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• why IEEE floating point number calculate exponent using a biased form?

  - by lenatis

  let's say, for the float type in c, according to the IEEE floating point specification, there are 8-bit used for the fraction filed, and it is calculated as first taken these 8-bit and translated it into an unsigned number, and then minus the BIASE, which is 2^7 - 1 = 127, and the result is an exponent ranges from -127 to 128, inclusive. But why can't we just treat these 8-bit pattern as a signed number, since the resulting range is [-128,127], which is almost the same as the previous one.

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• How do I construct a 3D model of a room from 2 stereo cameras? What is the determining factor to an

  - by yasumi

  Currently, I have extracted depth points to construct a 3D model from 2 stereo cameras. The methods I have used are openCV graphCut method and a software from http://sourceforge.net/projects/reconststereo/. However, the generated 3D models are not very accurate, which leads me to question: 1) What is the problem with pixel-based method? 2) Should I change my pixel-based method to feature-based or object-recognition-based method? Is there a best method? 3) Are there any other ways to do such reconstruction? Additionally, the depth extracted comes only from 2 images. What if I am turning the camera 360 degrees to obtain a video? Looking forward to suggestion on how to combine this depth information. Thank you very much :)

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• Optimally place a pie slice in a rectangle.

  - by Lisa

  Given a rectangle (w, h) and a pie slice with start angle and end angle, how can I place the slice optimally in the rectangle so that it fills the room best (from an optical point of view, not mathematically speaking)? I'm currently placing the pie slice's center in the center of the rectangle and use the half of the smaller of both rectangle sides as the radius. This leaves plenty of room for certain configurations. Examples to make clear what I'm after, based on the precondition that the slice is drawn like a unit circle: A start angle of 0 and an end angle of PI would lead to a filled lower half of the rectangle and an empty upper half. A good solution here would be to move the center up by 1/4*h. A start angle of 0 and an end angle of PI/2 would lead to a filled bottom right quarter of the rectangle. A good solution here would be to move the center point to the top left of the rectangle and to set the radius to the smaller of both rectangle sides. This is fairly easy for the cases I've sketched but it becomes complicated when the start and end angles are arbitrary. I am searching for an algorithm which determines center of the slice and radius in a way that fills the rectangle best. Pseudo code would be great since I'm not a big mathematician.

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• How to create a bookmark under "computer" in the Sidebar of the nautilus file manager in 12.04?

  - by Jiskya

  Somehow, I removed the Downloads bookmark in the Sidebar under "Computer". Is there any way I can make a new one? Possibly with the same icon? I still have my Downloads directory. I just don't have the bookmark under "Computer" anymore, and it has the ordinary folder icon. I know it's not the most significant question, but it's a question nonetheless. Also, I'm not sure, but it may be important to note that I'm using unity 2d.

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• does it make sense to send password information during email communication from websites

  - by Samuel

  Most of the online sites on registration do send a link to activate the site and on any further correspondence with the end user they provide information about the site and also provide the login credentials with password in clear text (as given below) Username - [email protected] Password - mysecretpassword What would you do in such a case? From a usability perspective does it make sense to send the password information in clear text or should you just avoid sending this information. I was under the impression that most of the passwords are MD5 hashed before storing in the database and hence the service provider will not have any access to clear text passwords, is this a security violation?

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• O(log N) == O(1) - Why not?

  - by phoku

  Whenever I consider algorithms/data structures I tend to replace the log(N) parts by constants. Oh, I know log(N) diverges - but does it matter in real world applications? log(infinity) < 100 for all practical purposes. I am really curious for real world examples where this doesn't hold. To clarify: I understand O(f(N)) I am curious about real world examples where the asymptotic behaviour matters more than the constants of the actual performance. If log(N) can be replaced by a constant it still can be replaced by a constant in O( N log N). This question is for the sake of (a) entertainment and (b) to gather arguments to use if I run (again) into a controversy about the performance of a design.

