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  • Creating a Rails query from a hash of user input

    - by Jamie
    I'm attempting to create a fairly complex search engine for a project using a variable number of search criteria. The user input is sorted into an array of hashes. The hashes contain the following information: { :column => "", :value => "", :operator => "", # Such as: =, !=, <, >, etc. :and_or => "", # Two possible values: "and" and "or" } How can I loop through this array and use the information in these hashes to make an ActiveRecord WHERE query?

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  • Is there a good way to get pixel-perfect collision detection in XNA?

    - by ashes999
    Is there a well-known way (or perhaps reusable bit of code) for pixel-perfect collision detection in XNA? I assume this would also use polygons (boxes/triangles/circles) for a first-pass, quick-test for collisions, and if that test indicated a collision, it would then search for a per-pixel collision. This can be complicated, because we have to account for scale, rotation, and transparency. WARNING: If you're using the sample code from the link from the answer below, be aware that the scaling of the matrix is commented out for good reason. You don't need to uncomment it out to get scaling to work.

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  • PHP secure logon script - md5 hash is not matching the hash i wrote to the database in a previous sc

    - by Chris Sobolewski
    I am trying to cobble together a login script in PHP as a learning project. This is the code for my database write when the user registers. Both of these values are written to the database. $this->salt = md5(uniqid()); $this->password = md5($password.$salt); Upon logging in, the following function is fired. For some function challengeLogin($submittedPassword, $publicSalt, $storedPassword){ if(md5($submittedPassword.$publicSalt) == $actualPassword){ return 0; }else{ return 1; }; } Unfortunately, on stepping through my code, the two values have never equaled. Can someone help me understand why?

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  • merging arrays of hashes

    - by Ben
    I have two arrays of hashes. Array1 => [{attribute_1 = A, attribute_2 = B}, {attribute_1 = A, attribute_2 = B}] Array2 => [{attribute_3 = C, attribute_2 = D}, {attribute_3 = C, attribute_4 = D}] Each hash in the array is holding attributes for an object. In the above example, there are two objects that I'm working with. There are two attributes in each array for each object How do I merge the two arrays? I am trying to get a single array (there is no way to get a single array from the start because I have to make two different API calls to get these attributes). DesiredArray => [{attribute_1 = A, attribute_2 = B, attribute_3 = C, attribute_2 = D}, {attribute_1 = A, attribute_2 = B, attribute_3 = C, attribute_2 = D}] I've tried a couple things, including the iteration methods and the merge method, but I've been unable to get the array I need.

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  • Ignoring extra keys in a hash passed in to create

    - by denniss
    Does rails provide a way to ignore extra keys that are passed in to create. Supposed User has two attributes, first_name and last_name. When I do User.create({ :first_name => "first", :last_name => "last", :age => 10}) that line gives me an UknonwnAttributeError. Well, that makes sense, it happens cause age is not one of the attributes. But is there a way to just ignore key-value pair that is not one of the attributes for User?

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  • Glib segfault g_free hash table

    - by Mike
    I'm not quite sure why if I try to free the data I get segfault. Any help will be appreciate it. static GHashTable *hashtable; static void add_inv(char *q) { gpointer old_key, old_value; if(!g_hash_table_lookup_extended(hashtable, q, &old_key, &old_value)){ g_hash_table_insert(hashtable, g_strdup(q), GINT_TO_POINTER(10)); }else{ (old_value)++; g_hash_table_insert(hashtable, g_strdup(q), old_value); g_hash_table_remove (hashtable, q); // segfault g_free(old_key); // segfault g_free(old_value); // segfault } } ... int main(int argc, char *argv[]){ hashtable = g_hash_table_new(g_str_hash, g_str_equal); ... g_hash_table_destroy(hashtable); }

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  • Hash Digest / Array Comparison in C#

    - by Erik Karulf
    Hi All, I'm writing an application that needs to verify HMAC-SHA256 checksums. The code I currently have looks something like this: static bool VerifyIntegrity(string secret, string checksum, string data) { // Verify HMAC-SHA256 Checksum byte[] key = System.Text.Encoding.UTF8.GetBytes(secret); byte[] value = System.Text.Encoding.UTF8.GetBytes(data); byte[] checksum_bytes = System.Text.Encoding.UTF8.GetBytes(checksum); using (var hmac = new HMACSHA256(key)) { byte[] expected_bytes = hmac.ComputeHash(value); return checksum_bytes.SequenceEqual(expected_bytes); } } I know that this is susceptible to timing attacks. Is there a message digest comparison function in the standard library? I realize I could write my own time hardened comparison method, but I have to believe that this is already implemented elsewhere.

