Décio Luiz Gazzoni Filho
decio at decpp.net
Mon Jul 25 07:25:59 CEST 2005
On Jul 25, 2005, at 1:01 AM, hatem Ibrahim wrote:
> Dear all
> I will be thankfull if someone iform me how to
> calculate logarithm to base 2.
> ( Is there any function to compute the log for mpz_t
> number? )
If you just want to count the number of bits (i.e. the ceiling of the
base-2 logarithm), then use the function mpz_sizeinbase(value,2).
This call is almost free, as far as I know. Now if you want the
floating-point value of the logarithm to a desired number of places
(a costly call as it involves series computation), then GMP doesn't
compute this -- you'll have to use MPFR as the other poster pointed out.
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