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  • Branchless memory manager?

    - by Richard Fabian
    Anyone thought about how to write a memory manager (in C++) that is completely branch free? I've written a pool, a stack, a queue, and a linked list (allocating from the pool), but I am wondering how plausible it is to write a branch free general memory manager. This is all to help make a really reusable framework for doing solid concurrent, in-order CPU, and cache friendly development. Edit: by branchless I mean without doing direct or indirect function calls, and without using ifs. I've been thinking that I can probably implement something that first changes the requested size to zero for false calls, but haven't really got much more than that. I feel that it's not impossible, but the other aspect of this exercise is then profiling it on said "unfriendly" processors to see if it's worth trying as hard as this to avoid branching.

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  • Creating a mask from a graphics context

    - by Magic Bullet Dave
    I want to be able to create a greyscale image with no alpha from a png in the app bundle. This works, and I get an image created: // Create graphics context the size of the overlapping rectangle UIGraphicsBeginImageContext(rectangleOfOverlap.size); CGContextRef ctx = UIGraphicsGetCurrentContext(); // More stuff CGContextDrawImage(ctx, drawRect2, [UIImage imageNamed:@"Image 01.png"].CGImage); // Create the new UIImage from the context UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext(); However the resulting image is 32 bits per pixel and has an alpha channel, so when I use CGCreateImageWithMask it doesn't work. I've tried creating a bitmap context thus: CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); CGContextRef ctx =CGBitmapContextCreate(nil, rectangleOfOverlap.size.width, rectangleOfOverlap.size.height, 8, rectangleOfOverlap.size.width , colorSpace, kCGImageAlphaNone); UIGraphicsGetImageFromCurrentImageContext returns zero and the resulting image is not created. Am I doing something dumb here? Any help would be greatly appreciated. Regards Dave

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  • Variable alpha blending in pylab

    - by Hooked
    How does one control the transparency over a 2D image in pylab? I'd like to give two sets of values (X,Y,Z,T) where X,Y are arrays of positions, Z is the color value, and T is the transparency to a function like imshow but it seems that the function only takes alpha as a scalar. As a concrete example, consider the code below that attempts to display two Gaussians. The closer the value is to zero, the more transparent I'd like the plot to be. from pylab import * side = linspace(-1,1,100) X,Y = meshgrid(side,side) extent = (-1,1,-1,1) Z1 = exp(-((X+.5)**2+Y**2)) Z2 = exp(-((X-.5)**2+(Y+.2)**2)) imshow(Z1, cmap=cm.hsv, alpha=.6, extent=extent) imshow(Z2, cmap=cm.hsv, alpha=.6, extent=extent) show() Note: I am not looking for a plot of Z1+Z2 (that would be trivial) but for a general way to specify the alpha blending across an image.

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  • How do I mix functions in complex SSRS expressions?

    - by Boydski
    I'm writing a report against a data repository that has null values within some of the columns. The problem is building expressions is as temperamental as a hormonal old lady and doesn't like my mixing of functions. Here's an expression I've written that does not work if the data in the field is null/nothing: =IIF( IsNumeric(Fields!ADataField.Value), RunningValue( IIF( DatePart("q", Fields!CreatedOn.Value) = "2", Fields!ADataField.Value, 0 ), Sum, Nothing ), Sum(0) ) (Pseudocode) "If the data is valid and if the data was created in the second quarter of the year, add it to the overall Sum, otherwise, add zero to the sum." Looks pretty straight forward. And the individual pieces of the expression work by themselves. IE: IsNumeric(), DatePart(), etc. But when I put them all together, the expression throws an error. I've attempted about every permutation of what's shown above, all to no avail. Null values in Fields!ADataField.Value cause errors. Thoughts?

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  • How can I further optimize this color difference function?

