Author: Robert Hyatt
Date: 06:44:34 07/15/03
Go up one level in this thread
On July 15, 2003 at 02:36:27, Uri Blass wrote: >On July 15, 2003 at 00:37:32, Robert Hyatt wrote: > >>On July 14, 2003 at 18:38:51, Uri Blass wrote: >> >>>On July 14, 2003 at 16:35:05, Robert Hyatt wrote: >>> >>>>On July 14, 2003 at 16:32:17, Robert Hyatt wrote: >>>> >>>> >>>>One thing more I should add. Cray Blitz searched about 20K on a single YMP >>>>CPU. On the genius PC (486/33) it could not hit 100 nodes per second. For >>>>a speed reference. >>> >>>I think that comparing the same program is misleading. >>>I guess that a programmer who needs to write the same algorithm for 486/33 is >>>going to write it in a different way. >> >>I think some of the things are simply _not_ going to be done. Too slow. > >What did you do in cray blitz that you believe that you cannot do on 486/33 >because of speed? 1. Quality mobility. Take the set of squares a piece directly attacks. Instead of counting mobility = sum of squares, compute a "usefulness score" for each square on the board, and compute mobility = sum of usefulness scores for the squares attacked by that piece. It is computationally intensive, but very fast on a vector machine. 2. King safety. What pieces attack the area around the king, and how close to the king are the squares that are attacked? What about indirect attacks such as two rooks or rook/queen or bishop/queen in "battery"? How hard is it to get defenders over to help? Again, all pretty straightforward to calculate, but way slow. Unless you have vectors. 3. Hash table. We did 8/16 probes. But not to consecutive table entries. We used another 9 bits from the hash signature to generate a random offset to probe to, to better distribute the entries and avoid clustering/chaining. Horribly slow on a PC. Absolutely free on a vector machine. I'm sure there are other things I have missed. One comparison. On the 486/33, Cray Blitz ran at under 100nps. Well under. It varied from a low of about 10, to a peak of maybe 75-80. Crafty on that same machine would hit around 3.5K to 5K. Figure a speed difference of about 100X at least. > >I mean to things that you think that the price in term of speed is more than >being 10 times slower because I assume that Crafty can hit at least 1000 nodes >per second on 486(I have not 486 to test so it is only a guess). > >Uri It's primarily a matter of a "different approach". Vectors allow things that are simply too slow with a PC, no matter what you try to do to make it efficient. On a PC, sequential memory addresses are _way_ more efficient than random accesses. On a vector machine this is not true at all. The first word of any vector is the slowest to access. The next N are free. And the next N don't have to be consecutive. They can be uniformly spaced through memory, or randomly spaced.
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