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/* Copyright 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 "mongo/platform/float_utils.h"
#include "mongo/util/assert_util.h"
namespace mongo {
/**
* These functions compare numbers using the same rules as BSON. Care is taken to always give
* numerically correct results when comparing different types. Returns are always -1, 0, or 1 to
* ensure it is safe to negate the result to invert the direction of the comparison.
*/
inline int compareInts(int lhs, int rhs) {
return lhs == rhs ? 0 : lhs < rhs ? -1 : 1;
}
inline int compareLongs(long long lhs, long long rhs) {
return lhs == rhs ? 0 : lhs < rhs ? -1 : 1;
}
inline int compareDoubles(double lhs, double rhs) {
if (lhs == rhs) return 0;
if (lhs < rhs) return -1;
if (lhs > rhs) return 1;
// If none of the above cases returned, lhs or rhs must be NaN.
if (isNaN(lhs)) return isNaN(rhs) ? 0 : -1;
dassert(isNaN(rhs));
return 1;
}
// This is the tricky one. Needs to support the following cases:
// * Doubles with a fractional component.
// * Longs that can't be precisely represented as a double.
// * Doubles outside of the range of Longs (including +/- Inf).
// * NaN (defined by us as less than all Longs)
// * Return value is always -1, 0, or 1 to ensure it is safe to negate.
inline int compareLongToDouble(long long lhs, double rhs) {
// All Longs are > NaN
if (isNaN(rhs)) return 1;
// Ints with magnitude <= 2**53 can be precisely represented as doubles.
// Additionally, doubles outside of this range can't have a fractional component.
static const long long kEndOfPreciseDoubles = 1ll << 53;
if (lhs <= kEndOfPreciseDoubles && lhs >= -kEndOfPreciseDoubles) {
return compareDoubles(lhs, rhs);
}
// Large magnitude doubles (including +/- Inf) are strictly > or < all Longs.
static const double kBoundOfLongRange = -static_cast<double>(LLONG_MIN); // positive 2**63
if (rhs >= kBoundOfLongRange) return -1; // Can't be represented in a Long.
if (rhs < -kBoundOfLongRange) return 1; // Can be represented in a Long.
// Remaining Doubles can have their integer component precisely represented as long longs.
// If they have a fractional component, they must be strictly > or < lhs even after
// truncation of the fractional component since low-magnitude lhs were handled above.
return compareLongs(lhs, rhs);
}
inline int compareDoubleToLong(double lhs, long long rhs) {
// Only implement the real logic once.
return -compareLongToDouble(rhs, lhs);
}
} // namespace mongo
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