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• How to go about signing text in a verifiable way from within ruby in a simple yet strong & portable

  - by roja

  Guys, I have been looking for a portable method to digitally sign arbitrary text which can be placed in a document and distributed while maintaining its verifiable origin. Here is an example: a = 'some text' a.sign(<private key>) # => <some signature in ASCII format> The contents of a can now be distributed freely. If a receiver wants to check the validity of said text they can do the following: b = 'some text' b.valid(<public key>, <signature supplied with text>) # => true/false Is there any library out there that already offers this kind of functionality? Ruby standard library contains SHA hashing code so at lest there is a portable way to perform the hashing but from that point I am struggling to find anything which fits purpose. Kind Regards, Roja

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• Why do virtual memory addresses for linux binaries start at 0x8048000?

  - by muteW

  Disassembling an ELF binary on a Ubuntu x86 system I couldn't help but notice that the code(.text) section starts from the virtual address 0x8048000 and all lower memory addresses seem to be unused. This seems to be rather wasteful and all Google turns up is either folklore involving STACK_TOP or protection against null-pointer dereferences. The latter case looks like it can be fixed by using a single page instead of leaving a 128MB gap. So my question is this - is there a definitive answer to why the layout has been fixed to these values or is it just an arbitrary choice?

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• How to write a value validation method for core data?

  - by mystify

  The docs say: you should implement methods of the form validate:error:, as defined by the NSKeyValueCoding protocol so lets say I have an attribute which is an int: friendAge I want to make sure that any friend may not be younger than 30. So how would I make that validation method? -validateFriendAge:error: What am I gonna do in there, exactly? And what shall I do with that NSError I get passed? I think it has an dictionary where I can return a humanly readable string in an arbitrary language (i.e. the one that's used currently), so I can output a reasonable error like: "Friend is not old enough"... how to do that?

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• How do I arbitrarily reorder lines in a text file using a Unix shell?

  - by Tim Bellis

  I've got a text file with an arbitrary number of lines, e.g.: one line some other line an additional line one more here I'd like to write a script to reorder those lines based on a given order. e.g. An input of 2 1 3 4 would swap the first and second lines. An input of 3 1 2 4 would put the 3rd line first, the 1st line second, the 2nd line third and keep the 4th line fourth. I could hack something together, but I'm wondering if there's an elegant solution? I can use either bash or ksh.

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• Right-click on a Listbox in a Silverlight 4 app.

  - by AngryHacker

  I am trying to implement what I used to take for granted in Winforms applications. I am a Silverlight noob, so hopefully all this is elementary. I have a listbox in a Silverlight 4 app. I'd like to do the following: Right-click on the listbox Have the item under the location where I click highlight itself I'd like a context menu to popup (with my own items in the context menu) From my research so far, it appears that there is no ContextMenu construct in Silverlight, instead we have to build up a Grid/Canvas structure and attach it to a Popup object, which is what is then popped up. My questions are as follows: To accomplish #2, I need some kind of hit test on the listbox. I can't figure out how to do that and my google-fu isn't helping. Once I do identify the index under the mouse, how do I actually select the item? Is there a reusable Context menu component somewhere that I can use? Extra credit if the component allows arbitrary sub-menus.

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• Can Visual Studio Express run from USB drive?

  - by system PAUSE

  Using an arbitrary Windows machine (2000/XP or later), I can install Eclipse CDT to a USB drive move that USB drive onto a different Windows machine--one that does not have any form of Eclipse software already installed, and potentially a different version of Windows (but 2000/XP or later) use Eclipse to develop application-level C/C++ programs on that second machine (and that includes using the debugger), running directly from the USB drive without copying anything to C:. I can do all this without having Administrator privileges on either machine. I can do the same with NetBeans, and with several other IDEs that support C/C++ development. Is it possible to do this with any version of Visual Studio Express? If not, can you explain the technical reason(s) this doesn't work?