    - by aLfa
    I have made this function to calculate color differences in the CIE Lab colorspace, but it lacks speed. Since I'm not a Java expert, I wonder if any Java guru around has some tips that can improve the speed here. The code is based on the matlab function mentioned in the comment block. /** * Compute the CIEDE2000 color-difference between the sample color with * CIELab coordinates 'sample' and a standard color with CIELab coordinates * 'std' * * Based on the article: * "The CIEDE2000 Color-Difference Formula: Implementation Notes, * Supplementary Test Data, and Mathematical Observations,", G. Sharma, * W. Wu, E. N. Dalal, submitted to Color Research and Application, * January 2004. * available at http://www.ece.rochester.edu/~gsharma/ciede2000/ */ public static double deltaE2000(double[] lab1, double[] lab2) { double L1 = lab1[0]; double a1 = lab1[1]; double b1 = lab1[2]; double L2 = lab2[0]; double a2 = lab2[1]; double b2 = lab2[2]; // Cab = sqrt(a^2 + b^2) double Cab1 = Math.sqrt(a1 * a1 + b1 * b1); double Cab2 = Math.sqrt(a2 * a2 + b2 * b2); // CabAvg = (Cab1 + Cab2) / 2 double CabAvg = (Cab1 + Cab2) / 2; // G = 1 + (1 - sqrt((CabAvg^7) / (CabAvg^7 + 25^7))) / 2 double CabAvg7 = Math.pow(CabAvg, 7); double G = 1 + (1 - Math.sqrt(CabAvg7 / (CabAvg7 + 6103515625.0))) / 2; // ap = G * a double ap1 = G * a1; double ap2 = G * a2; // Cp = sqrt(ap^2 + b^2) double Cp1 = Math.sqrt(ap1 * ap1 + b1 * b1); double Cp2 = Math.sqrt(ap2 * ap2 + b2 * b2); // CpProd = (Cp1 * Cp2) double CpProd = Cp1 * Cp2; // hp1 = atan2(b1, ap1) double hp1 = Math.atan2(b1, ap1); // ensure hue is between 0 and 2pi if (hp1 < 0) { // hp1 = hp1 + 2pi hp1 += 6.283185307179586476925286766559; } // hp2 = atan2(b2, ap2) double hp2 = Math.atan2(b2, ap2); // ensure hue is between 0 and 2pi if (hp2 < 0) { // hp2 = hp2 + 2pi hp2 += 6.283185307179586476925286766559; } // dL = L2 - L1 double dL = L2 - L1; // dC = Cp2 - Cp1 double dC = Cp2 - Cp1; // computation of hue difference double dhp = 0.0; // set hue difference to zero if the product of chromas is zero if (CpProd != 0) { // dhp = hp2 - hp1 dhp = hp2 - hp1; if (dhp > Math.PI) { // dhp = dhp - 2pi dhp -= 6.283185307179586476925286766559; } else if (dhp < -Math.PI) { // dhp = dhp + 2pi dhp += 6.283185307179586476925286766559; } } // dH = 2 * sqrt(CpProd) * sin(dhp / 2) double dH = 2 * Math.sqrt(CpProd) * Math.sin(dhp / 2); // weighting functions // Lp = (L1 + L2) / 2 - 50 double Lp = (L1 + L2) / 2 - 50; // Cp = (Cp1 + Cp2) / 2 double Cp = (Cp1 + Cp2) / 2; // average hue computation // hp = (hp1 + hp2) / 2 double hp = (hp1 + hp2) / 2; // identify positions for which abs hue diff exceeds 180 degrees if (Math.abs(hp1 - hp2) > Math.PI) { // hp = hp - pi hp -= Math.PI; } // ensure hue is between 0 and 2pi if (hp < 0) { // hp = hp + 2pi hp += 6.283185307179586476925286766559; } // LpSqr = Lp^2 double LpSqr = Lp * Lp; // Sl = 1 + 0.015 * LpSqr / sqrt(20 + LpSqr) double Sl = 1 + 0.015 * LpSqr / Math.sqrt(20 + LpSqr); // Sc = 1 + 0.045 * Cp double Sc = 1 + 0.045 * Cp; // T = 1 - 0.17 * cos(hp - pi / 6) + // + 0.24 * cos(2 * hp) + // + 0.32 * cos(3 * hp + pi / 30) - // - 0.20 * cos(4 * hp - 63 * pi / 180) double hphp = hp + hp; double T = 1 - 0.17 * Math.cos(hp - 0.52359877559829887307710723054658) + 0.24 * Math.cos(hphp) + 0.32 * Math.cos(hphp + hp + 0.10471975511965977461542144610932) - 0.20 * Math.cos(hphp + hphp - 1.0995574287564276334619251841478); // Sh = 1 + 0.015 * Cp * T double Sh = 1 + 0.015 * Cp * T; // deltaThetaRad = (pi / 3) * e^-(36 / (5 * pi) * hp - 11)^2 double powerBase = hp - 4.799655442984406; double deltaThetaRad = 1.0471975511965977461542144610932 * Math.exp(-5.25249016001879 * powerBase * powerBase); // Rc = 2 * sqrt((Cp^7) / (Cp^7 + 25^7)) double Cp7 = Math.pow(Cp, 7); double Rc = 2 * Math.sqrt(Cp7 / (Cp7 + 6103515625.0)); // RT = -sin(delthetarad) * Rc double RT = -Math.sin(deltaThetaRad) * Rc; // de00 = sqrt((dL / Sl)^2 + (dC / Sc)^2 + (dH / Sh)^2 + RT * (dC / Sc) * (dH / Sh)) double dLSl = dL / Sl; double dCSc = dC / Sc; double dHSh = dH / Sh; return Math.sqrt(dLSl * dLSl + dCSc * dCSc + dHSh * dHSh + RT * dCSc * dHSh); }

