Consider this simple implementation of endian_reverse:
+ template <class T>
+inline T endian_reverse(T x) BOOST_NOEXCEPT
+{
+ std::reverse(reinterpret_cast<unsigned char*>(&x),
+ reinterpret_cast<unsigned char*>(&x) + sizeof(T));
+ return x;
+}
+
+Under what conditions with this code fail?
+It will fail if an object of type T has one or more
+bit patterns that cause a failure. Failures usually occur when an invalid
+or otherwise special bit pattern is loaded into or saved from a hardware
+register.
The problem could in theory occur with both integers and floating +point numbers, but the +two's complement integers ubiquitous in modern computer architectures do not +have any invalid or otherwise special bit patterns that cause failure when +byte-wise reversed.
+But floating point numbers are a different story. Even if we limit +discussion to IEEE 754 (aka ISO/IEC/IEEE 60559) binary representations of 4 and +8 byte sizes, several problems are easy to demonstrate:
+...
+ template <class T>
+inline void endian_reverse_inplace(T& x)
+{
+ std::reverse(reinterpret_cast<unsigned char*>(&x),
+ reinterpret_cast<unsigned char*>(&x) + sizeof(T));
+}
+
+This is the same as the current (i.e integer) customization point +interface, so there is no need for any change.
+Warning: Even thought x may have had a valid
+value on the originating platform, after calling this function the value of
+x may differ or be invalid on this platform.
+ template <class T>
+inline void endian_reverse_copy(const T& from, T& to)
+{
+ std::reverse_copy(reinterpret_cast<const unsigned char*>(&from),
+ reinterpret_cast<const unsigned char*>(&from) + sizeof(T),
+ reinterpret_cast<unsigned char*>(&to));
+}
+
+Warning: Even thought from may have been a valid value on
+the originating platform, after calling this function the value of to
+may differ or be invalid on this platform.
++template <class T> +inline T endian_reverse_to_native(const T& x) BOOST_NOEXCEPT +{ + T tmp; + std::reverse_copy(reinterpret_cast<const unsigned char*>(&x), + reinterpret_cast<const unsigned char*>(&x) + sizeof(T), + reinterpret_cast<unsigned char*>(&tmp)); + return tmp; +}+
Warning: Even thought x may have had a valid value on the
+originating platform, the value of returned by this function may differ or be
+invalid on this platform.
Last revised: 27 March, 2015
+© Copyright Beman Dawes, 2015
+Distributed under the Boost Software License, Version 1.0. See www.boost.org/ LICENSE_1_0.txt
+ ++ + + + \ No newline at end of file