pugixml.cpp

/**
 * pugixml parser - version 1.8
 * --------------------------------------------------------
 * Copyright (C) 2006-2017, by Arseny Kapoulkine (arseny.kapoulkine@gmail.com)
 * Report bugs and download new versions at http://pugixml.org/
 *
 * This library is distributed under the MIT License. See notice at the end
 * of this file.
 *
 * This work is based on the pugxml parser, which is:
 * Copyright (C) 2003, by Kristen Wegner (kristen@tima.net)
 */

#ifndef SOURCE_PUGIXML_CPP
#define SOURCE_PUGIXML_CPP

#include "pugixml.hpp"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <limits.h>

#ifdef PUGIXML_WCHAR_MODE
#	include <wchar.h>
#endif

#ifndef PUGIXML_NO_XPATH
#	include <math.h>
#	include <float.h>
#endif

#ifndef PUGIXML_NO_STL
#	include <istream>
#	include <ostream>
#	include <string>
#endif

// For placement new
#include <new>

#ifdef _MSC_VER
#	pragma warning(push)
#	pragma warning(disable: 4127) // conditional expression is constant
#	pragma warning(disable: 4324) // structure was padded due to __declspec(align())
#	pragma warning(disable: 4702) // unreachable code
#	pragma warning(disable: 4996) // this function or variable may be unsafe
#endif

#ifdef __INTEL_COMPILER
#	pragma warning(disable: 177) // function was declared but never referenced
#	pragma warning(disable: 279) // controlling expression is constant
#	pragma warning(disable: 1478 1786) // function was declared "deprecated"
#	pragma warning(disable: 1684) // conversion from pointer to same-sized integral type
#endif

#if defined(__BORLANDC__) && defined(PUGIXML_HEADER_ONLY)
#	pragma warn -8080 // symbol is declared but never used; disabling this inside push/pop bracket does not make the warning go away
#endif

#ifdef __BORLANDC__
#	pragma option push
#	pragma warn -8008 // condition is always false
#	pragma warn -8066 // unreachable code
#endif

#ifdef __SNC__
// Using diag_push/diag_pop does not disable the warnings inside templates due to a compiler bug
#	pragma diag_suppress=178 // function was declared but never referenced
#	pragma diag_suppress=237 // controlling expression is constant
#endif

// Inlining controls
#if defined(_MSC_VER) && _MSC_VER >= 1300
#	define PUGI__NO_INLINE __declspec(noinline)
#elif defined(__GNUC__)
#	define PUGI__NO_INLINE __attribute__((noinline))
#else
#	define PUGI__NO_INLINE
#endif

// Branch weight controls
#if defined(__GNUC__)
#	define PUGI__UNLIKELY(cond) __builtin_expect(cond, 0)
#else
#	define PUGI__UNLIKELY(cond) (cond)
#endif

// Simple static assertion
#define PUGI__STATIC_ASSERT(cond) { static const char condition_failed[(cond) ? 1 : -1] = {0}; (void)condition_failed[0]; }

// Digital Mars C++ bug workaround for passing char loaded from memory via stack
#ifdef __DMC__
#	define PUGI__DMC_VOLATILE volatile
#else
#	define PUGI__DMC_VOLATILE
#endif

// Integer sanitizer workaround
#ifdef __has_attribute
#	if __has_attribute(no_sanitize)
#		define PUGI__UNSIGNED_OVERFLOW __attribute__((no_sanitize("unsigned-integer-overflow")))
#	else
#		define PUGI__UNSIGNED_OVERFLOW
#	endif
#else
#	define PUGI__UNSIGNED_OVERFLOW
#endif

// Borland C++ bug workaround for not defining ::memcpy depending on header include order (can't always use std::memcpy because some compilers don't have it at all)
#if defined(__BORLANDC__) && !defined(__MEM_H_USING_LIST)
using std::memcpy;
using std::memmove;
using std::memset;
#endif

// Some MinGW versions have headers that erroneously omit LLONG_MIN/LLONG_MAX/ULLONG_MAX definitions in strict ANSI mode
#if defined(PUGIXML_HAS_LONG_LONG) && defined(__MINGW32__) && defined(__STRICT_ANSI__) && !defined(LLONG_MAX) && !defined(LLONG_MIN) && !defined(ULLONG_MAX)
#	define LLONG_MAX 9223372036854775807LL
#	define LLONG_MIN (-LLONG_MAX-1)
#	define ULLONG_MAX (2ULL*LLONG_MAX+1)
#endif

