Bug Fixes since Version 4.1 Visit the project Roadmap for more details.fuv: 1.0 release, codename Chopper Joe: features: search/replace :o to open file :s to save file :q to quitASP.NET MVC Project Awesome, jQuery Ajax helpers (controls): 1.7: A rich set of helpers (controls) that you can use to build highly responsive and interactive Ajax-enabled Web applications. These helpers include Autocomplete, AjaxDropdown, Lookup, Confirm Dialog, Popup Form, Popup and Pager html generation optimized new features for the lookup (add additional search data ) live demo went aeroEnhSim: EnhSim 2.3.6 BETA: 2.3.6 BETAThis release supports WoW patch 4.06 at level 85 To use this release, you must have the Microsoft Visual C++ 2010 Redistributable Package installed. This can be downloaded from http://www.microsoft.com/downloads/en/details.aspx?FamilyID=A7B7A05E-6DE6-4D3A-A423-37BF0912DB84 To use the GUI you must have the .NET 4.0 Framework installed. This can be downloaded from http://www.microsoft.com/downloads/en/details.aspx?FamilyID=9cfb2d51-5ff4-4491-b0e5-b386f32c0992 Changes since 2.3.0 ...TestApi - a library of Test APIs: TestApi v0.6: TestApi v0.6 comes with the following changes: TestApi code development has been moved to Codeplex: Moved TestApi soluton to VS 2010; Moved all source code to Codeplex. All development work is done there now. Fault Injection API: Integrated the unmanaged FaultInjectionEngine.dll COM component in the build; Cleaned up FaultInjectionEngine.dll to build at warning level 4; Implemented “FaultScope” which allows for in-process fault injection; Added automation scripts & sample program; ...AutoLoL: AutoLoL v1.5.5: AutoChat now allows up to 6 items. Items with nr. 7-0 will be removed! News page url's are now opened in the default browser Added a context menu to the system tray icon (thanks to Alex Banagos) AutoChat now allows configuring the Chat Keys and the Modifier Key The recent files list now supports compact and full mode Fix: Swapped mouse buttons are now properly detected Fix: Sometimes the Play button was pressed while still greyed out Champion: Karma Note: You can also run the u...mojoPortal: 2.3.6.2: see release notes on mojoportal.com http://www.mojoportal.com/mojoportal-2362-released.aspx Note that we have separate deployment packages for .NET 3.5 and .NET 4.0 The deployment package downloads on this page are pre-compiled and ready for production deployment, they contain no C# source code. To download the source code see the Source Code Tab I recommend getting the latest source code using TortoiseHG, you can get the source code corresponding to this release here.Rawr: Rawr 4.0.19 Beta: Rawr is now web-based. The link to use Rawr4 is: http://elitistjerks.com/rawr.phpThis is the Cataclysm Beta Release. More details can be found at the following link http://rawr.codeplex.com/Thread/View.aspx?ThreadId=237262 As of the 4.0.16 release, you can now also begin using the new Downloadable WPF version of Rawr!This is a pre-alpha release of the WPF version, there are likely to be a lot of issues. If you have a problem, please follow the Posting Guidelines and put it into the Issue Trac...IronRuby: 1.1.2: IronRuby 1.1.2 is a servicing release that keeps on improving compatibility with Ruby 1.9.2 and includes IronRuby integration to Visual Studio 2010. We decided to drop 1.8.6 compatibility mode in all post-1.0 releases. We recommend using IronRuby 1.0 if you need 1.8.6 compatibility. In this release we fixed several major issues: - problems that blocked Gem installation in certain cases - regex syntax: the parser was replaced with a new one that is much more compatible with Ruby 1.9.2 - cras...Pyxis 2: Production Release: Pyxis 2.0.0.13 - Full Production Release This release of Pyxis 2 offers you a wide range of features: Launch Applications in their own threads & domains Render alpha-blended icons on the desktop Support for SD & USB drives Online App Store Dynamic & Static IP support Menus & Modals Over a dozen GUI controls File selection dialogs Folder selection dialog Application, Bootloader, and Firmware Updating Update Release Notes Much More!Microsoft All-In-One Code Framework: Sample Browser v2 (CTP Release): Sample Browser v2 (CTP Release) http://i3.codeplex.com/Project/Download/FileDownload.aspx?ProjectName=1code&DownloadId=205917MVVM Light Toolkit: MVVM Light Toolkit V3 SP1 (4): There was a small issue