Re: [Boost-users] About naming of integer log in base 2

Subject: Re: [Boost-users] About naming of integer log in base 2
From: Murilo Adriano Vasconcelos (muriloufg_at_[hidden])
Date: 2010-07-17 13:52:50

Hi,

>  The initial intent was log2(0) = -1, you can check if your compiler isn't
> GCC that count_leading_zeros(T(0)) is always sizeof(T) * 8 (all bits are
> leading zeros).
>
> But one of the intents of this implementation is performance so, using
> compiler optimized functions is desired.
>
>
>
> So the function to be analyzed in this case is count_leading_zeros.
>
>
>
> I can see the ‘need for speed’, but that doesn’t change the argument for
> using policies to allow users to control at compile time how exceptional
> situations are handled.  Policies should have no effect on run time, apart
> from any checks implied by the chosen policy.
>
>
>
> Paul
>

Paul:

What if I make 2 versions of ilog2:

   - unchecked_ilog2(T value) - don't checks the input value
   - ilog2(T value) - returns -1 if value == 0 else returns
   unchecked_ilog2(value)

Following the line of:
http://www.boost.org/doc/libs/1_43_0/libs/math/doc/sf_and_dist/html/math_toolkit/special/factorials/sf_factorial.html

Steven:

I will maintain the name ilog2 for now.

Best,

-- 
Murilo Adriano Vasconcelos
http://murilo.wordpress.com