// In some environments MSVC is a compiler but the CRT lacks certain MSVC-specific features
#if defined(_MSC_VER) && !defined(__S3E__)
#	define PUGI__MSVC_CRT_VERSION _MSC_VER
#endif

#ifdef PUGIXML_HEADER_ONLY
#	define PUGI__NS_BEGIN namespace pugi { namespace impl {
#	define PUGI__NS_END } }
#	define PUGI__FN inline
#	define PUGI__FN_NO_INLINE inline
#else
#	if defined(_MSC_VER) && _MSC_VER < 1300 // MSVC6 seems to have an amusing bug with anonymous namespaces inside namespaces
#		define PUGI__NS_BEGIN namespace pugi { namespace impl {
#		define PUGI__NS_END } }
#	else
#		define PUGI__NS_BEGIN namespace pugi { namespace impl { namespace {
#		define PUGI__NS_END } } }
#	endif
#	define PUGI__FN
#	define PUGI__FN_NO_INLINE PUGI__NO_INLINE
#endif

// uintptr_t
#if (defined(_MSC_VER) && _MSC_VER < 1600) || (defined(__BORLANDC__) && __BORLANDC__ < 0x561)
namespace pugi
{
#	ifndef _UINTPTR_T_DEFINED
	typedef size_t uintptr_t;
#	endif

	typedef unsigned __int8 uint8_t;
	typedef unsigned __int16 uint16_t;
	typedef unsigned __int32 uint32_t;
}
#else
#	include <stdint.h>
#endif

// Memory allocation
PUGI__NS_BEGIN
	PUGI__FN void* default_allocate(size_t size)
	{
		return malloc(size);
	}

	PUGI__FN void default_deallocate(void* ptr)
	{
		free(ptr);
	}

	template <typename T>
	struct xml_memory_management_function_storage
	{
		static allocation_function allocate;
		static deallocation_function deallocate;
	};

	// Global allocation functions are stored in class statics so that in header mode linker deduplicates them
	// Without a template<> we'll get multiple definitions of the same static
	template <typename T> allocation_function xml_memory_management_function_storage<T>::allocate = default_allocate;
	template <typename T> deallocation_function xml_memory_management_function_storage<T>::deallocate = default_deallocate;

	typedef xml_memory_management_function_storage<int> xml_memory;
PUGI__NS_END

// String utilities
PUGI__NS_BEGIN
	// Get string length
	PUGI__FN size_t strlength(const char_t* s)
	{
		assert(s);

	#ifdef PUGIXML_WCHAR_MODE
		return wcslen(s);
	#else
		return strlen(s);
	#endif
	}

	// Compare two strings
	PUGI__FN bool strequal(const char_t* src, const char_t* dst)
	{
		assert(src && dst);

	#ifdef PUGIXML_WCHAR_MODE
		return wcscmp(src, dst) == 0;
	#else
		return strcmp(src, dst) == 0;
	#endif
	}

	// Compare lhs with [rhs_begin, rhs_end)
	PUGI__FN bool strequalrange(const char_t* lhs, const char_t* rhs, size_t count)
	{
		for (size_t i = 0; i < count; ++i)
			if (lhs[i] != rhs[i])
				return false;

		return lhs[count] == 0;
	}

	// Get length of wide string, even if CRT lacks wide character support
	PUGI__FN size_t strlength_wide(const wchar_t* s)
	{
		assert(s);

	#ifdef PUGIXML_WCHAR_MODE
		return wcslen(s);
	#else
		const wchar_t* end = s;
		while (*end) end++;
		return static_cast<size_t>(end - s);
	#endif
	}
PUGI__NS_END

// auto_ptr-like object for exception recovery
PUGI__NS_BEGIN
	template <typename T> struct auto_deleter
	{
		typedef void (*D)(T*);

		T* data;
		D deleter;

		auto_deleter(T* data_, D deleter_): data(data_), deleter(deleter_)
		{
		}

		~auto_deleter()
		{
			if (data) deleter(data);
		}

		T* release()
		{
			T* result = data;
			data = 0;
			return result;
		}
	};
PUGI__NS_END