with the previous release that caused errors when installing the templates in VS10 Express. This release corrects the error. Only use this if you encountered issues when installing the previous release. No changes in the binaries.Finestra Virtual Desktops: 1.0: Finally the version 1.0 release! Sorry for the long delay since the last release, but I think that you'll find this release to be really smooth, really stable, and a really great enhancement to Windows. New features include: Windows 7 taskbar integration Major performance and usability improvements Redesigned look and feel New name: Finestra Better automatic updating Much faster full-screen switcher Fixes Windows 7 hotkey collisions by default Updated installerFacebook C# SDK: 5.0.2 (BETA): PLEASE TAKE A FEW MINUTES TO GIVE US SOME FEEDBACK: Facebook C# SDK Survey This is third BETA release of the version 5 branch of the Facebook C# SDK. Remember this is a BETA build. Some things may change or not work exactly as planned. We are absolutely looking for feedback on this release to help us improve the final 5.X.X release. This release contains some breaking changes. Particularly with authentication. After spending time reviewing the trouble areas that people are having using th...ASP.NET MVC SiteMap provider: MvcSiteMapProvider 3.0.0 for MVC3: Using NuGet?MvcSiteMapProvider is also listed in the NuGet feed. Learn more... Like the project? Consider a donation!Donate via PayPal via PayPal. ChangelogTargeting ASP.NET MVC 3 and .NET 4.0 Additional UpdatePriority options for generating XML sitemaps Allow to specify target on SiteMapTitleAttribute One action with multiple routes and breadcrumbs Medium Trust optimizations Create SiteMapTitleAttribute for setting parent title IntelliSense for your sitemap with MvcSiteMapSchem...patterns & practices SharePoint Guidance: SharePoint Guidance 2010 Hands On Lab: SharePoint Guidance 2010 Hands On Lab consists of six labs: one for logging, one for service location, and four for application setting manager. Each lab takes about 20 minutes to walk through. Each lab consists of a PDF document. You can go through the steps in the doc to create solution and then build/deploy the solution and run the lab. For those of you who wants to save the time, we included the final solution so you can just build/deploy the solution and run the lab.Value Injecter - object(s) to -> object mapper: 2.3: it lets you define your own convention-based matching algorithms (ValueInjections) in order to match up (inject) source values to destination values. inject from multiple sources in one InjectFrom added ConventionInjectionMobile Device Detection and Redirection: 0.1.11.11: Improvements to Beta Release The following changes have been made in version 0.1.11.11: BlackBerry Version 6 devices (such as the 9800 Torch) are now correctly identified with a dedicated handler. Android powered devices are now correctly identified. Minor change to Provider.cs to improve performance and optimise data sent to 51Degrees.mobi if the option is enabled. GC.collect is no longer called at any point. All garbage collection now happens automatically IMPORTANT CHANGES This rele...TweetSharp: TweetSharp v2.0.0.0 - Preview 10: Documentation for this release may be found at http://tweetsharp.codeplex.com/wikipage?title=UserGuide&referringTitle=Documentation. Note: This code is currently preview quality. Preview 9 ChangesAdded support for trends Added support for Silverlight 4 Elevated WP7 fixes Third Party Library VersionsHammock v1.1.7: http://hammock.codeplex.com Json.NET 4.0 Release 1: http://json.codeplex.comNew Projectsbisolu_sendus: bisolu smsBlack & Scholes: Black & Scholes OptionsCosLabs: CosLabs makes it easy to see the full capabilities of the Cosmos operating system toolkit. CosLabs has a number of experiments to find new and unique uses for Cosmos. It's developed in C#.DeployToAzure: DeployToAzure allows automating deployment of Windows Azure project and making it a part of TFS 2010 build process without using PowerShell and Azure Management CmdLets. Digital: Educational purposesDiscogsNet: DiscogsNet is a .NET library to query the Discogs.com API and parse the Discogs XML data dump files. It's developed in C# and usable from any .NET language. The API of the library is focused on ease of use and intuitiveness.DJME - The jQuery extensions for ASP.NET MVC: DJME - The