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  • How do I design a cryptographic hash function?

    - by Eyal
    After reading the following about why one-way hash functions are one-way, I would like to know how to design a hash function. http://stackoverflow.com/questions/1038307/help-me-better-understand-cryptographic-hash-functions/1047106#1047106 Before everyone gets on my case: Yes, I know that it's a bad idea to not use a proven and tested hash function. I would still like to know how it's done. I'm familiar with Feistel-network ciphers but those are necessarily reversible, horrible for a cryptographic hash. Is there some sort of construction that is well-used in cryptographic hashing? Something that makes it very one-way?

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  • How to replace "(" with "\(" in the regexp, Emacs/elisp flavor?

    - by polyglot
    Question as title. More specifically, I'm rather tired of having to type \(, etc. every time I want a parenthesis in Emacs's (interactive) regexp functions (not to mention the \\( in code). So I wrote something like (defadvice query-replace-regexp (before my-query-replace-regexp activate) (ad-set-arg 0 (replace-regexp-in-string "(" "\\\\(" (ad-get-arg 0))) (ad-set-arg 0 (replace-regexp-in-string ")" "\\\\)" (ad-get-arg 0))))) in hope that I can conveniently forget about emacs's idiosyncrasy in regexp during "interaction mode". Except I cannot get the regexp right... (replace-regexp-in-string "(" "\\\\(" "(abc") gives \\(abc instead of the wanted \(abc. Other variations on the number of slashes just gives errors. Thoughts? Since I started questioning, might as well ask another one: since lisp code is not supposed to use interactive functions, advicing query-replace-regexp should be okay, am I correct?

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  • how to: handle exceptions, best practices

    - by b0x0rz
    need to implement a global error handling, so maybe you can help out with the following example... i have this code: public bool IsUserAuthorizedToSignIn(string userEMailAddress, string userPassword) { // get MD5 hash for use in the LINQ query string passwordSaltedHash = this.PasswordSaltedHash(userEMailAddress, userPassword); // check for email / password / validity using (UserManagementDataContext context = new UserManagementDataContext()) { var users = from u in context.Users where u.UserEMailAdresses.Any(e => e.EMailAddress == userEMailAddress) && u.UserPasswords.Any(p => p.PasswordSaltedHash == passwordSaltedHash) && u.IsActive == true select u; // true if user found return (users.Count() == 1) ? true : false; } } and the md5 as well: private string PasswordSaltedHash(string userEMailAddress, string userPassword) { MD5 hasher = MD5.Create(); byte[] data = hasher.ComputeHash(Encoding.Default.GetBytes(userPassword + userEMailAddress)); StringBuilder stringBuilder = new StringBuilder(); for (int i = 0; i < data.Length; i++) { stringBuilder.Append(data[i].ToString("x2")); } Trace.WriteLine(String.Empty); Trace.WriteLine("hash: " + stringBuilder.ToString()); return stringBuilder.ToString(); } so, how would i go about handling exceptions from these functions? they first one is called from the Default.aspx page. the second one is only called from other functions from the class library. what is the best practice? surround code INSIDE each function with try-catch surround the FUNCTION CALL with try-catch something else?? what to do if exceptions happen? in this example: this is a user sign in, so somehow even if everything fails, the user should get some meaningful info - along the lines: sign in ok (just redirect), sign in not ok (wrong user name / password), sign in not possible due to internal problems, sorry (exception happened). for the first function i am worried if there is a problem with database access. not sure if there is anything that needs to be handled in the second one. thnx for the info. how would you do it? need specific info on this (easier for me to understand), but also general info on how to handle other tasks/functions. i looked around the internet but everyone has different things to say, so unsure what to do... will go with either most votes here, or most logicaly explained answer :) thank you.

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  • Overloading framework methods in objective-c, or retaining local changes with framework updates.

