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• erroneous Visual C float / double conversion?

  - by RED SOFT ADAIR

  In Visual C++ i wrote the following sample in a C++ program: float f1 = 42.48f; double d1 = 42.48; double d2 = f1; I compiled the program with Visual Studio 2005. In the debugger i see the following values: f1 42.480000 float d1 42.479999999999997 double d2 42.479999542236328 double d1 by my knowledege is OK, but d2 is wrong. The problem occurs as well with /fp=precise as with /fp=strict as with /fp=fast. Whats the problem here? Any hint how to avoid this Problem? This leads to serious numerical problems.

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• Graph - strongly connected components

  - by HardCoder1986

  Hello! Is there any fast way to determine the size of the largest strongly connected component in a graph? I mean, like, the obvious approach would mean determining every SCC (could be done using two DFS calls, I suppose) and then looping through them and taking the maximum. I'm pretty sure there has to be some better approach if I only need to have the size of that component and only the largest one, but I can't think of a good solution. Any ideas? Thanks.

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• Maximum Possible File Name Length in Windows Kernel

  - by Lambert

  I was wondering, what is the longest possible name length allowed by the Windows kernel? E.g.: I know the kernel uses UNICODE_STRING structures to hold all object paths, and since the byte length of a wide-character string is stored inside a USHORT, that allows for a maximum path length of 2^15 - 1 characters. Is there a similar, hard restriction on a file name (rather than path)? (I don't care if NTFS or FAT32 imposes a particular restriction; I'm looking for the longest possible theoretically allowed name in the kernel, assuming no additional file system or shell restrictions.) (Edit: For those wondering why this even matters, consider that normally, traversing a directory is achieved by FindFirstFile/FindNextFile calls, one call per file. Given the function named NtQueryDirectoryFile, which is the underlying system call and which returns multiple file names per call, it's actually possible to take advantage of this maximum-length restriction on the path to make an extremely-fast directory traverser that uses solely the stack as a buffer. Now I'm trying to extend that concept, and I need to know the maximum size of a file name.)

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• Animating translation and scaling of view in Android

  - by hgpc

  I have to animate a view from state A to B with changes to its scale, position and scrolling. I know everything about state A (widthA, heightA, topA, leftA, scrollXA, scrollYA) and state B (widthB, heightB, topB, leftB, scrollXB, scrollYB). So far I wrote the following code: AnimationSet animation = new AnimationSet(true); int toXDelta; // What goes here? int toYDelta; // What goes here? TranslateAnimation translateAnimation = new TranslateAnimation(1, toXDelta, 1, toYDelta); translateAnimation.setDuration(duration); animation.addAnimation(translateAnimation); float scale = (float) widthB / (float) widthA; ScaleAnimation scaleAnimation = new ScaleAnimation(1, scale, 1, scale); scaleAnimation.setDuration(duration); animation.addAnimation(scaleAnimation); animation.setAnimationListener(new AnimationListener() { @Override public void onAnimationEnd(Animation arg0) { view.clearAnimation(); // Change view to state B } @Override public void onAnimationRepeat(Animation arg0) {} @Override public void onAnimationStart(Animation arg0) {} }); view.startAnimation(animation); Is this the right way to do this? If so, how should I calculate the values of toXDelta and toYDelta? I'm having trouble finding the exact formula. Thanks!

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• Compute weighted averages for large numbers

  - by Travis

  I'm trying to get the weighted average of a few numbers. Basically I have: Price - 134.42 Quantity - 15236545 There can be as few as one or two or as many as fifty or sixty pairs of prices and quantities. I need to figure out the weighted average of the price. Basically, the weighted average should give very little weight to pairs like Price - 100000000.00 Quantity - 3 and more to the pair above. The formula I currently have is: ((price)(quantity) + (price)(quantity) + ...)/totalQuantity So far I have this done: double optimalPrice = 0; int totalQuantity = 0; double rolling = 0; System.out.println(rolling); Iterator it = orders.entrySet().iterator(); while(it.hasNext()) { System.out.println("inside"); Map.Entry order = (Map.Entry)it.next(); double price = (Double)order.getKey(); int quantity = (Integer)order.getValue(); System.out.println(price + " " + quantity); rolling += price * quantity; totalQuantity += quantity; System.out.println(rolling); } System.out.println(rolling); return totalQuantity / rolling; The problem is I very quickly max out the "rolling" variable. How can I actually get my weighted average? Thanks!

