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/*
* 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:
OverflowSafeInt() : m_value(0) { }
OverflowSafeInt(const OverflowSafeInt& other) { this->m_value = other.m_value; }
OverflowSafeInt(const int64 int_) { this->m_value = int_; }
inline OverflowSafeInt& operator = (const OverflowSafeInt& other) { this->m_value = other.m_value; return *this; }
inline 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 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 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 OverflowSafeInt operator + (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result += other; return result; }
inline OverflowSafeInt operator + (const int other) const { OverflowSafeInt result = *this; result += (int64)other; return result; }
inline OverflowSafeInt operator + (const uint other) const { OverflowSafeInt result = *this; result += (int64)other; return result; }
inline OverflowSafeInt operator - (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result -= other; return result; }
inline OverflowSafeInt operator - (const int other) const { OverflowSafeInt result = *this; result -= (int64)other; return result; }
inline OverflowSafeInt operator - (const uint other) const { OverflowSafeInt result = *this; result -= (int64)other; return result; }
inline OverflowSafeInt& operator ++ () { return *this += 1; }
inline OverflowSafeInt& operator -- () { return *this += -1; }
inline OverflowSafeInt operator ++ (int) { OverflowSafeInt org = *this; *this += 1; return org; }
inline 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 OverflowSafeInt& operator *= (const int factor)
{
#ifdef HAS_OVERFLOW_BUILTINS
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 OverflowSafeInt operator * (const int64 factor) const { OverflowSafeInt result = *this; result *= factor; return result; }
inline OverflowSafeInt operator * (const int factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
inline OverflowSafeInt operator * (const uint factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
inline OverflowSafeInt operator * (const uint16 factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
inline OverflowSafeInt operator * (const byte factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
/* Operators for division */
inline OverflowSafeInt& operator /= (const int64 divisor) { this->m_value /= divisor; return *this; }
inline OverflowSafeInt operator / (const OverflowSafeInt& divisor) const { OverflowSafeInt result = *this; result /= divisor.m_value; return result; }
inline OverflowSafeInt operator / (const int divisor) const { OverflowSafeInt result = *this; result /= divisor; return result; }
inline OverflowSafeInt operator / (const uint divisor) const { OverflowSafeInt result = *this; result /= (int)divisor; return result; }
/* Operators for modulo */
inline OverflowSafeInt& operator %= (const int divisor) { this->m_value %= divisor; return *this; }
inline OverflowSafeInt operator % (const int divisor) const { OverflowSafeInt result = *this; result %= divisor; return result; }
/* Operators for shifting */
inline OverflowSafeInt& operator <<= (const int shift) { this->m_value <<= shift; return *this; }
inline OverflowSafeInt operator << (const int shift) const { OverflowSafeInt result = *this; result <<= shift; return result; }
inline OverflowSafeInt& operator >>= (const int shift) { this->m_value >>= shift; return *this; }
inline OverflowSafeInt operator >> (const int shift) const { OverflowSafeInt result = *this; result >>= shift; return result; }
/* Operators for (in)equality when comparing overflow safe ints */
inline bool operator == (const OverflowSafeInt& other) const { return this->m_value == other.m_value; }
inline bool operator != (const OverflowSafeInt& other) const { return !(*this == other); }
inline bool operator > (const OverflowSafeInt& other) const { return this->m_value > other.m_value; }
inline bool operator >= (const OverflowSafeInt& other) const { return this->m_value >= other.m_value; }
inline bool operator < (const OverflowSafeInt& other) const { return !(*this >= other); }
inline bool operator <= (const OverflowSafeInt& other) const { return !(*this > other); }
/* Operators for (in)equality when comparing non-overflow safe ints */
inline bool operator == (const int other) const { return this->m_value == other; }
inline bool operator != (const int other) const { return !(*this == other); }
inline bool operator > (const int other) const { return this->m_value > other; }
inline bool operator >= (const int other) const { return this->m_value >= other; }
inline bool operator < (const int other) const { return !(*this >= other); }
inline bool operator <= (const int other) const { return !(*this > other); }
inline operator int64 () const { return this->m_value; }
};
/* Sometimes we got int64 operator OverflowSafeInt instead of vice versa. Handle that properly */
template <class T> inline OverflowSafeInt<T> operator + (int64 a, OverflowSafeInt<T> b) { return b + a; }
template <class T> inline OverflowSafeInt<T> operator - (int64 a, OverflowSafeInt<T> b) { return -b + a; }
template <class T> inline OverflowSafeInt<T> operator * (int64 a, OverflowSafeInt<T> b) { return b * a; }
template <class T> inline OverflowSafeInt<T> operator / (int64 a, 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 OverflowSafeInt<T> operator + (int a, OverflowSafeInt<T> b) { return b + a; }
template <class T> inline OverflowSafeInt<T> operator - (int a, OverflowSafeInt<T> b) { return -b + a; }
template <class T> inline OverflowSafeInt<T> operator * (int a, OverflowSafeInt<T> b) { return b * a; }
template <class T> inline OverflowSafeInt<T> operator / (int a, 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 OverflowSafeInt<T> operator + (uint a, OverflowSafeInt<T> b) { return b + a; }
template <class T> inline OverflowSafeInt<T> operator - (uint a, OverflowSafeInt<T> b) { return -b + a; }
template <class T> inline OverflowSafeInt<T> operator * (uint a, OverflowSafeInt<T> b) { return b * a; }
template <class T> inline OverflowSafeInt<T> operator / (uint a, 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 OverflowSafeInt<T> operator + (byte a, OverflowSafeInt<T> b) { return b + (uint)a; }
template <class T> inline OverflowSafeInt<T> operator - (byte a, OverflowSafeInt<T> b) { return -b + (uint)a; }
template <class T> inline OverflowSafeInt<T> operator * (byte a, OverflowSafeInt<T> b) { return b * (uint)a; }
template <class T> inline OverflowSafeInt<T> operator / (byte a, OverflowSafeInt<T> b) { return (OverflowSafeInt<T>)a / (int)b; }
typedef OverflowSafeInt<int64> OverflowSafeInt64;
typedef OverflowSafeInt<int32> OverflowSafeInt32;
#undef HAS_OVERFLOW_BUILTINS
#endif /* OVERFLOWSAFE_TYPE_HPP */
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