#ifdef PUGIXML_COMPACT
PUGI__NS_BEGIN
	class compact_hash_table
	{
	public:
		compact_hash_table(): _items(0), _capacity(0), _count(0)
		{
		}

		void clear()
		{
			if (_items)
			{
				xml_memory::deallocate(_items);
				_items = 0;
				_capacity = 0;
				_count = 0;
			}
		}

		void* find(const void* key)
		{
			if (_capacity == 0) return 0;

			item_t* item = get_item(key);
			assert(item);
			assert(item->key == key || (item->key == 0 && item->value == 0));

			return item->value;
		}

		void insert(const void* key, void* value)
		{
			assert(_capacity != 0 && _count < _capacity - _capacity / 4);

			item_t* item = get_item(key);
			assert(item);

			if (item->key == 0)
			{
				_count++;
				item->key = key;
			}

			item->value = value;
		}

		bool reserve()
		{
			if (_count + 16 >= _capacity - _capacity / 4)
				return rehash();

			return true;
		}

	private:
		struct item_t
		{
			const void* key;
			void* value;
		};

		item_t* _items;
		size_t _capacity;

		size_t _count;

		bool rehash();

		item_t* get_item(const void* key)
		{
			assert(key);
			assert(_capacity > 0);

			size_t hashmod = _capacity - 1;
			size_t bucket = hash(key) & hashmod;

			for (size_t probe = 0; probe <= hashmod; ++probe)
			{
				item_t& probe_item = _items[bucket];

				if (probe_item.key == key || probe_item.key == 0)
					return &probe_item;

				// hash collision, quadratic probing
				bucket = (bucket + probe + 1) & hashmod;
			}

			assert(false && "Hash table is full");
			return 0;
		}

		static PUGI__UNSIGNED_OVERFLOW unsigned int hash(const void* key)
		{
			unsigned int h = static_cast<unsigned int>(reinterpret_cast<uintptr_t>(key));

			// MurmurHash3 32-bit finalizer
			h ^= h >> 16;
			h *= 0x85ebca6bu;
			h ^= h >> 13;
			h *= 0xc2b2ae35u;
			h ^= h >> 16;

			return h;
		}
	};

	PUGI__FN_NO_INLINE bool compact_hash_table::rehash()
	{
		compact_hash_table rt;
		rt._capacity = (_capacity == 0) ? 32 : _capacity * 2;
		rt._items = static_cast<item_t*>(xml_memory::allocate(sizeof(item_t) * rt._capacity));

		if (!rt._items)
			return false;

		memset(rt._items, 0, sizeof(item_t) * rt._capacity);

		for (size_t i = 0; i < _capacity; ++i)
			if (_items[i].key)
				rt.insert(_items[i].key, _items[i].value);

		if (_items)
			xml_memory::deallocate(_items);

		_capacity = rt._capacity;
		_items = rt._items;

		assert(_count == rt._count);

		return true;
	}

PUGI__NS_END
#endif

PUGI__NS_BEGIN
#ifdef PUGIXML_COMPACT
	static const uintptr_t xml_memory_block_alignment = 4;
#else
	static const uintptr_t xml_memory_block_alignment = sizeof(void*);
#endif

	// extra metadata bits
	static const uintptr_t xml_memory_page_contents_shared_mask = 64;
	static const uintptr_t xml_memory_page_name_allocated_mask = 32;
	static const uintptr_t xml_memory_page_value_allocated_mask = 16;
	static const uintptr_t xml_memory_page_type_mask = 15;

	// combined masks for string uniqueness
	static const uintptr_t xml_memory_page_name_allocated_or_shared_mask = xml_memory_page_name_allocated_mask | xml_memory_page_contents_shared_mask;
	static const uintptr_t xml_memory_page_value_allocated_or_shared_mask = xml_memory_page_value_allocated_mask | xml_memory_page_contents_shared_mask;