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  • accessing a value of a nested hash

    - by st
    Hello! I am new to perl and I have a problem that's very simple but I cannot find the answer when consulting my perl book. When printing the result of Dumper($request); I get the following result: $VAR1 = bless( { '_protocol' => 'HTTP/1.1', '_content' => '', '_uri' => bless( do{\(my $o = 'http://myawesomeserver.org:8081/counter/')}, 'URI::http' ), '_headers' => bless( { 'user-agent' => 'Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.4) Gecko/20080528 Epiphany/2.22 Firefox/3.0', 'connection' => 'keep-alive', 'cache-control' => 'max-age=0', 'keep-alive' => '300', 'accept' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'accept-language' => 'en-us,en;q=0.5', 'accept-encoding' => 'gzip,deflate', 'host' => 'localhost:8081', 'accept-charset' => 'ISO-8859-1,utf-8;q=0.7,*;q=0.7' }, 'HTTP::Headers' ), '_method' => 'GET', '_handle' => bless( \*Symbol::GEN0, 'FileHandle' ) }, 'HTTP::Server::Simple::Dispatched::Request' ); How can I access the values of '_method' ('GET') or of 'host' ('localhost:8081'). I know that's an easy question, but perl is somewhat cryptic at the beginning. Thank you, St.

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  • how to Compute the average probe length for success and failure - Linear probe (Hash Tables)

    - by fang_dejavu
    hi everyone, I'm doing an assignment for my Data Structures class. we were asked to to study linear probing with load factors of .1, .2 , .3, ...., and .9. The formula for testing is: The average probe length using linear probing is roughly Success-- ( 1 + 1/(1-L)**2)/2 or Failure-- (1+1(1-L))/2. we are required to find the theoretical using the formula above which I did(just plug the load factor in the formula), then we have to calculate the empirical (which I not quite sure how to do). here is the rest of the requirements **For each load factor, 10,000 randomly generated positive ints between 1 and 50000 (inclusive) will be inserted into a table of the "right" size, where "right" is strictly based upon the load factor you are testing. Repeats are allowed. Be sure that your formula for randomly generated ints is correct. There is a class called Random in java.util. USE it! After a table of the right (based upon L) size is loaded with 10,000 ints, do 100 searches of newly generated random ints from the range of 1 to 50000. Compute the average probe length for each of the two formulas and indicate the denominators used in each calculationSo, for example, each test for a .5 load would have a table of size approximately 20,000 (adjusted to be prime) and similarly each test for a .9 load would have a table of approximate size 10,000/.9 (again adjusted to be prime). The program should run displaying the various load factors tested, the average probe for each search (the two denominators used to compute the averages will add to 100), and the theoretical answers using the formula above. .** how do I calculate the empirical success?

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  • Creating a unique key based on file content in python

    - by Cawas
    I got many, many files to be uploaded to the server, and I just want a way to avoid duplicates. Thus, generating a unique and small key value from a big string seemed something that a checksum was intended to do, and hashing seemed like the evolution of that. So I was going to use hash md5 to do this. But then I read somewhere that "MD5 are not meant to be unique keys" and I thought that's really weird. What's the right way of doing this? edit: by the way, I took two sources to get to the following, which is how I'm currently doing it and it's working just fine, with Python 2.5: import hashlib def md5_from_file (fileName, block_size=2**14): md5 = hashlib.md5() f = open(fileName) while True: data = f.read(block_size) if not data: break md5.update(data) f.close() return md5.hexdigest()

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  • Question about the mathematical properties of hashes

    - by levand
    Take a commonly used binary hash function - for example, SHA-256. As the name implies, it outputs a 256 bit value. Let A be the set of all possible 256 bit binary values. A is extremely large, but finite. Let B be the set of all possible binary values. B is infinite. Let C be the set of values obtained by running SHA-256 on every member of B. Obviously this can't be done in practice, but I'm guessing we can still do mathematical analysis of it. My Question: By necessity, C ? A. But does C = A?

