Computer Chess Club Archives


Search

Terms

Messages

Subject: Re: hash collisions

Author: Georg v. Zimmermann

Date: 09:09:05 07/10/02

Go up one level in this thread


On July 10, 2002 at 10:38:46, Robert Hyatt wrote:

>On July 10, 2002 at 03:19:38, Gian-Carlo Pascutto wrote:
>
>>On July 09, 2002 at 17:59:17, Robert Hyatt wrote:
>>
>>>Seems that the search is far more resistant to such errors than anybody has
>>>thought previously.
>>
>>'I told you so!'
>>
>>Many times, even. Each time you all get off and scare someone who uses
>>32-bit hashing to death. Hah!
>>
>>--
>>GCP
>
>
>Just because things have gone "well" in the testing so far, doesn't mean
>a hash error won't break something, somewhere.  64 bit hash signatures are
>cheap enough to be worthwhile insurance...

Do you really use 64 bits ?

  temp_hashkey=(wtm) ? HashKey : ~HashKey;

// this gets the possible hash entry, it checks around 24 bits for a 4MB table
  htable=trans_ref_a+((int) temp_hashkey&hash_maska);
  word1=htable->word1;
  word2=word1^htable->word2;
// this one checks another 32bits
  if (word2 == temp_hashkey) do {

that leaves 8 bits unchecked, or what am I missing ?


Georg



This page took 0 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.