2 files changed, 39 insertions, 0 deletions
diff --git a/src/mongo/bson/bsonelement.h b/src/mongo/bson/bsonelement.h
index e0b3b8e4414..1d31c647901 100644
--- a/src/mongo/bson/bsonelement.h
+++ b/src/mongo/bson/bsonelement.h
@@ -373,6 +373,11 @@ public:
     bool isNumber() const;
 
     /**
+     * True if element is a NaN double or decimal.
+     */
+    bool isNaN() const;
+
+    /**
      * Return double value for this field. MUST be NumberDouble type.
      */
     double _numberDouble() const {
@@ -1005,6 +1010,21 @@ inline bool BSONElement::isNumber() const {
     }
 }
 
+inline bool BSONElement::isNaN() const {
+    switch (type()) {
+        case NumberDouble: {
+            double d = _numberDouble();
+            return std::isnan(d);
+        }
+        case NumberDecimal: {
+            Decimal128 d = _numberDecimal();
+            return d.isNaN();
+        }
+        default:
+            return false;
+    }
+}
+
 inline Decimal128 BSONElement::numberDecimal() const {
     switch (type()) {
         case NumberDouble:
diff --git a/src/mongo/bson/bsonelement_test.cpp b/src/mongo/bson/bsonelement_test.cpp
index 8a2a7c3fc52..4e5bc3f6f07 100644
--- a/src/mongo/bson/bsonelement_test.cpp
+++ b/src/mongo/bson/bsonelement_test.cpp
@@ -283,6 +283,25 @@ TEST(BSONElement, SafeNumberDoubleNegativeBound) {
               (double)BSONElement::kSmallestSafeLongLongAsDouble);
 }
 
+TEST(BSONElement, IsNaN) {
+    ASSERT(BSON("" << std::numeric_limits<double>::quiet_NaN()).firstElement().isNaN());
+    ASSERT(BSON("" << -std::numeric_limits<double>::quiet_NaN()).firstElement().isNaN());
+    ASSERT(BSON("" << Decimal128::kPositiveNaN).firstElement().isNaN());
+    ASSERT(BSON("" << Decimal128::kNegativeNaN).firstElement().isNaN());
+
+    ASSERT_FALSE(BSON("" << std::numeric_limits<double>::infinity()).firstElement().isNaN());
+    ASSERT_FALSE(BSON("" << -std::numeric_limits<double>::infinity()).firstElement().isNaN());
+    ASSERT_FALSE(BSON("" << Decimal128::kPositiveInfinity).firstElement().isNaN());
+    ASSERT_FALSE(BSON("" << Decimal128::kNegativeInfinity).firstElement().isNaN());
+    ASSERT_FALSE(BSON("" << Decimal128{"9223372036854775808.5"}).firstElement().isNaN());
+    ASSERT_FALSE(BSON("" << Decimal128{"-9223372036854775809.99"}).firstElement().isNaN());
+    ASSERT_FALSE(BSON("" << 12345LL).firstElement().isNaN());
+    ASSERT_FALSE(BSON(""
+                      << "foo")
+                     .firstElement()
+                     .isNaN());
+}
+
 TEST(BSONElementIntegerParseTest, ParseIntegerElementToNonNegativeLongRejectsNegative) {
     BSONObj query = BSON("" << -2LL);
     ASSERT_NOT_OK(query.firstElement().parseIntegerElementToNonNegativeLong());