// BITSET2
//
//  Copyright Claas Bontus
//
//  Use, modification and distribution is subject to the
//  Boost Software License, Version 1.0. (See accompanying
//  file LICENSE.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
// Project home: https://github.com/ClaasBontus/bitset2
//

#pragma once

#include <climits>
#include <cstddef>

namespace detail
{
/// https://graphics.stanford.edu/~seander/bithacks.html#ReverseParallel
template <class T>
struct reverse_bits {
    enum : size_t { n_bits = sizeof(T) * CHAR_BIT, n_bits_h = n_bits >> 1 };

    constexpr reverse_bits() noexcept
    {
        static_assert((n_bits & (n_bits - 1)) == 0, "Number of bits in data type is not a power of 2");
    }

    /// \brief Reverses bits in val.
    constexpr T operator()(T val) const noexcept { return rvrs(val); }

private:
    constexpr T rvrs(T val, T mask = T(~T(0)) >> n_bits_h, size_t s = n_bits_h) const noexcept
    {
        return s == 0 ? val : rvrs(((val >> s) & mask) | ((val << s) & ~mask), mask ^ (mask << (s >> 1)), s >> 1);
    }
}; // struct reverse_bits


} // namespace detail