Author: Eugene Nalimov
Date: 21:43:59 06/26/02
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SHLD/SHRD x86 instuctions shift pair of 32-bit registers left/right and return high/low 32 bits. So for shift by constant amount you need exactly 2 instructions -- for left shift, shld+shl. For right shift, shrd+shr. Shift by variable amount is more complicated if you don't know that shift amount is less than 32, but those instructions still help. Eugene On June 27, 2002 at 00:03:06, Robert Hyatt wrote: >On June 25, 2002 at 20:00:47, Dieter Buerssner wrote: > >>On June 25, 2002 at 19:46:20, Robert Hyatt wrote: >> >>>The issue is this: how many instructions to do task x? For bitboards, the >>>instruction count on a 32 bit machine jumps by a factor of two unless shifts >>>are being done where it goes up even further. >> >>Why should it go up further for shifts? >> >>Dieter > > >You can't just do two 32 bit operations. You shift one end. You have to >save the part you shift out. You shift the other end. Then fold in the >part you saved from the first shift...
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