Author: Frank Phillips
Date: 11:20:43 05/29/04
Go up one level in this thread
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'? > > >> >> >>Bas.
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