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• Count of memory copies in *nix systems between packet at NIC and user application?

  - by Michael_73

  Hi there, This is just a general question relating to some high-performance computing I've been wondering about. A certain low-latency messaging vendor speaks in its supporting documentation about using raw sockets to transfer the data directly from the network device to the user application and in so doing it speaks about reducing the messaging latency even further than it does anyway (in other admittedly carefully thought-out design decisions). My question is therefore to those that grok the networking stacks on Unix or Unix-like systems. How much difference are they likely to be able to realise using this method? Feel free to answer in terms of memory copies, numbers of whales rescued or areas the size of Wales ;) Their messaging is UDP-based, as I understand it, so there's no problem with establishing TCP connections etc. Any other points of interest on this topic would be gratefully thought about! Best wishes, Mike

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• A balanced binary search tree which is also a heap

  - by saeedn

  I'm looking for a data structure where each element in it has two keys. With one of them the structure is a BST and looking at the other one, data structure is a heap. With a little search, I found a structure called Treap. It uses the heap property with a random distribution on heap keys to make the BST balanced! What I want is a Balanced BST, which can be also a heap. The BST in Treap could be unbalanced if I insert elements with heap Key in the order of my choice. Is there such a data structure?

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• How can I help fellow students struggling in programming classes?

  - by David Barry

  I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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• Focus CSS tag in Internet Explorer 8

  - by Sam

  This is driving me nuts. http://www.cssdrive.com/index.php/examples/exampleitem/focus_pseudo_class This is an example of using the hover pseudo-class. Works fine in Chrome and IE. When I save locally it works fine in Chrome but won't work in IE. What am I doing wrong!? <link rel="Stylesheet" href="style.css" /> <form> <p>1) Name:<br /> <input type="text" size="40"></p> <p>2) Email address:<br /> <input type="text" size="40"></p> <p>3) Comments:<br /> <textarea rows="5" name="comments" cols="45" wrap="virtual"></textarea></p> <p><input id="actualsubmit" type="submit" value="Submit"></p> </form> style.css: input:focus, textarea:focus{ background-color: lightyellow; }

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• filtering elements from list of lists in Python?

  - by user248237

  I want to filter elements from a list of lists, and iterate over the elements of each element using a lambda. For example, given the list: a = [[1,2,3],[4,5,6]] suppose that I want to keep only elements where the sum of the list is greater than N. I tried writing: filter(lambda x, y, z: x + y + z >= N, a) but I get the error: <lambda>() takes exactly 3 arguments (1 given) How can I iterate while assigning values of each element to x, y, and z? Something like zip, but for arbitrarily long lists. thanks, p.s. I know I can write this using: filter(lambda x: sum(x)..., a) but that's not the point, imagine that these were not numbers but arbitrary elements and I wanted to assign their values to variable names.

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• Apache basic auth, mod_authn_dbd and password salt

  - by Cristian Vrabie

  Using Apache mod_auth_basic and mod_authn_dbd you can authenticate a user by looking up that user's password in the database. I see that working if the password is held in clear, but what if we use a random string as a salt (also stored in the database) then store the hash of the concatenation? mod_authn_dbd requires you to specify a query to select that password not to decide if the user is authenticated of not. So you cannot use that query to concatenate the user provided password with the salt then compare with the stored hash. AuthDBDUserRealmQuery "SELECT password FROM authn WHERE user = %s AND realm = %s" Is there a way to make this work?

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• VB.net Network Graph code/algorithm

  - by Jens

  For a school project we need to visualise a computer network graph. The number of computers with specific properties are read from an XML file, and then a graph should be created. Ad random computers are added and removed. Is there any open source project or algorithm that could help us visualising this in VB.net? Or would you suggest us to switch to java. Update: We eventually switched java and used the Jung libraries because this was easier for us to understand and implement.

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• best way to output a full precision double into a text file

  - by flevine100

  Hi, I need to use an existing text file to store some very precise values. When read back in, the numbers essentially need to be exactly equivalent to the ones that were originally written. Now, a normal person would use a binary file... for a number of reasons, that's not possible in this case. So... do any of you have a good way of encoding a double as a string of characters (aside from increasing the precision). My first thought was to cast the double to a char[] and write out the chars. I don't think that's going to work because some of the characters are not visible, produce sounds, and even terminate strings ('\0'... I'm talkin to you!) Thoughts?

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• How can I create numbered map markers in Google Maps V3?