#ifdef PUGIXML_COMPACT
	#define PUGI__GETHEADER_IMPL(object, page, flags) // unused
	#define PUGI__GETPAGE_IMPL(header) (header).get_page()
#else
	#define PUGI__GETHEADER_IMPL(object, page, flags) (((reinterpret_cast<char*>(object) - reinterpret_cast<char*>(page)) << 8) | (flags))
	// this macro casts pointers through void* to avoid 'cast increases required alignment of target type' warnings
	#define PUGI__GETPAGE_IMPL(header) static_cast<impl::xml_memory_page*>(const_cast<void*>(static_cast<const void*>(reinterpret_cast<const char*>(&header) - (header >> 8))))
#endif

	#define PUGI__GETPAGE(n) PUGI__GETPAGE_IMPL((n)->header)
	#define PUGI__NODETYPE(n) static_cast<xml_node_type>((n)->header & impl::xml_memory_page_type_mask)

	struct xml_allocator;

	struct xml_memory_page
	{
		static xml_memory_page* construct(void* memory)
		{
			xml_memory_page* result = static_cast<xml_memory_page*>(memory);

			result->allocator = 0;
			result->prev = 0;
			result->next = 0;
			result->busy_size = 0;
			result->freed_size = 0;

		#ifdef PUGIXML_COMPACT
			result->compact_string_base = 0;
			result->compact_shared_parent = 0;
			result->compact_page_marker = 0;
		#endif

			return result;
		}

		xml_allocator* allocator;

		xml_memory_page* prev;
		xml_memory_page* next;

		size_t busy_size;
		size_t freed_size;

	#ifdef PUGIXML_COMPACT
		char_t* compact_string_base;
		void* compact_shared_parent;
		uint32_t* compact_page_marker;
	#endif
	};

	static const size_t xml_memory_page_size =
	#ifdef PUGIXML_MEMORY_PAGE_SIZE
		(PUGIXML_MEMORY_PAGE_SIZE)
	#else
		32768
	#endif
		- sizeof(xml_memory_page);

	struct xml_memory_string_header
	{
		uint16_t page_offset; // offset from page->data
		uint16_t full_size; // 0 if string occupies whole page
	};

	struct xml_allocator
	{
		xml_allocator(xml_memory_page* root): _root(root), _busy_size(root->busy_size)
		{
		#ifdef PUGIXML_COMPACT
			_hash = 0;
		#endif
		}

		xml_memory_page* allocate_page(size_t data_size)
		{
			size_t size = sizeof(xml_memory_page) + data_size;

			// allocate block with some alignment, leaving memory for worst-case padding
			void* memory = xml_memory::allocate(size);
			if (!memory) return 0;

			// prepare page structure
			xml_memory_page* page = xml_memory_page::construct(memory);
			assert(page);

			page->allocator = _root->allocator;

			return page;
		}

		static void deallocate_page(xml_memory_page* page)
		{
			xml_memory::deallocate(page);
		}

		void* allocate_memory_oob(size_t size, xml_memory_page*& out_page);

		void* allocate_memory(size_t size, xml_memory_page*& out_page)
		{
			if (PUGI__UNLIKELY(_busy_size + size > xml_memory_page_size))
				return allocate_memory_oob(size, out_page);

			void* buf = reinterpret_cast<char*>(_root) + sizeof(xml_memory_page) + _busy_size;

			_busy_size += size;

			out_page = _root;

			return buf;
		}

	#ifdef PUGIXML_COMPACT
		void* allocate_object(size_t size, xml_memory_page*& out_page)
		{
			void* result = allocate_memory(size + sizeof(uint32_t), out_page);
			if (!result) return 0;

			// adjust for marker
			ptrdiff_t offset = static_cast<char*>(result) - reinterpret_cast<char*>(out_page->compact_page_marker);

			if (PUGI__UNLIKELY(static_cast<uintptr_t>(offset) >= 256 * xml_memory_block_alignment))
			{
				// insert new marker
				uint32_t* marker = static_cast<uint32_t*>(result);

				*marker = static_cast<uint32_t>(reinterpret_cast<char*>(marker) - reinterpret_cast<char*>(out_page));
				out_page->compact_page_marker = marker;

