Re: [boost] Bits and Ints: Intention Request

Subject: Re: [boost] Bits and Ints: Intention Request
From: Murilo Adriano Vasconcelos (muriloufg_at_[hidden])
Date: 2010-07-14 16:43:59

But maybe it can be a good point to use enable_if<> to for 8 and 16-bit
integrals specializations and use the correct __builtin for the others like:

template <typename T>
inline int count_leading_zeros(T value)
{
#ifndef BOOST_HAS_NO_INT64_T
       return __builtin_clzll(value) - (64 - (sizeof(T) << 3));
#else
       return __builtin_clz(value) - (32 - (sizeof(T) << 3));
#endif
}

template<>
inline int count_leading_zeros(unsigned int value)
{
        return __builtin_clz(value);
}

template<>
inline int count_leading_zeros(unsigned long int value)
{
        return __builtin_clzl(value);
}

template<>
inline int count_leading_zeros(unsigned long long int value)
{
        return __builtin_clzll(value);
}

What do you think?

2010/7/14 Murilo Adriano Vasconcelos <muriloufg_at_[hidden]>

> I did that way because GCC do not have those __builtin functions for 16-bit
> and 8-bit integral types.
> So, that way I implemented it works for 64, 32, 16 an 8-bit *unsigned*
> integral values.
>
> 2010/7/14 Tim Blechmann <tim_at_[hidden]>
>
> hi,
>>
>> >    - *Count Leading Zeros*
>>
>> as for:
>>
>> template <typename T>
>> inline int count_leading_zeros(T value)
>> {
>> #ifndef BOOST_HAS_NO_INT64_T
>>        return __builtin_clzll(value) - (64 - (sizeof(T) << 3));
>> #else
>>        return __builtin_clz(value) - (32 - (sizeof(T) << 3));
>> #endif
>> }
>>
>> __builtin_clz comes in different versions for unsigned int, unsigned long
>> and unsigned long long. i think the safest way to make use of the correct
>> version is by using template specialization ... maybe similar to [1] ... i
>> am also not sure, how it will behave for signed types ...
>>
>> but it is great to see an ilog2 implementation ...
>>
> =)
>
>
>>
>> cheers, tim
>>
>> [1]
>>
>> http://tim.klingt.org/git?p=boost_heap.git;a=blob;f=boost/heap/detail/ilog2.hpp
>>
>>
>> --
>> tim_at_[hidden]
>> http://tim.klingt.org
>>
>> Cheat your landlord if you can and must, but do not try to shortchange
>> the Muse. It cannot be done. You can't fake quality any more than you
>> can fake a good meal.
>>  William S. Burroughs
>>
>>
>> _______________________________________________
>> Unsubscribe & other changes:
>> http://lists.boost.org/mailman/listinfo.cgi/boost
>>
>
> Best,
>
>
> --
> Murilo Adriano Vasconcelos
> http://murilo.wordpress.com
>

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