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  • Easiest way to find the correct kademlia bucket

    - by Martin
    In the Kademlia protocol node IDs are 160 bit numbers. Nodes are stored in buckets, bucket 0 stores all the nodes which have the same ID as this node except for the very last bit, bucket 1 stores all the nodes which have the same ID as this node except for the last 2 bits, and so on for all 160 buckets. What's the fastest way to find which bucket I should put a new node into? I have my buckets simply stored in an array, and need a method like so: Bucket[] buckets; //array with 160 items public Bucket GetBucket(Int160 myId, Int160 otherId) { //some stuff goes here } The obvious approach is to work down from the most significant bit, comparing bit by bit until I find a difference, I'm hoping there is a better approach based around clever bit twiddling. Practical note: My Int160 is stored in a byte array with 20 items, solutions which work well with that kind of structure will be preferred.

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  • Graph representation

    - by Carlucho
    Given graph, how could i represent it using adj matrix?. I have read lots of tutorials, post, slides, etc but i cant get my head round it, i just need that little push.

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  • Read from file hexadecimal number and change their representation style

    - by user576844
    I want to write a program changing the notation of all hexadecimal numbers found in an assembly source file from traditional (h) to C-style (0x). I have started the coding part but am not sure how can I detect the hexadecimal numbers and eventually change the style and save it back in the file... I have started writing the program.. ## Mips program - .data fin: .ascii "" # filename for input msg0: .asciiz "aaaa" msg1: .asciiz "Please enter the input file name:" buffer: .asciiz "" .text #----------------------- li $v0, 4 la $a0, msg1 syscall li $v0, 8 la $a0, fin li $a1, 21 syscall jal fileRead #read from file move $s1, $v0 #$t0 = total number of bytes li $t0, 0 # Loop counter loop: bge $t0, $s1, end #if end of file reached OR if there is an error in the file lb $t5, buffer($t0) #load next byte from file jal checkhexa #check for hexadecimal numbers addi $t0, $t0, 1 #increment loop counter j loop end: jal output jal fileClose li $v0, 10 syscall fileRead: # Open file for reading li $v0, 13 # system call for open file la $a0, fin # input file name li $a1, 0 # flag for reading li $a2, 0 # mode is ignored syscall # open a file move $s0, $v0 # save the file descriptor # reading from file just opened li $v0, 14 # system call for reading from file move $a0, $s0 # file descriptor la $a1, buffer # address of buffer from which to read li $a2, 100000 # hardcoded buffer length syscall # read from file jr $ra Any help would be appreciated.

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  • Generic Rails Route Representation?

    - by Flemish Bee Cycle
    Given one or more instances of a model (AR or DM, whatever). Is it possible to generate the route in the requirement form, by which I mean "/foos/:id" Given the route: resource :foo do resource :bar end generate_route_method [@foo,@bar] - "/foos/:id/bars/:id" I'm not talking about #foos_path or #polymorphic_path, rather, literally generating the string containing the wildcard components (i.e ":id"), the same as it would appear as if you did "rake routes".

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  • Efficient representation of Hierarchies in Hibernate.

    - by Alison G
    I'm having some trouble representing an object hierarchy in Hibernate. I've searched around, and haven't managed to find any examples doing this or similar - you have my apologies if this is a common question. I have two types which I'd like to persist using Hibernate: Groups and Items. * Groups are identified uniquely by a combination of their name and their parent. * The groups are arranged in a number of trees, such that every Group has zero or one parent Group. * Each Item can be a member of zero or more Groups. Ideally, I'd like a bi-directional relationship allowing me to get: * all Groups that an Item is a member of * all Items that are a member of a particular Group or its descendants. I also need to be able to traverse the Group tree from the top in order to display it on the UI. The basic object structure would ideally look like this: class Group { ... /** @return all items in this group and its descendants */ Set<Item> getAllItems() { ... } /** @return all direct children of this group */ Set<Group> getChildren() { ... } ... } class Item { ... /** @return all groups that this Item is a direct member of */ Set<Group> getGroups() { ... } ... } Originally, I had just made a simple bi-directional many-to-many relationship between Items and Groups, such that fetching all items in a group hierarchy required recursion down the tree, and fetching groups for an Item was a simple getter, i.e.: class Group { ... private Set<Item> items; private Set<Group> children; ... /** @return all items in this group and its descendants */ Set<Item> getAllItems() { Set<Item> allItems = new HashSet<Item>(); allItems.addAll(this.items); for(Group child : this.getChildren()) { allItems.addAll(child.getAllItems()); } return allItems; } /** @return all direct children of this group */ Set<Group> getChildren() { return this.children; } ... } class Item { ... private Set<Group> groups; /** @return all groups that this Item is a direct member of */ Set<Group> getGroups() { return this.groups; } ... } However, this resulted in multiple database requests to fetch the Items in a Group with many descendants, or for retrieving the entire Group tree to display in the UI. This seems very inefficient, especially with deeper, larger group trees. Is there a better or standard way of representing this relationship in Hibernate? Am I doing anything obviously wrong or stupid? My only other thought so far was this: Replace the group's id, parent and name fields with a unique "path" String which specifies the whole ancestry of a group, e.g.: /rootGroup /rootGroup/aChild /rootGroup/aChild/aGrandChild The join table between Groups and Items would then contain group_path and item_id. This immediately solves the two issues I was suffering previously: 1. The entire group hierarchy can be fetched from the database in a single query and reconstructed in-memory. 2. To retrieve all Items in a group or its descendants, we can select from group_item where group_path='N' or group_path like 'N/%' However, this seems to defeat the point of using Hibernate. All thoughts welcome!

