find position of most significant bit ?

[Karl Hasselström]

On 2002-11-27 11:22:00 -0500, delta trinity wrote:
> 
> Then, I guess the fastest way to check, if you have a x86 class processor, 
> is to use the 'bsr' assembly instruction (bit scan reverse):
> 
> (Assuming you've put the A->_mp_d[ABS(A->_mp_size)] value into edx.  You 
> could also use a memory refference)
> 
> bsr   eax,edx
> 
> Then, eax contain index of most significant bit.

Use the count_leading_zeros macro. It is defined in terms of some
inline assembly something for lots of processors. It seems to use the
bsrl instruction for at least some x86 variants.

-- 
Kalle Hasselström, kha@treskal.com
      www.treskal.com/kalle