    - by Jeff B
    I am using cocos2d to build an iPhone game. It's mostly done, but along the way I came across some things that I would like to handle better. I am fairly new to Objective C, and honestly I do more Perl scripting in my day-to-day job than anything, so my C skills are a little rusty. One of them is the fact that I have modified cocos2d files for some specific cases in my game. However, when I update to a new version, I have to manually pull my changes forward. So, the question is, what is the best way to deal with this? Some options I have thought of: Overload/redefine the cocos2d classes. I was under the impression that I cannot overload existing class functions, so I don't think this will work. Create patches that I re-apply after library updates. I don't think this will work as the new files won't necessarily be the same as the old ones, and if they were, I could just copy the whole file forward. Turn in my changes to Cocos2d. Not an option as my changes are very specific to my application. Am I missing something obvious? UPDATE: I will explain what I am doing to be more clear. Cocos2d has a CCNode object, which can contain children, etc. I added a shadow, which is very similar to a child, but handled a little differently. The shadow has an offset from the parent, and translates with it's parent, rotates around it's own center when the parent rotates, etc. The shadow is not included as a true child, however, so given the correct z-index, the shadows can render under ALL other objects, but still move with the parent. To do this I added addShadow functions to CCNode, and modified the setPosition and setRotate functions to move the shadowSprite: CCNode.m: -(id) init { if ((self=[super init]) ) { ... shadowSprite_ = nil; ... } } ... -(BOOL) addShadow: (CCNode*) child offset: (CGPoint) offset { shadowSprite_ = child; shadowSprite_.position = CGPointMake(position_.x+offset.x, position_.y+offset.y); return YES; } ... -(void) setRotation: (float)newRotation { rotation_ = newRotation; isTransformDirty_ = isInverseDirty_ = YES; if(shadowSprite_) { [shadowSprite_ setRotation: newRotation]; } } There is more, of course, including the prototypes in the .h file, but that is the basics. I don't think I need shadowSprite to be a property, because I don't need to access it after it has been added.

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  • How do I improve my performance with this singly linked list struct within my program?

    - by Jesus
    Hey guys, I have a program that does operations of sets of strings. We have to implement functions such as addition and subtraction of two sets of strings. We are suppose to get it down to the point where performance if of O(N+M), where N,M are sets of strings. Right now, I believe my performance is at O(N*M), since I for each element of N, I go through every element of M. I'm particularly focused on getting the subtraction to the proper performance, as if I can get that down to proper performance, I believe I can carry that knowledge over to the rest of things I have to implement. The '-' operator is suppose to work like this, for example. Declare set1 to be an empty set. Declare set2 to be a set with { a b c } elements Declare set3 to be a set with ( b c d } elements set1 = set2 - set3 And now set1 is suppose to equal { a }. So basically, just remove any element from set3, that is also in set2. For the addition implementation (overloaded '+' operator), I also do the sorting of the strings (since we have to). All the functions work right now btw. So I was wondering if anyone could a) Confirm that currently I'm doing O(N*M) performance b) Give me some ideas/implementations on how to improve the performance to O(N+M) Note: I cannot add any member variables or functions to the class strSet or to the node structure. The implementation of the main program isn't very important, but I will post the code for my class definition and the implementation of the member functions: strSet2.h (Implementation of my class and struct) // Class to implement sets of strings // Implements operators for union, intersection, subtraction, // etc. for sets of strings // V1.1 15 Feb 2011 Added guard (#ifndef), deleted using namespace RCH #ifndef _STRSET_ #define _STRSET_ #include <iostream> #include <vector> #include <string> // Deleted: using namespace std; 15 Feb 2011 RCH struct node { std::string s1; node * next; }; class strSet { private: node * first; public: strSet (); // Create empty set strSet (std::string s); // Create singleton set strSet (const strSet &copy); // Copy constructor ~strSet (); // Destructor int SIZE() const; bool isMember (std::string s) const; strSet operator + (const strSet& rtSide); // Union strSet operator - (const strSet& rtSide); // Set subtraction strSet& operator = (const strSet& rtSide); // Assignment }; // End of strSet class #endif // _STRSET_ strSet2.cpp (implementation of member functions) #include <iostream> #include <vector> #include <string> #include "strset2.h" using namespace std; strSet::strSet() { first = NULL; } strSet::strSet(string s) { node *temp; temp = new node; temp->s1 = s; temp->next = NULL; first = temp; } strSet::strSet(const strSet& copy) { if(copy.first == NULL) { first = NULL; } else { node *n = copy.first; node *prev = NULL; while (n) { node *newNode = new node; newNode->s1 = n->s1; newNode->next = NULL; if (prev) { prev->next = newNode; } else { first = newNode; } prev = newNode; n = n->next; } } } strSet::~strSet() { if(first != NULL) { while(first->next != NULL) { node *nextNode = first->next; first->next = nextNode->next; delete nextNode; } } } int strSet::SIZE() const { int size = 0; node *temp = first; while(temp!=NULL) { size++; temp=temp->next; } return size; } bool strSet::isMember(string s) const { node *temp = first; while(temp != NULL) { if(temp->s1 == s) { return true; } temp = temp->next; } return false; } strSet strSet::operator + (const strSet& rtSide) { strSet newSet; newSet = *this; node *temp = rtSide.first; while(temp != NULL) { string newEle = temp->s1; if(!isMember(newEle)) { if(newSet.first==NULL) { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = NULL; newSet.first = newNode; } else if(newSet.SIZE() == 1) { if(newEle < newSet.first->s1) { node *tempNext = newSet.first; node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = tempNext; newSet.first = newNode; } else { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = NULL; newSet.first->next = newNode; } } else { node *prev = NULL; node *curr = newSet.first; while(curr != NULL) { if(newEle < curr->s1) { if(prev == NULL) { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = curr; newSet.first = newNode; break; } else { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = curr; prev->next = newNode; break; } } if(curr->next == NULL) { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = NULL; curr->next = newNode; break; } prev = curr; curr = curr->next; } } } temp = temp->next; } return newSet; } strSet strSet::operator - (const strSet& rtSide) { strSet newSet; newSet = *this; node *temp = rtSide.first; while(temp != NULL) { string element = temp->s1; node *prev = NULL; node *curr = newSet.first; while(curr != NULL) { if( element < curr->s1 ) break; if( curr->s1 == element ) { if( prev == NULL) { node *duplicate = curr; newSet.first = newSet.first->next; delete duplicate; break; } else { node *duplicate = curr; prev->next = curr->next; delete duplicate; break; } } prev = curr; curr = curr->next; } temp = temp->next; } return newSet; } strSet& strSet::operator = (const strSet& rtSide) { if(this != &rtSide) { if(first != NULL) { while(first->next != NULL) { node *nextNode = first->next; first->next = nextNode->next; delete nextNode; } } if(rtSide.first == NULL) { first = NULL; } else { node *n = rtSide.first; node *prev = NULL; while (n) { node *newNode = new node; newNode->s1 = n->s1; newNode->next = NULL; if (prev) { prev->next = newNode; } else { first = newNode; } prev = newNode; n = n->next; } } } return *this; }