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  • Typecast to a type from just the string representation of the type name

    - by Water Cooler v2
    sTypeName = ... //do some string stuff here to get the name of the type /* The Assembly.CreateInstance function returns a type of System.object. I want to type cast it to the type whose name is sTypeName. assembly.CreateInstance(sTypeName) So, in effect I want to do something like: */ assembly.CreateInstance(sTypeName) as Type.GetType(sTypeName); How do I do that? And, what do I take on the left side of the assignment expression, assuming this is C# 2.0. I don't have the var keyword.

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  • date representation in user interface

    - by Samuel
    Most of the sites capture the date (e.g. birth date) information as either a single entity (i.e via a calendar control) or instead as separate fields (date, month, year). Are there any benefits in showing them as separate fields? Are they represented in the database as DATE data type or as separate fields. I am just trying to understand the pros & cons of representing the date field.

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  • Debugging an XBAP application with 64-bit browser

    - by Anne Schuessler
    We have an XBAP application that fails when opened in Internet Explorer 8 64 bit. We only get a pretty generic error which makes it hard to determine where the error is coming from. I'm trying to find a way to debug the application with IE 8 64 bit, but I haven't figured out how to do this. I can't set the 64 bit version as the standard browser and overwriting the browser path in the browsers.xml for Visual Studio doesn't work as well. It just gets overwritten as soon as I hit F5 to debug to point to the 32 bit IE. I have figured out how to start the application from Debug with the 64 bit browser by changing the Debug options from "Start browser with URL" to "Start external program" and setting the command line arguments to point to the bin folder. Unfortunately then the XBAP is looking for its config.deploy file which doesn't seem to be generated during regular debug. This doesn't happen when using "Start browser with URL" and the application doesn't seem to care for this file then. Does anybody know why there's a difference between "Start browser with URL" and "Start external program" in the Debug options which might cause this difference in behavior when Debug is started? Also, does anybody know how to successfully debug an XBAP with a 64-bit browser?

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  • 32/64 bit problems with Eclipse CDT on Ubuntu

    - by waffleShirt
    I have just recently started running Linux on my PC and I am trying to start learning OpenGL. I am using the latest version of Eclipse CDT as my IDE, and my system is Ubuntu 10.10, 64 bit version. The problem I am having is that whenever I try to run a build from within the IDE I get the error message "Launch Failed. Binary Not Found." Ive done a lot of looking around on the internet but I still cant solve the problem. I know for a fact that the binary is built, it can be run from a terminal window. According to posts I have seen the problem is that Eclipse tries to run a 32 bit binary, but GCC 4.4.5 defaults to 64 bit binaries on a 64 bit system. Ive seen a lot of information about using the -m32 flag in makefiles, but then I still get the following output in Eclipse: make all g++ -o HelloWorld2 main.o /usr/bin/ld: i386 architecture of input file `main.o' is incompatible with i386:x86-64 output /usr/bin/ld: final link failed: Invalid operation collect2: ld returned 1 exit status make: *** [HelloWorld2] Error 1 What I would like to know is how to either get Eclipse to launch the 64 bit binaries, or have Eclipse correctly compile 32 bit binaries.

