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Add read32le to detail/hash_range.hpp

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This commit is contained in:
Peter Dimov
2023-02-02 04:09:54 +02:00
parent 45270ae11e
commit c07630ac60
1 changed files with 31 additions and 70 deletions
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101
include/boost/container_hash/detail/hash_range.hpp
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@@ -38,6 +38,8 @@ template<> struct is_char_type<std::byte>: public boost::true_type {};
#endif #endif
// generic version
template<class It> template<class It>
inline typename boost::enable_if_< inline typename boost::enable_if_<
!is_char_type<typename std::iterator_traits<It>::value_type>::value, !is_char_type<typename std::iterator_traits<It>::value_type>::value,
@@ -52,6 +54,34 @@ std::size_t >::type
return seed; return seed;
} }
// specialized char[] version
template<class It> inline boost::uint32_t read32le( It p )
{
// clang 5+, gcc 5+ figure out this pattern and use a single mov on x86
// gcc on s390x and power BE even knows how to use load-reverse
boost::uint32_t w =
static_cast<boost::uint32_t>( static_cast<unsigned char>( p[0] ) ) |
static_cast<boost::uint32_t>( static_cast<unsigned char>( p[1] ) ) << 8 |
static_cast<boost::uint32_t>( static_cast<unsigned char>( p[2] ) ) << 16 |
static_cast<boost::uint32_t>( static_cast<unsigned char>( p[3] ) ) << 24;
return w;
}
#if defined(_MSC_VER) && !defined(__clang__)
template<class T> inline boost::uint32_t read32le( T* p )
{
boost::uint32_t w;
std::memcpy( &w, p, 4 );
return w;
}
#endif
template<class It> template<class It>
inline typename boost::enable_if_< inline typename boost::enable_if_<
is_char_type<typename std::iterator_traits<It>::value_type>::value && is_char_type<typename std::iterator_traits<It>::value_type>::value &&
@@ -63,15 +93,7 @@ std::size_t>::type
for( ; n >= 4; first += 4, n -= 4 ) for( ; n >= 4; first += 4, n -= 4 )
{ {
// clang 5+, gcc 5+ figure out this pattern and use a single mov on x86 boost::uint32_t w = read32le( first );
// gcc on s390x and power BE even knows how to use load-reverse
boost::uint32_t w =
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) << 8 |
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[2] ) ) << 16 |
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[3] ) ) << 24;
hash_combine( seed, w ); hash_combine( seed, w );
} }
@@ -117,67 +139,6 @@ std::size_t>::type
return seed; return seed;
} }
#if defined(_MSC_VER) && !defined(__clang__)
template<class T>
inline typename boost::enable_if_<is_char_type<T>::value, std::size_t>::type
hash_range( std::size_t seed, T const* first, T const* last )
{
std::size_t n = static_cast<std::size_t>( last - first );
for( ; n >= 4; first += 4, n -= 4 )
{
boost::uint32_t w;
std::memcpy( &w, first, 4 );
hash_combine( seed, w );
}
{
// add a trailing suffix byte of 0x01 because otherwise sequences of
// trailing zeroes are indistinguishable from end of string
boost::uint32_t w = 0x01u;
switch( n )
{
case 1:
w =
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
0x0100u;
break;
case 2:
w =
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) << 8 |
0x010000u;
break;
case 3:
w =
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) << 8 |
static_cast<boost::uint32_t>( static_cast<unsigned char>( first[2] ) ) << 16 |
0x01000000u;
break;
}
hash_combine( seed, w );
}
return seed;
}
#endif
template<class It> template<class It>
inline typename boost::enable_if_< inline typename boost::enable_if_<
is_char_type<typename std::iterator_traits<It>::value_type>::value && is_char_type<typename std::iterator_traits<It>::value_type>::value &&