Author: Robert Hyatt
Date: 19:21:55 05/29/04
Go up one level in this thread
On May 29, 2004 at 22:01:23, James Swafford wrote: >On May 29, 2004 at 21:23:28, Robert Hyatt 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 is _not_ necessarily a bug. >> >>Your hash table entry can have a draft > depth, while the real search you will >>do will only go to depth. A deeper search might say fail high while a shallower >>search fails low. >> >>That test is no good... >> > >That was suggested below, so I modifed the test to only set >the 'hash_says_fh' flag if the hash depth == current search depth, >and disabled null move, extensions, other hash table cutoffs, >etc. > >On move 41 of WAC, it happened again. I've not even >begun to hunt it down (maybe just a collision?), but >I will. > Again, that will _not_ work. You still probe the table below the point where you decide to do a search to see if the table result is correct. And down into the tree there you can get different results again. You simply can not test the hashing that way. Unless you restrict _all_ hash probes to only match on exact depth as well... By "all" I mean _all_ and not just the probes where you are going to validate them by a search... >-- >James > > > >> >>> >>>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
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