typedef struct _INTERLOCK_SEQ
{
     union
     {
          struct
          {
               WORD Depth;
               WORD FreeEntryOffset;
          };
          struct
          {
               ULONG OffsetAndDepth;
               ULONG Sequence;
          };
          INT64 Exchg;
     };
} INTERLOCK_SEQ, *PINTERLOCK_SEQ;

Windows Vista Kernel Structures