jQuery extensions for ASP.NET MVC is a lightweight framework which helps you build rich user interfaces for ASP.NET MVC while enjoying great developer productivity. DokuDB: Visio AddIn to document different versions of a databaseDtsConfig Explorer: This project is a windows froms application that helps explore a SSIS dtsconfig file with an easy wayEveryDNS Service: Windows service to automatically send your current IP address to everydns.net for dynamic domains. Automatically monitors and sends IP address changes without having to be logged in. The project is built in C# targeting the .NET 4.0 framework.EvoSim - Evolution Simulation: EvoSim is a pet project to learn aspects of MVVM, WPF/Silverlight, and Parallel Processing features of .NET 4. The goal is to simulate a world filled with creatures that move, eat, reproduce, and die according to Darwinian evolutionary principles. It is tile and turn based.EZStorage: A storage library for XNA based on EasyStorage but abstracting in an XML based file list for each folder, allowing file listings on all folders and details like file creation dates which are no longer possible in XNA 4.0ForeverBell's Snake: A snake game written in VB.NET.Glauca Browser: This is a browser with a webkit core inside.Grauers SharePoint 2010 Custom MasterPage Feature: This is a SharePoint 2010 Custom MastePage feature. Custom Master and custom CSS Blog post about the project: http://www.grauers.net/archive/2011/02/07/build-a-sharepoint-2010-custom-mastepage-with-visual-studio-2010.aspxHamming Code Sample: HamCode demonstrate how the hamming code work, result of coded and decoded data. Shows the benefits of hamming method/codeHydroDesktop Mercurial Test: This is a trial version of the HydroDesktop project (hydrodesktop.codeplex.com) running on Mercurial source code repository. We first want to test whether the data update/download is happening fine before switching the official HydroDesktop website to the new system.LateBindingApi: Creates .Net Proxy Components from COM Type Libraries.Middlesex County College Library Wireless Auto Login: The Middlesex County College Library Wireless Auto Login automatically logs a computer in to the Middlesex County College (Edison, NJ) Library's WifiMobility: Mobility is a small program that reads from a text file. The text file includes everything about the program, right down to that cute little bunny on your desktop! Try Mobility today!OpenMFC: OpenMFC is opensource version of MFC for using with C/C++ compiler without MFC.Orchard Content Sharing: This Orchard module adds content sharing functionality via integration with AddThis.com sharing service.Orchard Wunder Weather Widget: This project is used to maintain the source code for the Wunder Weather widget in the Orchard gallery.Professional Audio Recorder: Professional Audio Recorder is a Audio Recorder for Windows Phone 7Python Node Info for Umbraco: Designed to assist Umbraco macro authors who are writing their macros in Python. Provides a helper macro that, when inserted into a page, will enable the display of an info panel showing the page node properties as represented in Python.Softina.Graphs: Softina.Graphs is a graph managment and algorithm utility. It includes a set of libraries to work with graph processing. It is written using .net framework with c# language and MS Visual Studio 2008. Client applications is created using devexpress components.spangesharp: Application to help people learn c#Visual Studio Private Extension Gallery: Add a new tab in the Visual Studio extension manager to manage private extensions.WCF Home Framework: Home Framework is a service-oriented framework able to facilitate deploy and management of wcf services in a mid-size scenario project.Windows Phone 7 Video Player: This project contains all the source of an application for Windows Phone 7 to consume an RSS Media exposed by our Smooth Streaming Video Player plugin for WordPress (http://smooth.codeplex.com).WOL Shopping List: This is a shoppingList version of WOL's NearMeWP7RSSReader: Updated RSSReader project for Windows Phone 7 using the RTM tools with the October 2010 update.Xen (XNA Extended) Framework: The Xen Framework is a set of libraries that provides and extends XNA 4.0 functionality to make game development easier and faster while producing clean, maintainable code. Xen frees you up to spend more time building your game.

