Add boost/core/bit.hpp (bit_cast, rotl, rotr)

include/boost/core/bit.hpp

@@ -0,0 +1,134 @@
+#ifndef BOOST_CORE_BIT_HPP_INCLUDED
+#define BOOST_CORE_BIT_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// boost/core/bit.hpp
+//
+// A portable version of the C++20 standard header <bit>
+//
+// Copyright 2020 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/static_assert.hpp>
+#include <limits>
+#include <cstring>
+
+#define BOOST_CORE_BIT_CONSTEXPR
+
+namespace boost
+{
+namespace core
+{
+
+// bit_cast
+template<class To, class From>
+To bit_cast( From const & from) BOOST_NOEXCEPT
+{
+    BOOST_STATIC_ASSERT( sizeof(To) == sizeof(From) );
+
+    To to;
+    std::memcpy( &to, &from, sizeof(To) );
+    return to;
+}
+
+// counting
+template<class T>
+BOOST_CORE_BIT_CONSTEXPR int countl_zero( T x ) BOOST_NOEXCEPT;
+
+template<class T>
+BOOST_CORE_BIT_CONSTEXPR int countl_one( T x ) BOOST_NOEXCEPT
+{
+    return boost::core::countl_zero( ~x );
+}
+
+template<class T>
+BOOST_CORE_BIT_CONSTEXPR int countr_zero( T x ) BOOST_NOEXCEPT;
+
+template<class T>
+BOOST_CORE_BIT_CONSTEXPR int countr_one( T x ) BOOST_NOEXCEPT
+{
+    return boost::core::countr_zero( ~x );
+}
+
+template<class T>
+BOOST_CORE_BIT_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT;
+
+// rotating
+template<class T>
+BOOST_CXX14_CONSTEXPR T rotl( T x, int s ) BOOST_NOEXCEPT
+{
+    unsigned const mask = std::numeric_limits<T>::digits - 1;
+    return x << (s & mask) | x >> ((-s) & mask);
+}
+
+template<class T>
+BOOST_CXX14_CONSTEXPR T rotr( T x, int s ) BOOST_NOEXCEPT
+{
+    unsigned const mask = std::numeric_limits<T>::digits - 1;
+    return x >> (s & mask) | x << ((-s) & mask);
+}
+
+// integral powers of 2
+template<class T>
+BOOST_CONSTEXPR bool has_single_bit( T x ) BOOST_NOEXCEPT
+{
+    return x != 0 && ( x & ( x - 1 ) ) == 0;
+}
+
+template<class T>
+BOOST_CONSTEXPR T bit_width( T x ) BOOST_NOEXCEPT
+{
+    return std::numeric_limits<T>::digits - boost::core::countl_zero( x );
+}
+
+template<class T>
+BOOST_CONSTEXPR T bit_ceil( T x ) BOOST_NOEXCEPT;
+
+template<class T>
+BOOST_CONSTEXPR T bit_floor( T x ) BOOST_NOEXCEPT
+{
+    return x == 0? 0: T(1) << ( boost::core::bit_width( x ) - 1 );
+}
+
+// endian
+
+#if !defined(BOOST_NO_CXX11_SCOPED_ENUMS)
+
+enum class endian
+{
+    little,
+    big,
+    // native = /* see description */
+};
+
+typedef endian endian_type;
+
+#else
+
+namespace endian
+{
+
+enum type
+{
+    little,
+    big,
+    // native = /* see description */
+};
+
+} // namespace endian
+
+typedef endian::type endian_type;
+
+#endif
+
+} // namespace core
+} // namespace boost
+
+#endif  // #ifndef BOOST_CORE_BIT_HPP_INCLUDED