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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <cstdint>
#ifdef _MSC_VER
#include <SafeInt.hpp>
#endif
#include "mongo/stdx/type_traits.h"
#include "mongo/util/assert_util.h"
namespace mongo::overflow {
/**
* Synopsis:
*
* bool mul(A a, A b, T* r);
* bool add(A a, A b, T* r);
* bool sub(A a, A b, T* r);
*
* The domain type `A` evaluates to `T`, which is deduced from the `r` parameter.
* That is, the input parameters are coerced into the type accepted by the output parameter.
* All functions return true if operation would overflow, otherwise they store result in `*r`.
*/
// MSVC : The SafeInt functions return false on overflow.
// GCC, Clang: The __builtin_*_overflow functions return true on overflow.
template <typename T>
constexpr bool mul(stdx::type_identity_t<T> a, stdx::type_identity_t<T> b, T* r) {
#ifdef _MSC_VER
return !SafeMultiply(a, b, *r);
#else
return __builtin_mul_overflow(a, b, r);
#endif
}
template <typename T>
constexpr bool add(stdx::type_identity_t<T> a, stdx::type_identity_t<T> b, T* r) {
#ifdef _MSC_VER
return !SafeAdd(a, b, *r);
#else
return __builtin_add_overflow(a, b, r);
#endif
}
template <typename T>
constexpr bool sub(stdx::type_identity_t<T> a, stdx::type_identity_t<T> b, T* r) {
#ifdef _MSC_VER
return !SafeSubtract(a, b, *r);
#else
return __builtin_sub_overflow(a, b, r);
#endif
}
/**
* Safe mod function which throws if the divisor is 0 and avoids potential overflow in cases where
* the divisor is -1. If the absolute value of the divisor is 1, mod will always return 0. We fast-
* path this to avoid the scenario where the dividend is the smallest negative long or int value and
* the divisor is -1. Naively performing this % may result in an overflow when the -2^N value is
* divided and becomes 2^N. See SERVER-43699.
*/
template <typename T>
constexpr T safeMod(T dividend, T divisor) {
uassert(51259, "can't mod by zero", divisor != 0);
return (divisor == 1 || divisor == -1 ? 0 : dividend % divisor);
}
} // namespace mongo::overflow
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