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  • Speed of QHash lookups using QStrings as keys.

    - by Ryan R.
    I need to draw a dynamic overlay on a QImage. The component parts of the overlay are defined in XML and parsed out to a QHash<QString, QPicture> where the QString is the name (such as "crosshairs") and the QPicture is the resolution independent drawing. I then draw components of the overlay as they are needed at a position determined during runtime. Example: I have 10 pictures in my QHash composing every possible element in a HUD. During a particular frame of video I need to draw 6 of them at different positions on the image. During the next frame something has changed and now I only need to draw 4 of them but 2 of those positions have changed. Now to my question: If I am trying to do this quickly, should I redefine my QHash as QHash<int, QPicture> and enumerate the keys to counteract the overhead caused by string comparisons; or are the comparisons not going to make a very big impact on performance? I can easily make the conversion to integer keys as the XML parser and overlay composer are completely separate classes; but I would like to use a consistent data structure across the application. Should I overcome my desire for consistency and re-usability in order to increase performance? Will it even matter very much if I do?

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  • [PHP] md5(uniqid) makes sense for random unique tokens?

    - by Exception e
    I want to create a token generator that generates tokens that cannot be guessed by the user and that are still unique (to be used for password resets and confirmation codes). I often see this code; does it make sense? md5(uniqid(rand(), true)); According to a comment uniqid($prefix, $moreEntopy = true) yields first 8 hex chars = Unixtime, last 5 hex chars = microseconds. I don't know how the $prefix-parameter is handled.. So if you don't set the $moreEntopy flag to true, it gives a predictable outcome. QUESTION: But if we use uniqid with $moreEntopy, what does hashing it with md5 buy us? Is it better than: md5(mt_rand())

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  • How do I call a function name that is stored in a hash in Perl?

    - by Ether
    I'm sure this is covered in the documentation somewhere but I have been unable to find it... I'm looking for the syntactic sugar that will make it possible to call a method on a class whose name is stored in a hash (as opposed to a simple scalar): use strict; use warnings; package Foo; sub foo { print "in foo()\n" } package main; my %hash = (func => 'foo'); Foo->$hash{func}; If I copy $hash{func} into a scalar variable first, then I can call Foo->$func just fine... but what is missing to enable Foo->$hash{func} to work? (EDIT: I don't mean to do anything special by calling a method on class Foo -- this could just as easily be a blessed object (and in my actual code it is); it was just easier to write up a self-contained example using a class method.) EDIT 2: Just for completeness re the comments below, this is what I'm actually doing (this is in a library of Moose attribute sugar, created with Moose::Exporter): # adds an accessor to a sibling module sub foreignTable { my ($meta, $table, %args) = @_; my $class = 'MyApp::Dir1::Dir2::' . $table; my $dbAccessor = lcfirst $table; eval "require $class" or do { die "Can't load $class: $@" }; $meta->add_attribute( $table, is => 'ro', isa => $class, init_arg => undef, # don't allow in constructor lazy => 1, predicate => 'has_' . $table, default => sub { my $this = shift; $this->debug("in builder for $class"); ### here's the line that uses a hash value as the method name my @args = ($args{primaryKey} => $this->${\$args{primaryKey}}); push @args, ( _dbObject => $this->_dbObject->$dbAccessor ) if $args{fkRelationshipExists}; $this->debug("passing these values to $class -> new: @args"); $class->new(@args); }, ); } I've replaced the marked line above with this: my $pk_accessor = $this->meta->find_attribute_by_name($args{primaryKey})->get_read_method_ref; my @args = ($args{primaryKey} => $this->$pk_accessor); PS. I've just noticed that this same technique (using the Moose meta class to look up the coderef rather than assuming its naming convention) cannot also be used for predicates, as Class::MOP::Attribute does not have a similar get_predicate_method_ref accessor. :(

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  • Ruby/Rails - Add records to an object with each loop iteration / Object vs Arrays

