text: /*
   * Copyright © 2018  Google, Inc.
   *
   *  This is part of HarfBuzz, a text shaping library.
   *
   * Permission is hereby granted, without written agreement and without
   * license or royalty fees, to use, copy, modify, and distribute this
   * software and its documentation for any purpose, provided that the
   * above copyright notice and the following two paragraphs appear in
   * all copies of this software.
   *
   * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
   * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
   * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
   * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
   * DAMAGE.
   *
   * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
   * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
   * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
   * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
   * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
   *
   * Google Author(s): Behdad Esfahbod
   */
  
  #ifndef HB_NULL_HH
  #define HB_NULL_HH
  
  #include "hb.hh"
  #include "hb-meta.hh"
  
  
  /*
   * Static pools
   */
  
  /* Global nul-content Null pool.  Enlarge as necessary. */
  
  #define HB_NULL_POOL_SIZE 384
  
  /* Use SFINAE to sniff whether T has min_size; in which case return T::null_size,
   * otherwise return sizeof(T). */
  
  /* The hard way...
   * https://stackoverflow.com/questions/7776448/sfinae-tried-with-bool-gives-compiler-error-template-argument-tvalue-invol
   */
  
  template <typename T, typename>
  struct _hb_null_size : hb_integral_constant<unsigned, sizeof (T)> {};
  template <typename T>
  struct _hb_null_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::null_size> {};
  
  template <typename T>
  using hb_null_size = _hb_null_size<T, void>;
  #define hb_null_size(T) hb_null_size<T>::value
  
  /* These doesn't belong here, but since is copy/paste from above, put it here. */
  
  /* hb_static_size (T)
   * Returns T::static_size if T::min_size is defined, or sizeof (T) otherwise. */
  
  template <typename T, typename>
  struct _hb_static_size : hb_integral_constant<unsigned, sizeof (T)> {};
  template <typename T>
  struct _hb_static_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::static_size> {};
  template <typename T>
  using hb_static_size = _hb_static_size<T, void>;
  #define hb_static_size(T) hb_static_size<T>::value
  
  
  /*
   * Null()
   */
  
  extern HB_INTERNAL
  uint64_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
  
  /* Generic nul-content Null objects. */
  template <typename Type>
  struct Null {
    static Type const & get_null ()
    {
      static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
      return *reinterpret_cast<Type const *> (_hb_NullPool);
    }
  };
  template <typename QType>
  struct NullHelper
  {
    typedef hb_remove_const<hb_remove_reference<QType>> Type;
    static const Type & get_null () { return Null<Type>::get_null (); }
  };
  #define Null(Type) NullHelper<Type>::get_null ()
  
  /* Specializations for arbitrary-content Null objects expressed in bytes. */
  #define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
  	} /* Close namespace. */ \
  	extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]; \
  	template <> \
  	struct Null<Namespace::Type> { \
  	  static Namespace::Type const & get_null () { \
  	    return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
  	  } \
  	}; \
  	namespace Namespace { \
  	static_assert (true, "Just so we take semicolon after.")
  #define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
  	const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::null_size]
  
  /* Specializations for arbitrary-content Null objects expressed as struct initializer. */
  #define DECLARE_NULL_INSTANCE(Type) \
  	extern HB_INTERNAL const Type _hb_Null_##Type; \
  	template <> \
  	struct Null<Type> { \
  	  static Type const & get_null () { \
  	    return _hb_Null_##Type; \
  	  } \
  	}; \
  	static_assert (true, "Just so we take semicolon after.")
  #define DEFINE_NULL_INSTANCE(Type) \
  	const Type _hb_Null_##Type
  
  /* Global writable pool.  Enlarge as necessary. */
  
  /* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
   * for correct operation. It only exist to catch and divert program logic bugs instead of
   * causing bad memory access. So, races there are not actually introducing incorrectness
   * in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
  extern HB_INTERNAL
  /*thread_local*/ uint64_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (uint64_t) - 1) / sizeof (uint64_t)];
  
  /* CRAP pool: Common Region for Access Protection. */
  template <typename Type>
  static inline Type& Crap () {
    static_assert (hb_null_size (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
    Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
    memcpy (obj, &Null(Type), sizeof (*obj));
    return *obj;
  }
  template <typename QType>
  struct CrapHelper
  {
    typedef hb_remove_const<hb_remove_reference<QType>> Type;
    static Type & get_crap () { return Crap<Type> (); }
  };
  #define Crap(Type) CrapHelper<Type>::get_crap ()
  
  template <typename Type>
  struct CrapOrNullHelper {
    static Type & get () { return Crap(Type); }
  };
  template <typename Type>
  struct CrapOrNullHelper<const Type> {
    static const Type & get () { return Null(Type); }
  };
  #define CrapOrNull(Type) CrapOrNullHelper<Type>::get ()
  
  
  /*
   * hb_nonnull_ptr_t
   */
  
  template <typename P>
  struct hb_nonnull_ptr_t
  {
    typedef hb_remove_pointer<P> T;
  
    hb_nonnull_ptr_t (T *v_ = nullptr) : v (v_) {}
    T * operator = (T *v_)   { return v = v_; }
    T * operator -> () const { return get (); }
    T & operator * () const  { return *get (); }
    T ** operator & () const { return &v; }
    /* Only auto-cast to const types. */
    template <typename C> operator const C * () const { return get (); }
    operator const char * () const { return (const char *) get (); }
    T * get () const { return v ? v : const_cast<T *> (&Null(T)); }
    T * get_raw () const { return v; }
  
    T *v;
  };
  
  
  #endif /* HB_NULL_HH */
  