SERVER-24525 Fix BSON encoding and decoding for decimal

3 files changed, 13 insertions, 5 deletions

diff --git a/src/mongo/bson/bsonelement.h b/src/mongo/bson/bsonelement.h
index 876e4a40050..ad8429da9be 100644
--- a/src/mongo/bson/bsonelement.h
+++ b/src/mongo/bson/bsonelement.h
@@ -304,7 +304,9 @@ public:
 
     /** Return decimal128 value for this field. MUST be NumberDecimal type. */
     Decimal128 _numberDecimal() const {
-        return Decimal128(ConstDataView(value()).read<LittleEndian<Decimal128::Value>>());
+        uint64_t low = ConstDataView(value()).read<LittleEndian<long long>>();
+        uint64_t high = ConstDataView(value() + sizeof(long long)).read<LittleEndian<long long>>();
+        return Decimal128(Decimal128::Value({low, high}));
     }
 
     /** Return long long value for this field. MUST be NumberLong type. */
diff --git a/src/mongo/bson/bsonobjbuilder.h b/src/mongo/bson/bsonobjbuilder.h
index 74593287942..10b8a93b80e 100644
--- a/src/mongo/bson/bsonobjbuilder.h
+++ b/src/mongo/bson/bsonobjbuilder.h
@@ -260,6 +260,7 @@ public:
     BSONObjBuilder& append(StringData fieldName, Decimal128 n) {
         _b.appendNum(static_cast<char>(NumberDecimal));
         _b.appendStr(fieldName);
+        // Make sure we write data in a Little Endian conforming manner
         _b.appendNum(n);
         return *this;
     }
diff --git a/src/mongo/bson/util/builder.h b/src/mongo/bson/util/builder.h
index 924d96e7f8b..53ad7d25ebe 100644
--- a/src/mongo/bson/util/builder.h
+++ b/src/mongo/bson/util/builder.h
@@ -212,6 +212,15 @@ public:
         appendNumImpl(j);
     }
 
+    void appendNum(Decimal128 j) {
+        BOOST_STATIC_ASSERT(sizeof(Decimal128::Value) == 16);
+        Decimal128::Value value = j.getValue();
+        long long low = value.low64;
+        long long high = value.high64;
+        appendNumImpl(low);
+        appendNumImpl(high);
+    }
+
     template <typename Int64_t,
               typename = stdx::enable_if_t<std::is_same<Int64_t, int64_t>::value &&
                                            !std::is_same<int64_t, long long>::value>>
@@ -222,10 +231,6 @@ public:
     void appendNum(unsigned long long j) {
         appendNumImpl(j);
     }
-    void appendNum(Decimal128 j) {
-        BOOST_STATIC_ASSERT(sizeof(Decimal128::Value) == 16);
-        appendNumImpl(j.getValue());
-    }
 
     void appendBuf(const void* src, size_t len) {
         if (len)