OpenTTD Source 20241224-master-gf74b0cf984
overflowsafe_type.hpp
Go to the documentation of this file.
1/*
2 * This file is part of OpenTTD.
3 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
4 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
5 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
6 */
7
10#ifndef OVERFLOWSAFE_TYPE_HPP
11#define OVERFLOWSAFE_TYPE_HPP
12
13#include "math_func.hpp"
14
15
16#ifdef __has_builtin
17# if __has_builtin(__builtin_add_overflow) && __has_builtin(__builtin_sub_overflow) && __has_builtin(__builtin_mul_overflow)
18# define HAS_OVERFLOW_BUILTINS
19# endif
20#endif
21
28template <class T>
29class OverflowSafeInt
30{
31private:
32 static constexpr T T_MAX = std::numeric_limits<T>::max();
33 static constexpr T T_MIN = std::numeric_limits<T>::min();
34
36 T m_value;
37public:
38 constexpr OverflowSafeInt() : m_value(0) { }
39
40 constexpr OverflowSafeInt(const OverflowSafeInt &other) : m_value(other.m_value) { }
41 constexpr OverflowSafeInt(const T int_) : m_value(int_) { }
42
43 inline constexpr OverflowSafeInt& operator = (const OverflowSafeInt& other) { this->m_value = other.m_value; return *this; }
44 inline constexpr OverflowSafeInt& operator = (T other) { this->m_value = other; return *this; }
45
46 inline constexpr OverflowSafeInt operator - () const { return OverflowSafeInt(this->m_value == T_MIN ? T_MAX : -this->m_value); }
47
53 inline constexpr OverflowSafeInt& operator += (const OverflowSafeInt& other)
54 {
55#ifdef HAS_OVERFLOW_BUILTINS
56 if (__builtin_add_overflow(this->m_value, other.m_value, &this->m_value)) [[unlikely]] {
57 this->m_value = (other.m_value < 0) ? T_MIN : T_MAX;
58 }
59#else
60 if (this->m_value > 0 && other.m_value > 0 && (T_MAX - other.m_value) < this->m_value) {
61 this->m_value = T_MAX;
62 } else if (this->m_value < 0 && other.m_value < 0 && (this->m_value == T_MIN || other.m_value == T_MIN || ((T_MAX + this->m_value) + other.m_value < (T_MIN + T_MAX)))) {
63 this->m_value = T_MIN;
64 } else {
65 this->m_value += other.m_value;
66 }
67#endif
68 return *this;
69 }
70
76 inline constexpr OverflowSafeInt& operator -= (const OverflowSafeInt& other)
77 {
78#ifdef HAS_OVERFLOW_BUILTINS
79 if (__builtin_sub_overflow(this->m_value, other.m_value, &this->m_value)) [[unlikely]] {
80 this->m_value = (other.m_value < 0) ? T_MAX : T_MIN;
81 }
82#else
83 if (this->m_value > 0 && other.m_value < 0 && (T_MAX + other.m_value) < this->m_value) {
84 this->m_value = T_MAX;
85 } else if (this->m_value < 0 && other.m_value > 0 && (T_MAX + this->m_value) < (T_MIN + T_MAX) + other.m_value) {
86 this->m_value = T_MIN;
87 } else {
88 this->m_value -= other.m_value;
89 }
90#endif
91 return *this;
92 }
93
94 /* Operators for addition and subtraction. */
95 inline constexpr OverflowSafeInt operator + (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result += other; return result; }
96 inline constexpr OverflowSafeInt operator + (const int other) const { OverflowSafeInt result = *this; result += (int64_t)other; return result; }
97 inline constexpr OverflowSafeInt operator + (const uint other) const { OverflowSafeInt result = *this; result += (int64_t)other; return result; }
98 inline constexpr OverflowSafeInt operator - (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result -= other; return result; }
99 inline constexpr OverflowSafeInt operator - (const int other) const { OverflowSafeInt result = *this; result -= (int64_t)other; return result; }
100 inline constexpr OverflowSafeInt operator - (const uint other) const { OverflowSafeInt result = *this; result -= (int64_t)other; return result; }
101
102 inline constexpr OverflowSafeInt& operator ++ () { return *this += 1; }
103 inline constexpr OverflowSafeInt& operator -- () { return *this += -1; }
104 inline constexpr OverflowSafeInt operator ++ (int) { OverflowSafeInt org = *this; *this += 1; return org; }
105 inline constexpr OverflowSafeInt operator -- (int) { OverflowSafeInt org = *this; *this += -1; return org; }
106
113 inline constexpr OverflowSafeInt& operator *= (const int factor)
114 {
115#ifdef HAS_OVERFLOW_BUILTINS
116 const bool is_result_positive = (this->m_value < 0) == (factor < 0); // -ve * -ve == +ve
117 if (__builtin_mul_overflow(this->m_value, factor, &this->m_value)) [[unlikely]] {
118 this->m_value = is_result_positive ? T_MAX : T_MIN;
119 }
120#else
121 if (factor == -1) {
