Add byteswap to bit.hpp

include/boost/core/bit.hpp

@@ -792,6 +792,60 @@ typedef endian::type endian_type;
 
 #undef BOOST_CORE_BIT_NATIVE_INITIALIZER
 
+// byteswap
+
+namespace detail
+{
+
+BOOST_CONSTEXPR inline boost::uint8_t byteswap_impl( boost::uint8_t x ) BOOST_NOEXCEPT
+{
+    return x;
+}
+
+BOOST_CONSTEXPR inline boost::uint16_t byteswap_impl( boost::uint16_t x ) BOOST_NOEXCEPT
+{
+    return (x << 8) | (x >> 8);
+}
+
+BOOST_CXX14_CONSTEXPR inline boost::uint32_t byteswap_impl( boost::uint32_t x ) BOOST_NOEXCEPT
+{
+    boost::uint32_t step16 = x << 16 | x >> 16;
+    return ((step16 << 8) & 0xff00ff00) | ((step16 >> 8) & 0x00ff00ff);
+}
+
+BOOST_CXX14_CONSTEXPR inline boost::uint64_t byteswap_impl( boost::uint64_t x ) BOOST_NOEXCEPT
+{
+    boost::uint64_t step32 = x << 32 | x >> 32;
+    boost::uint64_t step16 = (step32 & 0x0000FFFF0000FFFFULL) << 16 | (step32 & 0xFFFF0000FFFF0000ULL) >> 16;
+    return (step16 & 0x00FF00FF00FF00FFULL) << 8 | (step16 & 0xFF00FF00FF00FF00ULL) >> 8;
+}
+
+} // namespace detail
+
+template<class T> BOOST_CXX14_CONSTEXPR T byteswap( T x ) BOOST_NOEXCEPT
+{
+    BOOST_STATIC_ASSERT( std::numeric_limits<T>::is_integer );
+
+    BOOST_STATIC_ASSERT( sizeof(T) == sizeof(boost::uint8_t) || sizeof(T) == sizeof(boost::uint16_t) || sizeof(T) == sizeof(boost::uint32_t) || sizeof(T) == sizeof(boost::uint64_t) );
+
+    BOOST_IF_CONSTEXPR ( sizeof(T) == sizeof(boost::uint8_t) )
+    {
+        return static_cast<T>( boost::core::detail::byteswap_impl( static_cast<boost::uint8_t>( x ) ) );
+    }
+    else BOOST_IF_CONSTEXPR ( sizeof(T) == sizeof(boost::uint16_t) )
+    {
+        return static_cast<T>( boost::core::detail::byteswap_impl( static_cast<boost::uint16_t>( x ) ) );
+    }
+    else BOOST_IF_CONSTEXPR ( sizeof(T) == sizeof(boost::uint32_t) )
+    {
+        return static_cast<T>( boost::core::detail::byteswap_impl( static_cast<boost::uint32_t>( x ) ) );
+    }
+    else
+    {
+        return static_cast<T>( boost::core::detail::byteswap_impl( static_cast<boost::uint64_t>( x ) ) );
+    }
+}
+
 } // namespace core
 } // namespace boost
 

test/Jamfile.v2

@@ -296,6 +296,8 @@ run bit_popcount_test.cpp
   : : : $(pedantic-errors) ;
 run bit_endian_test.cpp
   : : : $(pedantic-errors) ;
+run bit_byteswap_test.cpp
+  : : : $(pedantic-errors) ;
 
 compile-fail bit_width_fail.cpp
   : <warnings>off ;
@@ -308,6 +310,7 @@ compile has_single_bit_test_cx.cpp ;
 compile bit_floor_test_cx.cpp ;
 compile bit_ceil_test_cx.cpp ;
 compile bit_popcount_test_cx.cpp ;
+compile bit_byteswap_test_cx.cpp ;
 
 run type_name_test.cpp ;
 

test/bit_byteswap_test.cpp

@@ -0,0 +1,26 @@
+// Test for boost/core/bit.hpp (byteswap)
+//
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/core/bit.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/cstdint.hpp>
+
+int main()
+{
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::int8_t)0x01 ), 0x01 );
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::uint8_t)0xF1 ), 0xF1 );
+
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::int16_t)0x0102 ), 0x0201 );
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::uint16_t)0xF1E2 ), 0xE2F1 );
+
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::int32_t)0x01020304 ), 0x04030201 );
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::uint32_t)0xF1E2D3C4u ), 0xC4D3E2F1u );
+
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::int64_t)0x0102030405060708ll ), 0x0807060504030201ll );
+    BOOST_TEST_EQ( boost::core::byteswap( (boost::uint64_t)0xF1E2D3C4B5A69788ull ), 0x8897A6B5C4D3E2F1ull );
+
+    return boost::report_errors();
+}

test/bit_byteswap_test_cx.cpp

@@ -0,0 +1,37 @@
+// constexpr test for boost/core/bit.hpp (bit_width)
+//
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+
+#elif defined(BOOST_MSVC) && BOOST_MSVC / 10 == 191
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC is " BOOST_STRINGIZE(BOOST_MSVC) )
+
+#else
+
+#include <boost/core/bit.hpp>
+#include <cstdint>
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+STATIC_ASSERT( boost::core::byteswap( (std::int8_t)0x01 ) == 0x01 );
+STATIC_ASSERT( boost::core::byteswap( (std::uint8_t)0xF1 ) == 0xF1 );
+
+STATIC_ASSERT( boost::core::byteswap( (std::int16_t)0x0102 ) == 0x0201 );
+STATIC_ASSERT( boost::core::byteswap( (std::uint16_t)0xF1E2 ) == 0xE2F1 );
+
+STATIC_ASSERT( boost::core::byteswap( (std::int32_t)0x01020304 ) == 0x04030201 );
+STATIC_ASSERT( boost::core::byteswap( (std::uint32_t)0xF1E2D3C4u ) == 0xC4D3E2F1u );
+
+STATIC_ASSERT( boost::core::byteswap( (std::int64_t)0x0102030405060708ll ) == 0x0807060504030201ll );
+STATIC_ASSERT( boost::core::byteswap( (std::uint64_t)0xF1E2D3C4B5A69788ull ) == 0x8897A6B5C4D3E2F1ull );
+
+#endif