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@gmail.com>
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@klingt.org>
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....
-- tim@klingt.org http://tim.klingt.org
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Best,
-- Murilo Adriano Vasconcelos http://murilo.wordpress.com
-- Murilo Adriano Vasconcelos http://murilo.wordpress.com