SERVER-57091 Fix infinite loop in GranularityRounderPreferredNumbers::roundDown

(cherry picked from commit 441bef2c968ab24fe52d910c26dc3ecac366d0eb)

2 files changed, 29 insertions, 0 deletions

diff --git a/jstests/aggregation/sources/bucketauto/granularity_near_zero.js b/jstests/aggregation/sources/bucketauto/granularity_near_zero.js
new file mode 100644
index 00000000000..7f456f9428d
--- /dev/null
+++ b/jstests/aggregation/sources/bucketauto/granularity_near_zero.js
@@ -0,0 +1,22 @@
+// Tests when the granularity rounder needs to approach zero to round correctly. This test was
+// designed to reproduce SERVER-57091.
+(function() {
+"use strict";
+const coll = db.server57091;
+coll.drop();
+coll.insertOne({});
+
+const res =
+    coll.aggregate([{
+            $bucketAuto: {
+                groupBy: {
+                    $reduce:
+                        {input: [], initialValue: 4.940656484124654e-324, in : {$size: ["$$value"]}}
+                },
+                buckets: NumberLong("8"),
+                granularity: "R80"
+            }
+        }])
+        .toArray();
+assert.eq(res, [{_id: {min: 0, max: 1.02e-321}, count: 1}]);
+})();
diff --git a/src/mongo/db/pipeline/granularity_rounder_preferred_numbers.cpp b/src/mongo/db/pipeline/granularity_rounder_preferred_numbers.cpp
index d99f640521c..efdcf46e432 100644
--- a/src/mongo/db/pipeline/granularity_rounder_preferred_numbers.cpp
+++ b/src/mongo/db/pipeline/granularity_rounder_preferred_numbers.cpp
@@ -306,6 +306,13 @@ Value GranularityRounderPreferredNumbers::roundDown(Value value) {
             multiplier /= 10.0;
         }
 
+        // It is possible to get a number so small that the resulting multiplier would have to be
+        // smaller than the precision of a double, in which case the multiplier would equal 0. In
+        // this case, we can round down to 0.0.
+        if (multiplier == 0) {
+            return Value(0.0);
+        }
+
         double previousMax;
         while (number > (_baseSeries.back() * multiplier)) {
             previousMax = _baseSeries.back() * multiplier;