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• php and XML range into array

  - by Mike

  The code below helps be to get the WHOLE XML and put it into an array. What I'm wondering is, what would be a good way to get the XML only from item 3 - 6 or any arbitrary range instead of the whole document. $mt_arr = array(); $d = new DOMDocument(); $d->load('http://news.google.com/?output=rss'); foreach ($d->getElementsByTagName('item') as $t) { $list = array ( 'title' => $t->getElementsByTagName('title')->item(0)->nodeValue); array_push($mt_arr, $list); } Thanks

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• Securely using exec with PHP to run ffmpeg

  - by Venkat D.

  I would like to run ffmpeg from PHP for video encoding purposes. I was thinking of using the exec or passthru commands. However, I have been warned that enabling these functions is a security risk. In the words of my support staff: The directive 'disable_functions' is used to disable any functions that allow the execution of system commands. This is for more security of the server. These PHP functions can be used to crack the server if not used properly. I'm guessing that if exec is enabled, then someone could (possibly) execute an arbitrary unix command. Does anyone know of a secure way to run ffmpeg from PHP? By the way, I'm on a dedicated server. Thanks ahead of time!

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• How to detect if breaking an edge will make a graph disjoint?

  - by the_graph_guy

  I have a graph that starts off with a single, root node. Nodes are added one by one to the graph. At node creation time, they have to be linked either to the root node, or to another node, by a single edge. Edges can also be created and deleted (one by one, between any two nodes). Nodes can be deleted one at a time. Node and edge creation, deletion operations can happen in any arbitrary order. OK, so here's my question: When an edge is deleted, is it possible do determine, in constant time (i.e. with an O(1) algorithm), if doing this will divide the graph into two disjoint subgraphs? If it will, then which side of the edge will the root node belong? I'm willing to maintain, within reasonable limits, any additional data structure that can facilitate the derivation of this information. Maybe it is not possible to do it in O(1), if so any pointers to literature will be appreciated.

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• python: find and replace numbers < 1 in text file

  - by hjp

  I'm pretty new to Python programming and would appreciate some help to a problem I have... Basically I have multiple text files which contain velocity values as such: 0.259515E+03 0.235095E+03 0.208262E+03 0.230223E+03 0.267333E+03 0.217889E+03 0.156233E+03 0.144876E+03 0.136187E+03 0.137865E+00 etc for many lines... What I need to do is convert all the values in the text file that are less than 1 (e.g. 0.137865E+00 above) to an arbitrary value of 0.100000E+01. While it seems pretty simple to replace specific values with the 'replace()' method and a while loop, how do you do this if you want to replace a range? thanks

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• jQuery .ajax request failing

  - by user1644808

  I currently have a jQuery ajax request set up like this $(document).ready( function() { $.ajax({ url : "http://www.my-computer.com:51000/getJson", cache : false, dataType: "json", success : renderPage, error: handleError }) }); If I manually naviate to http://www.my-computer.com:51000/getJson, I see it returns a json string correctly, but with the above request, I always fall into "handleError" method, with textStatus "error" and not much helpful information. Can anyone help? Thanks! EDIT: sorry about the my-computer domain. this stackoverflow submission won't let me input localhost, so I put in an arbitrary domain instead. I've tried firebug, but had no luck in getting the json back.

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• Centre of a circle that intersects two points

  - by Jason

  Given two points in a 2D plane, and a circle of radius r that intersects both of those points, what would be the formula to calculate the centre of that circle? I realise there would two places the circle can be positioned. I would want the circle whose centre is encountered first in a clockwise direction when sweeping the line that joins the two points around one of those points, starting from an arbitrary angle. I guess that is the next stage in my problem, after I find an answer for the first part. I'm hoping the whole calculation can be done without trigonometry for speed. I'm starting with integer coordinates and will end with integer coordinates, if that helps.

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• averaging matrix efficiently

  - by user248237

  in Python, given an n x p matrix, e.g. 4 x 4, how can I return a matrix that's 4 x 2 that simply averages the first two columns and the last two columns for all 4 rows of the matrix? e.g. given: a = array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]) return a matrix that has the average of a[:, 0] and a[:, 1] and the average of a[:, 2] and a[:, 3]. I want this to work for an arbitrary matrix of n x p assuming that the number of columns I am averaging of n is obviously evenly divisible by n. let me clarify: for each row, I want to take the average of the first two columns, then the average of the last two columns. So it would be: 1 + 2 / 2, 3 + 4 / 2 <- row 1 of new matrix 5 + 6 / 2, 7 + 8 / 2 <- row 2 of new matrix, etc. which should yield a 4 by 2 matrix rather than 4 x 4. thanks.