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• How to decide on going into management?

  - by Rob Wells

  I read the transcript of a speech by Richard Hamming included as a part of this SO question and the speech had a quote that got me thinking about when someone should move into development. When your vision of what you want to do is what you can do single-handedly, then you should pursue it. The day your vision, what you think needs to be done, is bigger than what you can do single-handedly, then you have to move toward management. And the bigger the vision is, the farther in management you have to go. Any other suggestions as to how you can decide if you want to move away from the coal face and into management?

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• Improving the join of two wave file?

  - by kaki

  I have written a code for joining two wave files.It works fine when i am joining larger segments but as i need to join very small segments the clarity is not good. I have learned that the signal processing technique such a windowed join can be used to improve the joining of file. y[n] = w[n]s[n] Multiply value of signal at sample number n by the value of a windowing function hamming window w[n]= .54 - .46*cos(2*Pi*n)/L 0 I am not understanding how to get the value to signal at sample n and how to implement this?? the code i am using for joining is import wave m=['C:/begpython/S0001_0002.wav', 'C:/begpython/S0001_0001.wav'] i=1 a=m[i] infiles = [a, "C:/begpython/S0001_0002.wav", a] outfile = "C:/begpython/S0001_00367.wav" data= [] data1=[] for infile in infiles: w = wave.open(infile, 'rb') data1=[w.getnframes] data.append( [w.getparams(), w.readframes(w.getnframes())] ) #data1 = [ord(character) for character in data1] #print data1 #data1 = ''.join(chr(character) for character in data1) w.close() output = wave.open(outfile, 'wb') output.setparams(data[0][0]) output.writeframes(data[0][1]) output.writeframes(data[1][1]) output.writeframes(data[2][1]) output.close()

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• Organization & Architecture UNISA Studies – Chap 6

  - by MarkPearl

  Learning Outcomes Discuss the physical characteristics of magnetic disks Describe how data is organized and accessed on a magnetic disk Discuss the parameters that play a role in the performance of magnetic disks Describe different optical memory devices Magnetic Disk The way data is stored on and retried from magnetic disks Data is recorded on and later retrieved form the disk via a conducting coil named the head (in many systems there are two heads) The writ mechanism exploits the fact that electricity flowing through a coil produces a magnetic field. Electric pulses are sent to the write head, and the resulting magnetic patterns are recorded on the surface below with different patterns for positive and negative currents The physical characteristics of a magnetic disk   Summarize from book   The factors that play a role in the performance of a disk Seek time – the time it takes to position the head at the track Rotational delay / latency – the time it takes for the beginning of the sector to reach the head Access time – the sum of the seek time and rotational delay Transfer time – the time it takes to transfer data RAID The rate of improvement in secondary storage performance has been considerably less than the rate for processors and main memory. Thus secondary storage has become a bit of a bottleneck. RAID works on the concept that if one disk can be pushed so far, additional gains in performance are to be had by using multiple parallel components. Points to note about RAID… RAID is a set of physical disk drives viewed by the operating system as a single logical drive Data is distributed across the physical drives of an array in a scheme known as striping Redundant disk capacity is used to store parity information, which guarantees data recoverability in case of a disk failure (not supported by RAID 0 or RAID 1) Interesting to note that the increase in the number of drives, increases the probability of failure. To compensate for this decreased reliability RAID makes use of stored parity information that enables the recovery of data lost due to a disk failure.   The RAID scheme consists of 7 levels…   Category Level Description Disks Required Data Availability Large I/O Data Transfer Capacity Small I/O Request Rate Striping 0 Non Redundant N Lower than single disk Very high Very high for both read and write Mirroring 1 Mirrored 2N Higher than RAID 2 – 5 but lower than RAID 6 Higher than single disk Up to twice that of a signle disk for read Parallel Access 2 Redundant via Hamming Code N + m Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Parallel Access 3 Bit interleaved parity N + 1 Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Independent Access 4 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, significantly lower than single disk for write Similar to RAID 0 for read, significantly lower than single disk for write Independent Access 5 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, lower than single disk for write Similar to RAID 0 for read, generally  lower than single disk for write Independent Access 6 Block interleaved parity N + 2 Highest of all listed alternatives Similar to RAID 0 for read; lower than RAID 5 for write Similar to RAID 0 for read, significantly lower than RAID 5  for write   Read page 215 – 221 for detailed explanation on RAID levels Optical Memory There are a variety of optical-disk systems available. Read through the table on page 222 – 223 Some of the devices include… CD CD-ROM CD-R CD-RW DVD DVD-R DVD-RW Blue-Ray DVD Magnetic Tape Most modern systems use serial recording – data is lade out as a sequence of bits along each track. The typical recording used in serial is referred to as serpentine recording. In this technique when data is being recorded, the first set of bits is recorded along the whole length of the tape. When the end of the tape is reached the heads are repostioned to record a new track, and the tape is again recorded on its whole length, this time in the opposite direction. That process continued back and forth until the tape is full. To increase speed, the read-write head is capable of reading and writing a number of adjacent tracks simultaneously. Data is still recorded serially along individual tracks, but blocks in sequence are stored on adjacent tracks as suggested. A tape drive is a sequential access device. Magnetic tape was the first kind of secondary memory. It is still widely used as the lowest-cost, slowest speed member of the memory hierarchy.