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• PHP APC - Why is loading cached array op codes slow?

  - by Aaron Kreider

  I'm using APC to reduce my loading time for my PHP files. My files load very fast, except for one file where I define more than 100 arrays. This 270 kb file takes 200 ms to load. The rest of the files are full of objects, methods, and functions. I'm wondering: does OP code caching not work as well for arrays? My APC cache should be big enough to handle all of my classes. Currently 40% of my cache is free. My hit rate is 99%. apc.shm_size=32 M apc.max_file_size = 1M apc.shm_segments= 1 APC 3.1.6 I'm using PHP 5.2, Apache 2, and Windows Vista.

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• Given two lines on a plane, how to find integer points closest to their intersection?

  - by Lukasz Lew

  I can't solve it: You are given 8 integers: A, B, C representing a line on a plane with equation A*x + B*y = C a, b, c representing another line x, y representing a point on a plane The two lines are not parallel therefore divide plane into 4 pieces. Point (x, y) lies inside of one these pieces. Problem: Write a fast algorithm that will find a point with integer coordinates in the same piece as (x,y) that is closest to the cross point of the two given lines. Note: This is not a homework, this is old Euler-type task that I have absolutely no idea how to approach. Update: You can assume that the 8 numbers on input are 32-bit signed integers. But you cannot assume that the solution will be 32 bit.

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• Most efficient way to save tile data of an isometric game

  - by Harmen

  Hello, I'm working on an isometric game for fast browsers that support <canvas>, which is great fun. To save information of each tile, I use a two-dimensional array which contains numbers representing a tile ID, like: var level = [[1, 1, 1, 2, 1, 0], [0, 1, 1, 2, 0, 1], [0, 1, 1, 2, 1, 1]]; var tiles = [ {name: 'grass', color: 'green'}, {name: 'water', color: 'blue'}, {name: 'forest', color: 'ForestGreen'} ]; So far it works great, but now I want to work with heights and slopes like in this picture: For each tile I need to save it's tile ID, height and information about which corners are turned upward. I came up with a simple idea about a bitwise representation of all four corners, like this: 1011 // top, bottom and left corner turned up My question is: what is the most efficient way to save these three values for each cell? Is it possible to save these three values as one integer?

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• Vehicle License Plate Detection

  - by Ash

  Hey all Basically for my final project at university, I'm developing a vehicle license plate detection application. Now I consider myself an intermediate programmer, however my mathematics knowledge lacks anything above secondary school, therefore producing detection formulae is basically impossible. I've spend a good amount of time looking up academic papers such as: http://www.scribd.com/doc/266575/Detecting-Vehicle-License-Plates-in-Images http://www.cic.unb.br/~mylene/PI_2010_2/ICIP10/pdfs/0003945.pdf http://www.eurasip.org/Proceedings/Eusipco/Eusipco2007/Papers/d3l-b05.pdf When it comes to the maths, I'm lost. Due to this testing various graphic images proved productive, for example: to However this approach is only catered to that particular image, and if the techniques were applied to different images, I'm sure a different, most likely poorer conversion would occur. I've read about a formula called the bottom hat morphology transform, which according to the first does the following: "Basically, the trans- formation keeps all the dark details of the picture, and eliminates everything else (including bigger dark regions and light regions)." Sadly I can't find much information on this, however the image within the documentation near the end of the report shows it's effectiveness. I'm aware this is complicated and vast, I'd just appreciate a little advice, even in terms of what transformation techniques I should focus on developing, or algorithm regarding edge detection or pixel detection. Few things I need to add Developing in C Sharp Confining the project to UK registration plates only I can basically choose the images to convert as a demonstration Thanks

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• MATLAB submatrix over variable dimensions

  - by rlbond

  I have a variable dimension matrix, X. I want a function that will get the first half of X in one dimension. I.E., I want something like this: function x = variableSubmatrix(x, d) if d == 1 switch ndims(x) case 1 x = x(1:end/2); case 2 x = x(1:end/2, :); case 3 x = x(1:end/2, :, :); (...) end elseif d == 2 switch ndims(x) case 2 x = x(:, 1:end/2); case 3 x = x(:, 1:end/2, :); (...) end elseif (...) end end I'm not quite sure how to do this. I need it to be fast, as this will be used many times in computation.