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• Referencing invalid memory locations with C++ Iterators

  - by themoondothshine

  I am a big fan of GCC, but recently I noticed a vague anomaly. Using __gnu_cxx::__normal_iterator (ie, the most common iterator type used in libstdc++, the C++ STL) it is possible to refer to an arbitrary memory location and even change its value without causing an exception! Is this expected behavior? If so, isn't a security loophole? Here's an example: #include <iostream> using namespace std; int main() { basic_string<char> str("Hello world!"); basic_string<char>::iterator iter = str.end(); iter += str.capacity() + 99999; *iter = 'x'; cout << "Value: " << *iter << endl; }

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• how to find out if a shape is passable

  - by jd

  I have a complex polygon (possibly concave) and a few of its edges marked as entry/exit points. there is a possibility that inside this polygon may lie one or more blockades of arbitrary shape. what approaches could I use to determine whether a path of certain width exists between a pair of entry/exit edges? having read through the question it looks like a homework type - it is not. I just wish to have a at least a few leads I could pursue, as this is new to me.

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• Is correct name enough to make it happen?

  - by Knowing me knowing you

  Guys, I've just dipped in to limits.h by MS. I tried to check what's the return type for max() fnc and to my surprise I see something like this: // TEMPLATE CLASS numeric_limits template<class _Ty> class numeric_limits : public _Num_base { // numeric limits for arbitrary type _Ty (say little or nothing) public: static _Ty (__CRTDECL min)() _THROW0() { // return minimum value return (_Ty(0)); } static _Ty (__CRTDECL max)() _THROW0() { // return maximum value return (_Ty(0));//EXACTLY THE SAME WHAT IN min<<------------------ } //... other stuff }; so how is it possiple that in both min and max return does exactly the same? So does it mean if I would write makeSanwich() return (_Ty(0)) it would make a sandwich for me? How is it possible that having this same code just fnc names different we are getting different results?

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• multitreading scheduling related java

  - by vichi

  class A implements Runnable{ B b=new B(); public void run(){ while(true){ System.out.println("H1"+Thread.currentThread().getName()); } } } public class Test { public static void main(String[] str){ A a1 =new A(); // A a2 =new A(); // Thread t1 =new Thread(a1, "Vichi"); Thread t2 =new Thread(a1,"Vishu"); t1.start(); t2.start(); } } what will be the ans: 1) only one of them will get the chance to execute 2) both will get chance in arbitrary manner please suggest possible ans with explations

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• Best way to have unique key over 500M varchar(255) records in mysql/innodb?

  - by taw

  I have url column with unique key over it - but its performance on updates is absolutely atrocious. I suspect that's because the index doesn't all fit in memory. So I was thinking, how about adding a column of md5(url) with 16 bytes of binary data and unique-keying that instead. What would be the best datatype for that? I'd love to be able to just see 32-character hex hash, while mysql would convert it to/from 16 binary bytes and index that, as programs using the database might have some troubles with arbitrary binary data that I'd rather avoid if possible (also I'm a bit afraid that mysql might get some strange ideas about character sets and for example overalocating storage for that by 3:1 because it thinks it might need utf8, how do I avoid that for cure?).

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• Is there a way to set the value of $? in a mock in Ruby?

  - by rleber

  I am testing some scripts that interface with system commands. Their logic depends on the return code of the system commands, i.e. the value of $?. So, as a simplified example, the script might say: def foo(command) output=`#{command}` if $?==0 'succeeded' else 'failed' end end In order to be able to test these methods properly, I would like to be able to stub out the Kernel backquote call, and set $? to an arbitrary value, to see if I get appropriate behavior from the logic in the method after the backquote call. I can't figure out a way to do this. (In case it matters, I'm testing using Test::Unit and Mocha.)

