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Merge branch 'unaligned-big-endian' of https://github.com/wijagels/endian into feature/pr-31

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Peter Dimov
2018-12-06 19:57:58 +02:00
parent de4aadcb11 327b501169
commit 9f67f19d35
1 changed files with 30 additions and 0 deletions
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30
include/boost/endian/buffers.hpp
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@ -283,6 +283,21 @@ namespace endian
inline inline
T load_big_endian(const void* bytes) BOOST_NOEXCEPT T load_big_endian(const void* bytes) BOOST_NOEXCEPT
{ {
# if defined(__x86_64__) || defined(_M_X64) || defined(__i386) || defined(_M_IX86)
// On x86 (which is little endian), unaligned loads are permitted
if (sizeof(T) == n_bytes) // GCC 4.9, VC++ 14.0, and probably others, elide this
// test and generate code only for the applicable return
// case since sizeof(T) and n_bytes are known at compile
// time.
{
// Avoids -fsanitize=undefined violations due to unaligned loads
// All major x86 compilers optimize a short-sized memcpy into a single instruction
T t = 0;
std::memcpy( &t, bytes, sizeof(T) );
return big_to_native(t);
}
# endif
return unrolled_byte_loops<T, n_bytes>::load_big return unrolled_byte_loops<T, n_bytes>::load_big
(static_cast<const unsigned char*>(bytes) + n_bytes); (static_cast<const unsigned char*>(bytes) + n_bytes);
} }
@ -314,6 +329,21 @@ namespace endian
inline inline
void store_big_endian(void* bytes, T value) BOOST_NOEXCEPT void store_big_endian(void* bytes, T value) BOOST_NOEXCEPT
{ {
# if defined(__x86_64__) || defined(_M_X64) || defined(__i386) || defined(_M_IX86)
// On x86 (which is little endian), unaligned stores are permitted
if (sizeof(T) == n_bytes) // GCC 4.9, VC++ 14.0, and probably others, elide this
// test and generate code only for the applicable return
// case since sizeof(T) and n_bytes are known at compile
// time.
{
// Avoids -fsanitize=undefined violations due to unaligned stores
// All major x86 compilers optimize a short-sized memcpy into a single instruction
boost::endian::native_to_big_inplace(value);
std::memcpy( bytes, &value, sizeof(T) );
return;
}
# endif
unrolled_byte_loops<T, n_bytes>::store_big unrolled_byte_loops<T, n_bytes>::store_big
(static_cast<char*>(bytes) + n_bytes, value); (static_cast<char*>(bytes) + n_bytes, value);
} }