Author: Robert Hyatt
Date: 21:29:06 02/18/03
Go up one level in this thread
On February 18, 2003 at 13:33:12, Tom Kerrigan wrote: >On February 16, 2003 at 03:03:03, Matt Taylor wrote: > >>On February 15, 2003 at 21:28:39, Tom Kerrigan wrote: >> >>>On February 13, 2003 at 19:40:45, Matt Taylor wrote: >>> >>>>You're not getting it. Logic on the processor for static branch prediction is >>>>80% accurate because auxillary information available to the compiler is thrown >>>>out. Consider the following loop: >>>>for(i = 0; i < 1000; i++) >>>> do_something(); >>> >>>You're the one who's not getting it if you think processors have logic for >>>static branch prediction (hint: processors do dynamic prediction) or if you >>>think these are the kinds of branches that matter for execution or compilation. >>>(Any branch prediction scheme would predict your branch with 99.9% accuracy.) >> >>Doesn't matter what you call it. AMD seems to think my Athlon has static branch >>prediction. I'm not sure why you disagree. > >I'm not sure why. Static prediction is defined as before runtime, at least for >all the definitions I've seen. Maybe they're referring to data that the Athlon >can collect for use with static predictors, i.e., profile directed compiling. Static can also mean "based on previous results". IE a killer move is a static move ordering idea, it is based on history, not on what is happening _right now_... I don't know that that is what they mean, of course. > >>>They are if they better represent computer chess than Crafty does. I'd bet most >>>chess programs out there don't use bitboards (i.e., 64 bit operations) or use >>>bitboards less than Crafty. Bitboards are almost certainly the reason why Crafty >>>performs well on I2 vs. the P4. >>Perhaps it is, perhaps it isn't. Athlon is much more efficient with 64-bit >>operations than Pentium 4 is, and the Athlon isn't pulling ahead by huge strides >>(in Crafty). > >How do you figure the Athlon is more efficient? And what do you mean by >operations? ANDing, ORing, etc.? How about loading, shifting, BSF, popcount, >etc.? > >-Tom
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