  - by kaneuniversal

  I'm working on a map that has multiple markers on it. These markers use a custom icon, but I'd also like to add numbers on top. I've seen how this has been accomplished using older versions of the API. How can I do this in V3? *Note -- the "title" attribute creates a tooltip when you mouseover the marker, but I want something that will be layered on top of the custom image even when you're not hovering on top of it. Here's the documentation for the marker class, and none of these attributes seem to help: http://code.google.com/apis/maps/documentation/v3/reference.html#MarkerOptions Thank you . . . . Michael

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• save the input value in a 2dimentsion array

  - by arash

  hi friends,how can i save the number that user enter in textbox in a 2 dimension array? for example: i have this numbers in textbox:45,78 and now i want to save 45,32 like this: array[0,0]=45 and array[0,1]=78 how can i do that?thanks,so much edited: oh,when i entered 1,2,3,4,5,6,7,8,9 in textbox and it takes [2,2]=56 private void button10_Click(object sender, EventArgs e) { int matrixDimention = 2; int[,] intValues = new int[matrixDimention + 1, matrixDimention + 1]; string[] splitValues = textBox9.Text.Split(','); for (int i = 0; i < splitValues.Length; i++) intValues[i % (matrixDimention + 1), i % (matrixDimention + 1)] = Convert.ToInt32(splitValues[i]); string a=intValues[2,2].ToString(); MessageBox.Show(a); } when i take: string a=intValues[2,1].ToString(); it shows 0

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• mkmapview cpu usage on iphone 3G

  - by mozveren

  Hello all, I have some troubles with iphone 3G and Mkmapview. After a certain random time, my application freeze. When I launch with performances tool, I can see that the application a lot of time to retrieve map tiles in cache. 19.6 7006 Foundation +[NSURLConnection(NSURLConnectionReallyInternal) 18.5 6613 GMM GMM::TileCachePrivate::runCacheThread() Its seems that the MkMapView component launch several threads to load the tiles in caches. How I can avoid this behavior ? The behavior seems to not make troubles on 3GS. Thanks

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• What is this for an IP in my google app engine log file?

  - by Christian Harms

  I get many normal log lines in my google app engine application. But today I go these instead the 4-part number: 2a01:e35:2f20:f770:6c54:3ee8:67fb:df8 What is this for an format? ipv6 are 6 numbers, mac address too... Normal logfile line: 187.14.44.208 - - [19/Mar/2010:14:31:35 -0700] "GET /geo_data.js HTTP/1.1" 200 776 "http://www.xxx.com.br/spl19/index.php?refid=gv_av_ri" "Mozilla/5.0 (Windows; U; Windows NT 5.1; pt-BR; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729),gzip(gfe)" This special logfile line: 2a01:e35:2f20:f770:6c54:3ee8:67fb:df8 - - [18/Mar/2010:17:00:37 -0700] "GET /geo_data.js HTTP/1.1" 500 450 "http://www.xxx.com.br/spl19/index.php?refid=cm_av_ri" "Mozilla/5.0 (Windows; U; Windows NT 6.1; pt-PT; rv:1.9.2) Gecko/20100115 Firefox/3.6,gzip(gfe)"

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• Service-Based Authentication Using Tokens

  - by jerhinesmith

  I'm having a tough time trying to find clear and concise examples of how one would implement a service-based authentication scheme using tokens. As far as I can tell, the basic steps are as follows: Client requests username/password from user Client passes username/password to identity provider Provider checks username/password and sends back a token if the user is valid Client does something with the token? The third and fourth step are where I'm getting stuck. I assume the "token" in this case just has to be either an encrypted string that the client can decrypt or some random string that gets stored somewhere (i.e. a database) that the client can then verify against, but I'm not really sure what the client is then supposed to do with the token or why you even need a token at all -- couldn't a simple user ID also suffice?