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• The risk of granting to IUSR* NTFS permissions on a folder on the server

  - by vtortola

  I have two web applications that must share a file in the server file system. Both apps are inside of "Inetpub\wwwroot". The file cannot be accessed freely from outside, so it is in a folder out of "Inetpub". I have granted full NTFS permissions to the user "IUSR_whatever" (is the user that runs IIS in anonymous requests) in that folder. The folder has only that file, and has no other use. It works so far :) But, what is the risk? what should I be afraid of? As I see it, as long the folder is out of the "InetPub" cannot be accessed, and as long the apps don't have any security flaw like "path traversal" or server side code injection, it should be safe enough.... But I'm always keen to be wrong :) What do you think? May the file or even the server itself get compromised because of this? Thanks.

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• WYSIWYG-editor with "add custom html feature" and secure (validated) html output?

  - by Tom

  I've been looking into some of the WYSIWYG editors (TinyMCE, FCKEditor, etc.) and they all seem to offer a lot of options. However, one vital feature that seems to lack is a simple "add custom html" option which would allow the user to input any of these embed-snippets you find all around the web these days, for example a youtube video. This is different than a "edit html/source" feature as that requires actual knowledge of html and there is the risk of the user writing invalid code. Another issue that I couldn't find much about is the output html. How would I make sure that this output causes no security invulnerabilities? Even when the user has the ability to add his own html? So, basically, is there an open source WYSIWYG editor which covers these 2 features?

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• Three most critical programming concepts

  - by Todd

  I know this has probably been asked in one form or fashion but I wanted to pose it once again within the context of my situation (and probably others here @ SO). I made a career change to Software Engineering some time ago without having an undergrad or grad degree in CS. I've supplemented my undergrad and grad studies in business with programming courses (VB, Java,C, C#) but never performed academic coursework in the other related disciplines (algorithms, design patterns, discrete math, etc.)...just mostly self-study. I know there are several of you who have either performed interviews and/or made hiring decisions. Given recent trends in demand, what would you say are the three most essential Comp Sci concepts that a developer should have a solid grasp of outside of language syntax? For example, I've seen blog posts of the "Absolute minimum X that every programmer must know" variety...that's what I'm looking for. Again if it's truly a redundancy please feel free to close; my feelings won't be hurt. (Closest ones I could find were http://stackoverflow.com/questions/164048/basic-programming-algorithmic-concepts- which was geared towards a true beginner, and http://stackoverflow.com/questions/648595/essential-areas-of-knowledge-which I didn't feel was concrete enough). Thanks in advance all! T.

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• Standard term for a thread I/O reorder buffer?

  - by Crashworks

  I have a case where many threads all concurrently generate data that is ultimately written to one long, serial file. I need to somehow serialize these writes so that the file gets written in the right order. ie, I have an input queue of 2048 jobs j0..jn, each of which produces a chunk of data oi. The jobs run in parallel on, say, eight threads, but the output blocks have to appear in the file in the same order as the corresponding input blocks — the output file has to be in the order o0o1o2... The solution to this is pretty self evident: I need some kind of buffer that accumulates and writes the output blocks in the correct order, similar to a CPU reorder buffer in Tomasulo's algorithm, or to the way that TCP reassembles out-of-order packets before passing them to the application layer. Before I go code it, I'd like to do a quick literature search to see if there are any papers that have solved this problem in a particularly clever or efficient way, since I have severe realtime and memory constraints. I can't seem to find any papers describing this though; a Scholar search on every permutation of [threads, concurrent, reorder buffer, reassembly, io, serialize] hasn't yielded anything useful. I feel like I must just not be searching the right terms. Is there a common academic name or keyword for this kind of pattern that I can search on?