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  • Should i use HttpResponse.End() for a fast webapp?

    - by acidzombie24
    HttpResponse.End() seems to throw an exception according to msdn. Right now i have the choice of returning a value to say end thread (it only goes 2 functions deep) or i can call end(). I know that throwing exceptions is significantly slower (read the comment for a C#/.NET test) so if i want a fast webapp should i consider not calling it when it is trivially easy to not call it? -edit- I do have a function call in certain functions and in the constructor in classes to ensure the user is logged in. So i call HttpResponse.End() in enough places although hopefully in regular site usage it doesn't occur too often.

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  • Windows API calls from assembly while minimizing program size

    - by takteek
    I'm trying to write a program in assembly and make the resulting executable as small as possible. Some of what I'm doing requires windows API calls to functions such as WriteProcessMemory. I've had some success with calling these functions, but after compiling and linking, my program comes out in the range of 14-15 KB. (From a source of less than 1 KB) I was hoping for much, much less than that. I'm very new to doing low level things like this so I don't really know what would need to be done to make the program smaller. I understand that the exe format itself takes up quite a bit of space. Can anything be done to minimize that? I should mention that I'm using NASM and GCC but I can easily change if that would help.

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  • Query to return internal details about stored function in MS-SQL database

    - by Anthony
    I have been given access to a ms-sql database that is currently used by 3rd party app. As such, I don't have any documentation on how that application stores the data or how it retrieves it. I can figure a few things out based on the names of various tables and the parameters that the user-defined functions takes and returns, but I'm still getting errors at every other turn. I was thinking that it would be really helpful if I could see what the stored functions were doing with the parameters given to return the output. Right now all I've been able to figure out is how to query for the input parameters and the output columns. Is there any built-in information_schema table that will expose what the function is doing between input and output?

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  • Help me understand this "Programming pearls" bitsort program

    - by ardsrk
    Jon Bentley in Column 1 of his book programming pearls introduces a technique for sorting a sequence of non-zero positive integers using bit vectors. I have taken the program bitsort.c from here and pasted it below: /* Copyright (C) 1999 Lucent Technologies */ /* From 'Programming Pearls' by Jon Bentley */ /* bitsort.c -- bitmap sort from Column 1 * Sort distinct integers in the range [0..N-1] */ #include <stdio.h> #define BITSPERWORD 32 #define SHIFT 5 #define MASK 0x1F #define N 10000000 int a[1 + N/BITSPERWORD]; void set(int i) { int sh = i>>SHIFT; a[i>>SHIFT] |= (1<<(i & MASK)); } void clr(int i) { a[i>>SHIFT] &= ~(1<<(i & MASK)); } int test(int i){ return a[i>>SHIFT] & (1<<(i & MASK)); } int main() { int i; for (i = 0; i < N; i++) clr(i); /*Replace above 2 lines with below 3 for word-parallel init int top = 1 + N/BITSPERWORD; for (i = 0; i < top; i++) a[i] = 0; */ while (scanf("%d", &i) != EOF) set(i); for (i = 0; i < N; i++) if (test(i)) printf("%d\n", i); return 0; } I understand what the functions clr, set and test are doing and explain them below: ( please correct me if I am wrong here ). clr clears the ith bit set sets the ith bit test returns the value at the ith bit Now, I don't understand how the functions do what they do. I am unable to figure out all the bit manipulation happening in those three functions. Please help.

