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mcherm : hash   19

Fibonacci Hashing: The Optimization that the World Forgot (or: a Better Alternative to Integer Modulo) | Probably Dance
Don't take mod of your hash value to select a bin in your hash table. Instead, multiply by the golden ratio.
algorithms  programming  hash 
june 2018 by mcherm
I Wrote The Fastest Hashtable | Probably Dance
A fast hashtable: linear probing with robin hood re-location of elements, and also a limit to the probe distance (if it exceeds the limit, resize the hashtable).
hash  algorithms  programming  via:HackerNews 
february 2017 by mcherm
Leapfrog Probing
An implementation of a lock-free concurrent hashtable -- and the writeup is REALLY excellent. (Read the whole chain of previous articles to get the entire story.)
concurrentprogramming  concurrency  parallelprogramming  hash  programming  computerscience 
may 2016 by mcherm
PyPy Status Blog: Faster, more memory efficient and more ordered dictionaries on PyPy
PyPy switches to a different data structure for storing hashes. The new structure is more friendly about keeping memory changes local for cache and GC improvements. It also uses substantially less memory. And it happens to make the order for iterating through a dictionary be the order in which the keys were added rather than a random order.
pypy  python  datastructures  hash  via:reddit 
february 2015 by mcherm
Robin Hood Hashing should be your default Hash Table implementation | A Random Walk Through Geek-Space
In a hash table, even out the lengths of probe chains by swapping elements when you find a longer probe chain. Lower variance in chain length leads to better performance, partly because of memory caches.
hash  datastructures  programming  algorithms  via:HackerNews 
april 2014 by mcherm
MegeFail :: fail0verflow
A textbook example of "don't do your own crypto".
cryptography  security  hash  mega 
january 2013 by mcherm
Storing Passwords Securely
Really good advice for storing passwords in an application. Don't just store a hash: use a salt, use multiple rounds (make it easy to increase the number of rounds, better yet do rounds that don't lose entropy, in fact, just use bcrypt. Also, encourage passphrases, use exponential backoff for repeated attempts, have a nonce outside the DB, and perhaps have client use assymetric to avoid sending the password over wire.
cryptography  security  programming  python  hash  salt  via:HackerNews 
june 2012 by mcherm
research!rsc: Random Hash Functions
It may be an April 1st posting, but this is an interesting idea. Since NAN values are not equal (even to THEMSELVES) perhaps they should generate a RANDOM value for their hash function.
via:HackerNews  computerscience  programming  hash  probabilisticcomputing 
april 2012 by mcherm
BCrypt Library for Java
Here is a java library for an acceptable hash function (bcrypt). SHA-1 is already weakening, and will be broken before too long. SHA-2 doesn’t exist yet. Use this (it might even win SHA-2).
via:BruceSchneier  cryptography  hash  java  programming  security 
july 2011 by mcherm
Lifetimes of cryptographic hash functions
Some comments on the state of hash functions, including a look at how long previous hash functions lasted.
via:BruceSchneier  cryptography  hash  programming  security 
july 2011 by mcherm
Simple Simhashing - a knol by Ryan Moulton
You have lots of sets and want to group them into bunches of "similar" ones (similar means shares lots of elements). This is a probabilistic algorithm that allows doing it in time LINEAR with the number of sets examined.
blogworthy  probabilisticcomputing  algorithms  computerscience  hash  programming 
november 2009 by mcherm
Schneier on Security: Ever Better Cryptanalytic Results Against SHA-1
Even better attacks against SHA-1 collisions: within a year or so we'll probably see the first ever illustration of a SHA-1 collision.
security  cryptography  hash  BruceSchneier  via:BruceSchneier 
june 2009 by mcherm
Problems with Hash Tables | Enfranchised Mind
Explanation of all the ways that a hash table can be BAD! Very well written.
programming  datastructures  hash 
may 2009 by mcherm
America's Next Top Hash Function Begins
Bruce Schneier talks about the competition to create a new standard hash function.
via:BruceSchneier  security  cryptography  hash  BruceSchneier 
november 2008 by mcherm
BBC NEWS | Technology | Letter lottery defines spam load
Curious thing: the percentage of email received which is spam varies significantly depending on the first letter of your name. Why this should be is not really explained.
spam  via:digg  hash 
september 2008 by mcherm
Enough With The Rainbow Tables: What You Need To Know About Secure Password Schemes
How to store passwords. Don't use MD5 or SHA256 - they're too fast. Bcrypt is a good choice. Better yet is SRP which does not store plaintext OR pass plaintext over the wire. But SRP *is* patented.
cryptography  md5  hash  ip-law  patent  salt 
may 2008 by mcherm
Programmer’s Toolbox Part 3: Consistent Hashing |
Consistent Hashing - an algorithm for distributing load across a number of machines in a way that is simple to implement and doesn't overburden any one machine. Useful especially for caching from web servers.
programming  algorithms  caching  scalability  hash 
march 2008 by mcherm

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