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• Sending passwords over the web

  - by Falmarri

  So I'm working on a mobile platform application that I'd like to have users authenticate over the web. I was wondering the best way to do security. The user is sending a password for HTTP to a php server wich authenticates against a mysql database on the same server. Obviously I don't want to send the password in plain text over the internet, but I also don't want to do 2 SHA hashes. This is what the server looks like (in pseudocode) $pass = $_POST['pass']; if ((get PASSWORD where USERNAME = USERNAME) == SHA($pass)) return PASS; This is pretty standard and I don't think there's any other way to do this. But I was wondering how I should prepare the data before sending it over the internet.

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• URIs vs Hidden Forms

  - by NateDogg

  I'm working in the Codeigniter framework, and want to send requests to my controller/model that have several variables involved. Is there a difference between passing those variables via a hidden form (i.e. using "post") as opposed to passing them through URIs (e.g. 'travel/$month/$day/')? What about security concerns? e.g. URIs: http://www.example.com/travel/$month/$day/ Hidden Form: form_hidden('month',$month); form_hidden('day',$day);

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• Convert a post-order binary tree traversal index to an level-order (breadth-first) index

  - by strfry

  Assuming a complete binary tree, each node can be adressed with the position it appears in a given tree traversal algorithm. For example, the node indices of a simple complete tree with height 3 would look like this: breadth first (aka level-order): 0 / \ 1 2 / \ / \ 3 4 5 6 post-order dept first: 6 / \ 2 5 / \ / \ 0 1 3 4 The height of the tree and an index in the post-order traversal is given. How can i calculate the breadth first index from this information?

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• How is a Gaussian filter used to determine scale at a pixel?

  - by guy

  How is a Gaussian filter used to determine scale at a pixel? cheers in advance

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• Track Pedestrians

  - by 2vision2

  I am using OpenCV sample code “peopledetect.cpp” to detect and track pedestrians. The code uses HoG for feature extraction and SVM for classification. Please find the reference paper used here. The camera is mounted on the wall at a height of 10 feet and 45 degree down. There is no restriction on the pedestrian movement within the frame. I want to track the detected pedestrians’ movement within the frame. The issue I am facing is pedestrians are detected only in the middle region of the frame as most of the features are not visible as soon as the pedestrian enters the frame region. I want to track each person’s movement in the entire frame region. How to do it? Is tracking required? Can anyone give any reference to blogs/codes?

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• I'm trying to implement 2 factor authentication on the cheap. How would I do that?

  - by Biff MaGriff

  Ok so I need 2 of the 3. Something the user knows. Something the user has. Something the user is. I have a system that is exposed to the internet and we need clients to connect in a secure manner to satisfy our security standards. I'm thinking when a user registers to use our system we send them an application that they install on their home system. The application generates a key based on a timed randomness algorithm. Our application server has the same algorithm so when the user submits their credentials with the key we know that they are a legitimate user. Is this a valid method of 2 factor authentication? What is another way of doing this? Are there any pitfalls that I should be aware of? Thanks for your help!

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• MD5 password twice

  - by NoviceCoding

  I know MD5's safety is under question lately and this is the reason a lot of people are using salt (I dont understand this at all btw) but I was wondering if you wanted to easily implement a safe system in php can you just md5 something twice? like test 098f6bcd4621d373cade4e832627b4f6 fb469d7ef430b0baf0cab6c436e70375 So basically: $val = 'test'; $val = md5($val); $val = md5($val); Would that solve the whole rainbow security stuff? Is there an easy/noob proof way of making secure database passwords in php?

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• Securing an ajax request

  - by asdasdsa

  i have a website that uses session cookies for security. it works fine and all, but any ajax requests right now are not secure. example being lets say a user is on a page. they can only get to this page if they are logged in with a session - so far so good. but now the ajax request they ask for is ajaxpages/somepage.php?somevar=something&anothervar=something if any other user decides to just go to that link themselves (without a session) they still get the same ajax output that was meant for logged in people. so obviously im going to have to pass session data across when i send an ajax request. anyone have any tips for the best way of doing this? ive never done this before and would rather use trusted methods than make up my own.

