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/*
* 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 640
template <typename T, typename>
struct _hb_has_min_size : hb_false_type {};
template <typename T>
struct _hb_has_min_size<T, hb_void_t<decltype (T::min_size)>>
: hb_true_type {};
template <typename T>
using hb_has_min_size = _hb_has_min_size<T, void>;
#define hb_has_min_size(T) hb_has_min_size<T>::value
template <typename T, typename>
struct _hb_has_null_size : hb_false_type {};
template <typename T>
struct _hb_has_null_size<T, hb_void_t<decltype (T::null_size)>>
: hb_true_type {};
template <typename T>
using hb_has_null_size = _hb_has_null_size<T, void>;
#define hb_has_null_size(T) hb_has_null_size<T>::value
/* Use SFINAE to sniff whether T has min_size; in which case return the larger
* of sizeof(T) and T::null_size, otherwise return sizeof(T).
*
* The main purpose of this is to let structs communicate that they are not nullable,
* by defining min_size but *not* null_size. */
/* 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,
(sizeof (T) > T::null_size ? sizeof (T) : 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::static_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
template <typename T, typename>
struct _hb_min_size : hb_integral_constant<unsigned, sizeof (T)> {};
template <typename T>
struct _hb_min_size<T, hb_void_t<decltype (T::min_size)>> : hb_integral_constant<unsigned, T::min_size> {};
template <typename T>
using hb_min_size = _hb_min_size<T, void>;
#define hb_min_size(T) hb_min_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[hb_null_size (Namespace::Type)]; \
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, "") /* Require semicolon after. */
#define DECLARE_NULL_NAMESPACE_BYTES_TEMPLATE1(Namespace, Type, Size) \
} /* Close namespace. */ \
extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Size]; \
template <typename Spec> \
struct Null<Namespace::Type<Spec>> { \
static Namespace::Type<Spec> const & get_null () { \
return *reinterpret_cast<const Namespace::Type<Spec> *> (_hb_Null_##Namespace##_##Type); \
} \
}; \
namespace Namespace { \
static_assert (true, "") /* Require semicolon after. */
#define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
const unsigned char _hb_Null_##Namespace##_##Type[sizeof (_hb_Null_##Namespace##_##Type)]
/* 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, "") /* Require 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, std::addressof (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 std::addressof (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 *> (std::addressof (Null (T))); }
T * get_raw () const { return v; }
private:
T *v;
};
#endif /* HB_NULL_HH */
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