SERVER-43764 Add more testing for special values in DoubleDoubleSummation

(cherry picked from commit abe90fb2090ead3fdbf9f62d5db50c88eb31d527)

2 files changed, 29 insertions, 9 deletions

diff --git a/src/mongo/db/pipeline/accumulator_sum.cpp b/src/mongo/db/pipeline/accumulator_sum.cpp
index 0200288cdfa..551bc181ee7 100644
--- a/src/mongo/db/pipeline/accumulator_sum.cpp
+++ b/src/mongo/db/pipeline/accumulator_sum.cpp
@@ -120,15 +120,7 @@ Value AccumulatorSum::getValue(bool toBeMerged) {
         case NumberDouble:
             return Value(nonDecimalTotal.getDouble());
         case NumberDecimal: {
-            double sum, error;
-            std::tie(sum, error) = nonDecimalTotal.getDoubleDouble();
-            Decimal128 total;  // zero
-            if (sum != 0) {
-                total = total.add(Decimal128(sum, Decimal128::kRoundTo34Digits));
-                total = total.add(Decimal128(error, Decimal128::kRoundTo34Digits));
-            }
-            total = total.add(decimalTotal);
-            return Value(total);
+            return Value(decimalTotal.add(nonDecimalTotal.getDecimal()));
         }
         default:
             MONGO_UNREACHABLE;
diff --git a/src/mongo/util/summation_test.cpp b/src/mongo/util/summation_test.cpp
index 72b29cc47de..c04e6b933ff 100644
--- a/src/mongo/util/summation_test.cpp
+++ b/src/mongo/util/summation_test.cpp
@@ -204,4 +204,32 @@ TEST(Summation, AddDoubles) {
     ASSERT_EQUALS(sum.getDouble(), doubleValuesSum);
     ASSERT(straightSum != sum.getDouble());
 }
+
+TEST(Summation, ConvertInfinityToDecimal) {
+    constexpr double infinity = std::numeric_limits<double>::infinity();
+    DoubleDoubleSummation sum;
+
+    sum.addDouble(infinity);
+    ASSERT_EQUALS(infinity, sum.getDouble());
+    ASSERT_TRUE(sum.getDecimal().isInfinite());
+    ASSERT_FALSE(sum.getDecimal().isNaN());
+
+    sum.addDouble(1);
+    ASSERT_EQUALS(infinity, sum.getDouble());
+    ASSERT_TRUE(sum.getDecimal().isInfinite());
+    ASSERT_FALSE(sum.getDecimal().isNaN());
+}
+
+TEST(Summation, ConvertNaNToDecimal) {
+    constexpr double nan = std::numeric_limits<double>::quiet_NaN();
+    DoubleDoubleSummation sum;
+
+    sum.addDouble(nan);
+    ASSERT_TRUE(sum.getDecimal().isNaN());
+    ASSERT_FALSE(sum.getDecimal().isInfinite());
+
+    sum.addDouble(1);
+    ASSERT_TRUE(sum.getDecimal().isNaN());
+    ASSERT_FALSE(sum.getDecimal().isInfinite());
+}
 }  // namespace mongo