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• Sql server execute permission; failure to apply permissions

  - by WestDiscGolf

  I've just migrated from SQL2000 to SQL2008 and I have started getting an execute permission issue on a stored proc which uses sp_OACreate. The rest of the system works fine with the db login which has been setup and added to the database. I've tried: USE master GO GRANT EXEC ON sp_OACreate TO [dbuser] GO But this fails with the following error: Msg 15151, Level 16, State 1, Line 1 Cannot find the user 'dbuser', because it does not exist or you do not have permission. I'm logged into the server as sa with full permissions. I can execute a similar sql statement and apply the permissions to a server role, however not a login/user. How do I apply the changes to the specific user/login? I can apply the permissions to the public role and it resolves my issue; however this seems to be a security issue to me which I don't really want to apply to the live server.

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• Regarding Standard Oxford Format for vlfeat sift

  - by Karl

  One of my upper classmen has gave me a data set for experimenting with vlfeat's SIFT, however, her extracted SIFT data for the frame part contains 5 dimensions. Recall from vl_sift function: [F,D] = VL_SIFT(I) Each column of D is the descriptor of the corresponding frame in F. F normally contains 4 dimensions which consists of x-coordinate, y-coordinate, scale, and orientation. So I asked her what is this 5th dimension, and she pointed me to search for "standard oxford format" for sift feature. The thing is I tried to search around regarding this standard oxford format and sift feature, but I got no luck in finding it at all. If somebody knows regarding this, could you please point me to the right direction?

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• CS Majors: Hardest concept(s) you learned in school?

  - by Mark Lubin

  For the CS majors out there what were the hardest CS classes or concepts that you learned in your undergraduate schooling? Did you find once you learned the basics,(data structs, OOP fundamentals, discrete math, pointers, recursion, etc) the rest followed naturally or did you hit a wall at any point in your higher classes like OS'es and Compilers? Thanks for the input!

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• How long can a hash left out in the open be considered safe?

  - by Xeoncross

  If I were to leave a SHA2 family hash out on my website - how long would it be considered safe? How long would I have before I could be sure that someone would find a collision for it and know what was hashed? I know that the amount of time would be based on the computational power of the one seeking to break it. It would also depend on the string length, but I'm curious just how secure hashes are. Since many of us run web-servers we constantly have to be prepared for the day when someone might make it all the way to the database which stores the user hashes. So, move the server security out of the way and then what do you have? This is a slightly theoretical area for many of the people I have talked with, so I would love to actually have some more information about average expectations for cracking.

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• SQLAuthority News Were sorry but your computer or network may be sending automated queries. To pro

  I use multiple browser many times when I am working with multiple projects simultaneously. Often I use Google Reader to read few feeds. Recently, I faced the following error and this error will not go. I even restarted my computer and rebooted my network. I am confident that my computer does not have viruses or [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Secure to store an ID in an ASP.NET control ID?

  - by Curtis White

  I'm auto-generating a form in my ASP.NET page. This is already tested and working. I want to know if: If there are any security problems with storing the database ID as part of my controls ID? I can see think of 2 issues: the id will be visible in page source (not really important in this case), and the possibility someone could change the name of the control somehow? This second possibility is more serious. Is this a potential problem and how to void it? If there would be a better preferred way to associate a unique data with any type of control? Is it possible to store a custom item in the viewstate for the control?

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• Can Spring access-denied-handler refer to popup?

  - by Rens Groenveld

  I am working with Spring Security 3.1.x and have implemented method annotation securities. As I want, when I perform a certain action while being logged in as a used that doesn't have the rights, I get a 403 acces is denied in my console! Perfect! Now I would like to catch this 403, and give the user a popup with a custom message. I don't want to redirect users to a page saying that they have no rights. Is there any way the access-denied-handler of Spring can take care of a popup? Or can it only redirect to another page? Maybe there are other options for me? Thanks in advance!

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