118 lines
3.5 KiB
C++
118 lines
3.5 KiB
C++
// 32 bit implementation based off of Boost hash
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// Only implementing 32 bit version of char based ranges
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#ifndef BOOST_HASH_DETAIL_HASH_RANGE_32_HPP
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#define BOOST_HASH_DETAIL_HASH_RANGE_32_HPP
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#include <boost_custom/container_hash/hash_fwd_32.hpp>
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#include <boost_custom/container_hash/version.hpp>
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#if BOOST_VERSION_HAS_HASH_RANGE
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#include <boost/container_hash/detail/hash_range.hpp>
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#else
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#include <boost/type_traits/integral_constant.hpp>
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#include <boost/type_traits/enable_if.hpp>
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#include <boost/type_traits/is_same.hpp>
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#include <boost/cstdint.hpp>
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#include <cstddef>
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#include <climits>
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#include <iterator>
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#endif // #if BOOST_VERSION_HAS_HASH_RANGE
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namespace boost
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{
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namespace hash_detail
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{
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#if !BOOST_VERSION_HAS_HASH_RANGE
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template<class T> struct is_char_type: public boost::false_type {};
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#if CHAR_BIT == 8
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template<> struct is_char_type<char>: public boost::true_type {};
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template<> struct is_char_type<signed char>: public boost::true_type {};
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template<> struct is_char_type<unsigned char>: public boost::true_type {};
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#if defined(__cpp_char8_t) && __cpp_char8_t >= 201811L
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template<> struct is_char_type<char8_t>: public boost::true_type {};
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#endif
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#if defined(__cpp_lib_byte) && __cpp_lib_byte >= 201603L
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template<> struct is_char_type<std::byte>: public boost::true_type {};
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#endif
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#endif
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#endif // #if !BOOST_VERSION_HAS_HASH_RANGE
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template<class It>
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inline typename boost::enable_if_<
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is_char_type<typename std::iterator_traits<It>::value_type>::value &&
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is_same<typename std::iterator_traits<It>::iterator_category, std::random_access_iterator_tag>::value,
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std::size_t>::type
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hash_range_32( uint32_t seed, It first, It last )
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{
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std::size_t n = static_cast<std::size_t>( last - first );
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for( ; n >= 4; first += 4, n -= 4 )
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{
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// clang 5+, gcc 5+ figure out this pattern and use a single mov on x86
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// gcc on s390x and power BE even knows how to use load-reverse
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boost::uint32_t w =
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) << 8 |
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[2] ) ) << 16 |
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[3] ) ) << 24;
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hash_combine_32( seed, w );
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}
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{
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// add a trailing suffix byte of 0x01 because otherwise sequences of
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// trailing zeroes are indistinguishable from end of string
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boost::uint32_t w = 0x01u;
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switch( n )
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{
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case 1:
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w =
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
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0x0100u;
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break;
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case 2:
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w =
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) << 8 |
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0x010000u;
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break;
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case 3:
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w =
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) << 8 |
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static_cast<boost::uint32_t>( static_cast<unsigned char>( first[2] ) ) << 16 |
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0x01000000u;
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break;
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}
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hash_combine_32( seed, w );
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}
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return seed;
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}
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} // namespace hash_detail
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} // namespace boost
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#endif // #ifndef BOOST_HASH_DETAIL_HASH_RANGE_32_HPP
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