VMS Help MACRO, /MIGRATION, Macros for 64-Bit Addressing, $IS 32BITS, Examples  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    1.$is_32bits  R9, 10$

      In this example, the compiler checks the sign extension of
      the low 32 bits of the 64-bit value at R9 using the default
      temporary register, R22. Depending on the type of branch
      and the outcome of the test, the program either branches or
      continues in line.

    2.$is_32bits  4(R8), 20$, 30$, R28

      In this example, the compiler checks the sign extension of
      the low 32 bits of the 64-bit value at 4(R8) using R28 as a
      temporary register and, based on the check, branches to either
      20$ or 30$.