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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 <cmath>
#include <limits>
#include <type_traits>
#include <boost/optional.hpp>
#include "mongo/base/static_assert.h"
#include "mongo/stdx/type_traits.h"
namespace mongo {
namespace detail {
/**
* The following three methods are conversion helpers that allow us to promote
* all numerical input to three top-level types: int64_t, uint64_t, and double.
*/
// Floating point numbers -> double
template <typename T>
typename stdx::enable_if_t<std::is_floating_point<T>::value, double> upconvert(T t) {
MONGO_STATIC_ASSERT(sizeof(double) >= sizeof(T));
return static_cast<double>(t);
}
// Signed integral types -> int64_t
template <typename T>
typename stdx::enable_if_t<std::is_integral<T>::value && std::is_signed<T>::value, int64_t>
upconvert(T t) {
MONGO_STATIC_ASSERT(sizeof(int64_t) >= sizeof(T));
return static_cast<int64_t>(t);
}
// Unsigned integral types -> uint64_t
template <typename T>
typename stdx::enable_if_t<std::is_integral<T>::value && !std::is_signed<T>::value, uint64_t>
upconvert(T t) {
MONGO_STATIC_ASSERT(sizeof(uint64_t) >= sizeof(T));
return static_cast<uint64_t>(t);
}
/**
* Compare two values of the same type. Return -1 if a < b, 0 if they are equal, and
* 1 if a > b.
*/
template <typename T>
int identityCompare(T a, T b) {
if (a == b) {
return 0;
}
return (a < b) ? -1 : 1;
}
inline int signedCompare(int64_t a, int64_t b) {
return identityCompare(a, b);
}
inline int signedCompare(double a, double b) {
return identityCompare(a, b);
}
inline int signedCompare(uint64_t a, uint64_t b) {
return identityCompare(a, b);
}
/**
* Compare unsigned and signed integers.
*/
inline int signedCompare(int64_t a, uint64_t b) {
if (a < 0) {
return -1;
}
auto aUnsigned = static_cast<uint64_t>(a);
return signedCompare(aUnsigned, b);
}
inline int signedCompare(uint64_t a, int64_t b) {
return -signedCompare(b, a);
}
/**
* Compare doubles and signed integers.
*/
inline int signedCompare(double a, int64_t b) {
// Casting int64_ts to doubles will round them
// and give the wrong result, so convert doubles to
// int64_ts if we can, then do the comparison.
if (a < -std::ldexp(1, 63)) {
return -1;
} else if (a >= std::ldexp(1, 63)) {
return 1;
}
auto aAsInt64 = static_cast<int64_t>(a);
return signedCompare(aAsInt64, b);
}
inline int signedCompare(int64_t a, double b) {
return -signedCompare(b, a);
}
/**
* Compare doubles and unsigned integers.
*/
inline int signedCompare(double a, uint64_t b) {
if (a < 0) {
return -1;
}
// Casting uint64_ts to doubles will round them
// and give the wrong result, so convert doubles to
// uint64_ts if we can, then do the comparison.
if (a >= std::ldexp(1, 64)) {
return 1;
}
auto aAsUInt64 = static_cast<uint64_t>(a);
return signedCompare(aAsUInt64, b);
}
inline int signedCompare(uint64_t a, double b) {
return -signedCompare(b, a);
}
/**
* For any t and u of types T and U, promote t and u to one of the
* top-level numerical types (int64_t, uint64_t, and double) and
* compare them.
*
* Return -1 if t < u, 0 if they are equal, 1 if t > u.
*/
template <typename T, typename U>
int compare(T t, U u) {
return signedCompare(upconvert(t), upconvert(u));
}
} // namespace detail
/**
* Given a number of some type Input and a desired numerical type Output,
* this method represents the input number in the output type if possible.
* If the given number cannot be exactly represented in the output type,
* this method returns a disengaged optional.
*
* ex:
* auto v1 = representAs<int>(2147483647); // v1 holds 2147483647
* auto v2 = representAs<int>(2147483648); // v2 is disengaged
* auto v3 = representAs<int>(10.3); // v3 is disengaged
*/
template <typename Output, typename Input>
boost::optional<Output> representAs(Input number) {
if (std::is_same<Input, Output>::value) {
return {static_cast<Output>(number)};
}
// If number is NaN and Output can also represent NaN, return NaN
// Note: We need to specifically handle NaN here because of the way
// detail::compare is implemented.
{
// We use ADL here to allow types, such as Decimal, to supply their
// own definitions of isnan(). If the Input type does not define a
// custom isnan(), then we fall back to using std::isnan().
using std::isnan;
if (std::is_floating_point<Input>::value && isnan(number)) {
if (std::is_floating_point<Output>::value) {
return {static_cast<Output>(number)};
}
}
}
// If Output is integral and number is a non-integral floating point value,
// return a disengaged optional.
if (std::is_floating_point<Input>::value && std::is_integral<Output>::value) {
if (!(std::trunc(number) == number)) {
return {};
}
}
const auto floor = std::numeric_limits<Output>::lowest();
const auto ceiling = std::numeric_limits<Output>::max();
// If number is out-of-bounds for Output type, fail.
if ((detail::compare(number, floor) < 0) || (detail::compare(number, ceiling) > 0)) {
return {};
}
// Our number is within bounds, safe to perform a static_cast.
auto numberOut = static_cast<Output>(number);
// Some integers cannot be exactly represented as floating point numbers.
// To check, we cast back to the input type if we can, and compare.
if (std::is_integral<Input>::value && std::is_floating_point<Output>::value) {
const auto inputFloor = std::numeric_limits<Input>::lowest();
const auto inputCeiling = std::numeric_limits<Input>::max();
// If it is not safe to cast back to the Input type, fail.
if ((detail::compare(numberOut, inputFloor) < 0) ||
(detail::compare(numberOut, inputCeiling) > 0)) {
return {};
}
if (number != static_cast<Input>(numberOut)) {
return {};
}
}
return {static_cast<Output>(numberOut)};
}
} // namespace mongo
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