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• Help with boost::lambda expression

  - by Venkat Shivanandan

  I tried to write a function that calculates a hamming distance between two codewords using the boost lambda library. I have the following code: #include <iostream> #include <numeric> #include <boost/function.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/if.hpp> #include <boost/bind.hpp> #include <boost/array.hpp> template<typename Container> int hammingDistance(Container & a, Container & b) { return std::inner_product( a.begin(), a.end(), b.begin(), (_1 + _2), boost::lambda::if_then_else_return(_1 != _2, 1, 0) ); } int main() { boost::array<int, 3> a = {1, 0, 1}, b = {0, 1, 1}; std::cout << hammingDistance(a, b) << std::endl; } And the error I am getting is: HammingDistance.cpp: In function ‘int hammingDistance(Container&, Container&)’: HammingDistance.cpp:15: error: no match for ‘operator+’ in ‘<unnamed>::_1 + <unnamed>::_2’ HammingDistance.cpp:17: error: no match for ‘operator!=’ in ‘<unnamed>::_1 != <unnamed>::_2’ /usr/include/c++/4.3/boost/function/function_base.hpp:757: note: candidates are: bool boost::operator!=(boost::detail::function::useless_clear_type*, const boost::function_base&) /usr/include/c++/4.3/boost/function/function_base.hpp:745: note: bool boost::operator!=(const boost::function_base&, boost::detail::function::useless_clear_type*) This is the first time I am playing with boost lambda. Please tell me where I am going wrong. Thanks.

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• Elegantly determine if more than one boolean is "true"

  - by Ola Tuvesson

  I have a set of five boolean values. If more than one of these are true I want to excecute a particular function. What is the most elegant way you can think of that would allow me to check this condition in a single if() statement? Target language is C# but I'm interested in solutions in other languages as well (as long as we're not talking about specific built-in functions). One interesting option is to store the booleans in a byte, do a right shift and compare with the original byte. Something like if(myByte && (myByte 1)) But this would require converting the separate booleans to a byte (via a bitArray?) and that seems a bit (pun intended) clumsy... [edit]Sorry, that should have been if(myByte & (myByte - 1)) [/edit] Note: This is of course very close to the classical "population count", "sideways addition" or "Hamming weight" programming problem - but not quite the same. I don't need to know how many of the bits are set, only if it is more than one. My hope is that there is a much simpler way to accomplish this.

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• C Population Count of unsigned 64-bit integer with a maximum value of 15

  - by BitTwiddler1011

  I use a population count (hamming weight) function intensively in a windows c application and have to optimize it as much as possible in order to boost performance. More than half the cases where I use the function I only need to know the value to a maximum of 15. The software will run on a wide range of processors, both old and new. I already make use of the POPCNT instruction when Intel's SSE4.2 or AMD's SSE4a is present, but would like to optimize the software implementation (used as a fall back if no SSE4 is present) as much as possible. Currently I have the following software implementation of the function: inline int population_count64(unsigned __int64 w) { w -= (w 1) & 0x5555555555555555ULL; w = (w & 0x3333333333333333ULL) + ((w 2) & 0x3333333333333333ULL); w = (w + (w 4)) & 0x0f0f0f0f0f0f0f0fULL; return int(w * 0x0101010101010101ULL) 56; } So to summarize: (1) I would like to know if it is possible to optimize this for the case when I only want to know the value to a maximum of 15. (2) Is there a faster software implementation (for both Intel and AMD CPU's) than the function above?

