1
2 /**
3 * Copyright (C) 2018-present MongoDB, Inc.
4 *
5 * This program is free software: you can redistribute it and/or modify
6 * it under the terms of the Server Side Public License, version 1,
7 * as published by MongoDB, Inc.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * Server Side Public License for more details.
13 *
14 * You should have received a copy of the Server Side Public License
15 * along with this program. If not, see
16 * <http://www.mongodb.com/licensing/server-side-public-license>.
17 *
18 * As a special exception, the copyright holders give permission to link the
19 * code of portions of this program with the OpenSSL library under certain
20 * conditions as described in each individual source file and distribute
21 * linked combinations including the program with the OpenSSL library. You
22 * must comply with the Server Side Public License in all respects for
23 * all of the code used other than as permitted herein. If you modify file(s)
24 * with this exception, you may extend this exception to your version of the
25 * file(s), but you are not obligated to do so. If you do not wish to do so,
26 * delete this exception statement from your version. If you delete this
27 * exception statement from all source files in the program, then also delete
28 * it in the license file.
29 */
30
31 #pragma once
32
33 #include <cmath>
34
35 #include "mongo/platform/decimal128.h"
36 #include "mongo/util/assert_util.h"
37
38 namespace mongo {
39
40 /**
41 * These functions compare numbers using the same rules as BSON. Care is taken to always give
42 * numerically correct results when comparing different types. Returns are always -1, 0, or 1 to
43 * ensure it is safe to negate the result to invert the direction of the comparison.
44 *
45 * lhs > rhs returns 1
46 * lhs < rhs returns -1
47 * lhs == rhs returns 0
48 *
49 */
50
compareInts(int lhs,int rhs)51 inline int compareInts(int lhs, int rhs) {
52 return lhs == rhs ? 0 : lhs < rhs ? -1 : 1;
53 }
54
compareLongs(long long lhs,long long rhs)55 inline int compareLongs(long long lhs, long long rhs) {
56 return lhs == rhs ? 0 : lhs < rhs ? -1 : 1;
57 }
58
compareDoubles(double lhs,double rhs)59 inline int compareDoubles(double lhs, double rhs) {
60 if (lhs == rhs)
61 return 0;
62 if (lhs < rhs)
63 return -1;
64 if (lhs > rhs)
65 return 1;
66
67 // If none of the above cases returned, lhs or rhs must be NaN.
68 if (std::isnan(lhs))
69 return std::isnan(rhs) ? 0 : -1;
70 dassert(std::isnan(rhs));
71 return 1;
72 }
73
74 // This is the tricky one. Needs to support the following cases:
75 // * Doubles with a fractional component.
76 // * Longs that can't be precisely represented as a double.
77 // * Doubles outside of the range of Longs (including +/- Inf).
78 // * NaN (defined by us as less than all Longs)
79 // * Return value is always -1, 0, or 1 to ensure it is safe to negate.
compareLongToDouble(long long lhs,double rhs)80 inline int compareLongToDouble(long long lhs, double rhs) {
81 // All Longs are > NaN
82 if (std::isnan(rhs))
83 return 1;
84
85 // Ints with magnitude <= 2**53 can be precisely represented as doubles.
86 // Additionally, doubles outside of this range can't have a fractional component.
87 static const long long kEndOfPreciseDoubles = 1ll << 53;
88 if (lhs <= kEndOfPreciseDoubles && lhs >= -kEndOfPreciseDoubles) {
89 return compareDoubles(lhs, rhs);
90 }
91
92 // Large magnitude doubles (including +/- Inf) are strictly > or < all Longs.
93 static const double kBoundOfLongRange = -static_cast<double>(LLONG_MIN); // positive 2**63
94 if (rhs >= kBoundOfLongRange)
95 return -1; // Can't be represented in a Long.
96 if (rhs < -kBoundOfLongRange)
97 return 1; // Can be represented in a Long.
