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
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
|
/*
* This file is part of OpenTTD.
* 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.
* 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.
* 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/>.
*/
/** @file overflowsafe_type.hpp An overflow safe integer-like type. */
#ifndef OVERFLOWSAFE_TYPE_HPP
#define OVERFLOWSAFE_TYPE_HPP
#include "math_func.hpp"
#include <limits>
#ifdef __has_builtin
# if __has_builtin(__builtin_add_overflow) && __has_builtin(__builtin_sub_overflow) && __has_builtin(__builtin_mul_overflow)
# define HAS_OVERFLOW_BUILTINS
# endif
#endif
/**
* Overflow safe template for integers, i.e. integers that will never overflow
* you multiply the maximum value with 2, or add 2, or subtract something from
* the minimum value, etc.
* @param T the type these integers are stored with.
*/
template <class T>
class OverflowSafeInt
{
private:
static constexpr T T_MAX = std::numeric_limits<T>::max();
static constexpr T T_MIN = std::numeric_limits<T>::min();
/** The non-overflow safe backend to store the value in. */
T m_value;
public:
constexpr OverflowSafeInt() : m_value(0) { }
constexpr OverflowSafeInt(const OverflowSafeInt& other) : m_value(other.m_value) { }
constexpr OverflowSafeInt(const int64 int_) : m_value(int_) { }
inline constexpr OverflowSafeInt& operator = (const OverflowSafeInt& other) { this->m_value = other.m_value; return *this; }
inline constexpr OverflowSafeInt operator - () const { return OverflowSafeInt(this->m_value == T_MIN ? T_MAX : -this->m_value); }
/**
* Safe implementation of addition.
* @param other the amount to add
* @note when the addition would yield more than T_MAX, it will be T_MAX.
*/
inline constexpr OverflowSafeInt& operator += (const OverflowSafeInt& other)
{
#ifdef HAS_OVERFLOW_BUILTINS
if (unlikely(__builtin_add_overflow(this->m_value, other.m_value, &this->m_value))) {
this->m_value = (other.m_value < 0) ? T_MIN : T_MAX;
}
#else
if (this->m_value > 0 && other.m_value > 0 && (T_MAX - other.m_value) < this->m_value) {
this->m_value = T_MAX;
} 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)))) {
this->m_value = T_MIN;
} else {
this->m_value += other.m_value;
}
#endif
return *this;
}
/**
* Safe implementation of subtraction.
* @param other the amount to subtract
* @note when the subtraction would yield less than T_MIN, it will be T_MIN.
*/
inline constexpr OverflowSafeInt& operator -= (const OverflowSafeInt& other)
{
#ifdef HAS_OVERFLOW_BUILTINS
if (unlikely(__builtin_sub_overflow(this->m_value, other.m_value, &this->m_value))) {
this->m_value = (other.m_value < 0) ? T_MAX : T_MIN;
}
#else
if (this->m_value > 0 && other.m_value < 0 && (T_MAX + other.m_value) < this->m_value) {
this->m_value = T_MAX;
} else if (this->m_value < 0 && other.m_value > 0 && (T_MAX + this->m_value) < (T_MIN + T_MAX) + other.m_value) {
this->m_value = T_MIN;
} else {
this->m_value -= other.m_value;
}
#endif
return *this;
}
/* Operators for addition and subtraction. */
inline constexpr OverflowSafeInt operator + (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result += other; return result; }
inline constexpr OverflowSafeInt operator + (const int other) const { OverflowSafeInt result = *this; result += (int64)other; return result; }
inline constexpr OverflowSafeInt operator + (const uint other) const { OverflowSafeInt result = *this; result += (int64)other; return result; }
inline constexpr OverflowSafeInt operator - (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result -= other; return result; }
inline constexpr OverflowSafeInt operator - (const int other) const { OverflowSafeInt result = *this; result -= (int64)other; return result; }
inline constexpr OverflowSafeInt operator - (const uint other) const { OverflowSafeInt result = *this; result -= (int64)other; return result; }
inline constexpr OverflowSafeInt& operator ++ () { return *this += 1; }
inline constexpr OverflowSafeInt& operator -- () { return *this += -1; }
inline constexpr OverflowSafeInt operator ++ (int) { OverflowSafeInt org = *this; *this += 1; return org; }
inline constexpr OverflowSafeInt operator -- (int) { OverflowSafeInt org = *this; *this += -1; return org; }
/**
* Safe implementation of multiplication.
