uint256.h raw
1 // Copyright (c) 2009-2010 Satoshi Nakamoto
2 // Copyright (c) 2009-present The Bitcoin Core developers
3 // Distributed under the MIT software license, see the accompanying
4 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
5
6 #ifndef BITCOIN_UINT256_H
7 #define BITCOIN_UINT256_H
8
9 #include <crypto/common.h>
10 #include <crypto/hex_base.h>
11 #include <span.h>
12 #include <util/strencodings.h>
13 #include <util/string.h>
14
15 #include <algorithm>
16 #include <array>
17 #include <cassert>
18 #include <cstdint>
19 #include <cstring>
20 #include <optional>
21 #include <string>
22 #include <string_view>
23
24 /** Template base class for fixed-sized opaque blobs. */
25 template<unsigned int BITS>
26 class base_blob
27 {
28 protected:
29 static constexpr int WIDTH = BITS / 8;
30 static_assert(BITS % 8 == 0, "base_blob currently only supports whole bytes.");
31 std::array<uint8_t, WIDTH> m_data;
32 static_assert(WIDTH == sizeof(m_data), "Sanity check");
33
34 public:
35 /* construct 0 value by default */
36 constexpr base_blob() : m_data() {}
37
38 /* constructor for constants between 1 and 255 */
39 constexpr explicit base_blob(uint8_t v) : m_data{v} {}
40
41 constexpr explicit base_blob(std::span<const unsigned char> vch)
42 {
43 assert(vch.size() == WIDTH);
44 std::copy(vch.begin(), vch.end(), m_data.begin());
45 }
46
47 consteval explicit base_blob(std::string_view hex_str);
48
49 constexpr bool IsNull() const
50 {
51 return std::all_of(m_data.begin(), m_data.end(), [](uint8_t val) {
52 return val == 0;
53 });
54 }
55
56 constexpr void SetNull()
57 {
58 std::fill(m_data.begin(), m_data.end(), 0);
59 }
60
61 /** Lexicographic ordering
62 * @note Does NOT match the ordering on the corresponding \ref
63 * base_uint::CompareTo, which starts comparing from the end.
64 */
65 constexpr int Compare(const base_blob& other) const { return std::memcmp(m_data.data(), other.m_data.data(), WIDTH); }
66
67 friend constexpr bool operator==(const base_blob& a, const base_blob& b) { return a.Compare(b) == 0; }
68 friend constexpr bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }
69
70 /** @name Hex representation
71 *
72 * The hex representation used by GetHex(), ToString(), and FromHex()
73 * is unusual, since it shows bytes of the base_blob in reverse order.
74 * For example, a 4-byte blob {0x12, 0x34, 0x56, 0x78} is represented
75 * as "78563412" instead of the more typical "12345678" representation
76 * that would be shown in a hex editor or used by typical
77 * byte-array / hex conversion functions like python's bytes.hex() and
78 * bytes.fromhex().
79 *
80 * The nice thing about the reverse-byte representation, even though it is
81 * unusual, is that if a blob contains an arithmetic number in little endian
82 * format (with least significant bytes first, and most significant bytes
83 * last), the GetHex() output will match the way the number would normally
84 * be written in base-16 (with most significant digits first and least
85 * significant digits last).
86 *
87 * This means, for example, that ArithToUint256(num).GetHex() can be used to
88 * display an arith_uint256 num value as a number, because
89 * ArithToUint256() converts the number to a blob in little-endian format,
90 * so the arith_uint256 class doesn't need to have its own number parsing
91 * and formatting functions.