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  • python iterators and thread-safety

    - by Igor
    I have a class which is being operated on by two functions. One function creates a list of widgets and writes it into the class: def updateWidgets(self): widgets = self.generateWidgetList() self.widgets = widgets the other function deals with the widgets in some way: def workOnWidgets(self): for widget in self.widgets: self.workOnWidget(widget) each of these functions runs in it's own thread. the question is, what happens if the updateWidgets() thread executes while the workOnWidgets() thread is running? I am assuming that the iterator created as part of the for...in loop will keep some kind of reference to the old self.widgets object? So I will finish iterating over the old list... but I'd love to know for sure.

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  • Need help with homework(very short code)

    - by b3y4z1d
    I have a code, and I need to have it done until friday or so.I'd say 95% of it is finished,but the functions and the function-calling could use some grooming. It is really simple for anyone who knows C++ pretty well, but I'm a newbie and I just can't seem to get through this with the functions so if anyone could take a look and correct the few mistakes or add a line or two if needed I'd be very grateful. Here is the link to the full code, you'll understand the purpose of the code once you see it. I use Borland C++ by the way if it helps. Thanks in advance!

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  • verilog or systemc for testbench

    - by Alphaneo
    I am assigned with the task of verifying some verilog based RTL code. Now, coding the RTL testbench using verilog seems to be very difficult (for me). So I would like to try one of the following. - Try providing a PLI interface to the RTL and thereby invoke 'C functions for testing - Using system 'C for interfacing the 'C functions PS: I already have a extensive 'C code that was used for testing the behavioral model. I am new to the world of hardware programming. Any pointers would be greatly appreciated.

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  • Jquery Delay Function Calls

    - by fizgig07
    I'm trying to find a way to delay all code that takes place after I make a service call. The reason for this delay is that my service returns code necesarry for the following functions and the result I pass is to these following functions is undefined. I have tried attaching the setTimeout() to the function that is called directly after the service call, but then it just skips the function I set the timeout on and jumps to the next function...My web method that I am calling is not that big and is not doing anything that is too intensive public bool GetSpreadsheetStatusForAdmin(string cacId) { SpreadSheetStatus result = new SpreadSheetStatus(); List<Data.Spreadsheet> spreadsheets = SpreadsheetManager.GetUserSpreadsheets(GetCurrent.Identity); if (spreadsheets.Count != 0) { foreach (Data.Spreadsheet spreadsheet in spreadsheets) { if (spreadsheet.Status == SpreadsheetStatus.Pending) { return true; } } } return false; } I had found the delay() and thought that might work, but I don't have jquery 1.4 and can't use it as of yet. is there anything that can help..?

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  • What's the purpose of having a separate "operator new[]" ?

    - by sharptooth
    Looks like operator new and operator new[] have exactly the same signature: void* operator new( size_t size ); void* operator new[]( size_t size ); and do exactly the same: either return a pointer to a big enough block of raw (not initialized in any way) memory or throw an exception. Also operator new is called internally when I create an object with new and operator new[] - when I create an array of objects with new[]. Still the above two special functions are called by C++ internally in exactly the same manner and I don't se how the two calls can have different meanings. What's the purpose of having two different functions with exactly the same signatures and exactly the same behavior?

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  • Outputting variable values in x86?

    - by Airjoe
    Hello All- I'm working on a homework assignment in x86 and it isn't working as I expect (surprise surprise!). I'd like to be able to output values of variables in x86 functions to ensure that the values are what I expect them to be. Is there a simple way to do this, or is it very complex? For what it's worth, the x86 functions are being used by a C file and compiled with gcc, so if that makes it simpler that is how I'm going about it. Thanks for the help.

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  • Php wrapper class for XML

    - by gms8994
    I'm working on a new class to wrap XML handling. I want my class to use simplexml if it's installed, and the built in XML functions if it's not. Can anyone give me some suggestions on a skeleton class to do this? It seems "wrong" to litter each method with a bunch of if statements, and that also seems like it would make it nearly impossible to correctly test. Any upfront suggestions would be great! EDIT: I'm talking about these built-in xml functions.