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• transform file/directory structure into 'tree' in javascript

  - by dave

  I have an array of objects that looks like this: [{ name: 'test', size: 0, type: 'directory', path: '/storage/test' }, { name: 'asdf', size: 170, type: 'directory', path: '/storage/test/asdf' }, { name: '2.txt', size: 0, type: 'file', path: '/storage/test/asdf/2.txt' }] There could be any number of arbitrary path's, this is the result of iterating through files and folders within a directory. What I'm trying to do is determine the 'root' node of these. Ultimately, this will be stored in mongodb and use materialized path to determine it's relationships. In this example, /storage/test is a root with no parent. /storage/test/asdf has the parent of /storage/test which is the parent to /storage/test/asdf/2.txt. My question is, how would you go about iterating through this array, to determine the parent's and associated children? Any help in the right direction would be great! Thank you

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• How to save an order (permutation) in an sql db

  - by Bendlas

  I have a tree structure in an sql table like so: CREATE TABLE containers ( container_id serial NOT NULL PRIMARY KEY, parent integer REFERENCES containers (container_id)) Now i want to define an ordering between nodes with the same parent. I Have thought of adding a node_index column, to ORDER BY, but that seem suboptimal, since that involves modifying the index of a lot of nodes when modifying the stucture. That could include adding, removing, reordering or moving nodes from some subtree to another. Is there a sql datatype for an ordered sequence, or an efficient way to emulate one? Doesn't need to be fully standard sql, I just need a solution for mssql and hopefully postgresql EDIT To make it clear, the ordering is arbitrary. Actually, the user will be able to drag'n'drop tree nodes in the GUI

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• Multiple Linked List in C

  - by LuckySlevin

  I have a problem about Linked Lists. I already know how to create structures and linked list. But now I have to create arbitrary number of linked list which are also be kept in another structure. Which means : struct list{int x, struct list *next; }; struct parent{int x, struct list *head, struct parent *next;} And after lists are created when i enter this input for example "123134 linked list should look like : 1 - 2 - 3 - 4 And for example 1 will contain 2-3 list inside of it, 3 will contain 1-4 list inside of it. I need a starting point and a spark from you. So how can i do this?

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• Extract substructure from a text file using bash or python

  - by Werner

  Hi, I have a huge text file, which follows the structure: SET TAG1 ... ... SET ... SET TAG2 ... ... SET ... ... I would like to extract for a specific TAG, (i.e. TAG54) its individual "substructure", which would be SET TAG54 ... ... SET Each substructure, for a given TAG_i contains always: first line:SET second line:TAG_i (in this case TAG54) an arbitrary number of lines last line:SET I wonder what would be the best way to do this, whether in bash or python, so for a given TAG, one can "extract" this substructure. Thanks

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• Loop through non-integer rows using SQL

  - by Jesse

  I know how to accomplish my task with .NET, but I wanted to do this just in SQL. I need to loop through all of the rows where the primary key is somewhat arbitrary. It can be a number or a series of letters, and probably any number of unusual things. I know I could do something like this... DECLARE @numRows INT SET @numRows = (SELECT COUNT(pkField) FROM myTable) DECLARE @I INT SET @I = 1 WHILE (@I <= @numRows) BEGIN --Do what I need to here SET @I = @I + 1 END ...if my rows were indexed in a contiguous fashion, but I don't know enough about SQL to do that if they're not. I keep coming across the use of "cursors," but I come across just as much reading about avoiding cursors. I found this SO solution but I'm not sure if that's what I'm needing? I appreciate any ideas.

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• How to schedule hundreds of thousands of tasks?

  - by wehriam

  We have hundreds of thousands of tasks that need to be run at a variety of arbitrary intervals, some every hour, some every day, and so on. The tasks are resource intensive and need to be distributed across many machines. Right now tasks are stored in a database with an "execute at this time" timestamp. To find tasks that need to be executed, we query the database for jobs that are due to be executed, then update the timestamps when the task is complete. Naturally this leads to a substantial write load on the database. As far as I can tell, we are looking for something to release tasks into a queue at a set interval. (Workers could then request tasks from that queue.) What is the best way to schedule recurring tasks at scale? For what it's worth we're largely using Python, although we have no problems using components (RabbitMQ?) written in other languages.

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