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  • Code golf: Reverse Polish notation (postfix) evaluator

    - by Dario
    After having had code-golf contests on ordinary mathematical expressions, I just thought it would also be quite interesting how short an evaluation function for postfix notation (RPN) can be. Examples for RPN: 1 2 + == 3 1 2 + 3 * == 9 0 1 2 3 + + - 2 6 * + 3 / 1 - == 1 3 2 / 2.0 + == 3.5 To make things shorter, only +, -, * and /, all just in their binary version, must be supported. Operators/Operands are delimited by one space, divsions by zero don't have to be handled. The resulting code should be a function that takes the postfix string as input and returns the resulting number.

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  • Windows Impersonation failed

    - by skprocks
    I am using following code to implement impersonation for the particular windows account,which is failing.Please help. using System.Security.Principal; using System.Runtime.InteropServices; public partial class Source_AddNewProduct : System.Web.UI.Page { [DllImport("advapi32.dll", SetLastError = true)] static extern bool LogonUser( string principal, string authority, string password, LogonSessionType logonType, LogonProvider logonProvider, out IntPtr token); [DllImport("kernel32.dll", SetLastError = true)] static extern bool CloseHandle(IntPtr handle); enum LogonSessionType : uint { Interactive = 2, Network, Batch, Service, NetworkCleartext = 8, NewCredentials } enum LogonProvider : uint { Default = 0, // default for platform (use this!) WinNT35, // sends smoke signals to authority WinNT40, // uses NTLM WinNT50 // negotiates Kerb or NTLM } //impersonation is used when user tries to upload an image to a network drive protected void btnPrimaryPicUpload_Click1(object sender, EventArgs e) { try { string mDocumentExt = string.Empty; string mDocumentName = string.Empty; HttpPostedFile mUserPostedFile = null; HttpFileCollection mUploadedFiles = null; string xmlPath = string.Empty; FileStream fs = null; StreamReader file; string modify; mUploadedFiles = HttpContext.Current.Request.Files; mUserPostedFile = mUploadedFiles[0]; if (mUserPostedFile.ContentLength >= 0 && Path.GetFileName(mUserPostedFile.FileName) != "") { mDocumentName = Path.GetFileName(mUserPostedFile.FileName); mDocumentExt = Path.GetExtension(mDocumentName); mDocumentExt = mDocumentExt.ToLower(); if (mDocumentExt != ".jpg" && mDocumentExt != ".JPG" && mDocumentExt != ".gif" && mDocumentExt != ".GIF" && mDocumentExt != ".jpeg" && mDocumentExt != ".JPEG" && mDocumentExt != ".tiff" && mDocumentExt != ".TIFF" && mDocumentExt != ".png" && mDocumentExt != ".PNG" && mDocumentExt != ".raw" && mDocumentExt != ".RAW" && mDocumentExt != ".bmp" && mDocumentExt != ".BMP" && mDocumentExt != ".TIF" && mDocumentExt != ".tif") { Page.RegisterStartupScript("select", "<script language=" + Convert.ToChar(34) + "VBScript" + Convert.ToChar(34) + "> MsgBox " + Convert.ToChar(34) + "Please upload valid picture file format" + Convert.ToChar(34) + " , " + Convert.ToChar(34) + "64" + Convert.ToChar(34) + " , " + Convert.ToChar(34) + "WFISware" + Convert.ToChar(34) + "</script>"); } else { int intDocLen = mUserPostedFile.ContentLength; byte[] imageBytes = new