How to sum all the values in a dictionary?
As you’d expect: sum(d.values())
hash
What column type/length should I use for storing a Bcrypt hashed password in a Database?
The modular crypt format for bcrypt consists of $2$, $2a$ or $2y$ identifying the hashing algorithm and format a two digit value denoting the cost parameter, followed by $ a 53 characters long base-64-encoded value (they use the alphabet ., /, 0–9, A–Z, a–z that is different to the standard Base 64 Encoding alphabet) consisting … Read more
C++ unordered_map using a custom class type as the key
To be able to use std::unordered_map (or one of the other unordered associative containers) with a user-defined key-type, you need to define two things: A hash function; this must be a class that overrides operator() and calculates the hash value given an object of the key-type. One particularly straight-forward way of doing this is to … Read more
Calculate MD5 checksum for a file
It’s very simple using System.Security.Cryptography.MD5: using (var md5 = MD5.Create()) { using (var stream = File.OpenRead(filename)) { return md5.ComputeHash(stream); } } (I believe that actually the MD5 implementation used doesn’t need to be disposed, but I’d probably still do so anyway.) How you compare the results afterwards is up to you; you can convert the … Read more
Why should hash functions use a prime number modulus?
Usually a simple hash function works by taking the “component parts” of the input (characters in the case of a string), and multiplying them by the powers of some constant, and adding them together in some integer type. So for example a typical (although not especially good) hash of a string might be: (first char) … Read more
node.js hash string?
If you just want to md5 hash a simple string I found this works for me. var crypto = require(‘crypto’); var name=”braitsch”; var hash = crypto.createHash(‘md5’).update(name).digest(‘hex’); console.log(hash); // 9b74c9897bac770ffc029102a200c5de
HashSet vs. List performance
A lot of people are saying that once you get to the size where speed is actually a concern that HashSet<T> will always beat List<T>, but that depends on what you are doing. Let’s say you have a List<T> that will only ever have on average 5 items in it. Over a large number of … Read more
How does a hash table work?
Here’s an explanation in layman’s terms. Let’s assume you want to fill up a library with books and not just stuff them in there, but you want to be able to easily find them again when you need them. So, you decide that if the person that wants to read a book knows the title … Read more
Fundamental difference between Hashing and Encryption algorithms
Well, you could look it up in Wikipedia… But since you want an explanation, I’ll do my best here: Hash Functions They provide a mapping between an arbitrary length input, and a (usually) fixed length (or smaller length) output. It can be anything from a simple crc32, to a full blown cryptographic hash function such … Read more
Why does Java’s hashCode() in String use 31 as a multiplier?
According to Joshua Bloch’s Effective Java (a book that can’t be recommended enough, and which I bought thanks to continual mentions on stackoverflow): The value 31 was chosen because it is an odd prime. If it were even and the multiplication overflowed, information would be lost, as multiplication by 2 is equivalent to shifting. The … Read more