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• Organization &amp; Architecture UNISA Studies &ndash; Chap 5

  - by MarkPearl

  Learning Outcomes Describe the operation of a memory cell Explain the difference between DRAM and SRAM Discuss the different types of ROM Explain the concepts of a hard failure and a soft error respectively Describe SDRAM organization Semiconductor Main Memory The two traditional forms of RAM used in computers are DRAM and SRAM DRAM (Dynamic RAM) Divided into two technologies… Dynamic Static Dynamic RAM is made with cells that store data as charge on capacitors. The presence or absence of charge in a capacitor is interpreted as a binary 1 or 0. Because capacitors have natural tendency to discharge, dynamic RAM requires periodic charge refreshing to maintain data storage. The term dynamic refers to the tendency of the stored charge to leak away, even with power continuously applied. Although the DRAM cell is used to store a single bit (0 or 1), it is essentially an analogue device. The capacitor can store any charge value within a range, a threshold value determines whether the charge is interpreted as a 1 or 0. SRAM (Static RAM) SRAM is a digital device that uses the same logic elements used in the processor. In SRAM, binary values are stored using traditional flip flop logic configurations. SRAM will hold its data as along as power is supplied to it. Unlike DRAM, no refresh is required to retain data. SRAM vs. DRAM DRAM is simpler and smaller than SRAM. Thus it is more dense and less expensive than SRAM. The cost of the refreshing circuitry for DRAM needs to be considered, but if the machine requires a large amount of memory, DRAM turns out to be cheaper than SRAM. SRAMS are somewhat faster than DRAM, thus SRAM is generally used for cache memory and DRAM is used for main memory. Types of ROM Read Only Memory (ROM) contains a permanent pattern of data that cannot be changed. ROM is non volatile meaning no power source is required to maintain the bit values in memory. While it is possible to read a ROM, it is not possible to write new data into it. An important application of ROM is microprogramming, other applications include library subroutines for frequently wanted functions, System programs, Function tables. A ROM is created like any other integrated circuit chip, with the data actually wired into the chip as part of the fabrication process. To reduce costs of fabrication, we have PROMS. PROMS are… Written only once Non-volatile Written after fabrication Another variation of ROM is the read-mostly memory, which is useful for applications in which read operations are far more frequent than write operations, but for which non volatile storage is required. There are three common forms of read-mostly memory, namely… EPROM EEPROM Flash memory Error Correction Semiconductor memory is subject to errors, which can be classed into two categories… Hard failure – Permanent physical defect so that the memory cell or cells cannot reliably store data Soft failure – Random error that alters the contents of one or more memory cells without damaging the memory (common cause includes power supply issues, etc.) Most modern main memory systems include logic for both detecting and correcting errors. Error detection works as follows… When data is to be read into memory, a calculation is performed on the data to produce a code Both the code and the data are stored When the previously stored word is read out, the code is used to detect and possibly correct errors The error checking provides one of 3 possible results… No errors are detected – the fetched data bits are sent out An error is detected, and it is possible to correct the error. The data bits plus error correction bits are fed into a corrector, which produces a corrected set of bits to be sent out An error is detected, but it is not possible to correct it. This condition is reported Hamming Code See wiki for detailed explanation. We will probably need to know how to do a hemming code – refer to the textbook (pg. 188 – 189) Advanced DRAM organization One of the most critical system bottlenecks when using high-performance processors is the interface to main memory. This interface is the most important pathway in the entire computer system. The basic building block of main memory remains the DRAM chip. In recent years a number of enhancements to the basic DRAM architecture have been explored, and some of these are now on the market including… SDRAM (Synchronous DRAM) DDR-DRAM RDRAM SDRAM (Synchronous DRAM) SDRAM exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states. SDRAM employs a burst mode to eliminate the address setup time and row and column line precharge time after the first access In burst mode a series of data bits can be clocked out rapidly after the first bit has been accessed SDRAM has a multiple bank internal architecture that improves opportunities for on chip parallelism SDRAM performs best when it is transferring large blocks of data serially There is now an enhanced version of SDRAM known as double data rate SDRAM or DDR-SDRAM that overcomes the once-per-cycle limitation of SDRAM

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• Will these optimizations to my Ruby implementation of diff improve performance in a Rails app?