byte[intDocLen]; mUserPostedFile.InputStream.Read(imageBytes, 0, mUserPostedFile.ContentLength); //xmlPath = @ConfigurationManager.AppSettings["ImagePath"].ToString(); xmlPath = Server.MapPath("./../ProductImages/"); mDocumentName = Guid.NewGuid().ToString().Replace("-", "") + System.IO.Path.GetExtension(mUserPostedFile.FileName); //if (System.IO.Path.GetExtension(mUserPostedFile.FileName) == ".jpg") //{ //} //if (System.IO.Path.GetExtension(mUserPostedFile.FileName) == ".gif") //{ //} mUserPostedFile.SaveAs(xmlPath + mDocumentName); //Remove commenting till upto stmt xmlPath = "./../ProductImages/"; to implement impersonation byte[] bytContent; IntPtr token = IntPtr.Zero; WindowsImpersonationContext impersonatedUser = null; try { // Note: Credentials should be encrypted in configuration file bool result = LogonUser(ConfigurationManager.AppSettings["ServiceAccount"].ToString(), "ad-ent", ConfigurationManager.AppSettings["ServiceAccountPassword"].ToString(), LogonSessionType.Network, LogonProvider.Default, out token); if (result) { WindowsIdentity id = new WindowsIdentity(token); // Begin impersonation impersonatedUser = id.Impersonate(); mUserPostedFile.SaveAs(xmlPath + mDocumentName); } else { throw new Exception("Identity impersonation has failed."); } } catch { throw; } finally { // Stop impersonation and revert to the process identity if (impersonatedUser != null) impersonatedUser.Undo(); // Free the token if (token != IntPtr.Zero) CloseHandle(token); } xmlPath = "./../ProductImages/"; xmlPath = xmlPath + mDocumentName; string o_image = xmlPath; //For impersoantion uncomment this line and comment next line //string o_image = "../ProductImages/" + mDocumentName; ViewState["masterImage"] = o_image; //fs = new FileStream(xmlPath, FileMode.Open, FileAccess.Read); //file = new StreamReader(fs, Encoding.UTF8); //modify = file.ReadToEnd(); //file.Close(); //commented by saurabh kumar 28may'09 imgImage.Visible = true; imgImage.ImageUrl = ViewState["masterImage"].ToString(); img_Label1.Visible = false; } //e.Values["TemplateContent"] = modify; //e.Values["TemplateName"] = mDocumentName.Replace(".xml", ""); } } catch (Exception ex) { ExceptionUtil.UI(ex); Response.Redirect("errorpage.aspx"); } } } The code on execution throws system.invalidoperation exception.I have provided full control to destination folder to the windows service account that i am impersonating.

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  • Storing a value in Memory Independent of Process

    - by Ganesh
    Hi, I need a way to store a value somewhere for temporarily by say Process A. Process A can exit the after storing the value in memory. After sometime Process B comes accesses the same location of memory and read the value. I need to store in memory, because I dont want the data to persistent across reboots. But as long as the system is up, it Independent of the Process the data must be accessible. I tried MailSlots and Temporary files in windows, both seem to have problem where the process reference count drops to zero , the entities dont persist in memory. What is a suitable mechanism for this in Windows preferably using Win32 API? Ganesh

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  • WebSphere MQ/MQSeries - Possible to send a message to multiple queues with single call?