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• Fun with casting and inheritance

  - by Vaccano

  NOTE: This question is written in a C# like pseudo code, but I am really going to ask which languages have a solution. Please don't get hung up on syntax. Say I have two classes: class AngleLabel: CustomLabel { public bool Bold; // code to allow the label to be on an angle } class Label: CustomLabel { public bool Bold; // Code for a normal label // Maybe has code not in an AngleLabel (align for example). } They both decend from this class: class CustomLabel: Control { protected bool Bold; } The bold field is exposed as public in the descended classes. No interfaces are available on the classes. Now, I have a method that I want to beable to pass in a CustomLabel and set the Bold property. Can this be done without having to 1) find out what the real class of the object is and 2) cast to that object and then 3) make seperate code for each variable of each label type to set bold. Kind of like this: public void SetBold(customLabel: CustomLabel) { AngleLabel angleLabel; NormalLabel normalLabel; if (angleLabel is AngleLabel ) { angleLabel= customLabel as AngleLabel angleLabel.Bold = true; } if (label is Label) { normalLabel = customLabel as Label normalLabel .Bold = true; } } It would be nice to maybe make one cast and and then set bold on one variable. What I was musing about was to make a fourth class that just exposes the bold variable and cast my custom label to that class. Would that work? If so, which languages would it work for? (This example is drawn from an old version of Delphi (Delphi 5)). I don't know if it would work for that language, (I still need to try it out) but I am curious if it would work for C++, C# or Java. If not, any ideas on what would work? (Remember no interfaces are provided and I can not modify the classes.) Any one have a guess?

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• Big-O for calculating all routes from GPS data

  - by HH

  A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is the amount of neighbour vertices. Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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• Color blindness: Are you aware of it? Do you design for it?

  - by User

  I'm curious whether many of us who do design or take design decisions have ever heard of this problem. I'm aware there are dangerous color combinations, like green + red. This is probably one of the most popular cases of color blindness. If you have green text on a red background and vice versa some people won't see anything. I've also seen in practice that green text on a blue background was not seen by one guy. What other color compositions should be avoided, and how often these cases are to be expected? Let us make some ranging by encounter probability who has the numbers. Addition: I've just remembered one very bad example that causes problems to just about everyone - blue text on a black background. It's unreadable for all intents and purposes. Never could understand what could possibly compel a web master to use this color combination...

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• SQL only row mapping record fetching

  - by Prasanna

  I have a customer call detail table in which call details of all customer stored. I have to find out the distinct aparty (means our customer ) who only calls our customers (means bparty also be our numbers) . There is no other domestic call , International calls made by A party (our customer) in this case. could you people please help me to find the same data. FILE INPUT oF SAMPLE CDR TABLE ROW NAME VALUES ANUMBER :-any mobile number(Domestic+International); for our customer it must like 70,070,0070,9370) BNUMBER :-any mobile number(Domestic+International); for our customer it must like 70,070,0070,9370 CALLTRANSACTION :-eg: 91,92,93 etc CALLTRANSACTIONTYPEC :-eg: MOC,MTC FILENAME :-MCS_01 etc TIME:- any time value Required Output DISTINCT ANUMBER :-for our customer it mobile number must start with 70 or 070 or 0070 or 9370 BNUMBER :- for our customer it mobile number must start with 70 or 070 or 0070 or 9370 means our customer only calls to our network customer ( No other doestic call or international calls made by our operator)

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• extension method phone format with country code as parameter

  - by frenchie

  Hi, I'm writing an extension method called ToPhoneFormat that formats a string of digits to phone numbers. Is it possible to add a parameter to the method that would enable me to call it like this: MyPhoneString.ToPhoneFormat(international code) That way, I could write MyPhoneString.ToPhoneFormat(1); to format a US phone number and MyPhoneString.ToPhoneFormat(33) to format a French phone number. I already wrote the method that does the formatting but I'm wondering how to build the constructor so that it works with a parameter when I'm calling it. Thanks.

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• What is the complexity of this specialized sort

  - by ADB

  I would like to know the complexity (as in O(...) ) of the following sorting algorithm: there are B barrels that contains a total of N elements, spread unevenly across the barrels. the elements in each barrel are already sorted The sort takes combines all the elements from each barrel in a single sorted list: using an array of size B to store the last sorted element of each barrel (starting at 0) check each barrel (at the last stored index) and find the smallest element copy the element in the final sorted array, increment array counter increment the last sorted element for the barrel we picked from perform those steps N times or in pseudo: for i from 0 to N smallest = MAX_ELEMENT foreach b in B if bIndex[b] < b.length && b[bIndex[b]] < smallest smallest_barrel = b smallest = b[bIndex[b]] result[i] = smallest bIndex[smallest_barrel] += 1 I thought that the complexity would be O(n), but the problem I have with finding the complexity is that if B grows, it has a larger impact than if N grows because it adds another round in the B loop. But maybe that has no effect on the complexity?

