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Use _BitScanForward

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This commit is contained in:
Peter Dimov
2020-12-29 02:02:33 +02:00
parent 8bd2239b0b
commit e8aa0c75b4
1 changed files with 36 additions and 0 deletions
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36
include/boost/core/bit.hpp
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@ -23,8 +23,10 @@
#if defined(_MSC_VER)
# include <intrin.h>
# pragma intrinsic(_BitScanForward)
# pragma intrinsic(_BitScanReverse)
# if defined(_M_X64)
# pragma intrinsic(_BitScanForward64)
# pragma intrinsic(_BitScanReverse64)
# endif
#endif // defined(_MSC_VER)
@ -235,15 +237,49 @@ namespace detail
inline int countr_impl( boost::uint32_t x ) BOOST_NOEXCEPT
{
#if defined(_MSC_VER)
unsigned long r;
if( _BitScanForward( &r, x ) )
{
return static_cast<int>( r );
}
else
{
return 32;
}
#else
static unsigned char const mod37[ 37 ] = { 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 ];
#endif
}
inline int countr_impl( boost::uint64_t x ) BOOST_NOEXCEPT
{
#if defined(_MSC_VER) && defined(_M_X64)
unsigned long r;
if( _BitScanForward64( &r, x ) )
{
return static_cast<int>( r );
}
else
{
return 64;
}
#else
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;
#endif
}
inline int countr_impl( boost::uint8_t x ) BOOST_NOEXCEPT