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Use __builtin_clz

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This commit is contained in:
Peter Dimov
2020-12-29 01:28:59 +02:00
parent 409c809cd8
commit aca46fae91
1 changed files with 52 additions and 8 deletions
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60
include/boost/core/bit.hpp
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@ -21,8 +21,6 @@
#include <limits>
#include <cstring>
#define BOOST_CORE_BIT_CONSTEXPR
namespace boost
{
namespace core
@ -40,7 +38,47 @@ To bit_cast( From const & from ) BOOST_NOEXCEPT
return to;
}
// counting
// countl
#if defined(__GNUC__) || defined(__clang__)
namespace detail
{
BOOST_CONSTEXPR inline int countl_impl( unsigned char x ) BOOST_NOEXCEPT
{
return x? __builtin_clz( x ) - ( std::numeric_limits<unsigned int>::digits - std::numeric_limits<unsigned char>::digits ): std::numeric_limits<unsigned char>::digits;
}
BOOST_CONSTEXPR inline int countl_impl( unsigned short x ) BOOST_NOEXCEPT
{
return x? __builtin_clz( x ) - ( std::numeric_limits<unsigned int>::digits - std::numeric_limits<unsigned short>::digits ): std::numeric_limits<unsigned short>::digits;
}
BOOST_CONSTEXPR inline int countl_impl( unsigned int x ) BOOST_NOEXCEPT
{
return x? __builtin_clz( x ): std::numeric_limits<unsigned int>::digits;
}
BOOST_CONSTEXPR inline int countl_impl( unsigned long x ) BOOST_NOEXCEPT
{
return x? __builtin_clzl( x ): std::numeric_limits<unsigned long>::digits;
}
BOOST_CONSTEXPR inline int countl_impl( unsigned long long x ) BOOST_NOEXCEPT
{
return x? __builtin_clzll( x ): std::numeric_limits<unsigned long long>::digits;
}
} // namespace detail
template<class T>
BOOST_CONSTEXPR int countl_zero( T x ) BOOST_NOEXCEPT
{
return boost::core::detail::countl_impl( x );
}
#else // defined(__GNUC__) || defined(__clang__)
namespace detail
{
@ -78,7 +116,7 @@ inline int countl_impl( boost::uint16_t x ) BOOST_NOEXCEPT
} // namespace detail
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countl_zero( T x ) BOOST_NOEXCEPT
int countl_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) );
@ -100,12 +138,16 @@ BOOST_CORE_BIT_CONSTEXPR int countl_zero( T x ) BOOST_NOEXCEPT
}
}
#endif // defined(__GNUC__) || defined(__clang__)
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countl_one( T x ) BOOST_NOEXCEPT
BOOST_CONSTEXPR int countl_one( T x ) BOOST_NOEXCEPT
{
return boost::core::countl_zero( static_cast<T>( ~x ) );
}
// countr
namespace detail
{
@ -135,7 +177,7 @@ inline int countr_impl( boost::uint16_t x ) BOOST_NOEXCEPT
} // namespace detail
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countr_zero( T x ) BOOST_NOEXCEPT
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) );
@ -158,11 +200,13 @@ BOOST_CORE_BIT_CONSTEXPR int countr_zero( T x ) BOOST_NOEXCEPT
}
template<class T>
BOOST_CORE_BIT_CONSTEXPR int countr_one( T x ) BOOST_NOEXCEPT
BOOST_CONSTEXPR int countr_one( T x ) BOOST_NOEXCEPT
{
return boost::core::countr_zero( static_cast<T>( ~x ) );
}
// popcount
namespace detail
{
@ -187,7 +231,7 @@ BOOST_CXX14_CONSTEXPR inline int popcount_impl( boost::uint64_t x ) BOOST_NOEXCE
} // namespace detail
template<class T>
BOOST_CORE_BIT_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT
BOOST_CXX14_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT
{
BOOST_STATIC_ASSERT( sizeof(T) <= sizeof(boost::uint64_t) );