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• How to effectively draw on desktop in C#?

  - by Lazlo

  I want to draw directly on the desktop in C#. From searching a bit, I ended up using a Graphics object from the Desktop HDC (null). Then, I painted normally using this Graphics object. The problem is that my shapes get lost when any part of the screen is redrawn. I tried a While loop, but it actually ends up drawing as fast as the application can, which is not the update rate of the desktop. Normally, I would need to put my drawing code in a "OnPaint" event, but such thing does not exist for the desktop. How would I do it? Example code: http://stackoverflow.com/questions/1536141/how-to-draw-directly-on-the-windows-desktop-c

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• Display using QtWebKit, whilst parsing xml

  - by Beren Scott

  I wish to use QtWebKit to load a url for display, but, that's the easy part, I can do that. What I wish to do is record / log xml as I go. My attention here is to record and database certain details on the fly, by recording those details. My problem is, how to do this all on the fly, without requesting the same url from the server twice, once for the xml, and the second time to view the url. My hope here, is to implement a very fast way of recording set data as the user passes over it. Take for example, rather then have to type out details displayed by a website, I wish to have those details chucked into a database as I the user views the website. Now, I am using QtWebKit, and I have everything pretty much solved viewing wise. I have a loadUrl() routine which calls load(url) inside the qwebview.h The problem is, how do I piggyback xml parsing on top of this?

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• PHP Form Validation

  - by JM4

  This question will undoubtedly be difficult to answer and ask in a way that makes sense but I'll try my best: I have a form which uses PHP to display certain sections of the form such as: <?php if ($_SESSION['EnrType'] == "Individual") { display only form information for individual enrollment } ?> and <?php if ($_SESSION['Num_Enrs'] > 6) { display only form information for 7 total members enrollment } ?> In each form piece, unique information is collected about each enrollee but the basic criteria for each enrollee is the same, i.e. All enrollee's must use have a value in the FirstName field. Each field is named according to the enrollee number, i.e. Num1FirstName; Num2FirstName. I have a PHP validation script which is absolutely fantastic and am not looking to change it but the issue I am running into is duplication of the script in order to validate ALL fields in one swoop. On submission, all POSTED items are run through my validation script and based on the rules set return an error if they do not equal true. Sample code: if (isset($_POST['submit'])) { // import the validation library require("validation.php"); $rules = array(); // stores the validation rules //All Enrollee Rules $rules[] = "required,Num1FirstName,Num2FirstName,The First Name field is required."; The script above does the following, $rules[] ="REQUIREMENT,fieldname,error message" where requirement gives criteria (in this case, simply that a value is passed), fieldname is the name of the field being validated, and error message returns the error used. My Goal is to use the same formula above and have $rules[] run through ALL firstnames and return the error posted ONLY if they exist (i.e. dont check for member #7's first name if it doesnt exist on the screen). If I simply put a comma between the 'fieldnames' this only checks for the first, then second, and so on so this wont work. Any ideas?

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• Storing a bucket of numbers in an efficient data structure

  - by BlitzKrieg

  I have a buckets of numbers e.g. - 1 to 4, 5 to 15, 16 to 21, 22 to 34,.... I have roughly 600,000 such buckets. The range of numbers that fall in each of the bucket varies. I need to store these buckets in a suitable data structure so that the lookups for a number is as fast as possible. So my question is what is the suitable data structure and a sorting mechanism for this type of problem. Thanks in advance

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• .NET values lookup

  - by Maciej

  Hi, I have a feeling of missing something obvious. UDP receiver application. It holds a collection of valid UDP sender IPs - only guys with IP on that list will be considered. Since that list must be looked at on every packet and UDPs are so volatile, that operation must be maximum fast. Good choice is Dictionary but it is a key-value structure and what I actually need here is a dictionary-like (hash lookup) key only structure. Is there something like that? Small annoyance rather than a bug but still. I can still use Dictionary Thanks, M.