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  • How can i get almost pixel perfect collision detection in a multiplayer game?

    - by Freddy
    I'm currently working on a multiplayer game for iPhone. The problem i have, as with all multiplayer games, is that the other user will always see everything at a non-constant delay. The game I'm making need to have a almost pixel perfect collision detection, but 1 or 2 pixels off is not that big of a deal. How can I possibly get this working? I guess I could just set local player to also be at X ms delay. However this will probably just be worse and feel sloppy when the user input. I know this problem is probably something network programmers deal with everyday and I would be glad if someone could give me a possible solution for this.

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  • Ruby: rules for implicit hashes

    - by flyer
    Why second output shows me only one element of Array? Is it still Array or Hash already? def printArray(arr) arr.each { | j | k, v = j.first printf("%s %s %s \n", k, v, j) } end print "Array 1\n" printArray( [ {kk: { 'k1' => 'v1' }}, {kk: { 'k2' => 'v2' }}, {kk: { 'k3' => 'v3' }}, ]) print "Array 2\n" printArray( [ kk: { 'k1' => 'v1' }, kk: { 'k2' => 'v2' }, kk: { 'k3' => 'v3' }, ]) exit # Output: # # Array 1 # kk {"k1"=>"v1"} {:kk=>{"k1"=>"v1"}} # kk {"k2"=>"v2"} {:kk=>{"k2"=>"v2"}} # kk {"k3"=>"v3"} {:kk=>{"k3"=>"v3"}} # Array 2 # kk {"k3"=>"v3"} {:kk=>{"k3"=>"v3"}}

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  • Accessing a nested hash in a controller

    - by Magicked
    I have the following (snipped) parameters passed into my controller. Parameters: {"commit"=>"OK", "action"=>"set_incident_incident_status_id", "id"=>"1", "controller"=>"incidents", "incident"=>{"incident_status_id"=>"1"}} I know that if I want to select the incident, I can do: @incident = Incident.find(params[:id]) How do I access the "incident"={"incident_status_id"="1"}? I thought to try something like: @incident_status = IncidentStatus.find(params[:incident => :incident_status_id]) But that didn't work. I'm assuming it's just a syntax problem at this point, and I haven't found a solution yet. Any help would be much appreciated!

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  • password/login system in php

    - by Jonathan
    For a login system in php would this be a suitable outline of how it would work: users types in username and password, clicks login button. Checks if user exists in database, if it does, then retrieve the salt for that user hash the password and salt (would this be done on the client or server side? I think client side would be better, but php is server side so how would you do this?) check value against value in database, if the values match then user has typed in correct password and they are logged in.

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  • Do encryption algorithms provide really unique results?

    - by Mikulas Dite
    I was wondering whether md5, sha1 and anothers return unique values. For example, sha1() for test returns a94a8fe5ccb19ba61c4c0873d391e987982fbbd3, which is 40 characters long. So, sha1 for strings larger than 40 chars must be the same (of course it's scrambled, because the given input may contain whitespaces and special chars etc.). Due to this, when we are storing users' passwords, they can enter either their original password or some super-long one, which nobody knows. Is this right, or do these hash algorithms provide really unique results - I'm quite sure it's hardly possible.

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  • Population count of rightmost n integers

    - by Jason Baker
    I'm implementing Bagwell's Ideal Hash Trie in Haskell. To find an element in a sub-trie, he says to do the following: Finding the arc for a symbol s, requires ?nding its corresponding bit in the bit map and then counting the one bits below it in the map to compute an index into the ordered sub-trie. What is the best way to do this? It sounds like the most straightforward way of doing this is to select the bits below that bit and do a population count on the resulting number. Is there a faster or better way to do this?

