detail/sbo_buffer.hpp

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sbo_buffer.hpp

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1		//
2		// Copyright (c) 2023 Dmitry Arkhipov (grisumbras@yandex.ru)
3		//
4		// Distributed under the Boost Software License, Version 1.0. (See accompanying
5		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6		//
7		// Official repository: https://github.com/boostorg/json
8		//
9
10
11		#ifndef BOOST_JSON_DETAIL_SBO_BUFFER_HPP
12		#define BOOST_JSON_DETAIL_SBO_BUFFER_HPP
13
14		#include <boost/core/detail/static_assert.hpp>
15		#include <boost/json/detail/config.hpp>
16		#include <boost/json/detail/except.hpp>
17		#include <string>
18		#include <array>
19
20		namespace boost {
21		namespace json {
22		namespace detail {
23
24		template< std::size_t N >
25		class sbo_buffer
26		{
27		struct size_ptr_pair
28		{
29		std::size_t size;
30		char* ptr;
31		};
32		BOOST_CORE_STATIC_ASSERT( N >= sizeof(size_ptr_pair) );
33
34		union {
35		std::array<char, N> buffer_;
36		std::size_t capacity_;
37		};
38		char* data_ = buffer_.data();
39		std::size_t size_ = 0;
40
41		bool
42	2180028x	is_small() const noexcept
43		{
44	2180028x	return data_ == buffer_.data();
45		}
46
47		void
48	6097x	dispose()
49		{
50	6097x	if( is_small() )
51	3272x	return;
52
53	2825x	delete[] data_;
54		#if defined(__GNUC__)
55		# pragma GCC diagnostic push
56		# pragma GCC diagnostic ignored "-Wmissing-field-initializers"
57		#endif
58	2825x	buffer_ = {};
59		#if defined(__GNUC__)
60		# pragma GCC diagnostic pop
61		#endif
62	5650x	data_ = buffer_.data();
63		}
64
65		static constexpr
66		std::size_t
67	15412x	max_size() noexcept
68		{
69	15412x	return BOOST_JSON_MAX_STRING_SIZE;
70		}
71
72		public:
73	2164607x	sbo_buffer()
74	2164607x	: buffer_()
75	2164607x	{}
76
77		sbo_buffer( sbo_buffer&& other ) noexcept
78		: size_(other.size_)
79		{
80		if( other.is_small() )
81		{
82		buffer_ = other.buffer_;
83		data_ = buffer_.data();
84		}
85		else
86		{
87		data_ = other.data_;
88		other.data_ = other.buffer_.data();
89		}
90		BOOST_ASSERT( other.is_small() );
91		}
92
93		sbo_buffer&
94		operator=( sbo_buffer&& other ) noexcept
95		{
96		if( &other == this )
97		return this;
98
99		if( other.is_small() )
100		{
101		buffer_ = other.buffer_;
102		data_ = buffer_.data();
103		}
104		else
105		{
106		data_ = other.data_;
107		other.data_ = other.buffer_.data();
108		}
109
110		size_ = other.size_;
111		other.size_ = 0;
112
113		return *this;
114		}
115
116	2164607x	~sbo_buffer()
117		{
118	2164607x	if( !is_small() )
119	3271x	delete[] data_;
120	2164607x	}
121
122		std::size_t
123	9324x	capacity() const noexcept
124		{
125	15734x	return is_small() ? buffer_.size() : capacity_;
126		}
127
128		void
129	1x	reset() noexcept
130		{
131	1x	dispose();
132	1x	clear();
133	1x	}
134
135		void
136	6242866x	clear()
137		{
138	6242866x	size_ = 0;
139	6242866x	}
140
141		void
142	11838x	grow( std::size_t size )
143		{
144	11838x	if( !size )
145	5741x	return;
146
147	9316x	if( max_size() - size_ < size )
148		{
149		BOOST_STATIC_CONSTEXPR source_location loc = BOOST_CURRENT_LOCATION;
150	1x	detail::throw_system_error( error::number_too_large, &loc );
151		}
152
153	9315x	std::size_t const old_capacity = this->capacity();
154	9315x	if( size <= old_capacity - size_ )
155	3219x	return;
156
157	6096x	std::size_t new_capacity = size_ + size;
158
159		// growth factor 2
160	6096x	if( old_capacity <= max_size() - old_capacity ) // check for overflow
161	6096x	new_capacity = (std::max)(old_capacity * 2, new_capacity);
162
163	6096x	char* new_data = new char[new_capacity];
164	6096x	std::memcpy(new_data, data_, size_);
165
166	6096x	dispose();
167	6096x	data_ = new_data;
168	6096x	capacity_ = new_capacity;
169		}
170
171		char*
172	11838x	append( char const* ptr, std::size_t size )
173		{
174	11838x	grow(size);
175
176	11837x	if(BOOST_JSON_LIKELY( size ))
177	9315x	std::memcpy( data_ + size_, ptr, size );
178	11837x	size_ += size;
179	11837x	return data_;
180		}
181
182		std::size_t
183	3066431x	size() noexcept
184		{
185	3066431x	return size_;
186		}
187		};
188
189		} // namespace detail
190		} // namespace json
191		} // namespace boost
192
193		#endif // BOOST_JSON_DETAIL_SBO_BUFFER_HPP
194