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• Python IPC, popen too slow

  - by UnableToLoad

  i need to run a subprocess (./myProgram) form python script and get output, actually i do this: import subprocess proc = subprocess.Popen('./generate_out', shell=False, stdout=subprocess.PIPE, ) while proc.poll() is None: out = proc.stdout.readline() data = doStuff(out) print(data) but is slow, sometimes pass a lot of time between the output produced by ./generate_out and the print(data), knowing that my doStuff() function is very fast, i think there is some buffer slowing down my pipe... Notes: ./generate_out, generates potentially an unlimited number of lines of finite length each. It seems that when too few chars are put in the pipe between the two processes nothing happens, then when enough is produced i get a huge print (non the expected behaviour!) sometimes i wait many seconds (10-20 and more) between generate_out print and python print) what can i do? maybe communicate() is faster? anithing else? Thank you a lot!

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• Split user.config into different files for faster saving

  - by HorstWalter

  In my c# Windows Forms application (.net 3.5 / VS 2008) I have 2 settings files resulting in one user.config file. One setting file consists of larger data, but is rarely changed. The frequently changed data are very few. However, since the saving of the settings is always writing the whole (XML) file it is always "slow". SettingsSmall.Default.Save(); // slow, even if SettingsSmall consists of little data Could I configure the settings somehow to result in two files, resulting in: SettingsSmall.Default.Save(); // should be fast SettingsBig.Default.Save(); // could be slow, is seldom saved I have seen that I can use the SecionInformation class for further customizing, however what would be the easiest approach for me? Is this possible by just changing the app.config (config.sections)?

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• What simple methods are there to wrap a c++ based object model with a COM interface

  - by Rich

  I have a pre-existing c++ object model which represents the business layer tier of an application. I want to be able to expose the object model to applications written in other languages i.e vbscript, VB, javascript etc. I believe the best way of doing this is to wrap the business objects with a COM layer. What fast and effective methods are there for doing this. Any advice, links to practical "How to" documentation would be very much appreciated. Because I'm starting a bounty on this , here's a few extra guidelines for potential bounty hunters :- 1)I've decided on an ATL approach 2)I'm now specifically looking for links to really good "how to and quickly" documentation on wrapping a pre-existing c++ object model to make it useable by a scripting language like javascript 3) Something with small working examples showing me what code needs to be added to what files, e.g what goes into the cpp , idl and hpp/h etc. It' must include an example I can compile test and change to get a better understanding.

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• delphi Ado update insert betwen 2 records

  - by user315957

  i nead to update recordes from one table to the other (this for the master Table and f«the same for the DetailTable. first a posicion the record of the record´s of the table i whant to copy update from: Tabelamestre(Local_deste_cliente) (1 record ) NInterv.text:=dbedit1.text; Begin with ADOTable_casa do Begin Close; SQL.Clear; SQL.Add('SELECT * from Vibrometria_'); SQL.Add('Where numeracao LIKE ''%'+NInterv.text ); Open; end; end now i need to update/insert the record´s from Vibrometria := Local_deste_cliente (TADOTABLE) Now i nead to get the record above and do the same for the 2 detail tables Vibrometria_Sub (J) := Tabeladetail (Variaveis_neste_local). ((J) Records and i stil have another table thar get a master record from (K) Tabeladetail (Variaveis_neste_local) Vibrometria_Sub1 (K) := Tabeladetail1(Variaveis_neste_local1). ((k) Records lest´s say i nead to update 1 to N starting in the first table!!!!!!!! is there a fast solucion for this!!!!!! Thanks

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• Is ORM (Linq, Hibernate...) really that useful?

  - by Peter

  I have been playing with some LINQ ORM (LINQ directly to SQL) and I have to admit I like its expressive powers . For small utility-like apps, It also works quite fast: dropping a SQL server on some surface and you're set to linq away. For larger apps however, the DAL never was that big of an issue to me to setup, nor maintain, and more often than not, once it was set, all the programming was not happening there anyway... My, honest - I am an ORM newbie - question : what is the big advantage of ORM over writing a decent DAL by hand? (seems like a double, couldn't find it though) UPDATE : OK its a double :-) I found it myself eventually : ORM vs Handcoded Data Access Layer

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• google spreadsheet api from android: google-api-java-client or handmade?

