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Revert integral hashing

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This commit is contained in:
Peter Dimov
2022-05-30 01:57:56 +03:00
parent f08204e29a
commit 14f8934bff
1 changed files with 49 additions and 20 deletions
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69
include/boost/container_hash/hash.hpp
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@@ -24,6 +24,7 @@
#include <boost/type_traits/is_enum.hpp>
#include <boost/type_traits/is_integral.hpp>
#include <boost/type_traits/is_floating_point.hpp>
#include <boost/type_traits/is_signed.hpp>
#include <boost/type_traits/make_unsigned.hpp>
#include <boost/type_traits/enable_if.hpp>
#include <boost/cstdint.hpp>
@@ -72,9 +73,13 @@ namespace boost
namespace hash_detail
{
template<class T, bool bigger_than_size_t = (sizeof(T) > sizeof(std::size_t)), bool size_t_64 = (sizeof(std::size_t) * CHAR_BIT >= 64)> struct hash_integral_impl;
template<class T,
bool bigger_than_size_t = (sizeof(T) > sizeof(std::size_t)),
std::size_t size_t_bits = sizeof(std::size_t) * CHAR_BIT,
std::size_t type_bits = sizeof(T) * CHAR_BIT>
struct hash_integral_impl;
template<class T, bool size_t_64> struct hash_integral_impl<T, false, size_t_64>
template<class T, std::size_t size_t_bits, std::size_t type_bits> struct hash_integral_impl<T, false, size_t_bits, type_bits>
{
static std::size_t fn( T v )
{
@@ -82,48 +87,72 @@ namespace boost
}
};
template<class T> struct hash_integral_impl<T, true, false>
template<class T> struct hash_integral_impl<T, true, 32, 64>
{
static std::size_t fn( T v )
{
// The bias makes negative numbers that fit into a ssize_t hash to themselves
// E.g. hash_value( -4LL ) == (size_t)-4
std::size_t seed = 0;
std::size_t const bias = (std::numeric_limits<std::size_t>::max)() / 4;
seed ^= static_cast<std::size_t>( v >> 32 ) + ( seed << 6 ) + ( seed >> 2 );
seed ^= static_cast<std::size_t>( v ) + ( seed << 6 ) + ( seed >> 2 );
// 4294967291 = 2^32-5, biggest prime under 2^32
// we use boost::uint32_t( -5 ), because g++ warns on 4294967291
return static_cast<std::size_t>(
( static_cast<typename boost::make_unsigned<T>::type>( v ) + bias )
% static_cast<boost::uint32_t>( -5 ) ) - bias;
return seed;
}
};
template<class T> struct hash_integral_impl<T, true, true>
template<class T> struct hash_integral_impl<T, true, 32, 128>
{
static std::size_t fn( T v )
{
std::size_t const bias = (std::numeric_limits<std::size_t>::max)() / 4;
std::size_t seed = 0;
// 18446744073709551557ULL = 2^64-59, biggest prime under 2^64
// we have to use boost::uint64_t( -59 ), because g++ warns in C++03 mode
seed ^= static_cast<std::size_t>( v >> 96 ) + ( seed << 6 ) + ( seed >> 2 );
seed ^= static_cast<std::size_t>( v >> 64 ) + ( seed << 6 ) + ( seed >> 2 );
seed ^= static_cast<std::size_t>( v >> 32 ) + ( seed << 6 ) + ( seed >> 2 );
seed ^= static_cast<std::size_t>( v ) + ( seed << 6 ) + ( seed >> 2 );
return static_cast<std::size_t>(
( static_cast<typename boost::make_unsigned<T>::type>( v ) + bias )
% static_cast<boost::uint64_t>( -59 ) ) - bias;
return seed;
}
};
template<class T> struct hash_integral_impl<T, true, 64, 128>
{
static std::size_t fn( T v )
{
std::size_t seed = 0;
seed ^= static_cast<std::size_t>( v >> 64 ) + ( seed << 6 ) + ( seed >> 2 );
seed ^= static_cast<std::size_t>( v ) + ( seed << 6 ) + ( seed >> 2 );
return seed;
}
};
} // namespace hash_detail
template <typename T>
typename boost::enable_if_<boost::is_integral<T>::value, std::size_t>::type
typename boost::enable_if_<boost::is_integral<T>::value && !boost::is_signed<T>::value, std::size_t>::type
hash_value( T v )
{
return hash_detail::hash_integral_impl<T>::fn( v );
}
template <typename T>
typename boost::enable_if_<boost::is_integral<T>::value && boost::is_signed<T>::value, std::size_t>::type
hash_value( T v )
{
typedef typename boost::make_unsigned<T>::type U;
if( v >= 0 )
{
return hash_value( static_cast<U>( v ) );
}
else
{
return ~hash_value( static_cast<U>( ~static_cast<U>( v ) ) );
}
}
// enumeration types
template <typename T>