122 this->m_value = (this->m_value == T_MIN) ? T_MAX : -this->m_value;
123 } else if (factor > 0 && this->m_value > 0 && (T_MAX / factor) < this->m_value) {
124 this->m_value = T_MAX;
125 } else if (factor > 0 && this->m_value < 0 && (T_MIN / factor) > this->m_value) {
126 this->m_value = T_MIN;
127 } else if (factor < 0 && this->m_value > 0 && (T_MIN / factor) < this->m_value) {
128 this->m_value = T_MIN;
129 } else if (factor < 0 && this->m_value < 0 && (T_MAX / factor) > this->m_value) {
130 this->m_value = T_MAX;
131 } else {
132 this->m_value *= factor;
133 }
134#endif
135 return *this;
136 }
137
138 /* Operators for multiplication. */
139 inline constexpr OverflowSafeInt operator * (const int64_t factor) const { OverflowSafeInt result = *this; result *= factor; return result; }
140 inline constexpr OverflowSafeInt operator * (const int factor) const { OverflowSafeInt result = *this; result *= (int64_t)factor; return result; }
141 inline constexpr OverflowSafeInt operator * (const uint factor) const { OverflowSafeInt result = *this; result *= (int64_t)factor; return result; }
142 inline constexpr OverflowSafeInt operator * (const uint16_t factor) const { OverflowSafeInt result = *this; result *= (int64_t)factor; return result; }
143 inline constexpr OverflowSafeInt operator * (const uint8_t factor) const { OverflowSafeInt result = *this; result *= (int64_t)factor; return result; }
144
145 /* Operators for division. */
146 inline constexpr OverflowSafeInt& operator /= (const int64_t divisor) { this->m_value /= divisor; return *this; }
147 inline constexpr OverflowSafeInt operator / (const OverflowSafeInt& divisor) const { OverflowSafeInt result = *this; result /= divisor.m_value; return result; }
148 inline constexpr OverflowSafeInt operator / (const int divisor) const { OverflowSafeInt result = *this; result /= divisor; return result; }
149 inline constexpr OverflowSafeInt operator / (const uint divisor) const { OverflowSafeInt result = *this; result /= (int)divisor; return result; }
150
151 /* Operators for modulo */
152 inline constexpr OverflowSafeInt& operator %= (const int divisor) { this->m_value %= divisor; return *this; }
153 inline constexpr OverflowSafeInt operator % (const int divisor) const { OverflowSafeInt result = *this; result %= divisor; return result; }
154
155 /* Operators for shifting. */
156 inline constexpr OverflowSafeInt& operator <<= (const int shift) { this->m_value <<= shift; return *this; }
157 inline constexpr OverflowSafeInt operator << (const int shift) const { OverflowSafeInt result = *this; result <<= shift; return result; }
158 inline constexpr OverflowSafeInt& operator >>= (const int shift) { this->m_value >>= shift; return *this; }
159 inline constexpr OverflowSafeInt operator >> (const int shift) const { OverflowSafeInt result = *this; result >>= shift; return result; }
160
161 /* Operators for (in)equality when comparing overflow safe ints. */
162 inline constexpr bool operator == (const OverflowSafeInt& other) const { return this->m_value == other.m_value; }
163 inline constexpr bool operator != (const OverflowSafeInt& other) const { return !(*this == other); }
164 inline constexpr bool operator > (const OverflowSafeInt& other) const { return this->m_value > other.m_value; }
165 inline constexpr bool operator >= (const OverflowSafeInt& other) const { return this->m_value >= other.m_value; }
166 inline constexpr bool operator < (const OverflowSafeInt& other) const { return !(*this >= other); }
167 inline constexpr bool operator <= (const OverflowSafeInt& other) const { return !(*this > other); }
168
169 /* Operators for (in)equality when comparing non-overflow safe ints. */
170 inline constexpr bool operator == (const int other) const { return this->m_value == other; }
171 inline constexpr bool operator != (const int other) const { return !(*this == other); }
172 inline constexpr bool operator > (const int other) const { return this->m_value > other; }
173 inline constexpr bool operator >= (const int other) const { return this->m_value >= other; }
174 inline constexpr bool operator < (const int other) const { return !(*this >= other); }
175 inline constexpr bool operator <= (const int other) const { return !(*this > other); }
176
177 inline constexpr operator T () const { return this->m_value; }
178
179 static inline constexpr OverflowSafeInt<T> max() { return T_MAX; }