    - by Jeffrey White
    I'm queuing messages to a WebSphere MQ queue (NB: A point-to-point queue -- not a topic) using a stored procedure in my Oracle database. Is there a way to publish each message to multiple queues with a single call? What I would like is to find a solution that would incur zero additional latency on my database compared to sending the message to a single queue. Solutions that involve changing my WebSphere MQ settings are certainly welcome! What I had in mind was somehow creating a "clone" queue that got all the same messages as the original one, but I've been unable to locate anything like this in the documentation. Thanks, Jeff

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  • Make UILabel show "No results" instead of "nan"

    - by Mike Rychev
    I have a small app, where user can make some calculations and solve equations. For example, if in a square equation discriminant is less than zero, the x1 and x2 values are "nan", so when I assign x1 and x2 values to UILabels they show "nan" as well. Writing a lot of if's like if(D<0) [label setText:[NSString stringWithFormat: @"No solutions"]]; Doesn't help-there are too many cases. I want to check if after [label setText:[NSString stringWithFormat: @"%f", x]]; label's value is "nan", the label's value will be set to @"No solutions". Doing simple if(label==@"nan") { //code } doesn't help. Thanks in advance!

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  • Is there any reason to throw a DivideByZeroException?

    - by Atomiton
    Are there any cases when it's a good idea to throw errors that can be avoided? I'm thinking specifically of the DivideByZeroException and NullReferenceException For example: double numerator = 10; double denominator = getDenominatorFromUser(); if( denominator == 0 ){ throw new DivideByZeroException("You can't divide by Zero!"); } Are there any reasons for throwing an error like this? NOTE: I'm not talking about catching these errors, but specifically in knowing if there are ever good reasons for throwing them.

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  • Querying current number of touches on screen without using events on iPhone

    - by nikhil
    I have an application that starts playing a sound when user touches the uiview and changing to different tones as the user slides the finger on the screen. The sound stops when the user lifts the finger. I am using the touchesBegan, Moved and Ended Events for this. My problem is touches Ended (and/or cancelled) is sometimes not fired properly and the sound keeps playing even after the finger is lifted from screen. So as a workaround I would like to implement a timer that would check for the number of touches on the screen and if it is zero it will check and stop the audioplayer if playing. I have been searching for some code that could get me the number of touches like UITouch *touches=[self getAllTouchesonScreen]; or something :)

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  • Quickly determine if a number is prime in Python for numbers < 1 billion

    - by Frór
    Hi, My current algorithm to check the primality of numbers in python is way to slow for numbers between 10 million and 1 billion. I want it to be improved knowing that I will never get numbers bigger than 1 billion. The context is that I can't get an implementation that is quick enough for solving problem 60 of project Euler: I'm getting the answer to the problem in 75 seconds where I need it in 60 seconds. http://projecteuler.net/index.php?section=problems&id=60 I have very few memory at my disposal so I can't store all the prime numbers below 1 billion. I'm currently using the standard trial division tuned with 6k±1. Is there anything better than this? Do I already need to get the Rabin-Miller method for numbers that are this large. primes_under_100 = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97] def isprime(n): if n <= 100: return n in primes_under_100 if n % 2 == 0 or n % 3 == 0: return False for f in range(5, int(n ** .5), 6): if n % f == 0 or n % (f + 2) == 0: return False return True How can I improve this algorithm?

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  • XNA 4.0 - What happens when the window is minimized?

