Author: Robert Hyatt
Date: 09:04:03 12/23/02
Go up one level in this thread
On December 23, 2002 at 04:25:22, Frank Phillips wrote:
>On December 22, 2002 at 21:29:07, Robert Hyatt wrote:
>
>>On December 22, 2002 at 06:44:04, Frank Phillips wrote:
>>
>>>On December 21, 2002 at 13:57:09, Vincent Diepeveen wrote:
>>>
>>>>On December 20, 2002 at 22:05:14, Walter Faxon wrote:
>>>>
>>>>>On December 20, 2002 at 05:40:35, Gerd Isenberg wrote:
>>>>>
>>>>>>On December 19, 2002 at 16:50:32, Dann Corbit wrote:
>>>>>>
>>>>>>>Suppose that we are searching at long time control, and the hash table rapidly
>>>>>>>fills up. This can throw move ordering in the toilet, if we can't find
>>>>>>>transpositions any more.
>>>>>>>
>>>>>>>What sort of replacement scheme is best for very long searches (several
>>>>>>>minutes)?
>>>>>>
>>>>>>Hi Dann,
>>>>>>
>>>>>>I use a two table approach.
>>>>>>
>>>>>>A primary big one, where i replace one of eight with the lowest
>>>>>>timestamp/draft/someFlags priority. Exact entries became a bit more resistance
>>>>>>against overwriting, the same for most left succesors of every root move (pv and
>>>>>>refutations lines).
>>>>>>
>>>>>>A smaller secondary one, with an always replacement scheme.
>>>>>>
>>>>>>In general i don't store or probe in qsearch. I use IID in __every__ interior
>>>>>>node without a move hint from hash.
>>>>>>
>>>>>>Regards,
>>>>>>Gerd
>>>>>
>>>>>
>>>>>Hi, Gerd.
>>>>>
>>>>>Good idea about IID!
>>>>>
>>>>>I have no chess program but it seems to me that one uses hashing for two
>>>>>reasons: (1) to save information that was expensive to compute but may not be
>>>>>immediately useful (closer to the root), and (2) to save information that wasn't
>>>>>very expensive to compute but may be useful very soon (close to the current
>>>>>node). That's why a two-table approach (or a one-table, two types of entry
>>>>>approach) is so often preferred.
>>>>
>>>>Not really.
>>>>
>>>>first there was a concept which most used with a single hash transposition.
>>>>then the 2 table concept was invented, but long before that already 8
>>>>probe concepts were there.
>>>>
>>>>Yet recently cache lines (starting with DDR ram and RDRAM) have increased
>>>>that much in length, that you for free can implement without risk a
>>>>concept of 4 probes in a row.
>>>>
>>>>That's obviously working a lot better than 2 slow accesses to ram at
>>>>random positions.
>>>>
>>>
>>>I am confused. Memory access for hash tables should be random - yes?
>>>Nevertheless, will not the following be together in memory. There could be more
>>>elements within the structure of course.
>>>
>>>
>>>typedef struct trans_record {
>>> TransRecordT top;
>>>#if defined TWO_LEVEL_HASH_TABLE
>>> TransRecordT bottom;
>>>#endif
>>>} HashRecordT;
>>
>>Of course it will. IN fact, this is my current hash table "entry"
>>
>>typedef struct {
>> TABLE_ENTRY prefer;
>> TABLE_ENTRY always[2];
>>} HASH_ENTRY;
>>
>>One entry "depth-preferred" as always, two entries "always store"
>>
>>They are in 48 consecutive bytes of memory.
>>
>>
>
>Bob
>
>Does your testing indicate that 3 level tables are better? I used to do it to
>use more of the available memory, since I use a standard table size of (2 ^
>power) to avoid using the mod operator, but was never convinced it was better -
>table look up and store is more complicated and can take slightly longer.
>
>Frank
I am not using a 3-level table. I am doing _exactly_ what I have been
doing for years, two tables. I use the lower N bits to access the three
entries as a single struct above. I use the NEXT single bit to choose
between the two always-store entries. My approach produces _exactly_ the
same node counts as the older separate table approach, for obvious reasons,
since they addressing is _identical_. The only difference is this is a couple
of percent faster since everything is in one or two cache lines, rathare than
always being in two cache lines in the older approach.
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.