180 static inline constexpr OverflowSafeInt<T> min() { return T_MIN; }
181};
182
183
184/* Sometimes we got int64_t operator OverflowSafeInt instead of vice versa. Handle that properly. */
185template <class T> inline constexpr OverflowSafeInt<T> operator + (const int64_t a, const OverflowSafeInt<T> b) { return b + a; }
186template <class T> inline constexpr OverflowSafeInt<T> operator - (const int64_t a, const OverflowSafeInt<T> b) { return -b + a; }
187template <class T> inline constexpr OverflowSafeInt<T> operator * (const int64_t a, const OverflowSafeInt<T> b) { return b * a; }
188template <class T> inline constexpr OverflowSafeInt<T> operator / (const int64_t a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
189
190/* Sometimes we got int operator OverflowSafeInt instead of vice versa. Handle that properly. */
191template <class T> inline constexpr OverflowSafeInt<T> operator + (const int a, const OverflowSafeInt<T> b) { return b + a; }
192template <class T> inline constexpr OverflowSafeInt<T> operator - (const int a, const OverflowSafeInt<T> b) { return -b + a; }
193template <class T> inline constexpr OverflowSafeInt<T> operator * (const int a, const OverflowSafeInt<T> b) { return b * a; }
194template <class T> inline constexpr OverflowSafeInt<T> operator / (const int a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
195
196/* Sometimes we got uint operator OverflowSafeInt instead of vice versa. Handle that properly. */
197template <class T> inline constexpr OverflowSafeInt<T> operator + (const uint a, const OverflowSafeInt<T> b) { return b + a; }
198template <class T> inline constexpr OverflowSafeInt<T> operator - (const uint a, const OverflowSafeInt<T> b) { return -b + a; }
199template <class T> inline constexpr OverflowSafeInt<T> operator * (const uint a, const OverflowSafeInt<T> b) { return b * a; }
200template <class T> inline constexpr OverflowSafeInt<T> operator / (const uint a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
201
202/* Sometimes we got byte operator OverflowSafeInt instead of vice versa. Handle that properly. */
203template <class T> inline constexpr OverflowSafeInt<T> operator + (const uint8_t a, const OverflowSafeInt<T> b) { return b + (uint)a; }
204template <class T> inline constexpr OverflowSafeInt<T> operator - (const uint8_t a, const OverflowSafeInt<T> b) { return -b + (uint)a; }
205template <class T> inline constexpr OverflowSafeInt<T> operator * (const uint8_t a, const OverflowSafeInt<T> b) { return b * (uint)a; }
206template <class T> inline constexpr OverflowSafeInt<T> operator / (const uint8_t a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
207
208typedef OverflowSafeInt<int64_t> OverflowSafeInt64;
209typedef OverflowSafeInt<int32_t> OverflowSafeInt32;
210
211/* Some basic "unit tests". Also has the bonus of confirming that constexpr is working. */
212static_assert(OverflowSafeInt32(INT32_MIN) - 1 == OverflowSafeInt32(INT32_MIN));
213static_assert(OverflowSafeInt32(INT32_MAX) + 1 == OverflowSafeInt32(INT32_MAX));
214static_assert(OverflowSafeInt32(INT32_MAX) * 2 == OverflowSafeInt32(INT32_MAX));
215static_assert(OverflowSafeInt32(INT32_MIN) * 2 == OverflowSafeInt32(INT32_MIN));
216
217/* Specialisation of the generic ClampTo function for overflow safe integers to normal integers. */
218template <typename To, typename From>
219constexpr To ClampTo(OverflowSafeInt<From> value) { return ClampTo<To>(From(value)); }
220
221#undef HAS_OVERFLOW_BUILTINS
222
223#endif /* OVERFLOWSAFE_TYPE_HPP */
OverflowSafeInt
Overflow safe template for integers, i.e.
Definition overflowsafe_type.hpp:30
OverflowSafeInt::operator+=
constexpr OverflowSafeInt & operator+=(const OverflowSafeInt &other)
Safe implementation of addition.
Definition overflowsafe_type.hpp:53
OverflowSafeInt::operator*=
constexpr OverflowSafeInt & operator*=(const int factor)
Safe implementation of multiplication.
Definition overflowsafe_type.hpp:113
OverflowSafeInt::m_value
T m_value
The non-overflow safe backend to store the value in.
Definition overflowsafe_type.hpp:36
OverflowSafeInt::operator-=
constexpr OverflowSafeInt & operator-=(const OverflowSafeInt &other)
Safe implementation of subtraction.
Definition overflowsafe_type.hpp:76
math_func.hpp
Integer math functions.
ClampTo
constexpr To ClampTo(From value)
Clamp the given value down to lie within the requested type.
Definition math_func.hpp:167