    - by Conrad Clark
    Hello. I'm learning F#, and decided to try making simple XNA games for windows using F# (pure enthusiasm) , and got a window with some images showing up. Here's the code: (*Methods*) member self.DrawSprites() = _spriteBatch.Begin() for i = 0 to _list.Length-1 do let spentity = _list.List.ElementAt(i) _spriteBatch.Draw(spentity.ImageTexture,new Rectangle(100,100,(int)spentity.Width,(int)spentity.Height),Color.White) _spriteBatch.End() (*Overriding*) override self.Initialize() = ChangeGraphicsProfile() _graphicsDevice <- _graphics.GraphicsDevice _list.AddSprite(0,"NagatoYuki",992.0,990.0) base.Initialize() override self.LoadContent() = _spriteBatch <- new SpriteBatch(_graphicsDevice) base.LoadContent() override self.Draw(gameTime : GameTime) = base.Draw(gameTime) _graphics.GraphicsDevice.Clear(Color.CornflowerBlue) self.DrawSprites() And the AddSprite Method: member self.AddSprite(ID : int,imageTexture : string , width : float, height : float) = let texture = content.Load<Texture2D>(imageTexture) list <- list @ [new SpriteEntity(ID,list.Length, texture,Vector2.Zero,width,height)] The _list object has a ContentManager, here's the constructor: type SpriteList(_content : ContentManager byref) = let mutable content = _content let mutable list = [] But I can't minimize the window, since when it regains its focus, i get this error: ObjectDisposedException Cannot access a disposed object. Object name: 'GraphicsDevice'. What is happening?

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  • Are there any online database schema drawing tools?

    - by Pure.Krome
    Hi folks, i wish to draw up some database schemas. Eg, table 1 has zero to many rows in table 2, etc. It's purely for visual purposes (eg. no sql code, etc). Are there any online tools / website that offer this? (please don't say: Use Sql Server Database Diagrams, print screen, upload to image hosting service). thanks :) EDIT: Please take note of the keyword - ONLINE. I don't want any desktop solutions (because I already have one of these).

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  • Socket Select with empty fd set

    - by whoi
    Hi; Suppose you have an fd set which can have zero or more sockets in it. When I try to call select operation on empty fd set, what I get is -1 as the number of fds which are set, meaning error. So what would you suggest to overcome this problem, you might say do not call if empty but I have a loop and any time fd set can hold 0 or more sockets. What is the best approach about this problem? (we are on C programming language)

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  • Java Math.cos() Method Does Not Return 0 When Expected

    - by dimo414
    Using Java on a Windows 7 PC (not sure if that matters) and calling Math.cos() on values that should return 0 (like pi/2) instead returns small values, but small values that, unless I'm misunderstanding, are much greater than 1 ulp off from zero. Math.cos(Math.PI/2) = 6.123233995736766E-17 Math.ulp(Math.cos(Math.PI/2)) = 1.232595164407831E-32 Is this in fact within 1 ulp and I'm simply confused? And would this be an acceptable wrapper method to resolve this minor inaccuracy? public static double cos(double a){ double temp = Math.abs(a % Math.PI); if(temp == Math.PI/2) return 0; return Math.cos(a); }

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  • JavaScript distributed computing project

    - by Ben L.
    I made a website that does absolutely nothing, and I've proven to myself that people like to stay there - I've already logged 11+ hours worth of cumulative time on the page. My question is whether it would be possible (or practical) to use the website as a distributed computing site. My first impulse was to find out if there were any JavaScript distributed computing projects already active, so that I could put a piece of code on the page and be done. Unfortunately, all I could find was a big list of websites that thought it might be a cool idea. I'm thinking that I might want to start with something like integer factorization - in this case, RSA numbers. It would be easy for the server to check if an answer was correct (simply test for modulus equals zero), and also easy to implement. Is my idea feasible? Is there already a project out there that I can use?

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  • How can I work around the fact that in C++, sin(3.14159265) is not 0?

    - by Adam Doyle
    In C++, const double Pi = 3.14159265; cout << sin(Pi); // displays: 3.58979e-009 it SHOULD display the number zero I understand this is because Pi is being approximated, but is there any way I can have a value of Pi hardcoded into my program that will return 0 for sin(Pi)? (a different constant maybe?) In case you're wondering what I'm trying to do: I'm converting polar to rectangular, and while there are some printf() tricks I can do to print it as "0.00", it still doesn't consistently return decent values (in some cases I get "-0.00") The lines that require sin and cosine are: x = r*sin(theta); y = r*cos(theta); BTW: My Rectangular - Polar is working fine... it's just the Polar - Rectangular Thanks! edit: I'm looking for a workaround so that I can print sin(some multiple of Pi) as a nice round number to the console (ideally without a thousand if-statements)

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  • SoundPool repeating issue for Samsung Galaxy S3