    - by ChrisWesAllen
    I'm trying to figure out how to add records to an existing object for each iteration of a loop. I'm having a hard time discovering the difference between an object and an array. I have this @events = Event.find(1) @loops = Choices.find(:all, :limit => 5) #so loop for 5 instances of choice model for loop in @loops @events = Event.find(:all,:conditions => ["event.id = ?", loop.event_id ]) end I'm trying to add a new events to the existing @events object based on the id of whatever the loop variable is. But the ( = ) operator just creates a new instance of the @events object. I tried ( += ) and ( << ) as operators but got the error "You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil" I tried created an array events = [] events << Event.find(1) @loops = Choices.find(:all, :limit => 5) #so loop for 5 instances of choice model for loop in @loops events << Event.find(:all,:conditions => ["event.id = ?", loop.event_id ]) end But I dont know how to call that arrays attributes within the view With objects I was able do create a loop within the view and call all the attributes of that object as well... <table> <% for event in @events %> <tr> <td><%= link_to event.title, event %></td> <td><%= event.start_date %></td> <td><%= event.price %></td> </tr> <% end %> </table> How could i do this with an array set? So the questions are 1) Whats the difference between arrays and objects? 2) Is there a way to add into the existing object for each iteration? 3) If I use an array, is there a way to call the attributes for each array record within the view?

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  • Ajax back button jquery - Need full example step by step.

    - by Latios88
    Hi. I need help supporting back button with jquery ajax.load method. I have tried a couple of plugins but i cant get any of them to work. I am loading my content like this: $('.pagination a').click(function(){ var url = $(this).attr('href'); ajaxLoad(url,null,'.container'); return false; }); Note: ajaxLoad function executes the jquery load method. Many 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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  • Combining Java hashcodes into a "master" hashcode

    - by Nick Wiggill
    I have a vector class with hashCode() implemented. It wasn't written by me, but uses 2 prime numbers by which to multiply the 2 vector components before XORing them. Here it is: /*class Vector2f*/ ... public int hashCode() { return 997 * ((int)x) ^ 991 * ((int)y); //large primes! } ...As this is from an established Java library, I know that it works just fine. Then I have a Boundary class, which holds 2 vectors, "start" and "end" (representing the endpoints of a line). The values of these 2 vectors are what characterize the boundary. /*class Boundary*/ ... public int hashCode() { return 1013 * (start.hashCode()) ^ 1009 * (end.hashCode()); } Here I have attempted to create a good hashCode() for the unique 2-tuple of vectors (start & end) constituting this boundary. My question: Is this hashCode() implementation going to work? (Note that I have used 2 different prime numbers in the latter hashCode() implementation; I don't know if this is necessary but better to be safe than sorry when trying to avoid common factors, I guess -- since I presume this is why primes are popular for hashing functions.)

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  • Native arrays and computing hashvalues (VB, C#)

    - by Jeffrey Kern
    I feel bad asking this question but I am currently not able to program and test this as I'm writing this on my cell-phone and not on my dev machine :P (Easy rep points if someone answers! XD ) Anyway, I've had experience with using hashvalues from String objects. E.g., if I have StringA and StringB both equal to "foo", they'll both compute out the same hashvalue, because they're set to equal values. Now what if I have a List, with T being a native data type. If I tried to compute the hashvalue of ListA and ListB, assuming that they'd both be the same size and contain the same information, wouldn't they have equal hashvalues as well?

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  • x=["key" => "value"]. How does it work in Ruby?

    - by Earlz
    Ok, so I was comparing some stuff in my own DSL to Ruby. One construct they both support is this x=["key" => "value"] Knowing the difference between arrays and hashes, I would think this to be illegal, but the result in Ruby is [{"key" => "value"}] Why is this? And with this kinda syntax why can't you do x=("key" => "value") Why is an array a special case for implicitly created hashes?

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  • why doesn't perl sort the hash key in numeric order ?

    - by Haiyuan Zhang
    #!/usr/bin/perl use strict; use warnings; my %hash; foreach ( 1 .. 10 ) { $hash{$_} = $_; } foreach ( sort(keys %hash) ) { print $_ . ": " . "$hash{$_}" . "\n" ; } execute the above code, the result is as below : 1: 1 10: 10 2: 2 3: 3 4: 4 5: 5 6: 6 7: 7 8: 8 9: 9 Yes, I expect "10: 10" to be the last one taht is printed . So I just need someone to explain why perl give me surprise in this case.