  - by grg-n-sox

  <tl;dr> In source version control diff patch generation, would it be worth it to use the optimizations listed at the very bottom of this writing (see <optimizations>) in my Ruby implementation of diff for making diff patches? </tl;dr> <introduction> I am programming something I have never done before and there might already be tools out there to do the exact thing I am programming but at this point I am having too much fun to care so I am still going to do it from scratch, even if there is a tool for this. So anyways, I am working on a Ruby on Rails app and need a certain feature. Basically I want each entry in a table of mine, let's say for example a table of video games, to have a stored chunk of text that represents a review or something of the sort for that table entry. However, I want this text to be both editable by any registered user and also keep track of different submissions in a version control system. The simplest solution I could think of is just implement a solution that keeps track of the text body and the diff patch history of different versions of the text body as objects in Ruby and then serialize it, preferably in human readable form (so I'll most likely use YAML for this) for editing if needed due to corruption by a software bug or a mistake is made by an admin doing some version editing. So at first I just tried to dive in head first into this feature to find that the problem of generating a diff patch is more difficult that I thought to do efficiently. So I did some research and came across some ideas. Some I have implemented already and some I have not. However, it all pretty much revolves around the longest common subsequence problem, as you would already know if you have already done anything with diff or diff-like features, and optimization the function that solves it. Currently I have it so it truncates the compared versions of the text body from the beginning and end until non-matching lines are found. Then it solves the problem using a comparison matrix, but instead of incrementing the value stored in a cell when it finds a matching line like in most longest common subsequence algorithms I have seen examples of, I increment when I have a non-matching line so as to calculate edit distance instead of longest common subsequence. Although as far as I can tell between the two approaches, they are essentially two sides of the same coin so either could be used to derive an answer. It then back-traces through the comparison matrix and notes when there was an incrementation and in which adjacent cell (West, Northwest, or North) to determine that line's diff entry and assumes all other lines to be unchanged. Normally I would leave it at that, but since this is going into a Rails environment and not just some stand-alone Ruby script, I started getting worried about needing to optimize at least enough so if a spammer that somehow knew how I implemented the version control system and knew my worst case scenario entry still wouldn't be able to hit the server that bad. After some searching and reading of research papers and articles through the internet, I've come across several that seem decent but all seem to have pros and cons and I am having a hard time deciding how well in this situation that the pros and cons balance out. So are the ones listed here worth it? I have listed them with known pros and cons. </introduction> <optimizations> Chop the compared sequences into multiple chucks of subsequences by splitting where lines are unchanged, and then truncating each section of unchanged lines at the beginning and end of each section. Then solve the edit distance of each subsequence. Pro: Changes the time increase as the changed area gets bigger from a quadratic increase to something more similar to a linear increase. Con: Figuring out where to split already seems like you have to solve edit distance except now you don't care how it is changed. Would be fine if this was solvable by a process closer to solving hamming distance but a single insertion would throw this off. Use a cryptographic hash function to both convert all sequence elements into integers and ensure uniqueness. Then solve the edit distance comparing the hash integers instead of the sequence elements themselves. Pro: The operation of comparing two integers is faster than the operation of comparing two strings, so a slight performance gain is received after every comparison, which can be a lot overall. Con: Using a cryptographic hash function takes time to convert all the sequence elements and may end up costing more time to do the conversion that you gain back from the integer comparisons. You could use the built in hash function for a string but that will not guarantee uniqueness. Use lazy evaluation to only calculate the three center-most diagonals of the comparison matrix and then only calculate additional diagonals as needed. And then also use this approach to possibly remove the need on some comparisons to compare all three adjacent cells as desribed here. Pro: Can turn an algorithm that always takes O(n * m) time and make it so only worst case scenario is that time, best case becomes practically linear, and average case is somewhere between the two. Con: It is an algorithm I've only seen implemented in functional programming languages and I am having a difficult time comprehending how to convert this into Ruby based on how it is described at the site linked to above. Make a C module and do the hard work at the native level in C and just make a Ruby wrapper for it so Ruby can make all the calls to it that it needs. Pro: I have to imagine that evaluating something like this in could be a LOT faster. Con: I have no idea how Rails handles apps with ruby code that has C extensions and it hurts the portability of the app. This is an optimization for after the solving of edit distance, but idea is to store additional combined diffs with the ones produced by each version to make a delta-tree data structure with the most recently made diff as the root node of the tree so getting to any version takes worst case time of O(log n) instead of O(n). Pro: Would make going back to an old version a lot faster. Con: It would mean every new commit, the delta-tree would get a new root node that will cost time to reorganize the delta-tree for an operation that will be carried out a lot more often than going back a version, not to mention the unlikelihood it will be an old version. </optimizations> So are these things worth the effort?

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