1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
// Copyright (c) 2017-2019, The Monero Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list
// of conditions and the following disclaimer in the documentation and/or other
// materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its contributors may be
// used to endorse or promote products derived from this software without specific
// prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#pragma once
#include <algorithm>
#include <cstdint>
#include <memory>
#include <type_traits>
namespace epee
{
/*!
\brief Non-owning sequence of data. Does not deep copy
Inspired by `gsl::span` and/or `boost::iterator_range`. This class is
intended to be used as a parameter type for functions that need to take a
writable or read-only sequence of data. Most common cases are `span<char>`
and `span<std::uint8_t>`. Using as a class member is only recommended if
clearly documented as not doing a deep-copy. C-arrays are easily convertible
to this type.
\note Conversion from C string literal to `span<const char>` will include
the NULL-terminator.
\note Never allows derived-to-base pointer conversion; an array of derived
types is not an array of base types.
*/
template<typename T>
class span
{
template<typename U>
static constexpr bool safe_conversion() noexcept
{
// Allow exact matches or `T*` -> `const T*`.
using with_const = typename std::add_const<U>::type;
return std::is_same<T, U>() ||
(std::is_const<T>() && std::is_same<T, with_const>());
}
public:
using value_type = T;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
using pointer = T*;
using const_pointer = const T*;
using reference = T&;
using const_reference = const T&;
using iterator = pointer;
using const_iterator = const_pointer;
constexpr span() noexcept : ptr(nullptr), len(0) {}
constexpr span(std::nullptr_t) noexcept : span() {}
//! Prevent derived-to-base conversions; invalid in this context.
template<typename U, typename = typename std::enable_if<safe_conversion<U>()>::type>
constexpr span(U* const src_ptr, const std::size_t count) noexcept
: ptr(src_ptr), len(count) {}
//! Conversion from C-array. Prevents common bugs with sizeof + arrays.
template<std::size_t N>
constexpr span(T (&src)[N]) noexcept : span(src, N) {}
constexpr span(const span&) noexcept = default;
span& operator=(const span&) noexcept = default;
/*! Try to remove `amount` elements from beginning of span.
\return Number of elements removed. */
std::size_t remove_prefix(std::size_t amount) noexcept
{
amount = std::min(len, amount);
ptr += amount;
len -= amount;
return amount;
}
constexpr iterator begin() const noexcept { return ptr; }
constexpr const_iterator cbegin() const noexcept { return ptr; }
constexpr iterator end() const noexcept { return begin() + size(); }
constexpr const_iterator cend() const noexcept { return cbegin() + size(); }
constexpr bool empty() const noexcept { return size() == 0; }
constexpr pointer data() const noexcept { return ptr; }
constexpr std::size_t size() const noexcept { return len; }
constexpr std::size_t size_bytes() const noexcept { return size() * sizeof(value_type); }
const T &operator[](size_t idx) const { return ptr[idx]; }
private:
T* ptr;
std::size_t len;
};
//! \return `span<const T::value_type>` from a STL compatible `src`.
template<typename T>
constexpr span<const typename T::value_type> to_span(const T& src)
{
// compiler provides diagnostic if size() is not size_t.
return {src.data(), src.size()};
}
//! \return `span<T::value_type>` from a STL compatible `src`.
template<typename T>
constexpr span<typename T::value_type> to_mut_span(T& src)
{
// compiler provides diagnostic if size() is not size_t.
return {src.data(), src.size()};
}
template<typename T>
constexpr bool has_padding() noexcept
{
return !std::is_standard_layout<T>() || alignof(T) != 1;
}
//! \return Cast data from `src` as `span<const std::uint8_t>`.
template<typename T>
span<const std::uint8_t> to_byte_span(const span<const T> src) noexcept
{
static_assert(!has_padding<T>(), "source type may have padding");
return {reinterpret_cast<const std::uint8_t*>(src.data()), src.size_bytes()};
}
//! \return `span<const std::uint8_t>` which represents the bytes at `&src`.
template<typename T>
span<const std::uint8_t> as_byte_span(const T& src) noexcept
{
static_assert(!std::is_empty<T>(), "empty types will not work -> sizeof == 1");
static_assert(!has_padding<T>(), "source type may have padding");
return {reinterpret_cast<const std::uint8_t*>(std::addressof(src)), sizeof(T)};
}
//! \return `span<std::uint8_t>` which represents the bytes at `&src`.
template<typename T>
span<std::uint8_t> as_mut_byte_span(T& src) noexcept
{
static_assert(!std::is_empty<T>(), "empty types will not work -> sizeof == 1");
static_assert(!has_padding<T>(), "source type may have padding");
return {reinterpret_cast<std::uint8_t*>(std::addressof(src)), sizeof(T)};
}
//! make a span from a std::string
template<typename T>
span<const T> strspan(const std::string &s) noexcept
{
static_assert(std::is_same<T, char>() || std::is_same<T, unsigned char>() || std::is_same<T, int8_t>() || std::is_same<T, uint8_t>(), "Unexpected type");
return {reinterpret_cast<const T*>(s.data()), s.size()};
}
}
|
