Author: Robert Hyatt
Date: 15:49:06 01/16/01
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On January 15, 2001 at 23:29:42, Larry Griffiths wrote: >On January 15, 2001 at 20:15:17, Ralf Elvsén wrote: > >>I looked ay the instruction set for the Itanium processor. >>As far as I could see there was no instruction to get the first/last >>bit set. >> >>Can someone with insight in processor design describe the >>considerations done by the designers when they decide to >>include or to not include such an instruction? (Assuming they >>are not chess programmers :) >> >>Is it possible to quantify how the "trouble" to include >>it scales with the number of bits? I.e. is it even less likely >>to be found in an 128-bit processor? >> >>Ralf > >I asked this question a while back. > >I think IA32 instructions might still be supported and maybe the BSF BSR >instructions are still available. > >Maybe you can verify this. > >Larry. I actually think that they are not supported if I recall Eugene's comments correctly. It is possible to find which byte is non-zero in a 64 bit word, but I think it then requires a 256-entry table look-up to find the set bit.
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