Add endian_load, use it in buffers.hpp

include/boost/endian/buffers.hpp

@@ -37,6 +37,7 @@
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
 #include <boost/predef/other/endian.h>
+#include <boost/endian/detail/endian_load.hpp>
 #include <boost/endian/conversion.hpp>
 #include <boost/type_traits/is_signed.hpp>
 #include <boost/type_traits/make_unsigned.hpp>
@@ -283,36 +284,14 @@ namespace endian
     inline
     T load_big_endian(const void* bytes) BOOST_NOEXCEPT
     {
-#   if defined(__x86_64__) || defined(_M_X64) || defined(__i386) || defined(_M_IX86)
+        return endian::endian_load<T, n_bytes, order::big>( static_cast<unsigned char const*>( bytes ) );
-      // All major x86 compilers elide this test and optimize out memcpy
-      // (the x86 architecture allows unaligned loads, but -fsanitize=undefined does not)
-      if (sizeof(T) == n_bytes)
-      {
-        T t;
-        std::memcpy( &t, bytes, sizeof(T) );
-        return endian::big_to_native(t);
-      }
-#   endif
-      return unrolled_byte_loops<T, n_bytes>::load_big
-        (static_cast<const unsigned char*>(bytes) + n_bytes);
     }
 
     template <typename T, std::size_t n_bytes>
     inline
     T load_little_endian(const void* bytes) BOOST_NOEXCEPT
     {
-#   if defined(__x86_64__) || defined(_M_X64) || defined(__i386) || defined(_M_IX86)
+        return endian::endian_load<T, n_bytes, order::little>( static_cast<unsigned char const*>( bytes ) );
-      // All major x86 compilers elide this test and optimize out memcpy
-      // (the x86 architecture allows unaligned loads, but -fsanitize=undefined does not)
-      if (sizeof(T) == n_bytes)
-      {
-        T t;
-        std::memcpy( &t, bytes, sizeof(T) );
-        return t; // or endian::little_to_native(t) if we ever extend the #ifdef to non-x86
-      }
-#   endif
-      return unrolled_byte_loops<T, n_bytes>::load_little
-        (static_cast<const unsigned char*>(bytes));
     }
 
