120 lines
4.4 KiB
C++
120 lines
4.4 KiB
C++
/*
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* Copyright © 2018 Google, Inc.
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*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Google Author(s): Behdad Esfahbod
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*/
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#ifndef HB_NULL_HH
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#define HB_NULL_HH
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#include "hb.hh"
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/*
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* Static pools
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*/
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/* Global nul-content Null pool. Enlarge as necessary. */
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#define HB_NULL_POOL_SIZE 264
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extern HB_INTERNAL
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hb_vector_size_impl_t const _hb_NullPool[(HB_NULL_POOL_SIZE + sizeof (hb_vector_size_impl_t) - 1) / sizeof (hb_vector_size_impl_t)];
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/* Generic nul-content Null objects. */
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template <typename Type>
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static inline Type const & Null (void) {
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static_assert (sizeof (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
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return *reinterpret_cast<Type const *> (_hb_NullPool);
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}
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#define Null(Type) Null<Type>()
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/* Specializaitons for arbitrary-content Null objects expressed in bytes. */
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#define DECLARE_NULL_NAMESPACE_BYTES(Namespace, Type) \
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} /* Close namespace. */ \
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extern HB_INTERNAL const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::min_size]; \
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template <> \
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/*static*/ inline const Namespace::Type& Null<Namespace::Type> (void) { \
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return *reinterpret_cast<const Namespace::Type *> (_hb_Null_##Namespace##_##Type); \
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} \
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namespace Namespace { \
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static_assert (true, "Just so we take semicolon after.")
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#define DEFINE_NULL_NAMESPACE_BYTES(Namespace, Type) \
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const unsigned char _hb_Null_##Namespace##_##Type[Namespace::Type::min_size]
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/* Specializaitons for arbitrary-content Null objects expressed as struct initializer. */
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#define DECLARE_NULL_INSTANCE(Type) \
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extern HB_INTERNAL const Type _hb_Null_##Type; \
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template <> \
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/*static*/ inline const Type& Null<Type> (void) { \
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return _hb_Null_##Type; \
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} \
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static_assert (true, "Just so we take semicolon after.")
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#define DEFINE_NULL_INSTANCE(Type) \
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const Type _hb_Null_##Type
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/* Specializaiton to disallow Null objects. */
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#define DECLARE_NULL_DISALLOW(Type) \
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template <> inline const Type& Null<Type> (void)
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#define DECLARE_NULL_NAMSPACE_DISALLOW(Namespace, Type) \
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} /* Close namespace. */ \
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template <> \
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/*static*/ inline const Namespace::Type& Null<Namespace::Type> (void) { \
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extern void *_hb_undefined; \
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return *reinterpret_cast<const Namespace::Type *> (_hb_undefined); \
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} \
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namespace Namespace { \
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static_assert (true, "Just so we take semicolon after.")
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/* Global writable pool. Enlarge as necessary. */
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/* To be fully correct, CrapPool must be thread_local. However, we do not rely on CrapPool
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* for correct operation. It only exist to catch and divert program logic bugs instead of
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* causing bad memory access. So, races there are not actually introducing incorrectness
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* in the code. Has ~12kb binary size overhead to have it, also clang build fails with it. */
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extern HB_INTERNAL
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/*thread_local*/ hb_vector_size_impl_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (hb_vector_size_impl_t) - 1) / sizeof (hb_vector_size_impl_t)];
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/* CRAP pool: Common Region for Access Protection. */
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template <typename Type>
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static inline Type& Crap (void) {
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static_assert (sizeof (Type) <= HB_NULL_POOL_SIZE, "Increase HB_NULL_POOL_SIZE.");
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Type *obj = reinterpret_cast<Type *> (_hb_CrapPool);
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*obj = Null(Type);
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return *obj;
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}
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#define Crap(Type) Crap<Type>()
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template <typename Type>
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struct CrapOrNull {
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static inline Type & get (void) { return Crap(Type); }
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};
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template <typename Type>
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struct CrapOrNull<const Type> {
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static inline Type const & get (void) { return Null(Type); }
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};
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#define CrapOrNull(Type) CrapOrNull<Type>::get ()
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#endif /* HB_NULL_HH */
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