Author: J. Wesley Cleveland
Date: 16:52:03 12/05/98
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On December 03, 1998 at 17:58:06, Andrew Dados wrote: > >On December 03, 1998 at 13:34:31, Inmann Werner wrote: > >>Thanks a lot Robert and Peter! >> >>It is what I need, and i am on the right path. >> >>But- >>are prozessors really as silly, not to have a simple code (in the prozessor) >>doing the bit testing? >> >>Werner > > All 32-bit Intel processors (and compatibles) since 386 have BSF/BSR >instructions made just this sort of bit testing/setting/resetting. For example >this assembler sequence: > >mov ecx,32 >bsf eax,ecx >jz @@nobits > >will give you number of first set bit in eax (5 in this case). Zero flag will be >set if no set bits >were present. BSR additionally resets first found bit. > > Andrew Unfortunately, these instructions are slower than an equivalent loop of "RISC-like" instructions.
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