				// since we don't reuse the page space until we reallocate it, we can just pretend that we freed the marker block
				// this will make sure deallocate_memory correctly tracks the size
				out_page->freed_size += sizeof(uint32_t);

				return marker + 1;
			}
			else
			{
				// roll back uint32_t part
				_busy_size -= sizeof(uint32_t);

				return result;
			}
		}
	#else
		void* allocate_object(size_t size, xml_memory_page*& out_page)
		{
			return allocate_memory(size, out_page);
		}
	#endif

		void deallocate_memory(void* ptr, size_t size, xml_memory_page* page)
		{
			if (page == _root) page->busy_size = _busy_size;

			assert(ptr >= reinterpret_cast<char*>(page) + sizeof(xml_memory_page) && ptr < reinterpret_cast<char*>(page) + sizeof(xml_memory_page) + page->busy_size);
			(void)!ptr;

			page->freed_size += size;
			assert(page->freed_size <= page->busy_size);

			if (page->freed_size == page->busy_size)
			{
				if (page->next == 0)
				{
					assert(_root == page);

					// top page freed, just reset sizes
					page->busy_size = 0;
					page->freed_size = 0;

				#ifdef PUGIXML_COMPACT
					// reset compact state to maximize efficiency
					page->compact_string_base = 0;
					page->compact_shared_parent = 0;
					page->compact_page_marker = 0;
				#endif

					_busy_size = 0;
				}
				else
				{
					assert(_root != page);
					assert(page->prev);

					// remove from the list
					page->prev->next = page->next;
					page->next->prev = page->prev;

					// deallocate
					deallocate_page(page);
				}
			}
		}

		char_t* allocate_string(size_t length)
		{
			static const size_t max_encoded_offset = (1 << 16) * xml_memory_block_alignment;

			PUGI__STATIC_ASSERT(xml_memory_page_size <= max_encoded_offset);

			// allocate memory for string and header block
			size_t size = sizeof(xml_memory_string_header) + length * sizeof(char_t);

			// round size up to block alignment boundary
			size_t full_size = (size + (xml_memory_block_alignment - 1)) & ~(xml_memory_block_alignment - 1);

			xml_memory_page* page;
			xml_memory_string_header* header = static_cast<xml_memory_string_header*>(allocate_memory(full_size, page));

			if (!header) return 0;

			// setup header
			ptrdiff_t page_offset = reinterpret_cast<char*>(header) - reinterpret_cast<char*>(page) - sizeof(xml_memory_page);

			assert(page_offset % xml_memory_block_alignment == 0);
			assert(page_offset >= 0 && static_cast<size_t>(page_offset) < max_encoded_offset);
			header->page_offset = static_cast<uint16_t>(static_cast<size_t>(page_offset) / xml_memory_block_alignment);

			// full_size == 0 for large strings that occupy the whole page
			assert(full_size % xml_memory_block_alignment == 0);
			assert(full_size < max_encoded_offset || (page->busy_size == full_size && page_offset == 0));
			header->full_size = static_cast<uint16_t>(full_size < max_encoded_offset ? full_size / xml_memory_block_alignment : 0);

			// round-trip through void* to avoid 'cast increases required alignment of target type' warning
			// header is guaranteed a pointer-sized alignment, which should be enough for char_t
			return static_cast<char_t*>(static_cast<void*>(header + 1));
		}

		void deallocate_string(char_t* string)
		{
			// this function casts pointers through void* to avoid 'cast increases required alignment of target type' warnings
			// we're guaranteed the proper (pointer-sized) alignment on the input string if it was allocated via allocate_string

			// get header
			xml_memory_string_header* header = static_cast<xml_memory_string_header*>(static_cast<void*>(string)) - 1;
			assert(header);

			// deallocate
			size_t page_offset = sizeof(xml_memory_page) + header->page_offset * xml_memory_block_alignment;
			xml_memory_page* page = reinterpret_cast<xml_memory_page*>(static_cast<void*>(reinterpret_cast<char*>(header) - page_offset));

			// if full_size == 0 then this string occupies the whole page
			size_t full_size = header->full_size == 0 ? page->busy_size : header->full_size * xml_memory_block_alignment;

			deallocate_memory(header, full_size, page);
		}

		bool reserve()
		{
		#ifdef PUGIXML_COMPACT
			return _hash->reserve();
		#else
			return true;
		#endif
		}

		xml_memory_page* _root;
		size_t _busy_size;

	#ifdef PUGIXML_COMPACT
		compact_hash_table* _hash;
	#endif
	};