    - by Alaa Eldin
    I'm trying to play a background sound for my application, I use SoundPool class, my problem is that, sound plays well only when I set the loop parameter with zero value, but it doesn't work for any other value. My code for initialization is: soundpool = new SoundPool(4, AudioManager.STREAM_MUSIC, 0); soundsMap = new HashMap<Integer, Integer>(); soundsMap.put(1, soundpool.load(this, R.raw.soundfile_1, 1)); soundsMap.put(2, soundpool.load(this, R.raw.soundfile_2, 1)); my code for playing is soundpool.play(1, 0.9f, 0.9f, 1, -1, 1f); as I mentioned sound works when I put (0) instead of (-1) for the loop value, anyone has any idea why (-1) or any value other than (0) doesn't work (there is no output sound) ?

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  • How to create a delayed queue in RabbitMQ?

    - by eandersson
    What is the easiest way to create a delay (or parking) queue with Python, Pika and RabbitMQ? I have seen an similar questions, but none for Python. I find this an useful idea when designing applications, as it allows us to throttle messages that needs to be re-queued again. There are always the possibility that you will receive more messages than you can handle, maybe the HTTP server is slow, or the database is under too much stress. I also found it very useful when something went wrong in scenarios where there is a zero tolerance to losing messages, and while re-queuing messages that could not be handled may solve that. It can also cause problems where the message will be queued over and over again. Potentially causing performance issues, and log spam.

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  • Globbing with MinGW on Windows

    - by Neil Butterworth
    I have an application built with the MinGW C++ compiler that works something like grep - acommand looks something like this: myapp -e '.*' *.txt where the thing that comes after the -e switch is a regex, and the thing after that is file name pattern. It seems that MinGW automatically expands (globs in UNIX terms) the command line so my regex gets mangled. I can turn this behaviour off, I discovered, by setting the global variable _CRT_glob to zero. This will be fine for bash and other sensible shell users, as the shell will expand the file pattern. For MS cmd.exe users however, it looks like I will have to expand the file pattern myself. So my question - does anyone know of a globbing library (or facility in MinGW) to do partial command line expansion? I'm aware of the _setargv feature of the Windows CRT, but that expands the full command line. Please note I've seen this question, but it really does not address partial expansion.

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  • Yield only as many are required from a generator

    - by Matt Joiner
    I wish to yield from a generator only as many items are required. In the following code a, b, c = itertools.count() I receive this exception: ValueError: too many values to unpack I've seen several related questions, however I have zero interest in the remaining items from the generator, I only wish to receive as many as I ask for, without providing that quantity in advance. It seems to me that Python determines the number of items you want, but then proceeds to try to read and store more than that number. How can I yield only as many items as I require, without passing in how many items I want?

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  • Query size of block device file in Python

    - by ??O?????
    Hello. I have a Python script that reads a file (typically from optical media) marking the unreadable sectors, to allow a re-attempt to read said unreadable sectors on a different optical reader. I discovered that my script does not work with block devices (e.g. /dev/sr0), in order to create a copy of the contained ISO9660/UDF filesystem, because os.stat().st_size is zero. The algorithm currently needs to know the filesize in advance; I can change that, but the issue (of knowing the block device size) remains, and it's not answered here, so I open this question. I am aware of the following two related SO questions: Determine the size of a block device (/proc/partitions, ioctl through ctypes) how to check file size in python? (about non-special files) Therefore, I'm asking: in Python, how can I get the file size of a block device file?

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  • Is -1 a magic number? An anti-pattern? A code smell? Quotes and guidelines from authorities

    - by polygenelubricants
    I've seen -1 used in various APIs, most commonly when searching into a "collection" with zero-based indices, usually to indicate the "not found" index. This "works" because -1 is never a legal index to begin with. It seems that any negative number should work, but I think -1 is almost always used, as some sort of (unwritten?) convention. I would like to limit the scope to Java at least for now. My questions are: What are the official words from Sun regarding using -1 as a "special" return value like this? What quotes are there regarding this issue, from e.g. James Gosling, Josh Bloch, or even other authoritative figures outside of Java? What were some of the notable discussions regarding this issue in the past?

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