bitfield

// vi:set ft=cpp: -*- Mode: C++ -*-
/*
 * (c) 2012 Alexander Warg <warg@os.inf.tu-dresden.de>,
 *     economic rights: Technische Universität Dresden (Germany)
 *
 * License: see LICENSE.spdx (in this directory or the directories above)
 */
 
#pragma once
 
#include "type_list"

namespace cxx {

template<typename T, unsigned LSB, unsigned MSB>
class Bitfield
{
private:
  typedef remove_reference_t<T> Base_type;
 
  static_assert(MSB >= LSB, "boundary mismatch in bit-field definition");
  static_assert(MSB < sizeof(Base_type) * 8, "MSB outside of bit-field type");
  static_assert(LSB < sizeof(Base_type) * 8, "LSB outside of bit-field type");

  template<unsigned BITS> struct Best_type
  {
    template< typename TY > struct Cmp { enum { value = (BITS <= sizeof(TY)*8) }; };
    typedef cxx::type_list<
      unsigned char,
      unsigned short,
      unsigned int,
      unsigned long,
      unsigned long long
    > Unsigned_types;
    typedef cxx::find_type_t<Unsigned_types, Cmp> Type;
  };
 
public:
  enum
  {
    Bits  = MSB + 1 - LSB, 
    Lsb = LSB,             
    Msb = MSB,             
  };

  static constexpr Base_type Low_mask
    = Base_type(~0ULL) >> (sizeof(Base_type) * 8 - Bits);
  static constexpr Base_type Mask = Low_mask << Lsb;

  typedef typename Best_type<Bits>::Type Bits_type;

  typedef typename Best_type<Bits + Lsb>::Type Shift_type;
 
private:
  static_assert(sizeof(Bits_type)*8 >= Bits, "error finding the type to store the bits");
  static_assert(sizeof(Shift_type)*8 >= Bits + Lsb, "error finding the type to keep the shifted bits");
  static_assert(sizeof(Bits_type) <= sizeof(Base_type), "size mismatch for Bits_type");
  static_assert(sizeof(Shift_type) <= sizeof(Base_type), "size mismatch for Shift_type");
  static_assert(sizeof(Bits_type) <= sizeof(Shift_type), "size mismatch for Shift_type and Bits_type");
 
public:
  static constexpr Bits_type get(Shift_type val)
  { return (val >> Lsb) & Low_mask; }

  static constexpr Base_type get_unshifted(Shift_type val)
  { return val & Mask; }

  static constexpr Base_type set_dirty(Base_type dest, Shift_type val)
  {
    //assert (!(val & ~Low_mask));
    return (dest & ~Mask) | (val << Lsb);
  }

  static constexpr Base_type set_unshifted_dirty(Base_type dest, Shift_type val)
  {
    //assert (!(val & ~Mask));
    return (dest & ~Mask) | val;
  }

  static Base_type set(Base_type dest, Bits_type val)
  { return set_dirty(dest, val & Low_mask); }

  static Base_type set_unshifted(Base_type dest, Shift_type val)
  { return set_unshifted_dirty(dest, val & Mask); }

  static constexpr Base_type val_dirty(Shift_type val) { return val << Lsb; }

  static constexpr Base_type val(Bits_type val) { return val_dirty(val & Low_mask); }

  static constexpr Base_type val_unshifted(Shift_type val) { return val & Mask; }

  template< typename TT >
  class Value_base
  {
  private:
    TT v;
 
  public:
    constexpr Value_base(TT t) : v(t) {}
    constexpr Bits_type get() const { return Bitfield::get(v); }
    constexpr Base_type get_unshifted() const { return Bitfield::get_unshifted(v); }
 
    void set(Bits_type val) { v = Bitfield::set(v, val); }
    void set_dirty(Bits_type val) { v = Bitfield::set_dirty(v, val); }
    void set_unshifted(Shift_type val) { v = Bitfield::set_unshifted(v, val); }
    void set_unshifted_dirty(Shift_type val) { v = Bitfield::set_unshifted_dirty(v, val); }
  };

  template< typename TT >
  class Value : public Value_base<TT>
  {
  public:
    constexpr Value(TT t) : Value_base<TT>(t) {}
    constexpr operator Bits_type () const { return this->get(); }
    constexpr Value &operator = (Bits_type val) { this->set(val); return *this; }
    constexpr Value &operator = (Value const &val)
    { this->set(val.get()); return *this; }
    Value(Value const &) = default;
  };

  template< typename TT >
  class Value_unshifted : public Value_base<TT>
  {
  public:
    constexpr Value_unshifted(TT t) : Value_base<TT>(t) {}
    constexpr operator Shift_type () const { return this->get_unshifted(); }
    constexpr Value_unshifted &operator = (Shift_type val) { this->set_unshifted(val); return *this; }
    constexpr Value_unshifted &operator = (Value_unshifted const &val)
    { this->set_unshifted(val.get_unshifted()); return *this; }
    Value_unshifted(Value_unshifted const &) = default;
  };

  typedef Value<Base_type &> Ref;
  typedef Value<Base_type volatile &> Ref_volatile;
  typedef Value<Base_type const> Val;

  typedef Value_unshifted<Base_type &> Ref_unshifted;
  typedef Value_unshifted<Base_type volatile &> Ref_unshifted_volatile;
  typedef Value_unshifted<Base_type const> Val_unshifted;
};
 
#define CXX_BITFIELD_MEMBER(LSB, MSB, name, data_member) \
 \
 \
  typedef cxx::Bitfield<decltype(data_member), LSB, MSB> name ## _bfm_t; \
 \
  constexpr typename name ## _bfm_t::Val name() const { return data_member; } \
  typename name ## _bfm_t::Val name() const volatile { return data_member; } \
 \
  constexpr typename name ## _bfm_t::Ref name() { return data_member; } \
  typename name ## _bfm_t::Ref_volatile name() volatile { return data_member; } \

 
#define CXX_BITFIELD_MEMBER_RO(LSB, MSB, name, data_member) \
 \
 \
  typedef cxx::Bitfield<decltype(data_member), LSB, MSB> name ## _bfm_t; \
 \
  constexpr typename name ## _bfm_t::Val name() const { return data_member; } \
  typename name ## _bfm_t::Val name() const volatile { return data_member; } \

 
#define CXX_BITFIELD_MEMBER_UNSHIFTED(LSB, MSB, name, data_member) \
 \
 \
  typedef cxx::Bitfield<decltype(data_member), LSB, MSB> name ## _bfm_t; \
 \
  constexpr typename name ## _bfm_t::Val_unshifted name() const { return data_member; } \
  typename name ## _bfm_t::Val_unshifted name() const volatile { return data_member; } \
 \
  constexpr typename name ## _bfm_t::Ref_unshifted name() { return data_member; } \
  typename name ## _bfm_t::Ref_unshifted_volatile name() volatile { return data_member; } \

 
#define CXX_BITFIELD_MEMBER_UNSHIFTED_RO(LSB, MSB, name, data_member) \
 \
 \
  typedef cxx::Bitfield<decltype(data_member), LSB, MSB> name ## _bfm_t; \
 \
  constexpr typename name ## _bfm_t::Val_unshifted name() const { return data_member; } \
  typename name ## _bfm_t::Val_unshifted name() const volatile { return data_member; } \

}