98
99 // Remaining Doubles can have their integer component precisely represented as long longs.
100 // If they have a fractional component, they must be strictly > or < lhs even after
101 // truncation of the fractional component since low-magnitude lhs were handled above.
102 return compareLongs(lhs, rhs);
103 }
104
compareDoubleToLong(double lhs,long long rhs)105 inline int compareDoubleToLong(double lhs, long long rhs) {
106 // Only implement the real logic once.
107 return -compareLongToDouble(rhs, lhs);
108 }
109
110 /** Decimal type comparisons
111 * These following cases need support:
112 * 1. decimal and decimal: directly compare (enforce ordering: NaN < -Inf < N < +Inf)
113 * 2. decimal and int: convert int to decimal and compare
114 * 3. decimal and long: convert long to decimal and compare
115 * 4. decimal to double: convert decimal to double with round toward negative.
116 * Check for exact conversion and determine ordering based on result.
117 */
118
119 // Case 1: Compare two decimal values, but enforce MongoDB's total ordering convention
compareDecimals(Decimal128 lhs,Decimal128 rhs)120 inline int compareDecimals(Decimal128 lhs, Decimal128 rhs) {
121 // When we're comparing, lhs is always a decimal, which means more often than not
122 // the rhs will be less than the lhs (decimal type has the largest capacity)
123 if (lhs.isGreater(rhs))
124 return 1;
125 if (lhs.isLess(rhs))
126 return -1;
127 if (lhs.isNaN())
128 return (rhs.isNaN() ? 0 : -1);
129 if (rhs.isNaN())
130 return 1;
131 else // lhs is necessarily equal to rhs
132 return 0;
133 }
134
135 // Compare decimal and int
compareDecimalToInt(Decimal128 lhs,int rhs)136 inline int compareDecimalToInt(Decimal128 lhs, int rhs) {
137 return compareDecimals(lhs, Decimal128(rhs));
138 }
139
compareIntToDecimal(int lhs,Decimal128 rhs)140 inline int compareIntToDecimal(int lhs, Decimal128 rhs) {
141 return -compareDecimalToInt(rhs, lhs);
142 }
143
144 // Compare decimal and long
compareDecimalToLong(Decimal128 lhs,long long rhs)145 inline int compareDecimalToLong(Decimal128 lhs, long long rhs) {
146 return compareDecimals(lhs, Decimal128(static_cast<int64_t>(rhs)));
147 }
148
compareLongToDecimal(long long lhs,Decimal128 rhs)149 inline int compareLongToDecimal(long long lhs, Decimal128 rhs) {
150 return -compareDecimalToLong(rhs, lhs);
151 }
152
153 // Compare decimal and double
compareDecimalToDouble(Decimal128 lhs,double rhs)154 inline int compareDecimalToDouble(Decimal128 lhs, double rhs) {
155 uint32_t sigFlags = Decimal128::SignalingFlag::kNoFlag;
156 double decToDouble = lhs.toDouble(&sigFlags, Decimal128::RoundingMode::kRoundTowardNegative);
157
158 if (decToDouble == rhs) {
159 // If our conversion was not exact, lhs was necessarily greater than rhs
160 // otherwise, they are equal
161 if (Decimal128::hasFlag(sigFlags, Decimal128::SignalingFlag::kInexact)) {
162 return 1;
163 } else {
164 return 0;
165 }
166 } else if (decToDouble < rhs) {
167 return -1;
168 } else if (decToDouble > rhs) {
169 return 1;
170 }
171
172 if (lhs.isNaN())
173 return (std::isnan(rhs) ? 0 : -1);
174 invariant(std::isnan(rhs));
175 return 1;
176 }
177
compareDoubleToDecimal(double lhs,Decimal128 rhs)178 inline int compareDoubleToDecimal(double lhs, Decimal128 rhs) {
179 return -compareDecimalToDouble(rhs, lhs);
180 }
181
182 } // namespace mongo
183