From de33887009680b5753db72f2ae6b776cfef14456 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Wed, 13 Mar 2019 01:44:29 +0200
Subject: [PATCH] Identify and static-assert the requirements of
 endian_load/endian_store

---
 include/boost/endian/detail/endian_load.hpp   | 30 ++++++++++++++
 include/boost/endian/detail/endian_store.hpp  | 28 +++++++++++++
 .../endian/detail/is_trivially_copyable.hpp   | 39 +++++++++++++++++++
 3 files changed, 97 insertions(+)
 create mode 100644 include/boost/endian/detail/is_trivially_copyable.hpp

diff --git a/include/boost/endian/detail/endian_load.hpp b/include/boost/endian/detail/endian_load.hpp
index c292e77..8fac68a 100644
--- a/include/boost/endian/detail/endian_load.hpp
+++ b/include/boost/endian/detail/endian_load.hpp
@@ -7,8 +7,12 @@
 // http://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/endian/detail/integral_by_size.hpp>
+#include <boost/endian/detail/is_trivially_copyable.hpp>
 #include <boost/endian/conversion.hpp>
 #include <boost/type_traits/is_signed.hpp>
+#include <boost/type_traits/is_integral.hpp>
+#include <boost/type_traits/is_enum.hpp>
+#include <boost/static_assert.hpp>
 #include <cstddef>
 #include <cstring>
 
@@ -26,6 +30,12 @@ template<class T, std::size_t N1, BOOST_SCOPED_ENUM(order) O1, std::size_t N2, B
 
 } // namespace detail
 
+// Requires:
+//
+//    1 <= N <= sizeof(T) <= 8
+//    T is TriviallyCopyable
+//    if N < sizeof(T), T is integral or enum
+
 template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) Order>
 inline T endian_load( unsigned char const * p ) BOOST_NOEXCEPT
 {
@@ -41,6 +51,8 @@ template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) O> struct endian_load_
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_trivially_copyable<T>::value );
+
         T t;
         std::memcpy( &t, p, N );
         return t;
@@ -53,6 +65,8 @@ template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) O1, BOOST_SCOPED_ENUM(
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_trivially_copyable<T>::value );
+
         typename integral_by_size<N>::type tmp;
         std::memcpy( &tmp, p, N );
 
@@ -70,6 +84,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 4,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 4 ];
 
         tmp[0] = p[0];
@@ -85,6 +101,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 4,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 4 ];
 
         tmp[0] = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
@@ -102,6 +120,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
 
         unsigned char fill = boost::is_signed<T>::value && ( p[4] & 0x80 )? 0xFF: 0x00;
@@ -124,6 +144,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
 
         unsigned char fill = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
@@ -148,6 +170,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
 
         unsigned char fill = boost::is_signed<T>::value && ( p[5] & 0x80 )? 0xFF: 0x00;
@@ -170,6 +194,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
 
         unsigned char fill = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
@@ -194,6 +220,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
 
         unsigned char fill = boost::is_signed<T>::value && ( p[6] & 0x80 )? 0xFF: 0x00;
@@ -216,6 +244,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8,
 {
     inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
 
         unsigned char fill = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
diff --git a/include/boost/endian/detail/endian_store.hpp b/include/boost/endian/detail/endian_store.hpp
index 33501b6..03edbbe 100644
--- a/include/boost/endian/detail/endian_store.hpp
+++ b/include/boost/endian/detail/endian_store.hpp
@@ -7,7 +7,9 @@
 // http://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/endian/detail/integral_by_size.hpp>
+#include <boost/endian/detail/is_trivially_copyable.hpp>
 #include <boost/endian/conversion.hpp>
+#include <boost/static_assert.hpp>
 #include <cstddef>
 #include <cstring>
 
@@ -25,6 +27,12 @@ template<class T, std::size_t N1, BOOST_SCOPED_ENUM(order) O1, std::size_t N2, B
 
 } // namespace detail
 
+// Requires:
+//
+//    1 <= N <= sizeof(T) <= 8
+//    T is TriviallyCopyable
+//    if N < sizeof(T), T is integral or enum
+
 template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) Order>
 inline void endian_store( T const & v, unsigned char * p ) BOOST_NOEXCEPT
 {
@@ -40,6 +48,8 @@ template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) O> struct endian_store
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_trivially_copyable<T>::value );
+
         std::memcpy( p, &v, N );
     }
 };
@@ -50,6 +60,8 @@ template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) O1, BOOST_SCOPED_ENUM(
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_trivially_copyable<T>::value );
+
         typename integral_by_size<N>::type tmp;
         std::memcpy( &tmp, &v, N );
 
@@ -65,6 +77,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 4,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 4 ];
         endian::endian_store<T, 4, order::little>( v, tmp );
 
@@ -78,6 +92,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 4,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 4 ];
         endian::endian_store<T, 4, order::big>( v, tmp );
 
@@ -93,6 +109,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 8,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
         endian::endian_store<T, 8, order::little>( v, tmp );
 
@@ -108,6 +126,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 8,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
         endian::endian_store<T, 8, order::big>( v, tmp );
 
@@ -125,6 +145,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 8,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
         endian::endian_store<T, 8, order::little>( v, tmp );
 
@@ -141,6 +163,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 8,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
         endian::endian_store<T, 8, order::big>( v, tmp );
 
@@ -159,6 +183,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 8,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
         endian::endian_store<T, 8, order::little>( v, tmp );
 
@@ -176,6 +202,8 @@ template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_store_impl<T, 8,
 {
     inline void operator()( T const & v, unsigned char * p ) const BOOST_NOEXCEPT
     {
+        BOOST_STATIC_ASSERT( is_integral<T>::value || is_enum<T>::value );
+
         unsigned char tmp[ 8 ];
         endian::endian_store<T, 8, order::big>( v, tmp );
 
diff --git a/include/boost/endian/detail/is_trivially_copyable.hpp b/include/boost/endian/detail/is_trivially_copyable.hpp
new file mode 100644
index 0000000..334cd46
--- /dev/null
+++ b/include/boost/endian/detail/is_trivially_copyable.hpp
@@ -0,0 +1,39 @@
+#ifndef BOOST_ENDIAN_DETAIL_IS_TRIVIALLY_COPYABLE_HPP_INCLUDED
+#define BOOST_ENDIAN_DETAIL_IS_TRIVIALLY_COPYABLE_HPP_INCLUDED
+
+// Copyright 2019 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/type_traits/has_trivial_copy.hpp>
+#include <boost/type_traits/has_trivial_assign.hpp>
+
+#if !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
+# include <type_traits>
+#endif
+
+namespace boost
+{
+namespace endian
+{
+namespace detail
+{
+
+#if !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
+
+using std::is_trivially_copyable;
+
+#else
+
+template<class T> struct is_trivially_copyable: boost::integral_constant<bool,
+    boost::has_trivial_copy<T>::value && boost::has_trivial_assign<T>::value> {};
+
+#endif
+
+} // namespace detail
+} // namespace endian
+} // namespace boost
+
+#endif  // BOOST_ENDIAN_DETAIL_IS_TRIVIALLY_COPYABLE_HPP_INCLUDED