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  • how can I display controller's variable (which is on a loop) on .html.erb page? ruby on rails

    - by rrz
    I have the following code listed below in my controller: struc = {'en' => 'english', 'es' => 'espaniol', 'de' => 'germany', 'fr' => 'french', 'it' => 'italy'} struc.each_pair do |key, value| @key=key @value=value end on my application.html.erb I have the following <select name="Language" onchange="location=this.options[this.selectedIndex].value;"> <option value="/<% @key %>/<%= @rem %>"><%= @value %></option> </select> Now how can i make the value of '@key' and '@value' appear recursively display on (application.html.erb)? Thanks in advance

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  • c# How to find if two objects are equal

    - by Simon G
    Hi, I'm needing to know the best way to compare two objects and to find out if there equal. I'm overriding both GethashCode and Equals. So a basic class looks like: public class Test { public int Value { get; set; } public string String1 { get; set; } public string String2 { get; set; } public override int GetHashCode() { return Value ^ String1.GetHashCode() ^ String2.GetHashCode(); } public override bool Equals( object obj ) { return GetHashCode() == obj.GetHashCode(); } } So for testing purposes I created two objects: Test t = new Test() { Value = 1, String1 ="One", String2 = "One" }; Test t2 = new Test() { Value = 1, String1 = "Two", String2 = "Two" }; bool areEqual = t.Equals( t2 ); In testing this areEqual returns true event though both objects are different. I realise this is because String1 and String2 are the same value in each object and thus cancels each other out when hashing. Is there a better way off hashing object that the method I have that will resolve my issue?

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  • Why this code does not do what I mean?

    - by Mike
    $w = 'self-powering'; %h = (self => 'self', power => 'pau?', ); if ($w =~ /(\w+)-(\w+)ing$/ && $1~~%h && $2~~%h && $h{$2}=~/?$/) { $p = $h{$1}.$h{$2}.'ri?'; print "$w:"," [","$p","] "; } I expect the output to be self-powering: selfpau?ri? But what I get is: self-powering: [ri?] My guess is something's wrong with the code $h{$2}=~/?$/ It seems that when I use $h{$2}!~/?$/ Perl will do what I mean but why I can't get "self-powering: selfpau?ri?"? What am I doing wrong? Any ideas? Thanks as always for any comments/suggestions/pointers :)

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  • How to decrypt a password from SQL server?

    - by sef
    I have this query in sql server 2000: select pwdencrypt('AAAA') which outputs an encrypted string of 'AAAA': 0x0100CF465B7B12625EF019E157120D58DD46569AC7BF4118455D12625EF019E157120D58DD46569AC7BF4118455D How can I convert (decrypt) the output from its origin (which is 'AAAA')?

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  • initializing hashes

    - by Paul
    Seems like I am frequently writing something like this... a_hash['x'] ? a_hash['x'] += ' some more text' : a_hash['x'] = 'first text' seems like there ought to be a better way, but I can't find it.

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  • Python - Why ever use SHA1 when SHA512 is more secure?

    - by orokusaki
    I don't mean for this to be a debate, but I'm trying to understand the technical rationale behind why so many apps use SHA1, when SHA512 is more secure. Perhaps it's simply for backwards compatibility. Besides the obvious larger size (128 chars vs 40), or slight speed differences, is there any other reason why folks use the former? Also, SHA-1 I believe was first cracked by a VCR's processor years ago. Has anyone cracked 512 yet (perhaps with a leaf blower), or is it still safe to use without salting?

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  • How to map string keys to unique integer IDs?

    - by Marek
    I have some data that comes regularily as a dump from a data souce with a string natural key that is long (up to 60 characters) and not relevant to the end user. I am using this key in a url. This makes urls too long and user unfriendly. I would like to transform the string keys into integers with the following requirements: The source dataset will change over time. The ID should be: non negative integer unique and constant even if the set of input keys changes preferrably reversible back to key (not a strong requirement) The database is rebuilt from scratch every time so I can not remember the already assigned IDs and match the new data set to existing IDs and generate sequential IDs for the added keys. There are currently around 30000 distinct keys and the set is constantly growing. How to implement a function that will map string keys to integer IDs? What I have thought about: 1. Built-in string.GetHashCode: ID(key) = Math.Abs(key.GetHashCode()) is not guaranteed to be unique (not reversible) 1.1 "Re-hashing" the built-in GetHashCode until a unique ID is generated to prevent collisions. existing IDs may change if something colliding is added to the beginning of the input data set 2. a perfect hashing function I am not sure if this can generate constant IDs if the set of inputs changes (not reversible) 3. translate to base 36/64/?? does not shorten the long keys enough What are the other options?

