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Type:
Bug
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: None
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None
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Storage Execution
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ALL
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Execution Team 2021-06-28, Execution Team 2021-07-12, Execution Team 2021-07-26, Execution Team 2021-08-09, Execution Team 2021-08-23, Execution Team 2021-09-06, Execution Team 2021-09-20, Execution Team 2021-10-04, Execution Team 2021-10-18, Execution Team 2021-11-01, Execution Team 2021-11-15, Execution Team 2021-11-29, Execution Team 2021-12-13, Execution Team 2021-12-27, Execution Team 2022-01-10, Execution Team 2022-01-24, Execution Team 2022-02-07, Execution Team 2022-02-21, Execution Team 2022-03-07, Execution Team 2022-03-21, Execution Team 2022-04-04, Execution Team 2022-04-18, Execution Team 2022-05-02, Execution Team 2022-05-16
By plugging values into DoubleDoubleSummation and calling getLong(), I've observed that it rounds non-integer values to the nearest integer (e.g., 4.6 rounds up to 5) but with strange tie-breaking behavior. All the values I've tested that end in .5 (nearest integer is a tie) round towards 0. For example, 2.5 becomes 2.
The most common tie-breaking modes round ties away from 0 (2.5 would become 3) or round ties toward the nearest even integer. The current behavior isn't necessarily wrong, but it is unconventional.
I wrote a short unit test to illustrate. Note that this test case passes on my local machine.
diff --git a/src/mongo/util/summation_test.cpp b/src/mongo/util/summation_test.cpp
index c04e6b933f..c18217d055 100644
--- a/src/mongo/util/summation_test.cpp
+++ b/src/mongo/util/summation_test.cpp
@@ -232,4 +232,38 @@ TEST(Summation, ConvertNaNToDecimal) {
ASSERT_TRUE(sum.getDecimal().isNaN());
ASSERT_FALSE(sum.getDecimal().isInfinite());
}
+
+TEST(Summation, RoundingDoubleToLong) {
+ {
+ DoubleDoubleSummation sum;
+ sum.addLong(2);
+ sum.addDouble(0.499);
+ // Rounds towards nearest integer.
+ ASSERT_EQ(sum.getLong(), 2);
+ }
+
+ {
+ DoubleDoubleSummation sum;
+ sum.addLong(2);
+ sum.addDouble(0.501);
+ // Rounds towards nearest integer.
+ ASSERT_EQ(sum.getLong(), 3);
+ }
+
+ {
+ DoubleDoubleSummation sum;
+ sum.addLong(2);
+ sum.addDouble(0.5);
+ // Breaks tie _toward_ 0.
+ ASSERT_EQ(sum.getLong(), 2);
+ }
+
+ {
+ DoubleDoubleSummation sum;
+ sum.addLong(-2);
+ sum.addDouble(-0.5);
+ // Breaks tie _toward_ 0.
+ ASSERT_EQ(sum.getLong(), -2);
+ }
+}
} // namespace mongo
- related to
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- Closed
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