92 *
93 * @{*/
94 std::string GetHex() const;
95 std::string ToString() const;
96 /**@}*/
97
98 constexpr const unsigned char* data() const { return m_data.data(); }
99 constexpr unsigned char* data() { return m_data.data(); }
100
101 constexpr unsigned char* begin() { return m_data.data(); }
102 constexpr unsigned char* end() { return m_data.data() + WIDTH; }
103
104 constexpr const unsigned char* begin() const { return m_data.data(); }
105 constexpr const unsigned char* end() const { return m_data.data() + WIDTH; }
106
107 static constexpr unsigned int size() { return WIDTH; }
108
109 constexpr uint64_t GetUint64(int pos) const { return ReadLE64(m_data.data() + pos * 8); }
110
111 template<typename Stream>
112 void Serialize(Stream& s) const
113 {
114 s << std::span(m_data);
115 }
116
117 template<typename Stream>
118 void Unserialize(Stream& s)
119 {
120 s.read(MakeWritableByteSpan(m_data));
121 }
122 };
123
124 template <unsigned int BITS>
125 consteval base_blob<BITS>::base_blob(std::string_view hex_str)
126 {
127 if (hex_str.length() != m_data.size() * 2) throw "Hex string must fit exactly";
128 auto str_it = hex_str.rbegin();
129 for (auto& elem : m_data) {
130 auto lo = util::ConstevalHexDigit(*(str_it++));
131 elem = (util::ConstevalHexDigit(*(str_it++)) << 4) | lo;
132 }
133 }
134
135 namespace detail {
136 /**
137 * Writes the hex string (in reverse byte order) into a new uintN_t object
138 * and only returns a value iff all of the checks pass:
139 * - Input length is uintN_t::size()*2
140 * - All characters are hex
141 */
142 template <class uintN_t>
143 std::optional<uintN_t> FromHex(std::string_view str)
144 {
145 if (uintN_t::size() * 2 != str.size() || !IsHex(str)) return std::nullopt;
146 uintN_t rv;
147 unsigned char* p1 = rv.begin();
148 unsigned char* pend = rv.end();
149 size_t digits = str.size();
150 while (digits > 0 && p1 < pend) {
151 *p1 = ::HexDigit(str[--digits]);
152 if (digits > 0) {
153 *p1 |= ((unsigned char)::HexDigit(str[--digits]) << 4);
154 p1++;
155 }
156 }
157 return rv;
158 }
159 /**
160 * @brief Like FromHex(std::string_view str), but allows an "0x" prefix
161 * and pads the input with leading zeroes if it is shorter than
162 * the expected length of uintN_t::size()*2.
163 *
164 * Designed to be used when dealing with user input.
165 */
166 template <class uintN_t>
167 std::optional<uintN_t> FromUserHex(std::string_view input)
168 {
169 input = util::RemovePrefixView(input, "0x");
170 constexpr auto expected_size{uintN_t::size() * 2};
171 if (input.size() < expected_size) {
172 auto padded = std::string(expected_size, '0');
173 std::copy(input.begin(), input.end(), padded.begin() + expected_size - input.size());
174 return FromHex<uintN_t>(padded);
175 }
176 return FromHex<uintN_t>(input);
177 }
178 } // namespace detail
179
180 /** 160-bit opaque blob.
181 * @note This type is called uint160 for historical reasons only. It is an opaque
182 * blob of 160 bits and has no integer operations.
183 */
184 class uint160 : public base_blob<160> {
185 public:
186 static std::optional<uint160> FromHex(std::string_view str) { return detail::FromHex<uint160>(str); }
187 constexpr uint160() = default;
188 constexpr explicit uint160(std::span<const unsigned char> vch) : base_blob<160>(vch) {}
189 };
190
191 /** 256-bit opaque blob.
192 * @note This type is called uint256 for historical reasons only. It is an
193 * opaque blob of 256 bits and has no integer operations. Use arith_uint256 if
194 * those are required.
195 */
196 class uint256 : public base_blob<256> {
197 public:
198 static std::optional<uint256> FromHex(std::string_view str) { return detail::FromHex<uint256>(str); }
199 static std::optional<uint256> FromUserHex(std::string_view str) { return detail::FromUserHex<uint256>(str); }
200 constexpr uint256() = default;
201 consteval explicit uint256(std::string_view hex_str) : base_blob<256>(hex_str) {}
202 constexpr explicit uint256(uint8_t v) : base_blob<256>(v) {}
203 constexpr explicit uint256(std::span<const unsigned char> vch) : base_blob<256>(vch) {}
204 static const uint256 ZERO;
205 static const uint256 ONE;
206 };
207
208 #endif // BITCOIN_UINT256_H
209