Bitcoin Core 28.99.0
P2P Digital Currency
overflow.h
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1// Copyright (c) 2021-2022 The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#ifndef BITCOIN_UTIL_OVERFLOW_H
6#define BITCOIN_UTIL_OVERFLOW_H
7
8#include <climits>
9#include <concepts>
10#include <limits>
11#include <optional>
12#include <type_traits>
13
14template <class T>
15[[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
16{
17 static_assert(std::is_integral<T>::value, "Integral required.");
18 if constexpr (std::numeric_limits<T>::is_signed) {
19 return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
20 (i < 0 && j < std::numeric_limits<T>::min() - i);
21 }
22 return std::numeric_limits<T>::max() - i < j;
23}
24
25template <class T>
26[[nodiscard]] std::optional<T> CheckedAdd(const T i, const T j) noexcept
27{
28 if (AdditionOverflow(i, j)) {
29 return std::nullopt;
30 }
31 return i + j;
32}
33
34template <class T>
35[[nodiscard]] T SaturatingAdd(const T i, const T j) noexcept
36{
37 if constexpr (std::numeric_limits<T>::is_signed) {
38 if (i > 0 && j > std::numeric_limits<T>::max() - i) {
39 return std::numeric_limits<T>::max();
40 }
41 if (i < 0 && j < std::numeric_limits<T>::min() - i) {
42 return std::numeric_limits<T>::min();
43 }
44 } else {
45 if (std::numeric_limits<T>::max() - i < j) {
46 return std::numeric_limits<T>::max();
47 }
48 }
49 return i + j;
50}
51
58template <std::integral T>
59constexpr std::optional<T> CheckedLeftShift(T input, unsigned shift) noexcept
60{
61 if (shift == 0 || input == 0) return input;
62 // Avoid undefined c++ behaviour if shift is >= number of bits in T.
63 if (shift >= sizeof(T) * CHAR_BIT) return std::nullopt;
64 // If input << shift is too big to fit in T, return nullopt.
65 if (input > (std::numeric_limits<T>::max() >> shift)) return std::nullopt;
66 if (input < (std::numeric_limits<T>::min() >> shift)) return std::nullopt;
67 return input << shift;
68}
69
77template <std::integral T>
78constexpr T SaturatingLeftShift(T input, unsigned shift) noexcept
79{
80 if (auto result{CheckedLeftShift(input, shift)}) return *result;
81 // If input << shift is too big to fit in T, return biggest positive or negative
82 // number that fits.
83 return input < 0 ? std::numeric_limits<T>::min() : std::numeric_limits<T>::max();
84}
85
86#endif // BITCOIN_UTIL_OVERFLOW_H
#define T(expected, seed, data)
std::optional< T > CheckedAdd(const T i, const T j) noexcept
Definition: overflow.h:26
constexpr T SaturatingLeftShift(T input, unsigned shift) noexcept
Left bit shift with safe minimum and maximum values.
Definition: overflow.h:78
bool AdditionOverflow(const T i, const T j) noexcept
Definition: overflow.h:15
T SaturatingAdd(const T i, const T j) noexcept
Definition: overflow.h:35
constexpr std::optional< T > CheckedLeftShift(T input, unsigned shift) noexcept
Left bit shift with overflow checking.
Definition: overflow.h:59