Revert "SERVER-15047 Remove undefined behavior from Timestamp"

This reverts commit e87716a9286b6aa6f63a513012e55f6e42f634a2.

1 files changed, 10 insertions, 9 deletions

diff --git a/src/mongo/db/ops/modifier_object_replace.cpp b/src/mongo/db/ops/modifier_object_replace.cpp
index 292a1534498..5ebbb4bd342 100644
--- a/src/mongo/db/ops/modifier_object_replace.cpp
+++ b/src/mongo/db/ops/modifier_object_replace.cpp
@@ -28,7 +28,6 @@
 
 #include "mongo/db/ops/modifier_object_replace.h"
 
-#include "mongo/base/data_cursor.h"
 #include "mongo/base/error_codes.h"
 #include "mongo/bson/mutable/document.h"
 #include "mongo/db/global_timestamp.h"
@@ -48,14 +47,16 @@ namespace mongo {
                 BSONElement e = i.next();
 
                 // Skip _id field -- we do not replace it
-                if (e.type() == bsonTimestamp &&
-                    e.fieldNameStringData() != idFieldName &&
-                    e.timestamp().getSecs() == 0 &&
-                    e.timestamp().getInc() == 0) {
-                    Timestamp ts(getNextGlobalTimestamp());
-                    DataCursor(const_cast<char*>(e.value()))
-                        .writeLEAndAdvance<uint32_t>(ts.getInc())
-                        .writeLE<uint32_t>(ts.getSecs());
+                if (e.type() == bsonTimestamp && e.fieldNameStringData() != idFieldName) {
+                    // TODO(emilkie): This is not endian-safe.
+                    unsigned long long &timestamp =
+                        *(reinterpret_cast<unsigned long long*>(
+                              const_cast<char *>(e.value())));
+                    if (timestamp == 0) {
+                        // performance note, this locks a mutex:
+                        Timestamp ts(getNextGlobalTimestamp());
+                        timestamp = ts.asULL();
+                    }
                 }
             }