1 files changed, 204 insertions, 0 deletions
diff --git a/src/hb-null.hh b/src/hb-null.hh
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+++ b/src/hb-null.hh
@@ -0,0 +1,204 @@
+/*
+ * 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"
+
+
+/*
+ * Static pools
+ */
+
+/* Global nul-content Null pool.  Enlarge as necessary. */
+
+#define HB_NULL_POOL_SIZE 9880
+
+/* 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<bool> struct _hb_bool_type {};
+
+template <typename T, typename B>
+struct _hb_null_size
+{ enum { value = sizeof (T) }; };
+template <typename T>
+struct _hb_null_size<T, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
+{ enum { value = T::null_size }; };
+
+template <typename T>
+struct hb_null_size
+{ enum { value = _hb_null_size<T, _hb_bool_type<true> >::value }; };
+#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 B>
+struct _hb_static_size
+{ enum { value = sizeof (T) }; };
+template <typename T>
+struct _hb_static_size<T, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
+{ enum { value = T::static_size }; };
+
+template <typename T>
+struct hb_static_size
+{ enum { value = _hb_static_size<T, _hb_bool_type<true> >::value }; };
+#define hb_static_size(T) hb_static_size<T>::value
+
+
+/* hb_assign (obj, value)
+ * Calls obj.set (value) if obj.min_size is defined and value has different type
+ * from obj, or obj = v otherwise. */
+
+template <typename T, typename V, typename B>
+struct _hb_assign
+{ static inline void value (T &o, const V v) { o = v; } };
+template <typename T, typename V>
+struct _hb_assign<T, V, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
+{ static inline void value (T &o, const V v) { o.set (v); } };
+template <typename T>
+struct _hb_assign<T, T, _hb_bool_type<(bool) (1 + (unsigned int) T::min_size)> >
+{ static inline void value (T &o, const T v) { o = v; } };
+
+template <typename T, typename V>
+static inline void hb_assign (T &o, const V v)
+{ _hb_assign<T, V, _hb_bool_type<true> >::value (o, v); }
+
+
+/*
+ * Null()
+ */
+
+extern HB_INTERNAL
+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)];
+
+/* Generic nul-content Null objects. */
+template <typename Type>
+static inline Type const & 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 typename hb_remove_const (typename hb_remove_reference (QType)) Type;
+  static const Type & get_null () { return Null<Type> (); }
+};
+#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 <> \
+	/*static*/ inline const Namespace::Type& Null<Namespace::Type> () { \
+	  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 <> \
+	/*static*/ inline const Type& Null<Type> () { \
+	  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*/ hb_vector_size_impl_t _hb_CrapPool[(HB_NULL_POOL_SIZE + sizeof (hb_vector_size_impl_t) - 1) / sizeof (hb_vector_size_impl_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 typename hb_remove_const (typename 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 typename 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 */