PHP's new hashtable implementation
22. December 2014 About three years ago I wrote an article analyzing the memory usage of arrays in PHP 5. As part of the work on the upcoming PHP 7, large parts of the Zend Engine have been rewritten with a focus on smaller data structures requiring fewer allocations. In this article I will provide an overview of the new hashtable implementation and show why it is more efficient than the previous
How I created two images with the same MD5 hash
I posted the following images the other day which although looking totally different have exactly the same MD5 hash (e06723d4961a0a3f950e7786f3766338) . The images were just two I lifted from the web in fact I could have chosen any image or indeed any arbitrary data and created a collision with it. Why is this surprising? MD5 was designed as a cryptographic hash function. These are supposed to pos
Hash functions: An empirical comparison - strchr.com
Abstract: Benchmark program for hash tables and comparison of 15 popular hash functions. Created 16 years ago by Peter Kankowski Last changed 3 years ago Contributors: Nils, Ace, Won, Andrew M., and Georgi 'Sanmayce' Filed under Algorithms Hash tables are popular data structures for storing key-value pairs. A hash function is used to map the key value (usually a string) to array index. The functio
Throw away the keys: Easy, Minimal Perfect Hashing
I know how to make and sell software online, and I can share my tips with you. Email | Twitter | LinkedIn | Comics | All articles CORRECTION: In this article, I incorrectly state that an acyclic finite state automata (aka a DAWG) cannot be used to retrieve values associated with its keys. I have since learned that it can. By storing in each internal node the number of leaf nodes that are reachable
Parallel Locality Sensitive Hashing Project
The PLSH project was a joint project between researchers at Intel's Parallel Computing Lab and MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) to develop a new parallelized variant of the Locality Sensitive Hashing Algorithm that supports real-time similarity search on massive streaming datasets across multiple nodes. Since its development, the LSH algorithm has proven to be
Robin Hood Hashing should be your default Hash Table implementation
A Random Walk Through Geek-Space Brain dumps and other ramblings from Sebastian Sylvan Robin Hood Hashing should be your default Hash Table implementation 8/May 2013 There’s a neat variation on open-addressing based hash tables called Robin Hood hashing. This technique isn’t very well-known, but it makes a huge practical difference because it both improves performance and space utilization compare
Hardening Perl’s Hash Function
In 2003 the Perl development community was made aware of an algorithmic complexity attack on the Perl’s hash table implementation[1]. This attack was similar to reports over the last few years of attacks on other languages and packages, such as the Java, Ruby and Python hash implementations. Written by Yves Orton The basic idea of this attack is to precompute a set of keys which would hash to the
Text Classification and Feature Hashing: Sparse Matrix-Vector Multiplication with Cython | Newsle Blog
by Erich Owens Optimizing the memory footprint of a classifier used here at Newsle set us down a rabbit hole of rewriting a basic Scipy function with Cython, something that only became a problem when our high-dimensional text spaces grew to a cartoonish size, thanks to the hashing trick. Here I motivate the use of the hashing trick, how we use sparse matrix-vector multiplication for text classific
Jean-Philippe Aumasson
Cryptographer, co-founder & chief security officer @ Taurus. Books Serious Cryptography (No Starch Press, 2017) Translations' covers 🚧 Second edition: to appear in 2024 (No Starch Press) 🚧 French translation: to appear in 2024 (Dunod) Petit Pingouin (self-published, 2021) Crypto Dictionary (No Starch Press, 2020) The Hash Function BLAKE (Springer, 2014) Crypto projects Hash functions BLAKE, BLAK
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GitHub - nashby/xxhash: Ruby wrapper for xxHash
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