VMS Help CC, Language topics, Builtin Functions, Add Aligned Word Interlocked  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The _ADAWI function adds its source operand to the destination.
  This operation is interlocked against similar operations by other
  processors or devices in the system.

  Syntax:

       typedef enum {_adawi_sum_neg=-1, _adawi_sum_zero,
                     _adawi_sum_pos} _ADAWI_STATUS;

       _ADAWI_STATUS _ADAWI(short __src, short *__dest);