Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.fsmpi.rwth-aachen.de!border2.nntp.ams2.giganews.com!border1.nntp.ams2.giganews.com!backlog3.nntp.ams3.giganews.com!backlog3.nntp.ams.giganews.com!Xl.tags.giganews.com!border1.nntp.ams.giganews.com!nntp.giganews.com!local2.nntp.ams.giganews.com!nntp.bt.com!news.bt.com.POSTED!not-for-mail
NNTP-Posting-Date: Wed, 23 Apr 2014 03:57:13 -0500
From: rossum <rossum48@coldmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: 64-bit hashing function
Date: Wed, 23 Apr 2014 09:57:11 +0100
Message-ID: <5mvel9lrq0upfvobfbssrait15iicoi6ak@4ax.com>
References: <kfh8l9p1hhphqv5l62am7if9bhnotfse6j@4ax.com>
User-Agent: ForteAgent/7.20.32.1218
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Lines: 32
X-Usenet-Provider: http://www.giganews.com
X-AuthenticatedUsername: NoAuthUser
X-Trace: sv3-eImb808wNCEDtbihBlDkWWXcnHrDWdqi5qkB8LY5BXeE+f1bR6DK9TobbBPMyMUclMJW21xuxQlYZZQ!wkZk9YR/ozj3smTBv7Ldfud8Lbmkkw8kzH5fAQVnXgqJYGTUXZF/7hBjyiL8WjkonnYGy7jZFFP9!Zltu
X-Complaints-To: abuse@btinternet.com
X-DMCA-Complaints-To: abuse@btinternet.com
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly
X-Postfilter: 1.3.40
X-Original-Bytes: 2046
Xref: csiph.com comp.lang.java.programmer:28196

On Sun, 20 Apr 2014 15:15:07 -0700, Roedy Green
<see_website@mindprod.com.invalid> wrote:

>What is your favourite 64-bit hashing function/digest? This is not for
>cryptography.  Ideally there is Java source available and it is fast. 
>
>I will be using it to collapse filenames down.  There is no malice or
>privacy to worry about.
>
>I would like similar filenames to generate different results.
I usually suggest the FNV hash for this sort of situation:
http://isthe.com/chongo/tech/comp/fnv/

It is a non-crypto (and hence fast) hash in sizes from 32 bit to 1024
bit and is simple to program:

  hash = offset_basis
  for each octet_of_data to be hashed
    hash = hash xor octet_of_data
    hash = hash * FNV_prime
  endfor
  return hash

For the 64 bit version:

  offset_basis = 14695981039346656037
  FNV_prime = 1099511628211
  hash is an unsigned 64 bit integer.

HTH

rossum