logrithm

[Décio Luiz Gazzoni Filho]

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.

Décio

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