Author: Vincent Diepeveen
Date: 12:05:29 11/19/02
Go up one level in this thread
On November 19, 2002 at 14:14:35, Robert Hyatt wrote: If you want to keep your thing at kindergarten level, bitboards is the way to go of course :) >On November 19, 2002 at 13:30:57, Christophe Theron wrote: > >>On November 19, 2002 at 13:15:09, Gerd Isenberg wrote: >> >>>On November 19, 2002 at 12:25:11, Gian-Carlo Pascutto wrote: >>> >>>>On November 19, 2002 at 11:35:24, Robert Hyatt wrote: >>>> >>>>>Bitboards have a bit of a performance advantage on 64 bit processors, >>>> >>>>Proof? >>>> >>>>-- >>>>GCP >>> >>>Hi Gian-Carlo, >>> >>>I think that's evident. If the none bitboarders have to use implicite native >>>data-width of 64 bit integers, they have to transfer 32 additional zero bits >>>without any additional information for each integer access. Of course you will >>>pack some data, but all the local ints... >>> >>>So the information density for bitboarders grows with 64bit-architectures >>>relative to none bitboarders. That also effects register usage, and that's IMHO >>>more important. On x86-32bit architectures you can only hold three bitboards in >>>registers, and thats even most a hard task. Actually, if you have a local >>>routine with three bitboards and a few ints on the stack, there are a lot >>>register/memory moves. Simply the data-width doubles the number of bitboard >>>registers, not considered the increase in general purpose registers, or with >>>hammer the number of mmx- and 128-bit xmm registers. >>> >>>Whether a bitboard based program is stronger than a none bitboard program >>>depends obviuosly also on other things, but in principle :) >>> >>>Cheers, >>>Gerd >> >> >> >>You have just explained why the bitboarders are less handicapped on 64 bits >>machines. >> >>You have not explained why they are supposed to have "a bit of performance >>advantage on 64 bits processors". >> >> >> >> Christophe > > >Actually he _did_ explain. A 32 bit program, running on a 64 bit machine, >simply passes >32 bit values around, taking _no_ advantage from the additional 32 bits of data >that is >available. A bitboard program, on the other hand, _does_ get an advantage. >Rather than >having to use two instructions for 64 bit AND/OR/XOR instructions, it can use >just one. >Rather than using even more to do 64 bit shifts, it uses just one. > >Seems intuitive that 64 bit programs will run faster on a 64 bit processor, even >if the 64 bit >processor executes instructions _exactly_ at the same speed (and using the same >number of >registers and so forth). All the 64 bit stuff reduces to a single instruction, >while the normal >chess program does _exactly_ the same work on either...
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