	PUGI__FN_NO_INLINE void* xml_allocator::allocate_memory_oob(size_t size, xml_memory_page*& out_page)
	{
		const size_t large_allocation_threshold = xml_memory_page_size / 4;

		xml_memory_page* page = allocate_page(size <= large_allocation_threshold ? xml_memory_page_size : size);
		out_page = page;

		if (!page) return 0;

		if (size <= large_allocation_threshold)
		{
			_root->busy_size = _busy_size;

			// insert page at the end of linked list
			page->prev = _root;
			_root->next = page;
			_root = page;

			_busy_size = size;
		}
		else
		{
			// insert page before the end of linked list, so that it is deleted as soon as possible
			// the last page is not deleted even if it's empty (see deallocate_memory)
			assert(_root->prev);

			page->prev = _root->prev;
			page->next = _root;

			_root->prev->next = page;
			_root->prev = page;

			page->busy_size = size;
		}

		return reinterpret_cast<char*>(page) + sizeof(xml_memory_page);
	}
PUGI__NS_END

#ifdef PUGIXML_COMPACT
PUGI__NS_BEGIN
	static const uintptr_t compact_alignment_log2 = 2;
	static const uintptr_t compact_alignment = 1 << compact_alignment_log2;

	class compact_header
	{
	public:
		compact_header(xml_memory_page* page, unsigned int flags)
		{
			PUGI__STATIC_ASSERT(xml_memory_block_alignment == compact_alignment);

			ptrdiff_t offset = (reinterpret_cast<char*>(this) - reinterpret_cast<char*>(page->compact_page_marker));
			assert(offset % compact_alignment == 0 && static_cast<uintptr_t>(offset) < 256 * compact_alignment);

			_page = static_cast<unsigned char>(offset >> compact_alignment_log2);
			_flags = static_cast<unsigned char>(flags);
		}

		void operator&=(uintptr_t mod)
		{
			_flags &= static_cast<unsigned char>(mod);
		}

		void operator|=(uintptr_t mod)
		{
			_flags |= static_cast<unsigned char>(mod);
		}

		uintptr_t operator&(uintptr_t mod) const
		{
			return _flags & mod;
		}

		xml_memory_page* get_page() const
		{
			// round-trip through void* to silence 'cast increases required alignment of target type' warnings
			const char* page_marker = reinterpret_cast<const char*>(this) - (_page << compact_alignment_log2);
			const char* page = page_marker - *reinterpret_cast<const uint32_t*>(static_cast<const void*>(page_marker));

			return const_cast<xml_memory_page*>(reinterpret_cast<const xml_memory_page*>(static_cast<const void*>(page)));
		}

	private:
		unsigned char _page;
		unsigned char _flags;
	};

	PUGI__FN xml_memory_page* compact_get_page(const void* object, int header_offset)
	{
		const compact_header* header = reinterpret_cast<const compact_header*>(static_cast<const char*>(object) - header_offset);

		return header->get_page();
	}

	template <int header_offset, typename T> PUGI__FN_NO_INLINE T* compact_get_value(const void* object)
	{
		return static_cast<T*>(compact_get_page(object, header_offset)->allocator->_hash->find(object));
	}

	template <int header_offset, typename T> PUGI__FN_NO_INLINE void compact_set_value(const void* object, T* value)
	{
		compact_get_page(object, header_offset)->allocator->_hash->insert(object, value);
	}

	template <typename T, int header_offset, int start = -126> class compact_pointer
	{
	public:
		compact_pointer(): _data(0)
		{
		}

		void operator=(const compact_pointer& rhs)
		{
			*this = rhs + 0;
		}

		void operator=(T* value)
		{
			if (value)
			{
				// value is guaranteed to be compact-aligned; 'this' is not
				// our decoding is based on 'this' aligned to compact alignment downwards (see operator T*)
				// so for negative offsets (e.g. -3) we need to adjust the diff by compact_alignment - 1 to
				// compensate for arithmetic shift rounding for negative values
				ptrdiff_t diff = reinterpret_cast<char*>(value) - reinterpret_cast<char*>(this);
				ptrdiff_t offset = ((diff + int(compact_alignment - 1)) >> compact_alignment_log2) - start;

				if (static_cast<uintptr_t>(offset) <= 253)
					_data = static_cast<unsigned char>(offset + 1);
				else
				{
					compact_set_value<header_offset>(this, value);