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• How to export data which are mapped to enumerations

  - by Joshua

  I have a set of data which needs to be imported from a excel sheet, lets take the simplest example. Note: the data might eventually support uploading any locale. e.g. assuming one of the fields denoting a user is gender mapped to an enumeration and stored in the database as 0 for male and 1 for female. 0 and 1 being short values. If I have to import the values I cannot expect the user to punch in numbers (since they are not intuitive and is cumbersome when the enumerations are bigger), what would be the correct way to map to enumerations. Should we ask them to provide a string value in these cases (e.g. male or female) and provide the transformation to a enum in our code by wring a method public static Gender Gender.fromString(String value)

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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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• How efficient is an if statement compared to a test that doesn't use an if? (C++)

  - by Keand64

  I need a program to get the smaller of two numbers, and I'm wondering if using a standard "if x is less than y" int a, b, low; if (a < b) low = a; else low = a; is more or less efficient than this: int a, b, low; low = b + ((a - b) & ((a - b) >> 31)); (or the variation of putting int delta = a - b at the top and rerplacing instances of a - b with that). I'm just wondering which one of these would be more efficient (or if the difference is to miniscule to be relevant), and the efficiency of if-else statements versus alternatives in general.

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• How can I retrieve the value of a PASTE (copy-pasta) event in a GWT TextBox?

  - by dominicbri7

  Hello fellow SO members, I want to prevent the user from copy-pasting values in my TextBox IF AND ONLY IF the values do not respect a certain condition. For instance, I created a DigitsOnlyTextBox which will be used for phone numbers. I already made it so only Character.isDigit characters can be typed into the box, and the user cannot copy-paste values into it, using : this.sinkEvents(Event.ONPASTE); and public void onBrowserEvent(Event event) { super.onBrowserEvent(event); // Permet d'empêcher le copier-coller, donc d'entrer des caractères non-numériques if (event.getTypeInt() == Event.ONPASTE) { event.stopPropagation(); event.preventDefault(); } } But I'd like to verify if the copy-pasted String is "digits only" and if so, let the event happen (therefore the text added). tl;dr : see title Thank you for your time. Sincerely.

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• How do I select a fixed number of rows for each group?

  - by Maiasaura

  Here is some example data in a mysql table a b distance 15 44 250 94 31 250 30 41 250 6 1 250 95 18 250 72 84 500 14 23 500 55 24 500 95 8 500 59 25 500 40 73 500 65 85 500 32 50 500 31 39 500 22 25 500 37 11 750 98 39 750 15 57 750 9 22 750 14 44 750 69 22 750 62 50 750 89 35 750 67 65 750 74 37 750 52 36 750 66 53 750 82 74 1000 79 22 1000 98 41 1000 How do I query this table such that I get 2 rows per distance selected at random? A successful query will produce something like a b distance 30 41 250 95 18 250 59 25 500 65 85 500 15 57 750 89 35 750 79 22 1000 98 41 1000

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• Threading calls to web service in a web service - (.net 2.0)

  - by Ryan Ternier

  Got a question regarding best practices for doing parallel web service calls, in a web service. Our portal will get a message, split that message into 2 messages, and then do 2 calls to our broker. These need to be on separate threads to lower the timeout. One solution is to do something similar to (pseudo code): XmlNode DNode = GetaGetDemoNodeSomehow(); XmlNode ENode = GetAGetElNodeSomehow(); XmlNode elResponse; XmlNode demResponse; Thread dThread = new Thread(delegate { //Web Service Call GetDemographics d = new GetDemographics(); demResponse = d.HIALRequest(DNode); }); Thread eThread = new Thread(delegate { //Web Service Call GetEligibility ge = new GetEligibility(); elResponse = ge.HIALRequest(ENode); }); dThread.Start(); eThread.Start(); dThread.Join(); eThread.Join(); //combine the resulting XML and return it. //Maybe throw a bit of logging in to make architecture happy Another option we thought of is to create a worker class, and pass it the service information and have it execute. This would allow us to have a bit more control over what is going on, but could add additional overhead. Another option brought up would be 2 asynchronous calls and manage the returns through a loop. When the calls are completed (success or error) the loop picks it up and ends. The portal service will be called about 50,000 times a day. I don't want to gold plate this sucker. I'm looking for something light weight. The services that are being called on the broker do have time out limits set, and are already heavily logged and audited, so I'm not worried on that part. This is .NET 2.0 , and as much as I would love to upgrade I can't right now. So please leave all the goodies of 2.0 out please.

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