* @param factor the factor to multiply this with.
* @note when the multiplication would yield more than T_MAX (or less than T_MIN),
* it will be T_MAX (respectively T_MIN).
*/
inline constexpr OverflowSafeInt& operator *= (const int factor)
{
#ifdef HAS_OVERFLOW_BUILTINS
const bool is_result_positive = (this->m_value < 0) == (factor < 0); // -ve * -ve == +ve
if (unlikely(__builtin_mul_overflow(this->m_value, factor, &this->m_value))) {
this->m_value = is_result_positive ? T_MAX : T_MIN;
}
#else
if (factor == -1) {
this->m_value = (this->m_value == T_MIN) ? T_MAX : -this->m_value;
} else if (factor > 0 && this->m_value > 0 && (T_MAX / factor) < this->m_value) {
this->m_value = T_MAX;
} else if (factor > 0 && this->m_value < 0 && (T_MIN / factor) > this->m_value) {
this->m_value = T_MIN;
} else if (factor < 0 && this->m_value > 0 && (T_MIN / factor) < this->m_value) {
this->m_value = T_MIN;
} else if (factor < 0 && this->m_value < 0 && (T_MAX / factor) > this->m_value) {
this->m_value = T_MAX;
} else {
this->m_value *= factor;
}
#endif
return *this;
}
/* Operators for multiplication. */
inline constexpr OverflowSafeInt operator * (const int64 factor) const { OverflowSafeInt result = *this; result *= factor; return result; }
inline constexpr OverflowSafeInt operator * (const int factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
inline constexpr OverflowSafeInt operator * (const uint factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
inline constexpr OverflowSafeInt operator * (const uint16 factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
inline constexpr OverflowSafeInt operator * (const byte factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
/* Operators for division. */
inline constexpr OverflowSafeInt& operator /= (const int64 divisor) { this->m_value /= divisor; return *this; }
inline constexpr OverflowSafeInt operator / (const OverflowSafeInt& divisor) const { OverflowSafeInt result = *this; result /= divisor.m_value; return result; }
inline constexpr OverflowSafeInt operator / (const int divisor) const { OverflowSafeInt result = *this; result /= divisor; return result; }
inline constexpr OverflowSafeInt operator / (const uint divisor) const { OverflowSafeInt result = *this; result /= (int)divisor; return result; }
/* Operators for modulo */
inline constexpr OverflowSafeInt& operator %= (const int divisor) { this->m_value %= divisor; return *this; }
inline constexpr OverflowSafeInt operator % (const int divisor) const { OverflowSafeInt result = *this; result %= divisor; return result; }
/* Operators for shifting. */
inline constexpr OverflowSafeInt& operator <<= (const int shift) { this->m_value <<= shift; return *this; }
inline constexpr OverflowSafeInt operator << (const int shift) const { OverflowSafeInt result = *this; result <<= shift; return result; }
inline constexpr OverflowSafeInt& operator >>= (const int shift) { this->m_value >>= shift; return *this; }
inline constexpr OverflowSafeInt operator >> (const int shift) const { OverflowSafeInt result = *this; result >>= shift; return result; }
/* Operators for (in)equality when comparing overflow safe ints. */
inline constexpr bool operator == (const OverflowSafeInt& other) const { return this->m_value == other.m_value; }
inline constexpr bool operator != (const OverflowSafeInt& other) const { return !(*this == other); }
inline constexpr bool operator > (const OverflowSafeInt& other) const { return this->m_value > other.m_value; }
inline constexpr bool operator >= (const OverflowSafeInt& other) const { return this->m_value >= other.m_value; }
inline constexpr bool operator < (const OverflowSafeInt& other) const { return !(*this >= other); }
inline constexpr bool operator <= (const OverflowSafeInt& other) const { return !(*this > other); }
