Author: James Swafford
Date: 13:11:42 05/29/04
Go up one level in this thread
On May 29, 2004 at 14:20:43, Frank Phillips wrote: >On May 29, 2004 at 12:50:57, James Swafford wrote: > >>On May 29, 2004 at 12:50:12, Bas Hamstra wrote: >> >>> >>> >>>On May 29, 2004 at 11:10:47, James Swafford wrote: >>> >>>>In a recent post, Tord suggested setting a flag in >>>>the search when the hash table suggests a fail high, and >>>>testing whether the search would indeed fail high. >>>> >>>>The idea seems so simple I'm embarassed I haven't thought >>>>of it before. :) >>>> >>>>I've been 'pretty sure' for a long time that I've got some >>>>nasty hash bugs. I'm in the mood to exterminate them. >>>> >>>>Last night I implemented Tord's idea and, to my dismay >>>>(but not to my surprise) my hash table is saying 'fail >>>>high' when the search wouldn't have failed high. And- >>>>it doesn't take very long. :) >>>> >>>>This seems like a nasty thing to debug. I'm comtemplating >>>>how I might go about it. I'm hoping some of you can >>>>provide some suggestions... >>>> >>>>-- >>>>James >>> >>>What you describe is not a good way of finding HT bugs, IMO. To start with, hash >>>can cause inconsistent search results, even with completely bugfree code. Want >>>to track hash bugs? Do this: write code to completely recalculate hashkey from >>>scratch. Compare this key with the incremental key at every node. Analyze and >>>fix differences until they are all gone. >> >>I already do this... my keys are fine. > >Have you added debug code to check that the position in the hash table is the >same as that 'on the board'? Probably not in the way you mean. If I get a 'hit', meaning there is an entry in the hash table, I do verify the full 64 bit key. I don't have any code to add the entire board structure to table, though. Is that what you mean? -- James > > >> >> >>> >>> >>>Bas.
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