boostorg/core
1
0
Fork 1
mirror of https://github.com/boostorg/core.git synced 2025-11-30 06:09:56 +01:00
Code Issues Packages Projects Releases Wiki Activity

Add popcount

Browse Source
This commit is contained in:
Peter Dimov
2020-12-29 01:06:22 +02:00
parent dc8aa5eb39
commit 409c809cd8
4 changed files with 84 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
include/boost/core/bit.hpp
View File

@@ -100,7 +100,6 @@ BOOST_CORE_BIT_CONSTEXPR int countl_zero( T x ) BOOST_NOEXCEPT
}
}
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countl_one( T x ) BOOST_NOEXCEPT
{
@@ -164,8 +163,43 @@ BOOST_CORE_BIT_CONSTEXPR int countr_one( T x ) BOOST_NOEXCEPT
return boost::core::countr_zero( static_cast<T>( ~x ) );
}
namespace detail
{
BOOST_CXX14_CONSTEXPR inline int popcount_impl( boost::uint32_t x ) BOOST_NOEXCEPT
{
x = x - ( ( x >> 1 ) & 0x55555555 );
x = ( x & 0x33333333 ) + ( ( x >> 2 ) & 0x33333333 );
x = ( x + ( x >> 4 ) ) & 0x0F0F0F0F;
return static_cast<unsigned>( ( x * 0x01010101 ) >> 24 );
}
BOOST_CXX14_CONSTEXPR inline int popcount_impl( boost::uint64_t x ) BOOST_NOEXCEPT
{
x = x - ( ( x >> 1 ) & 0x5555555555555555 );
x = ( x & 0x3333333333333333 ) + ( ( x >> 2 ) & 0x3333333333333333 );
x = ( x + ( x >> 4 ) ) & 0x0F0F0F0F0F0F0F0F;
return static_cast<unsigned>( ( x * 0x0101010101010101 ) >> 56 );
}
} // namespace detail
template<class T>
BOOST_CORE_BIT_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT;
BOOST_CORE_BIT_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT
{
BOOST_STATIC_ASSERT( sizeof(T) <= sizeof(boost::uint64_t) );
if( sizeof(T) <= sizeof(boost::uint32_t) )
{
return boost::core::detail::popcount_impl( static_cast<boost::uint32_t>( x ) );
}
else
{
return boost::core::detail::popcount_impl( static_cast<boost::uint64_t>( x ) );
}
}
// rotating