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question about symmertic evaluation
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Robert Hyatt



Joined: 27 Feb 2006
Posts: 15820
Location: Birmingham, AL
PostPost subject: Re: question about symmertic evaluation    Posted: Thu May 24, 2007 8:13 pm Reply to topic Reply with quote
Gerd Isenberg wrote:
bob wrote:

The thing is it interlaces nicely with other instructions around it... I have been using several divides in my code to scale parts of the evaluation, and it made absolutely no difference in my NPS...


K8 32-bit idiv is 42 cycles vector path. I can't imagine that this is noise in Crafty. As mentioned, division (and modulus) by constant is therefor target of heavy compiler optimizations, like division by power of two or other tricks based on reciprocal multiplication.
Code:
x idiv (2**i) ::= ( x + ((x>>31) & ((2**i)-1)) ) >> i

Using cdq instead of mov, sar 31 here by the compiler is another reason to simply trust them. Otoh one should be aware that idiv is an expensive, complex instruction compared to add/sub/shift and even imul.


However, when a program spends > 50% of the total search time inside the evaluation, 2-3 divides don't even show up in the timing and don't affect my NPS at all. Verified by lots of testing of course...
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Subject Author Date/Time
question about symmertic evaluation Uri Blass Wed May 23, 2007 7:53 pm
      Re: question about symmertic evaluation Uri Blass Wed May 23, 2007 8:45 pm
      Re: question about symmertic evaluation Gerd Isenberg Wed May 23, 2007 8:46 pm
            Re: question about symmertic evaluation Uri Blass Wed May 23, 2007 9:04 pm
            Re: question about symmertic evaluation Robert Hyatt Wed May 23, 2007 9:51 pm
                  Re: question about symmertic evaluation Uri Blass Wed May 23, 2007 10:04 pm
                  Re: question about symmertic evaluation Gerd Isenberg Wed May 23, 2007 10:09 pm
                        Re: question about symmertic evaluation Robert Hyatt Thu May 24, 2007 12:01 am
                              Re: question about symmertic evaluation Gerd Isenberg Thu May 24, 2007 7:37 am
                                    Re: question about symmertic evaluation H.G.Muller Thu May 24, 2007 8:06 am
                                          Re: question about symmertic evaluation Gerd Isenberg Thu May 24, 2007 9:24 am
                                                Re: question about symmertic evaluation H.G.Muller Thu May 24, 2007 10:39 am
                                                Re: question about symmertic evaluation Gerd Isenberg Thu May 24, 2007 11:36 am
                                                      Re: question about symmertic evaluation H.G.Muller Thu May 24, 2007 11:55 am
                                                Re: question about symmertic evaluation Gerd Isenberg Thu May 24, 2007 7:46 pm
                                          Re: question about symmertic evaluation Robert Hyatt Thu May 24, 2007 8:18 pm
                                                Re: question about symmertic evaluation Gerd Isenberg Thu May 24, 2007 8:55 pm
                                                      Re: question about symmertic evaluation Uri Blass Fri May 25, 2007 10:44 am
                                                            Re: question about symmertic evaluation Gerd Isenberg Fri May 25, 2007 6:28 pm
                                                                  Re: question about symmertic evaluation Uri Blass Fri May 25, 2007 7:42 pm
                                                                        Re: question about symmertic evaluation Gerd Isenberg Fri May 25, 2007 8:00 pm
                                    Re: question about symmertic evaluation Robert Hyatt Thu May 24, 2007 8:13 pm
                                          Re: question about symmertic evaluation Gerd Isenberg Thu May 24, 2007 8:33 pm
                                                Re: question about symmertic evaluation Robert Hyatt Sat May 26, 2007 1:05 am
                                                      Re: question about symmertic evaluation Gerd Isenberg Sat May 26, 2007 7:18 am
                                                            Re: question about symmertic evaluation Robert Hyatt Sat May 26, 2007 5:08 pm
                                                                  Re: question about symmertic evaluation Robert Hyatt Sat May 26, 2007 5:25 pm
                                                                  Re: question about symmertic evaluation Gerd Isenberg Sat May 26, 2007 6:23 pm
                                                                        Re: question about symmertic evaluation Robert Hyatt Sun May 27, 2007 2:48 pm
                  Re: question about symmertic evaluation Steven Edwards Thu May 24, 2007 3:42 am
                        Re: question about symmertic evaluation Robert Hyatt Thu May 24, 2007 8:20 pm
      Re: question about symmertic evaluation Robert Hyatt Wed May 23, 2007 9:50 pm
      Re: question about symmertic evaluation William H. Rogers Fri May 25, 2007 7:48 pm
            Re: question about symmertic evaluation Uri Blass Sat May 26, 2007 11:38 am
                  Re: question about symmertic evaluation H.G.Muller Sat May 26, 2007 2:07 pm
      Re: question about symmertic evaluation Vincent Diepeveen Sat May 26, 2007 7:27 pm
            Re: question about symmertic evaluation Gerd Isenberg Sat May 26, 2007 8:20 pm
            Re: question about symmertic evaluation Uri Blass Sat May 26, 2007 9:29 pm
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