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  • Looking for an array (vs linked list) hashtable implementation in C

    - by kingusiu
    hi, I'm looking for a hashtable implementation in C that stores its objects in (twodimensional) arrays rather than linked lists. i.e. if a collision happens, the object that is causing the collision will be stored in the next free row index rather than pushed to the head and first element of a linked list. plus, the objects themselves must be copied to the hashtable, rather than referenced by pointers. (the objects do not live for the whole lifetime of the program but the table does). I know that such an implementation might have serious efficiency drawbacks and is not the "standard way of hashing" but as I work on a very special system-architecture i need those characteristics. thanks

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  • Using intermediate array for hashCode and equals

    - by Basilevs
    As its a pain to handle structural changes of the class in two places I often do: class A { private B bChild; private C cChild; private Object[] structure() { return new Object[]{bChild, cChild}; } int hashCode() { Arrays.hashCode(structure); } boolean equals(Object that) { return Arrays.equals(this.structure(), ((A)that).structure()); } } What's bad about this approach besides boxing of primitives? Can it be improved?

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  • (PHP) 1)How to genrate Secreate key on User & Client Side ? 3) How to Compare Server side MD5 and Client side Md5 ?

    - by user557994
    /* In Below Code .. My problem is that 1) How to genrate Secreate key on User Side ? 2) How to genrate Secreate key on Client Side ? 3) How to Compare Server side MD5 and Client side Md5 ? Can you solve my problem ? */ $gid = $_GET['id']; if($gid=="") { $filename = "counter.txt"; $fp = fopen( $filename, "r" ) or die("Couldn't Generate Whiteboard"); while ( ! feof( $fp ) ) { $countfile = fgets( $fp); $countfile++; } fclose( $fp ); $fp = fopen( $filename, "w" ) or die("Couldn't generate whiteboard"); fwrite( $fp, $countfile ); fclose( $fp ); $doc = new DOMDocument('1.0', 'UTF-8'); $ele = $doc-createElement( 'root' ); $ele-nodeValue = $uvar; $doc-appendChild( $ele ); $test = $doc-save("$countfile.xml"); genkey($id); echo ""; $uvar=$_POST['msgval']; exit; } else { if($uvar == "") { $xdoc = new DOMDocument( '1.0', 'UTF-8' ); $xdoc-Load("$gid.xml"); $candidate = $xdoc-getElementsByTagName('root')-item(0); $newElement = $xdoc -createElement('root'); $txtNode = $xdoc -createTextNode ($root); $newElement - appendChild($txtNode); $candidate - appendChild($newElement); $msg = $candidate-nodeValue; } } function genkey($id) { $encrypt_key = "GJHsahakst1468464a"; $key = MD5("$id","$$encrypt_key"); return $key; } ? function sendRequest() { var uvar = document.getElementById('txtHint').value; var xmlhttp = new XMLHttpRequest(); xmlhttp.onreadystatechange = function() { if(xmlhttp.readyState == 4 && xmlhttp.status==200) { document.getElementById('txtHint').value = ""; } } xmlhttp.open("POST","post.php?id=",true); xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded"); xmlhttp.send("umsg="+uvar); return; } Msg " /

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  • Clojure: I have many sorted maps and want to reduce in order all there values a super maps of keys -> vector

    - by Alex Foreman
    I have seen this but can't work out how to apply it (no pun intended) to my situation. I have a sorted list of maps like this: (note there can be more than two keys in the map) ({name1 3, name2 7}, {name1 35, name2 7}, {name1 0, name2 3}) What I am after is this data structure afterwards: ({:name1 [3,35,0]}, {:name2 [7,7,3]}) Ive been struggling with this for a while and cant seem to get anywhere near. Caveats: The data must stay sorted and I have N keywords not just two.

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  • How can I check if a value is in a list in Perl?

    - by ablimit
    I have a file in which every line is an integer which represents an id. What I want to do is just check whether some specific ids are in this list. But the code didn't work. It never tells me it exists even if 123 is a line in that file. I don't know why? Help appreciated. open (FILE, "list.txt") or die ("unable to open !"); my @data=<FILE>; my %lookup =map {chop($_) => undef} @data; my $element= '123'; if (exists $lookup{$element}) { print "Exists"; } Thanks in advance.

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  • Encrypt hashed passwords?

    - by Industrial
    Hi everyone, Is it common sense to encrypt hashed&salted passwords that are stored in a database with a strong encryption (AES 192 or so) or are we just aiming for the stars? Of course, the encryption key will not be in the database itself, but will be kept at a safe place. Thanks a lot!

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