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  • What is the equivalent to IScriptControl for Web.UI.Page?

    - by Jeff Dege
    We've been using IScriptControl to tie javascript objects to our UserControls and ServerControls, and it's worked fine. The problem is that ASP.NET seems to provide no method to tie a javascript object to a Page. Up to now, we've been putting plain functions in the global namespace, but I am developing a serious allergy to that practice. It'd be easy enough to wrap our functions into a javascript class, and to include the javascript file on the page, but how to instantiate the object, how to reference it from callback events, and how to pass data to it from the code-behind, I haven't figured out. Or rather, the methods we've been using up to now (hidden fields, emitted javascript strings, etc.), really bug me. Anyone have better ideas?

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  • Web App fails when moved to production environment. Which server permissions do I need?

    - by Ashley Ward
    I have developed a small web app. This app allows users to upload images. It also produces text files with the names of those images (the names are stored and retrieved to/from an MySQL Database.) I have developed this app using MAMP. To create the uploaded image files I use the PHP function imagejpeg('my/path/name.jpg') and to delete the files I use the PHP function unlink('folder1/folder2/name.jpg') to write to the text document I am using the function fopen('folder1/folder2/name.txt', 'w') all three of these functions produce errors related to permissions - now the site has been moved to a live hosting environment. Why is this? and what permissions do I need to set the folder's folder1 and folder2 to? I know that permission 777 is generally bad because it opens up your server to the public. However what I have found is that the functions fail to work unless I use 777 on the folders. Can anyone shed any light on my dilemma?

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  • Class template specializations with shared functionality

    - by Thomas
    I'm writing a simple maths library with a template vector type: template<typename T, size_t N> class Vector { public: Vector<T, N> &operator+=(Vector<T, N> const &other); // ... more operators, functions ... }; Now I want some additional functionality specifically for some of these. Let's say I want functions x() and y() on Vector<T, 2> to access particular coordinates. I could create a partial specialization for this: template<typename T> class Vector<T, 3> { public: Vector<T, 3> &operator+=(Vector<T, 3> const &other); // ... and again all the operators and functions ... T x() const; T y() const; }; But now I'm repeating everything that already existed in the generic template. I could also use inheritance. Renaming the generic template to VectorBase, I could do this: template<typename T, size_t N> class Vector : public VectorBase<T, N> { }; template<typename T> class Vector<T, 3> : public VectorBase<T, 3> { public: T x() const; T y() const; }; However, now the problem is that all operators are defined on VectorBase, so they return VectorBase instances. These cannot be assigned to Vector variables: Vector<float, 3> v; Vector<float, 3> w; w = 5 * v; // error: no conversion from VectorBase<float, 3> to Vector<float, 3> I could give Vector an implicit conversion constructor to make this possible: template<typename T, size_t N> class Vector : public VectorBase<T, N> { public: Vector(VectorBase<T, N> const &other); }; However, now I'm converting from Vector to VectorBase and back again. Even though the types are the same in memory, and the compiler might optimize all this away, it feels clunky and I don't really like to have potential run-time overhead for what is essentially a compile-time problem. Is there any other way to solve this?

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  • Why doesn't MySQL support millisecond precision?

    - by Byron Whitlock
    So I just found the most frustrating bug ever in MySQL. Apparently the TIMESTAMP field, and supporting functions do not support any greater precision than seconds!? So I am using PHP and Doctrine, and I really need those microseconds (I am using the actAs: [Timestampable] property). I found a that I can use a BIGINT field to store the values. But will doctrine add the milliseconds? I think it just assigns NOW() to the field. I am also worried the date manipulation functions (in SQL) sprinkled through the code will break. I also saw something about compiling a UDF extension. This is not an acceptable workaround because I or a future maintainer will upgrade and poof, change gone. Has anyone found a suitable workaround?

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  • An agenda in Korn Shell: New / Edit / Delete / View appointment

    - by Abaco
    As stated in the title, I have to write a simple script which should perform some typical agenda's functions. The script must use crontab. The functions are: Creating a new appointment Edit an existent appointment Delete an appointment List the appointment I really don't have a clue how to do this, can you help me with some hint? Maybe a bit of sweet code? Thank you very much, Abaco EDIT: To be more specific on my question Point 1: how can I edit a crontab thorugh ksh? How can I insert a new line? Can you link me some documentation or a bit of code about this?

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