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  • Creating a simple java hash server

    - by Blankman
    Is it possible to create a simple server in Java that returns a response based on a given key? So it would be a simple program, that stores a hashmap and returns the result based on a key provided by the client. What would be the fasted implementation, to have it over HTTP or a socket? The client will be a web based application.

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  • Hashing and salting values

    - by Avanst
    I am developing a small web app that internally authenticates users. Once the user is authenticated my web app then passes some information such as userID and Person's name to a third party web application. The third party developer is suggesting that we hash and salt the values. Forgive my ignorance, but what exactly does that mean? I am writing the app in Java. So what I am planning on doing is hashing the userID, Person's name, and some Math.random() value as the salt with Apache Commons Digest Utils SHA512 and passing that hashed string along with the userID and person's name. Is that the standard practice? I should be passing the third party the salt as well correct?

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  • How can I map URLs to filenames with perl?

    - by eugene y
    In a simple webapp I need to map URLs to filenames or filepaths. This app has a requirement that it can depend only on modules in the core Perl ditribution (5.6.0 and later). The problem is that filename length on most filesystems is limited to 255. Another limit is about 32k subdirectories in a single folder. My solution: my $filename = $url; if (length($filename) > $MAXPATHLEN) { # if filename longer than 255 my $part1 = substr($filename, 0, $MAXPATHLEN - 13); # first 242 chars my $part2 = crypt(0, substr($filename, $MAXPATHLEN - 13)); # 13 chars hash $filename = $part1.$part2; } $filename =~ s!/!_!g; # escape directory separator Is it reliable ? How can it be improved ?

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  • Ruby hash value truthiness and symbols

    - by John Topley
    Could somebody please explain why the variable named foo remains true in the code below, even though it's set to false when the method is called? And why the symbol version behaves as expected? def test(options = {}) foo = options[:foo] || true bar = options[:bar] || :true puts "foo is #{foo}, bar is #{bar}" end >> test(:foo => false, :bar => :false) foo is true, bar is false I've only tried this using Ruby 1.8.7.

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  • Merging hashes into one hash in perl

    - by Nick
    how do I get this: $VAR1 = { '999' => { '998' => [ '908', '906', '0', '998', '907' ] } }; $VAR1 = { '999' => { '991' => [ '913', '920', '918', '998', '916', '919', '917', '915', '912', '914' ] } }; $VAR1 = { '999' => { '996' => [] } }; $VAR1 = { '999' => { '995' => [] } }; $VAR1 = { '999' => { '994' => [] } }; $VAR1 = { '999' => { '993' => [] } }; $VAR1 = { '999' => { '997' => [ '986', '987', '990', '984', '989', '988' ] } }; $VAR1 = { '995' => { '101' => [] } }; $VAR1 = { '995' => { '102' => [] } }; $VAR1 = { '995' => { '103' => [] } }; $VAR1 = { '995' => { '104' => [] } }; $VAR1 = { '995' => { '105' => [] } }; $VAR1 = { '995' => { '106' => [] } }; $VAR1 = { '995' => { '107' => [] } }; $VAR1 = { '994' => { '910' => [] } }; $VAR1 = { '993' => { '909' => [] } }; $VAR1 = { '993' => { '904' => [] } }; $VAR1 = { '994' => { '985' => [] } }; $VAR1 = { '994' => { '983' => [] } }; $VAR1 = { '993' => { '902' => [] } }; $VAR1 = { '999' => { '992' => [ '905' ] } }; to this: $VAR1 = { '999:' => [ { '992' => [ '905' ] }, { '993' => [ { '909' => [] }, { '904' => [] }, { '902' => [] } ] }, { '994' => [ { '910' => [] }, { '985' => [] }, { '983' => [] } ] }, { '995' => [ { '101' => [] }, { '102' => [] }, { '103' => [] }, { '104' => [] }, { '105' => [] }, { '106' => [] }, { '107' => [] } ] }, { '996' => [] }, { '997' => [ '986', '987', '990', '984', '989', '988' ] }, { '998' => [ '908', '906', '0', '998', '907' ] }, { '991' => [ '913', '920', '918', '998', '916', '919', '917', '915', '912', '914' ] } ]}; in Perl?

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