/* Operators for (in)equality when comparing non-overflow safe ints. */
inline constexpr bool operator == (const int other) const { return this->m_value == other; }
inline constexpr bool operator != (const int other) const { return !(*this == other); }
inline constexpr bool operator > (const int other) const { return this->m_value > other; }
inline constexpr bool operator >= (const int other) const { return this->m_value >= other; }
inline constexpr bool operator < (const int other) const { return !(*this >= other); }
inline constexpr bool operator <= (const int other) const { return !(*this > other); }
inline constexpr operator int64 () const { return this->m_value; }
};
/* Sometimes we got int64 operator OverflowSafeInt instead of vice versa. Handle that properly. */
template <class T> inline constexpr OverflowSafeInt<T> operator + (const int64 a, const OverflowSafeInt<T> b) { return b + a; }
template <class T> inline constexpr OverflowSafeInt<T> operator - (const int64 a, const OverflowSafeInt<T> b) { return -b + a; }
template <class T> inline constexpr OverflowSafeInt<T> operator * (const int64 a, const OverflowSafeInt<T> b) { return b * a; }
template <class T> inline constexpr OverflowSafeInt<T> operator / (const int64 a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
/* Sometimes we got int operator OverflowSafeInt instead of vice versa. Handle that properly. */
template <class T> inline constexpr OverflowSafeInt<T> operator + (const int a, const OverflowSafeInt<T> b) { return b + a; }
template <class T> inline constexpr OverflowSafeInt<T> operator - (const int a, const OverflowSafeInt<T> b) { return -b + a; }
template <class T> inline constexpr OverflowSafeInt<T> operator * (const int a, const OverflowSafeInt<T> b) { return b * a; }
template <class T> inline constexpr OverflowSafeInt<T> operator / (const int a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
/* Sometimes we got uint operator OverflowSafeInt instead of vice versa. Handle that properly. */
template <class T> inline constexpr OverflowSafeInt<T> operator + (const uint a, const OverflowSafeInt<T> b) { return b + a; }
template <class T> inline constexpr OverflowSafeInt<T> operator - (const uint a, const OverflowSafeInt<T> b) { return -b + a; }
template <class T> inline constexpr OverflowSafeInt<T> operator * (const uint a, const OverflowSafeInt<T> b) { return b * a; }
template <class T> inline constexpr OverflowSafeInt<T> operator / (const uint a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
/* Sometimes we got byte operator OverflowSafeInt instead of vice versa. Handle that properly. */
template <class T> inline constexpr OverflowSafeInt<T> operator + (const byte a, const OverflowSafeInt<T> b) { return b + (uint)a; }
template <class T> inline constexpr OverflowSafeInt<T> operator - (const byte a, const OverflowSafeInt<T> b) { return -b + (uint)a; }
template <class T> inline constexpr OverflowSafeInt<T> operator * (const byte a, const OverflowSafeInt<T> b) { return b * (uint)a; }
template <class T> inline constexpr OverflowSafeInt<T> operator / (const byte a, const OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
typedef OverflowSafeInt<int64> OverflowSafeInt64;
typedef OverflowSafeInt<int32> OverflowSafeInt32;
/* Some basic "unit tests". Also has the bonus of confirming that constexpr is working. */
static_assert(OverflowSafeInt32(INT32_MIN) - 1 == OverflowSafeInt32(INT32_MIN));
static_assert(OverflowSafeInt32(INT32_MAX) + 1 == OverflowSafeInt32(INT32_MAX));
static_assert(OverflowSafeInt32(INT32_MAX) * 2 == OverflowSafeInt32(INT32_MAX));
static_assert(OverflowSafeInt32(INT32_MIN) * 2 == OverflowSafeInt32(INT32_MIN));
#undef HAS_OVERFLOW_BUILTINS
#endif /* OVERFLOWSAFE_TYPE_HPP */
|
