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Add countr_zero, countr_one

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This commit is contained in:
Peter Dimov
2020-12-28 21:52:02 +02:00
parent 045487ba96
commit a47eebf41a
5 changed files with 114 additions and 4 deletions
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67
include/boost/core/bit.hpp
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@@ -17,6 +17,7 @@
#include <boost/config.hpp>
#include <boost/static_assert.hpp>
#include <boost/cstdint.hpp>
#include <limits>
#include <cstring>
@@ -28,8 +29,9 @@ namespace core
{
// bit_cast
template<class To, class From>
To bit_cast( From const & from) BOOST_NOEXCEPT
To bit_cast( From const & from ) BOOST_NOEXCEPT
{
BOOST_STATIC_ASSERT( sizeof(To) == sizeof(From) );
@@ -39,6 +41,17 @@ To bit_cast( From const & from) BOOST_NOEXCEPT
}
// counting
namespace detail
{
BOOST_CXX14_CONSTEXPR int countl_impl( boost::uint32_t x ) BOOST_NOEXCEPT
{
return 0;
}
} // namespace detail
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countl_zero( T x ) BOOST_NOEXCEPT;
@@ -48,8 +61,56 @@ BOOST_CORE_BIT_CONSTEXPR int countl_one( T x ) BOOST_NOEXCEPT
return boost::core::countl_zero( ~x );
}
namespace detail
{
inline int countr_impl( boost::uint32_t x ) BOOST_NOEXCEPT
{
static unsigned char const mod37[] = { 32, 0, 1, 26, 2, 23, 27, 0, 3, 16, 24, 30, 28, 11, 0, 13, 4, 7, 17, 0, 25, 22, 31, 15, 29, 10, 12, 6, 0, 21, 14, 9, 5, 20, 8, 19, 18 };
return mod37[ ( -(boost::int32_t)x & x ) % 37 ];
}
inline int countr_impl( boost::uint64_t x ) BOOST_NOEXCEPT
{
return static_cast<boost::uint32_t>( x ) != 0?
boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x ) ):
boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x >> 32 ) ) + 32;
}
inline int countr_impl( boost::uint8_t x ) BOOST_NOEXCEPT
{
return boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x ) | 0x100 );
}
inline int countr_impl( boost::uint16_t x ) BOOST_NOEXCEPT
{
return boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x ) | 0x10000 );
}
} // namespace detail
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countr_zero( T x ) BOOST_NOEXCEPT;
BOOST_CORE_BIT_CONSTEXPR int countr_zero( T x ) BOOST_NOEXCEPT
{
BOOST_STATIC_ASSERT( sizeof(T) == sizeof(boost::uint8_t) || sizeof(T) == sizeof(boost::uint16_t) || sizeof(T) == sizeof(boost::uint32_t) || sizeof(T) == sizeof(boost::uint64_t) );
if( sizeof(T) == sizeof(boost::uint8_t) )
{
return boost::core::detail::countr_impl( static_cast<boost::uint8_t>( x ) );
}
else if( sizeof(T) == sizeof(boost::uint16_t) )
{
return boost::core::detail::countr_impl( static_cast<boost::uint16_t>( x ) );
}
else if( sizeof(T) == sizeof(boost::uint32_t) )
{
return boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x ) );
}
else
{
return boost::core::detail::countr_impl( static_cast<boost::uint64_t>( x ) );
}
}
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countr_one( T x ) BOOST_NOEXCEPT
@@ -61,6 +122,7 @@ template<class T>
BOOST_CORE_BIT_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT;
// rotating
template<class T>
BOOST_CXX14_CONSTEXPR T rotl( T x, int s ) BOOST_NOEXCEPT
{
@@ -76,6 +138,7 @@ BOOST_CXX14_CONSTEXPR T rotr( T x, int s ) BOOST_NOEXCEPT
}
// integral powers of 2
template<class T>
BOOST_CONSTEXPR bool has_single_bit( T x ) BOOST_NOEXCEPT
{