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Groups > comp.lang.java.programmer > #28155

Re: 64-bit hashing function

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On 21.04.14 00.15, Roedy Green 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.

If you could live with very rare collisions, a 32 bit hash will do as 
well. String.getHashCode will be fine in this case. It will usually not 
return the same values for similar strings.

If you can't deal with collisions, even a longer hash might not hit the 
target. Hash codes always /may/ create collisions, although they are 
very seldom for reasonable hashing algorithms.

If you absolutely want to have 64 bits and you have no well known good 
64 bit hash, use two /different/ 32 bit hash codes instead. E.g. 
String.getHashCode and CRC32.


Marcel

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Thread

64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-20 15:15 -0700
  Re: 64-bit hashing function Arne Vajhøj <arne@vajhoej.dk> - 2014-04-20 19:37 -0400
  Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-20 22:18 -0700
  Re: 64-bit hashing function Marcel Müller <news.5.maazl@spamgourmet.org> - 2014-04-21 09:19 +0200
    Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 00:51 -0700
      Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 02:05 -0700
        Re: 64-bit hashing function taqmcg@gmail.com - 2014-04-21 11:49 -0700
          Re: 64-bit hashing function taqmcg@gmail.com - 2014-04-21 12:01 -0700
        Re: 64-bit hashing function wolfgang zeidler <invalid@invalid.invalid> - 2014-04-22 20:42 +0200
      Re: 64-bit hashing function Marcel Müller <news.5.maazl@spamgourmet.org> - 2014-04-21 12:51 +0200
        Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 06:31 -0700
          Re: 64-bit hashing function Marcel Müller <news.5.maazl@spamgourmet.org> - 2014-04-21 16:40 +0200
            Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 20:45 -0700
              Re: 64-bit hashing function Marcel Müller <news.5.maazl@spamgourmet.org> - 2014-04-22 09:46 +0200
        Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 06:38 -0700
          Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 06:55 -0700
        Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 10:09 -0700
          Re: 64-bit hashing function markspace <markspace@nospam.nospam> - 2014-04-21 11:46 -0700
            Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 20:55 -0700
              Re: 64-bit hashing function markspace <markspace@nospam.nospam> - 2014-04-22 08:39 -0700
            Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 20:56 -0700
            Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 21:05 -0700
              Re: 64-bit hashing function markspace <markspace@nospam.nospam> - 2014-04-22 08:15 -0700
            Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-25 02:29 -0700
          Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-21 20:53 -0700
          Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-05-08 10:12 -0700
            Re: 64-bit hashing function Simon Lewis <simonlewis2001@gmail.com> - 2014-05-08 21:27 +0200
  Re: 64-bit hashing function rossum <rossum48@coldmail.com> - 2014-04-23 09:57 +0100
    Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-04-25 04:08 -0700
      Re: 64-bit hashing function Mike Amling <mamling@chaff.us> - 2014-05-05 11:03 -0500
        Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-05-29 16:00 -0700
        Re: 64-bit hashing function Roedy Green <see_website@mindprod.com.invalid> - 2014-05-29 16:16 -0700

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