  - by yetanothercoderu

  For working with google spreadsheet api from android (2.2) - google suggests using google-api-java-client for android. For that you have to include 5 jars to your android application: guava-r09.jar google-http-client-extensions-android2-1.6.0-beta.jar google-api-client-extensions-android2-1.6.0-beta.jar google-http-client-1.6.0-beta.jar google-api-client-1.6.0-beta.jar and digging into google-api-java-client javadocs for fast-changing api. Does it worth the effort? in term of android specifics and device fragmentation? Isn't it reasonable to write your own simple http response parser or take small existing library like google-spreadsheet-lib-android ? Thanks! UPD: choosed google-api-java-client finally as it has all routine stuff (like parsing http, xml) out of box

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• Should I use Drupal or Kohana-type framework for a web "application"

  - by Andres

  The debate is that I need a PHP Framework/Drupal with the flexibility to add custom features to a potentially large application (web and with an api). However, with a framework, like Kohana, I see myself tackling and re-inventing the wheel with the simple stuff like account management and cms stuff. Account management and quick data collection, like fast form creation, are tedious in Kohana but appear incredible simple in Drupal. On the other hand, based on my limited Drupal experience, I doubt building rapid custom "features" and allowing users to create "groups" and to manage their own roles within those groups is something Drupal can easily accomplish. To simplify, is Drupal capable of true Web Applications; where the application is a service and provides custom results to each user? Can it provide a dashboard-like interface for users to change their settings or preferences? Can it aggregate data from particular users to provide better results/info to others? If so, please point me to some knowledge :-)

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• Maximizing the number of threads to fully utilize all available resources without hindering overall

  - by Matt

  Let's say I have to generate a bunch of result files, and I want to make it as fast as possible. Each result file is generated independently of any other result file; in fact, one could say that each result file is agnostic to every other result file. The resources used to generate each result file is also unique to each. How can I dynamically decide the optimal number of threads to run simultaneously in order to minimize the overall run time? Is my only option to write my own thread manager that watches performance counters and adjust accordingly or does there exists some solid classes that already accomplish this?

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• 2D Histogram in R: Converting from Count to Frequency within a Column

  - by Jac

  Would appreciate help with generating a 2D histogram of frequencies, where frequencies are calculated within a column. My main issue: converting from counts to column based frequency. Here's my starting code: # expected packages library(ggplot2) library(plyr) # generate example data corresponding to expected data input x_data = sample(101:200,10000, replace = TRUE) y_data = sample(1:100,10000, replace = TRUE) my_set = data.frame(x_data,y_data) # define x and y interval cut points x_seq = seq(100,200,10) y_seq = seq(0,100,10) # label samples as belonging within x and y intervals my_set$x_interval = cut(my_set$x_data,x_seq) my_set$y_interval = cut(my_set$y_data,y_seq) # determine count for each x,y block xy_df = ddply(my_set, c("x_interval","y_interval"),"nrow") # still need to convert for use with dplyr # convert from count to frequency based on formula: freq = count/sum(count in given x interval) ################ TRYING TO FIGURE OUT ################# # plot results fig_count <- ggplot(xy_df, aes(x = x_interval, y = y_interval)) + geom_tile(aes(fill = nrow)) # count fig_freq <- ggplot(xy_df, aes(x = x_interval, y = y_interval)) + geom_tile(aes(fill = freq)) # frequency I would appreciate any help in how to calculate the frequency within a column. Thanks! jac EDIT: I think the solution will require the following steps 1) Calculate and store overall counts for each x-interval factor 2) Divide the individual bin count by its corresponding x-interval factor count to obtain frequency. Not sure how to carry this out though. .

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• SOS: AudioFormat when writing to file in FreeTTS

  - by user330793

  Very annoying problem. I have developed a freeTTS application of the freetts class that write captured audio to file however I am having some very annoying problems. When setting the audio player to singlefileaudio player I try to also set the audioformat with my own default values for sampleRate, sampleSizeInBits, channels, signed and bigEndian. Now I access AudioPlayer.get methods to show these values in runtime just to ensure they are set to what I set them and they match those values. However when file writing completes and I check the properties of the resulting wave file, they are set to the audioPlayer default settings. Normally this will be fine except I have to read the files into another application which has fixed audio property settings so I always get a resulting output that sounds like am fast forwarding the sound and listening to it at the same time. Obviously because of the different sampling rates. I need help please. Thanx, Henry

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