					_data = 255;
				}
			}
			else
				_data = 0;
		}

		operator T*() const
		{
			if (_data)
			{
				if (_data < 255)
				{
					uintptr_t base = reinterpret_cast<uintptr_t>(this) & ~(compact_alignment - 1);

					return reinterpret_cast<T*>(base + ((_data - 1 + start) << compact_alignment_log2));
				}
				else
					return compact_get_value<header_offset, T>(this);
			}
			else
				return 0;
		}

		T* operator->() const
		{
			return *this;
		}

	private:
		unsigned char _data;
	};

	template <typename T, int header_offset> class compact_pointer_parent
	{
	public:
		compact_pointer_parent(): _data(0)
		{
		}

		void operator=(const compact_pointer_parent& rhs)
		{
			*this = rhs + 0;
		}

		void operator=(T* value)
		{
			if (value)
			{
				// value is guaranteed to be compact-aligned; 'this' is not
				// our decoding is based on 'this' aligned to compact alignment downwards (see operator T*)
				// so for negative offsets (e.g. -3) we need to adjust the diff by compact_alignment - 1 to
				// compensate for arithmetic shift behavior for negative values
				ptrdiff_t diff = reinterpret_cast<char*>(value) - reinterpret_cast<char*>(this);
				ptrdiff_t offset = ((diff + int(compact_alignment - 1)) >> compact_alignment_log2) + 65533;

				if (static_cast<uintptr_t>(offset) <= 65533)
				{
					_data = static_cast<unsigned short>(offset + 1);
				}
				else
				{
					xml_memory_page* page = compact_get_page(this, header_offset);

					if (PUGI__UNLIKELY(page->compact_shared_parent == 0))
						page->compact_shared_parent = value;

					if (page->compact_shared_parent == value)
					{
						_data = 65534;
					}
					else
					{
						compact_set_value<header_offset>(this, value);

						_data = 65535;
					}
				}
			}
			else
			{
				_data = 0;
			}
		}

		operator T*() const
		{
			if (_data)
			{
				if (_data < 65534)
				{
					uintptr_t base = reinterpret_cast<uintptr_t>(this) & ~(compact_alignment - 1);

					return reinterpret_cast<T*>(base + ((_data - 1 - 65533) << compact_alignment_log2));
				}
				else if (_data == 65534)
					return static_cast<T*>(compact_get_page(this, header_offset)->compact_shared_parent);
				else
					return compact_get_value<header_offset, T>(this);
			}
			else
				return 0;
		}

		T* operator->() const
		{
			return *this;
		}

	private:
		uint16_t _data;
	};

	template <int header_offset, int base_offset> class compact_string
	{
	public:
		compact_string(): _data(0)
		{
		}

		void operator=(const compact_string& rhs)
		{
			*this = rhs + 0;
		}

		void operator=(char_t* value)
		{
			if (value)
			{
				xml_memory_page* page = compact_get_page(this, header_offset);

				if (PUGI__UNLIKELY(page->compact_string_base == 0))
					page->compact_string_base = value;

				ptrdiff_t offset = value - page->compact_string_base;

				if (static_cast<uintptr_t>(offset) < (65535 << 7))
				{
					// round-trip through void* to silence 'cast increases required alignment of target type' warnings
					uint16_t* base = reinterpret_cast<uint16_t*>(static_cast<void*>(reinterpret_cast<char*>(this) - base_offset));

					if (*base == 0)
					{
						*base = static_cast<uint16_t>((offset >> 7) + 1);
						_data = static_cast<unsigned char>((offset & 127) + 1);
					}
					else
					{
						ptrdiff_t remainder = offset - ((*base - 1) << 7);

						if (static_cast<uintptr_t>(remainder) <= 253)
						{
							_data = static_cast<unsigned char>(remainder + 1);
						}
						else
						{
							compact_set_value<header_offset>(this, value);

							_data = 255;
						}
					}
				}
				else
				{
					compact_set_value<header_offset>(this, value);

					_data = 255;
				}
			}
			else
			{
				_data = 0;
			}
		}

		operator char_t*() const
		{
			if (_data)
			{
				if (_data < 255)
				{
					xml_memory_page* page = compact_get_page(this, header_offset);

					// round-trip through void* to silence 'cast increases required alignment of target type' warnings