Author: James Swafford
Date: 19:50:44 05/29/04
Go up one level in this thread
On May 29, 2004 at 22:21:55, Robert Hyatt wrote: >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. > I don't understand what you're saying. I probe the table towards the top of my search (only time check comes before that). I'm not allowing _any_ cutoffs during this test. No fail highs, no fail lows, no exact scores. I'm simply recording that the hash table says I _should_ fail high, and I only do that IF the depth recorded in the table is exactly the same as 'depth' in the search. >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... I just disabled the other hash probes. Do you still think the test is flawed? > > > > > >>-- >>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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