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  • Given a Member Access lambda expression, convert it to a specific string representation with full ac

    - by Nathan
    Given an Expression<Func<T, object>> (e.g. x = x.Prop1.SubProp), I want to create a string "Prop1.SubProp" for as deep as necessary. In the case of a single access (e.g. x = x.Prop1), I can easily do this with: MemberExpression body = (expression.Body.NodeType == ExpressionType.Convert) ? (MemberExpression)((UnaryExpression)expression.Body).Operand : (MemberExpression)expression.Body; return body.Member.Name; However, if there is deeper nesting, e.g. x = x.Prop1.SubProp1, this only gets the most deeply nested name, e.g. "SubProp1" instead of "Prop1.SubProp1" Is there anyway to access the full property path of a lambda expression?

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  • Travelling Salesman Problem Constraint Representation

    - by alex25
    Hey! I read a couple of articles and sample code about how to solve TSP with Genetic Algorithms and Ant Colony Optimization etc. But everything I found didn't include time (window) constraints, eg. "I have to be at customer x before 12am)" and assumed symmetry. Can somebody point me into the direction of some sample code or articles that explain how I can add constraints to TSP and how I can represent those in code. Thanks!

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  • Javascript CS-PRNG - 64-bit random

    - by Jack
    Hi, I need to generate a cryptographically secure 64-bit unsigned random integer in Javascript. The first problem is that Javascript only allows 64-bit signed integers, so 9223372036854775808 is the biggest supported integer without going into floating point use I think? To fix this I can use a big number library, no problem. My Method: var randNum = SHA256( randBigInt(128, 0) ) % 2^64; Where SHA256() is a secure hash function and randBigInt() is defined below as a non-crypto PRNG, im giving it a 128bit seed so brute force shouldn't be a problem. randBigInt(n,s) //return an n-bit random BigInt (n>=1). If s=1, then the most significant of those n bits is set to 1. Is this a secure method to generate a cryptographically secure 64-bit random int? And importantly does taking the 2^64 mod guarantee 100% I have a 64-bit number? An abstract example, say this number is prime (it isn't i know), I will use it in the Galois Field [2^p], where p must be 64bits so that every possible 1-63bit number is a field element. In this query, my random int must be larger than any 63-bit number. And Im not sure im correct in taking the 2^64 mod of a 256bit hash output. Thanks (hope that makes sense)

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  • RESTfully request sub-parts of a representation be of a certain content-type

    - by Grayside
    I am requesting (via Accept: application/json) that an API I'm designing respond as JSON. However, I want the values within that JSON to be specified to conform to text/plain or text/html depending on the capabilities of the client. What is the RESTful best practice for a "sub-type"? How would this work if I formally switched to HAL as the top-level container? Accept: application/json+text/plain { "value": "Hello World" } Accept: application/json+text/html { "value": "<h2>Hello World</h2>" }

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  • Representation of a DateTime as the local to remote user

    - by TwoSecondsBefore
    Hello! I was confused in the problem of time zones. I am writing a web application that will contain some news with dates of publication, and I want the client to see the date of publication of the news in the form of corresponding local time. However, I do not know in which time zone the client is located. I have three questions. I have to ask just in case: does DateTimeOffset.UtcNow always returns the correct UTC date and time, regardless of whether the server is dependent on daylight savings time? For example, if the first time I get the value of this property for two minutes before daylight savings time (or before the transition from daylight saving time back) and the second time in 2 minutes after the transfer, whether the value of properties in all cases differ by only 4 minutes? Or here require any further logic? (Question #1) Please see the following example and tell me what you think. I posted the news on the site. I assume that DateTimeOffset.UtcNow takes into account the time zone of the server and the daylight savings time, and so I immediately get the correct UTC server time when pressing the button "Submit". I write this value to a MS SQL database in the field of type datetime2(0). Then the user opens a page with news and no matter how long after publication. This may occur even after many years. I did not ask him to enter his time zone. Instead, I get the offset of his current local time from UTC using the javascript function following way: function GetUserTimezoneOffset() { var offset = new Date().getTimezoneOffset(); return offset; } Next I make the calculation of the date and time of publication, which will show the user: public static DateTime Get_Publication_Date_In_User_Local_DateTime( DateTime Publication_Utc_Date_Time_From_DataBase, int User_Time_Zone_Offset_Returned_by_Javascript) { int userTimezoneOffset = User_Time_Zone_Offset_Returned_by_Javascript; // For // example Javascript returns a value equal to -300, which means the // current user's time differs from UTC to 300 minutes. Ie offset // is UTC +6. In this case, it may be the time zone UTC +5 which // currently operates summer time or UTC +6 which currently operates the // standard time. // Right? (Question #2) DateTimeOffset utcPublicationDateTime = new DateTimeOffset(Publication_Utc_Date_Time_From_DataBase, new TimeSpan(0)); // get an instance of type DateTimeOffset for the // date and time of publication for further calculations DateTimeOffset publication_DateTime_In_User_Local_DateTime = utcPublicationDateTime.ToOffset(new TimeSpan(0, - userTimezoneOffset, 0)); return publication_DateTime_In_User_Local_DateTime.DateTime;// return to user } Is the value obtained correct? Is this the right approach to solving this problem? (Question #3)