     template <typename T, std::size_t n_bytes>

include/boost/endian/detail/endian_load.hpp

@@ -0,0 +1,265 @@
+#ifndef BOOST_ENDIAN_DETAIL_ENDIAN_LOAD_HPP_INCLUDED
+#define BOOST_ENDIAN_DETAIL_ENDIAN_LOAD_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/endian/conversion.hpp>
+#include <boost/type_traits/is_signed.hpp>
+#include <cstddef>
+#include <cstring>
+
+namespace boost
+{
+namespace endian
+{
+
+namespace detail
+{
+
+template<class T, std::size_t N1, BOOST_SCOPED_ENUM(order) O1, std::size_t N2, BOOST_SCOPED_ENUM(order) O2> struct endian_load_impl
+{
+};
+
+} // namespace detail
+
+template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) Order>
+inline T endian_load( unsigned char const * p ) BOOST_NOEXCEPT
+{
+    return detail::endian_load_impl<T, sizeof(T), endian::order::native, N, Order>()( p );
+}
+
+namespace detail
+{
+
+template<std::size_t N> struct integral_by_size
+{
+};
+
+template<> struct integral_by_size<1>
+{
+    typedef uint8_t type;
+};
+
+template<> struct integral_by_size<2>
+{
+    typedef uint16_t type;
+};
+
+template<> struct integral_by_size<4>
+{
+    typedef uint32_t type;
+};
+
+template<> struct integral_by_size<8>
+{
+    typedef uint64_t type;
+};
+
+// same endianness, same size
+
+template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) O> struct endian_load_impl<T, N, O, N, O>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        T t;
+        std::memcpy( &t, p, N );
+        return t;
+    }
+};
+
+// same size, reverse endianness
+
+template<class T, std::size_t N, BOOST_SCOPED_ENUM(order) O1, BOOST_SCOPED_ENUM(order) O2> struct endian_load_impl<T, N, O1, N, O2>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        typename integral_by_size<N>::type tmp;
+        std::memcpy( &tmp, p, N );
+
+        endian_reverse_inplace( tmp );
+
+        T t;
+        std::memcpy( &t, &tmp, N );
+        return t;
+    }
+};
+
+// expanding load 3 -> 4
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 4, Order, 3, order::little>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 4 ];
+
+        tmp[0] = p[0];
+        tmp[1] = p[1];
+        tmp[2] = p[2];
+        tmp[3] = boost::is_signed<T>::value && ( p[2] & 0x80 )? 0xFF: 0x00;
+
+        return endian::endian_load<T, 4, order::little>( tmp );
+    }
+};
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 4, Order, 3, order::big>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 4 ];
+
+        tmp[0] = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
+        tmp[1] = p[0];
+        tmp[2] = p[1];
+        tmp[3] = p[2];
+
+        return endian::endian_load<T, 4, order::big>( tmp );
+    }
+};
+
+// expanding load 5 -> 8
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8, Order, 5, order::little>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 8 ];
+
+        unsigned char fill = boost::is_signed<T>::value && ( p[4] & 0x80 )? 0xFF: 0x00;
+
+        tmp[0] = p[0];
+        tmp[1] = p[1];
+        tmp[2] = p[2];
+        tmp[3] = p[3];
+        tmp[4] = p[4];
+
+        tmp[5] = fill;
+        tmp[6] = fill;
+        tmp[7] = fill;
+
+        return endian::endian_load<T, 8, order::little>( tmp );
+    }
+};
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8, Order, 5, order::big>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 8 ];
+
+        unsigned char fill = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
+
+        tmp[0] = fill;
+        tmp[1] = fill;
+        tmp[2] = fill;
+
+        tmp[3] = p[0];
+        tmp[4] = p[1];
+        tmp[5] = p[2];
+        tmp[6] = p[3];
+        tmp[7] = p[4];
+
+        return endian::endian_load<T, 8, order::big>( tmp );
+    }
+};
+
+// expanding load 6 -> 8
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8, Order, 6, order::little>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 8 ];
+
+        unsigned char fill = boost::is_signed<T>::value && ( p[5] & 0x80 )? 0xFF: 0x00;
+
+        tmp[0] = p[0];
+        tmp[1] = p[1];
+        tmp[2] = p[2];
+        tmp[3] = p[3];
+        tmp[4] = p[4];
+        tmp[5] = p[5];
+
+        tmp[6] = fill;
+        tmp[7] = fill;
+
+        return endian::endian_load<T, 8, order::little>( tmp );
+    }
+};
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8, Order, 6, order::big>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 8 ];
+
+        unsigned char fill = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
+
+        tmp[0] = fill;
+        tmp[1] = fill;
+
+        tmp[2] = p[0];
+        tmp[3] = p[1];
+        tmp[4] = p[2];
+        tmp[5] = p[3];
+        tmp[6] = p[4];
+        tmp[7] = p[5];
+
+        return endian::endian_load<T, 8, order::big>( tmp );
+    }
+};
+
+// expanding load 7 -> 8
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8, Order, 7, order::little>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 8 ];
+
+        unsigned char fill = boost::is_signed<T>::value && ( p[6] & 0x80 )? 0xFF: 0x00;
+
+        tmp[0] = p[0];
+        tmp[1] = p[1];
+        tmp[2] = p[2];
+        tmp[3] = p[3];
+        tmp[4] = p[4];
+        tmp[5] = p[5];
+        tmp[6] = p[6];
+
+        tmp[7] = fill;
+
+        return endian::endian_load<T, 8, order::little>( tmp );
+    }
+};
+
+template<class T, BOOST_SCOPED_ENUM(order) Order> struct endian_load_impl<T, 8, Order, 7, order::big>
+{
+    inline T operator()( unsigned char const * p ) const BOOST_NOEXCEPT
+    {
+        unsigned char tmp[ 8 ];
+
+        unsigned char fill = boost::is_signed<T>::value && ( p[0] & 0x80 )? 0xFF: 0x00;
+
+        tmp[0] = fill;
+
+        tmp[1] = p[0];
+        tmp[2] = p[1];
+        tmp[3] = p[2];
+        tmp[4] = p[3];
+        tmp[5] = p[4];
+        tmp[6] = p[5];
+        tmp[7] = p[6];
+
+        return endian::endian_load<T, 8, order::big>( tmp );
+    }
+};
+
+} // namespace detail
+
+} // namespace endian
+} // namespace boost
+
+#endif  // BOOST_ENDIAN_DETAIL_ENDIAN_LOAD_HPP_INCLUDED