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  • Difference between "bit-number" in filesystem and that in OS (like 32,64 bit)?

    - by learner
    I encountered 2 terms ,"FAT32", a file system and "Windows Vista 32 bit". I found that the meaning of a 32 bit OS is that that the OS deals with data in chunks of minimum size 32 bits. I don't quite understand the depth of that, but I figure ,every file in that system with that OS should have a minimum size of 32 bits. I also read that these 32 bits are used to hold data of files' location(reference) and details. Which of it is it? I have also read that 4 GB of RAM is all that is needed at the most if you're on a 32 bit OS. But I don't understand why. If there are 32 bits to hold info about files and their locations,there can be 2^32 possible combinations of it. But I have found in many places,2^32 is divided by 1024 thrice to get 4GB. Why? Did that 2^32 become equal to 2^32 bytes? And about filesystems I read a similar explanation for what 32 means in FAT32. It is supposed to mean that 32 bits are used to number file system block. Now how is different from the number before the OS?

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  • Processor, OS : 32bit, 64 bit

    - by Sandbox
    I am new to programming and come from a non-CS background (no formal degree). I mostly program winforms using C#. I am confused about 32 bit and 64 bit.... I mean, have heard about 32 bit OS, 32 bit processor and based on which a program can have maximum memory. How it affects the speed of a program. There are lot more questions which keep coming to mind. I tried to go through some Computer Organization and Architecture books. But, either I am too dumb to understand what is written in there or the writers assume that the reader has some CS background. Can someone explain me these things in a plain simple English or point me to something which does that. EDIT: I have read things like In 32-bit mode, they can access up to 4GB memory; in 64-bit mode, they can access much much more....I want to know WHY to all such things. BOUNTY: Answers below are really good....esp one by Martin. But, I am looking at a thorough explanation, but in plain simple English.

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  • Towards HEATMAP representation - R -

    - by user3710390
    I am trying to plot a simple heatmap of some data distribution in R. My data = matrix (5000 x3( Time , Complexity, Localisation )). Time ( 0- 7000) Cmplx (0-4) Localisation (1-15). i.e Time Cmplx Localisation 567 3 1 54 0 2 345 3 12 567 4 12 345 2 9 989 4 7 ... ... ... The idea is to plot the Time in relation to each Cmplx and each Localisation (Something like accumarray in mathlab) Have someone an idea? Thanks in advance, Guillon_

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  • Haskell graph data type representation

    - by John Retallack
    I want to represent a graph in Haskell in the following manner: For each node I want to store it's value and a list of adjacent nodes,the problem which i'm having difficulties with is that I want the adjacent nodes to be stored as references to other nodes. For example: I want node ny to be stored as („NY“ (l p)) where l and p are adjacent nodes,and not as („NY“ („London“ „Paris“)). I tried something like this : data Node a = Node { value :: a , neighbors :: [Node a] }deriving (Show) let n1 = Node {value=1, neighbors=[n2]} let n2 = Node {value=1, neighbors=[n1 n3]} let n3 = Node {value=1, neighbors=[n2]} But i get en error in let,What am I doing wrong ?

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  • Calculate average in LINQ C# with string representation of property name

    - by Paul
    I need to calculate a whole bunch of averages on an List of Surveys. The surveys have lots of properties that are int and double valued. I am creating a business object to handle all the calculations (there are like 100) and I'd rather not code 100 different methods for finding the average for a particular property. I'd like to be able to have the UI pass a string (representing the property) and have the the business object return an average for that property. So, like... int AverageHeightInInches = MyObject.GetIntAverage("HeightInInches"); . . . Then have linq code to calculate the result. Thanks!

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